RU2360341C2 - Quasi three-level solid laser and method of operation - Google Patents

Abstract

FIELD: electricity; medicine.

SUBSTANCE: invention relates to solid laser, namely to lasers with laser diode pumping. The invention can be applied in medicine and cosmetology in industrial scope. Quasi three-level solid laser includes laser diode, active element, laser diode radiation focusing device and laser resonator. The laser contains laser diode temperature sensor, current and laser diode temperature control unit having electrical connection with laser diode, thermal stabilisation unit and diode temperature sensor. The laser diode control unit is designed so that it can control various currents and laser diode temperatures. Method of quasi three-level solid laser operation provides for transmitting current via laser diode. The laser diode radiation is focused inside the above-mentioned active element placed between input and output mirrors. After that the radiation is reflected from the output surface of active element. Radiation from the active element is transmitted though input and output surfaces of the active element. In addition, the radiation falling on the output mirror of resonator is partially transmitted through it whereas radiation from laser diode reflected from the laser elements is simultaneously reduced during transients related to laser diode switching on or changing diode radiation power. The current flowing through laser diode is changed so that the length of laser diode radiation wave coincides with the centre of active element absorption line.

EFFECT: improved reliability of laser, extended lifetime and increased mean power of radiation.

34 cl, 4 dwg

Description

The invention relates to the field of solid-state lasers, in particular to laser diode-pumped lasers, and is industrially applicable in medicine and cosmetology.

A solid-state laser is known in which the active element is configured to provide an even number of radiation passes through it [Zavartsev Yu.V., Zagumenny AI, Zerouk F., Kutovoi SA, Mikhailov VA, Podreshetnikov V. V., Sirotkin A.A., Scherbakov I.A. "Quasi-three-level Nd: GdVO4 - laser at λ = 456 nm with diode pumping." Quantum Electronics, 33 (7), 651 (2003)]. In this laser, the pump radiation is absorbed as it passes from the input to output surfaces of the active element according to the Lambert – Bouguer – Beer law. The intensity of this radiation continues to decrease after reflection from the output surface of the active element, however, with a double pass, the total intensity of the pump radiation localized inside the active element is significantly higher than with a single pass. With a single pass, the length of the active element is usually chosen such that the absorption of the pump radiation in the active element is 80-95%. With a double pass of the pump radiation, the length of the active element can be reduced by more than two times at the same value of the pump absorption. Due to this, with two-pass pumping, the intracavity absorption losses for a quasi-three-level laser are reduced in proportion to the length of the active element (i.e., approximately twice). Such a decrease in intracavity losses leads to a significant increase in the laser efficiency and average output radiation power.

In addition, the average density of the pump power in an active element with a double pass of radiation is on average greater than with a single pass pump. Due to this, an absorption saturation effect takes place, leading to a decrease in the resonance absorption coefficient of the generated intracavity radiation. The population of the ground state decreases and, accordingly, the absorption of the intracavity radiation generated from the ground state decreases. Other things being equal, this effect also leads to an increase in the laser efficiency.

An active element is known made of a single-cation or mixed vanadate crystal doped with Nd ³⁺ or Tm ³⁺ ions [AIZagumennyi, VAMikhailov, VIVlasov, AASirotkin, VVPodreshetnikov, Yu.L. Kalachev, Yu.D. Zavartsev, SAKutovoi and IAShcherbakov. "DiodePumped Lasers Based on GdVO4 Crystal." Laser Physics, Vol.13, No.3, pp.1-8].

A known control unit configured to vary the current through a laser diode [LDD-10 power supply company ATC-SEMICONDUCTOR DEVICES, St. Petersburg, www.atcsd.ru].

A known control unit configured to vary the temperature of the laser diode [Power supply LDD-10 company ATS-SEMICONDUCTOR DEVICES, St. Petersburg, www.atcsd.ru].

A known laser diode control unit based on a microcontroller device [LDD-10 power supply company ATS-SEMICONDUCTOR DEVICES, St. Petersburg, www.atcsd.ru].

Known spectral selector made with the possibility of changing the wavelength of the radiation [Walter Koechner "Solid-State Laser Engineering", Springer Series in Optical Sciencess, Fourth Edition, 1996, p.235].

Known frequency doubler made of a nonlinear optical crystal from the group of KTiOPO ₄ , KNbO ₃ , LiNbO ₃ , LiJO ₃ , β-BaB ₂ O ₄ , LiB ₃ O ₅ .

A known method and device for controlling the current through a laser diode so that the wavelength of the laser diode coincides with the center of the absorption line of the active element of the laser pumped by this laser diode [LDD-10 power supply company ATS-SEMICONDUCTOR DEVICES, St. Petersburg. www.atcsd.ru].

A known solid-state laser containing a longitudinal optical pump source made in the form of a laser diode, an active element, a device for focusing the pump radiation into the active element and a laser cavity [US patent 5751751]. The active element of the laser is made of a crystal doped with a rare-earth element. The laser contains a nonlinear radiation frequency doubler.

The disadvantage of this analogue is the lack of reliability, relatively small service life and relatively low average radiation power, which is associated with the reflected pump radiation entering the laser diode and the mismatch of the pump radiation wavelength with the center of the absorption line of the active laser element.

Closest to the claimed one is a known quasi-three-level solid-state laser containing a longitudinal pump radiation source made in the form of a laser diode, an active element, a device for focusing the laser diode radiation into the active element and the laser resonator, the active element being configured to provide an even number of passes of the pump radiation through him [VASychugov, VAMikhailov, VAKondratyuk, N. M. Lyndin, Yu. Fram, AIZagumennyi, Yu.D. Zavartsev, PAStudenikin. Short-wavelength (λ = 914 nm) microlaser operatig on an Nd ³⁺ : YVO ₄ crystal. Quantum Electronics, 2000, v. 30, No. 1, p.13-14].

The disadvantage of this closest analogue is the lack of reliability, relatively small service life and relatively low average radiation power, which is associated with the reflected pump radiation entering the laser diode and the mismatch of the pump radiation wavelength with the center of the absorption line of the active laser element

A known method of operation of a longitudinal-diode-pumped solid-state laser, in which a current is passed through a laser diode, the laser diode radiation is focused inside the active element located between the input and output mirrors, and then it is reflected from the output surface of the active element, the radiation emitted by the active element is passed through the input and output surfaces of the active element, and the radiation incident on the output mirror of the resonator is partially passed through it.

[Patent US 5751751.]

The disadvantage of this analogue is the lack of reliability, relatively small service life and relatively low average radiation power, which is associated with the reflected pump radiation entering the laser diode and the mismatch of the pump radiation wavelength with the center of the absorption line of the active laser element.

Closest to the claimed is a known method of operation of a quasi-three-level solid-state laser with longitudinal diode pumping, during which a current is passed through a laser diode, the laser diode radiation is focused inside the active element located between the input and output mirrors, and reflect from the output surface of the active element, and the radiation emitted by the active element is passed through the input and output surfaces of the active element, the radiation incident on the output mirror torus partially passed therethrough.

The disadvantage of this closest analogue is the lack of reliability, relatively short service life and relatively low average radiation power, which is associated with the reflected pump radiation entering the laser diode and the mismatch of the pump radiation wavelength with the center of the absorption line of the active laser element.

Using the claimed invention, the technical problem is solved to increase the reliability of the laser, increase its service life and increase the average radiation power.

This goal is achieved by the fact that the known quasi-three-level solid-state laser containing a laser diode for longitudinal pumping, an active element, a device for focusing the radiation of a laser diode into an active element and a laser cavity, the active element being configured to provide an even number of passes of the radiation of the laser pump diode through it, further comprises a laser diode temperature sensor, a thermal stabilization unit, a laser diode current and temperature control unit, electrically connected to azernym diode, and the sensor unit of thermal stabilization of the laser diode temperature and current control unit and the temperature of the laser diode is configured to simultaneously varying the diode laser current and temperature.

In particular, the current and temperature control unit of the laser diode can be made on the basis of a microcontroller device.

In particular, the angle between the propagation axis of the radiation of the laser diode and the optical axis of the laser cavity can be in the range from 1 to 10 °.

In particular, the laser may further comprise an optical isolation device mounted between the laser diode and the active element, the optical isolation device can be configured to attenuate pump radiation reflected from the optical elements of the laser resonator. In this case, the optical isolation device can be made in the form of a 45-degree Faraday cell for the radiation wavelength of the laser diode or contain a polarizer and a quarter-wave plate, sequentially mounted on the propagation axis of the radiation of the laser diode. An alternative is that the optical isolation device can be made in the form of a transparent optically inhomogeneous plate, providing irregular deviations of the radiation transmitted through it at an angle of not more than 5 ° over the beam cross section. If this angle exceeds 5 °, then the size of the focus area of the pump radiation in the active element increases, which leads to an unacceptable decrease in the efficiency of the laser.

In particular, the focusing device may comprise two lenses. In this case, a segment of optical fiber with a length L satisfying the ratio L> 20 D, where D is the diameter of the optical fiber, both ends of the fiber located in the foci of the lenses, can be located between the lenses. With a shorter length of the optical fiber, the image of the emitter of the pump diode is partially transmitted through the fiber and thereby leads to an unacceptably large transmission of the pump radiation reflected back to the emitter.

In addition, the lenses can be made with optical spherical aberration in the range from 0.1 to 0.2 of the optical power of the device for focusing the radiation of a laser diode into an active element. If the optical aberration is less than 0.1 of the optical power of the focusing device, then the magnitude of the defocusing of the pump radiation reflected backwards caused by this lens and its attenuation on the diode emitter is unacceptably small and does not give a significant optical isolation effect. If it exceeds 0.2 of the optical power of the focusing device, then the size of the focus area of the pump radiation in the active element increases, which leads to an unacceptable decrease in the efficiency of the laser.

In particular, the active element can be mounted to move across the optical axis of the resonator.

In particular, the active element may contain at least one crystal of a single cationic or mixed vanadate doped with Nd ³⁺ or Tm ³⁺ ions. In this case, the vanadate crystal can be described by one of the chemical formulas A _1-x Nd _x VO ₄ , where A is at least one of the elements of the group Y, Gd, Lu, 0.005≤x≤0.04, or A _{1-x + y} Nd _x V _1-y O _4-z , where A is at least one of the elements of the group Sc, Y, La, Gd, Lu, 0.005≤x≤0.04; 0.005≤y≤0.03; 0.001≤z≤0.1, or [A _1-b B _1.5b ] _{1 + yx} Nd _x V _1-y O _4-z , where A is at least one of the elements of the group Sc, Y, La, Gd, Lu , In - at least one of the elements of the group Mg, Ca, Zn, Sr, 1.5 × 10 ^-5 ≤b≤0,2; 0.005≤x≤0.04; 0.005≤y≤0.03; 0.001≤z≤0.25, or A _1-x Tm _x VO ₄ , where A is at least one of the elements of the group Y, Gd, Lu, 0.005≤x≤0.12, or

A _{1-x + y} Tm _x V _1-y O _4-z , where A is at least one of the elements of the group Sc, Y, La, Gd, Lu, 0.005≤x≤0.12; 0.005≤y≤0.03; 0.001≤z≤0.1, or [A _1-b , B _1.5b ] _{1 + yx} Tm _x V _1-y O _4-z , where A is at least one of the elements of the group Sc, Y, La, Gd, Lu, B - at least one of the elements of the group Mg, Ca, Zn, Sr, 1.5 × 10 ^-5 ≤b≤0,2; 0.005≤x≤0.12; 0.005≤y≤0.03; 0.001≤z≤0.25.

In particular, the active element may contain a rare-earth silicate crystal doped with Tm ³⁺ ions and described by the chemical formula A _{2 + 2y-x} Tm _x Si _1-y O _{5 + y} , where A is at least one of the elements of the Sc group, Y, Gd, Lu; 0.005≤x≤0.15; 0≤y≤0.09.

In particular, the laser may further comprise a Brewster plate mounted in the laser cavity.

In particular, the laser may further comprise a nonlinear optical frequency converter mounted in the laser cavity. In this case, the nonlinear optical frequency converter can be made in the form of a frequency doubler, for example, from a nonlinear optical crystal from the group

KTiOPO ₄ , KNbO ₃ , LiNbO ₃ , LiIO ₃ , β-BaB ₂ O ₄ , LiB ₃ O ₅ .

In particular, the laser may further comprise a deflecting element mounted in the laser cavity between the active element and the nonlinear optical frequency converter, and a laser source made in the form of a diode-pumped solid-state laser and containing an additional active element, and the laser source can be installed in this way that its radiation and radiation at the output of the deflecting element propagate along the same direction. For example, the deflecting element can be made in the form of a dichroic mirror or polarizer.

In particular, the laser source can be electrically connected with an additional power supply unit, an additional thermal stabilization unit, an additional control unit and an additional temperature sensor of the laser diode, as well as an additional active element, an additional device for focusing the radiation of an additional laser diode into an additional active element and an additional laser resonator. In addition, the active element can be made of a vanadate crystal, the additional active element can be made of a YLiFO ₃ crystal doped with Nd ions, and the nonlinear optical frequency converter can be made of a KTiOPO ₄ crystal. In particular, a spectral selector configured to change the radiation wavelength can be installed in the laser cavity. In this case, the spectral selector can be made in the form of a Fabry-Perot interferometer, a Lio filter, or a dispersion prism.

This goal is also achieved by the fact that in the known method of operation of a quasi-three-level solid-state laser with longitudinal diode pumping, during which a current is passed through the laser diode, the radiation of the laser diode is focused inside the active element located between the input and output mirrors, and then reflect from the output surface of the active element, the radiation emitted by the active element is passed through the input and output surfaces of the active element, and the radiation incident on the output the kalo of the resonator is partially passed through it, the radiation reflected from the laser elements is attenuated, and during transients associated with turning on the laser diode or changing the radiation power, the current through the laser diode is changed so that the wavelength of the laser diode coincides with the center absorption lines of the active element of the laser.

In particular, before changing the current through the laser diode, it is possible to measure the dependence of the radiation wavelength of the laser diode on the current passed through it, which is entered into the memory of the current and temperature control unit of the laser diode.

In particular, the plane of polarization of the laser diode radiation can be rotated by 45 ° using a Faraday cell installed between the laser diode and the input mirror.

In particular, the radiation of a laser diode can be converted into circularly polarized using a polarizer and a quarter-wave plate, sequentially installed between the laser diode and the input mirror.

In particular, the radiation of a laser diode can be converted into circularly polarized using a polarizer and a quarter-wave plate, sequentially installed between the laser diode and the input mirror.

In particular, the radiation of a laser diode can be scattered with a transparent optically inhomogeneous plate mounted between the laser diode and the input mirror.

In particular, the intensity distribution of the laser diode radiation beam over its cross-sectional area can be changed using an optical fiber length L> 20 D, installed between the laser diode and the input mirror of the laser cavity, where D is the diameter of the optical fiber, or using a lens made with optical spherical aberration in the range from 0.1 to 0.2 of the optical power of the device for focusing the radiation of a laser diode into an active element.

In particular, the radiation propagating inside the laser cavity can be passed through a nonlinear optical frequency converter mounted in front of the output mirror. In this case, using a nonlinear optical frequency converter, you can double the laser radiation frequency or mix laser radiation with different wavelengths so that the laser emits the radiation of the total frequency.

The inventive quasi-three-level solid-state laser and the method of its operation are connected by a single inventive concept, since they are a device and a method of its use.

The essence of the invention is as follows. By varying the current through the laser diode current and temperature control unit, the current through the laser diode so that the wavelength of the laser diode coincides with the center of the absorption line of the active element of the laser, increase the reliability of the laser and increase the average output radiation power. Additionally, increasing the reliability of the laser and increasing its operating life is achieved by reducing the intensity of the pump radiation reflected back to the laser diode from the optical elements of the laser by introducing into the laser between the laser diode and the active element an optical isolation device that practically does not attenuate the radiation incident on the active element pumping.

The invention is illustrated by drawings, where Figs. 1-3 are block diagrams of embodiments of a quasi-three-level solid-state laser, and Fig. 4 shows plots of the time dependence of the current through the laser diode and the temperature of this diode.

The quasi-three-level laser (Fig. 1) contains a laser diode block 1, which includes a laser diode 2 with an emitter 3. The laser diode block 1 is in thermal contact with the thermal stabilization device 4 connected to the temperature control block of the laser diode 5, which make up the thermal stabilization block, electrically connected to the power supply unit 6. The laser diode unit 1 is connected to the power supply unit 6 using the control unit of the laser diode 7 and the current and temperature control unit of the laser diode, made based on the microcontroller device 8. The microcontroller device 8 and the control unit of the thermal stabilization system 5 are electrically connected to the temperature sensor 9, which is in thermal contact with the laser diode 2.

On the optical axis of the laser diode 2 (FIG. 1), a first focusing device lens 10, an optical isolation system 11, a second focusing device lens 12 and a laser resonator including an input mirror of the resonator 13, a first transparent cooling plate 14, an active element 15 are sequentially arranged , the second transparent cooling plate 16 and the output mirror of the resonator 17. The plates 14 and 16 are in thermal contact with the active element 15.

The second embodiment of a quasi-three-level laser (Fig. 2) is characterized in that in front of the output mirror of the resonator 17, a nonlinear optical crystal 18 is installed on the optical axis, which serves as a radiation frequency doubler.

The third embodiment of the quasi-three-level laser (Fig. 3) is characterized in that it additionally contains a deflecting element made in the form of a dichroic mirror 19, which is mounted in front of the nonlinear optical crystal 18, which serves in this case as a radiation frequency adder. The deflected radiation and the radiation of a laser source, also made in the form of a solid-state laser with diode pumping and set in such a way that its radiation and radiation at the output of the deflecting element propagate along the same direction, are summed up. The laser source contains an additional output mirror 20, an additional active element 21, an additional input mirror 22, additional lenses 23 and 24, between which an additional optical isolation device 25 is installed, a block 26 of an additional laser diode 27, connected with an additional thermal stabilization unit 28.

The laser (figure 1) works as follows. Blocks 4-8 provide such operating conditions for the laser diode 2, in which the wavelength of its radiation during switching on, off, and changing the radiation power of the diode 2 coincides with the maximum absorption of the active element 15, which is provided by the introduction of a control unit for the current and temperature of the laser diode 8 based on a microcontroller device into which the measured dependences of the radiation wavelength of the laser diode 2 on the current and temperature passed through it are introduced. The pump radiation from the emitter 3 of the laser diode 2 passes sequentially through the first lens 10, the optical isolation device 11, the second lens 12, the input mirror of the resonator 13, the first transparent cooling plate 14 and focuses inside the active element 15. Absorbing the pump radiation from the laser diode 2, active element 15 emits radiation in accordance with the scheme of operation of a quasi-three-level laser. The pump radiation is reflected from the mirror deposited on the output surface of the active element 15. This reflected pump radiation propagates in the opposite direction, passing sequentially in the reverse order all the above optical elements and focuses on the emitter 3. This pump radiation, which fell back to the emitter 3, is attenuated due to absorption in the active element, reflection losses from the optical elements of the laser, losses introduced by the optical isolation device 11, and due to optical aberration optical elements in the path of the laser pump radiation. Typical values of the fraction of the pump intensity that returned back to the emitter 3 in the absence of an optical isolation device 11 can reach 10-20% or more. In the claimed invention, the proportion of radiation reflected back decreases to 1-4% or less, i.e. more than 5-20 times compared with the closest analogue.

The laser cavity (Fig. 1) is formed by the input mirror 13 and the output mirror 17. The mirror 13 is completely reflective at the wavelength of the laser transition occurring according to the quasi-three-level generation scheme, and transparent at the wavelength of the pump radiation by the laser diode 2 and at all other possible wavelengths laser transitions of the active element 15. Mirror 17 is partially transparent at the wavelength of the laser transition and is illuminated at all wavelengths of other possible laser transitions of the active element 15. Laser generation is excited ezhdu Mirrors 13 and 17 under the action of the pump radiation into the active element 15.

For the efficient operation of the laser (Fig. 1) at high average radiation powers, additional transparent cooling plates 14 and 16 are used, made of heat-conducting materials and which are in thermal contact with the surface of the active element 15. The surfaces of the plates 14 and 16 are coated with a length to minimize intracavity losses pump waves, the main and other most effective transitions of the active element 15.

In the laser (FIG. 2), a nonlinear optical crystal 18 of the laser frequency doubler is located inside the resonator, in which the radiation at the fundamental frequency circulating inside the resonator is converted to radiation at the double frequency. The output mirror 17 of the resonator is made completely reflecting at a wavelength of radiation of the fundamental frequency, and this mirror is bleached for radiation at a double frequency. As a result, the radiation at the fundamental frequency is locked in the cavity, and the radiation of the second harmonic is emitted.

If a Brewster plate is installed between the second transparent cooling plate 16 and the nonlinear optical crystal 18, this ensures stable laser generation of linearly polarized output radiation.

It should be noted that when a frequency doubler 18 is removed from the laser cavity and the output mirror 17 is replaced by another mirror partially transparent on the length of the main laser transition with a quasi-three-level generation scheme, a laser with such changes will ensure efficient generation at the wavelength of the main transition with a quasi-three-level generation scheme .

The laser (figure 3) works as follows. The pumping of the active element 15 of the laser is carried out in the same way as for lasers, the schemes of which are depicted in figure 1 and figure 2. Laser generation is excited in the resonator formed by the input mirror 13, the output mirror 17. Due to the installation of a deflecting element 19 inside the resonator, the radiation is excited in this resonator with a polarization perpendicular to the plane of the drawing. The resonator of the laser source is formed by an additional input mirror 22 and an additional output mirror 20. The additional active element 21 is pumped in the same way as in a laser (Fig. 1). When using a non-quasi-three-level scheme for generating a laser source, an additional optical isolation device 25 may not be used. The output radiation of the laser source has a polarization lying in the plane of the drawing. This output radiation passes through the deflecting element 19 with minimal attenuation and enters the nonlinear optical crystal 18 of the frequency adder, where both emissions are added, and the laser (Fig. 3) generates at the total frequency. This radiation is output through the output mirror 17, partially transparent to radiation at the total frequency.

The power supply and thermal stabilization of the laser diode 2 usually consists of the following electrically connected units: power supply unit 6, current control unit of the laser diode 7 and temperature control unit of the laser diode 5. The disadvantage of such a system with two-pass pumping of the active element 15 is the existence of time intervals when turning on or turning off the laser when the wavelength of the pump radiation is outside the absorption band of the active element 15. This leads to reflection of the pump radiation This leads to emitter 3 of the laser diode 2 and to its rapid degradation or destruction.

To eliminate this drawback, the claimed invention uses a current and temperature control unit of the laser diode 8, made on the basis of microcontroller device 8 (Fig.1-3). The microcontroller device 8 is connected to the current control unit of the laser diode 7, the temperature control unit of the laser diode 5 and to the temperature sensor 9, while the connection between the unit 5 and the sensor 9 is broken. The microcontroller device 8 contains information about the dependence of the temperature of the emitter 3 on the current through the laser diode 2 at a given case temperature of the laser diode 2. Since the temperature of the emitter 3 determines the radiation wavelength of the laser diode 2, it is necessary to increase the case temperature at low currents to maintain the radiation wavelength constant laser diode 2. A program is entered into the microcontroller device 8, which, when the current of the laser diode 2 changes, in accordance with the above dependence, is set flushes the desired body temperature that achieves the highest absorption of the radiation of the laser diode 2 in the active element 15. Thus, when establishing any current of the laser diode 2 is reached the minimum back reflection of the pump radiation and, thus, increases the reliability of the quasi-three laser.

The time dependences of the temperature of the laser diode 2 and the current through it are shown in Fig. 4 (curves 29 and 30, respectively). From the moment of switching on to the time t _{1, the} current through the laser diode increases from 0 to a threshold value

I _then , at which its generation begins. At this moment, the parameters of the thermal stabilization device 4 of the diode are such that the temperature of the laser diode 2 case reaches a value of T _then , at which the radiation wavelength corresponds to the center of the absorption line of the active element 15. In this case, the absorption of the pump radiation in the active element 15 will be maximum. From time t ₁ to time t _{2, the} current through the laser diode 2 increases according to a predetermined law, for example, linear. The temperature of the laser diode 2 then begins to decrease according to such a law, when each current value of the diode 2 corresponds to the temperature of the diode 2, at which the diode 2 will generate radiation that exactly matches the center of the absorption line of the active element 15. Such changes in the current and temperature of the diode 2 continue until t ₃ , when the current of the diode 2 reaches a predetermined nominal value of I _o and, accordingly, the diode temperature - the values of T _o at which the required output laser characteristics are achieved, for example, power output. From this moment, the values of the diode current and the diode temperature remain unchanged for the entire period of stable operation of the laser diode, ending at time t ₄ . The laser diode 2 is safely turned off in the reverse order. The current of the diode 2 decreases, and its temperature rises until t ₅ stops the generation of the diode. After that, the temperature of diode 2 gradually decreases to room temperature.

During the operation of lasers, there are restrictions on the rate of change of temperature of intracavity optical elements, since at high speed of heating or cooling of such elements they can be destroyed. For example, KNb0 ₃ , which is widely used as a nonlinear optical crystal for frequency conversion, is destroyed when the heating rate exceeds 5 deg / min. Therefore, the heating or cooling rate of the laser diode 2 and the rate of increase or decrease of its output power must be maintained at a safe level that does not lead to the destruction of the nonlinear optical crystal and other intracavity optical elements. In this regard, the slope of curves 29 and 30 (Fig. 4) at the initial and final time intervals should not exceed the maximum capabilities of the heated and thermostabilized optical elements of the laser resonator.

In lasers (Fig. 1 - Fig. 3), the temperature of the diode 2 is controlled by the microcontroller device 8 through the control unit 5, made in the form of a Peltier element based on the data on the current through the diode 2. The signal from the temperature sensor 9 (thermistor) entering the microcontroller device 8 is a feedback signal necessary to maintain the required current temperature of the laser housing 2. This temperature is calculated by the formula:

T _t = T ₀ + K (I ₀ -I _t ),

where T _t is the current temperature of diode 2, T ₀ is the temperature of diode 2 at the operating current, K is a coefficient determined experimentally and depends on the thermal resistance pn junction - case and direct voltage drop across diode 2, I _t is the current current of the diode 2, I ₀ - operating current of the diode.

Thus, when the currents of the diode 2 are lower than the working one, the housing of the diode 2 is maintained at a temperature higher than the working one, thereby ensuring a constant temperature of the radiating transition.

The control unit of the laser diode 7 sets the rate of increase or decrease of the current of diode 2. Using the control unit 5 (Peltier element) sets the permissible rate of change of the temperature of the diode 2. From the microcontroller device 8 to the Peltier control unit 5 commands (voltages) that change the temperature of the diode 2 so that the radiation wavelength of the diode 2 coincides with the absorption line of the active element 15. At the moment of reaching the specified nominal value, the current through the diode 2 and the current through the Peltier element 5 stabilize with omoschyu appropriate electronic circuitry. When a signal to turn off the laser is supplied to the laser control unit 7, this unit generates control signals that begin to reduce the current I through the laser diode 2 at an acceptable speed to a threshold value of I _pore . Accordingly, the temperature of the diode 2 is changed, which maintains the coincidence of the radiation wavelength and the absorption band of the active element 15.

In the claimed invention, as an optical isolation device, it is proposed to use optical fiber. For this, the length of the optical fiber should be such that any image in the fiber is distorted to a close to uniform distribution of intensity over the cross-sectional area of the fiber. It is known that such a fiber length should exceed the fiber diameter by 10-50 times. With a fiber diameter of 0.5 mm, the fiber length required for optical isolation is only 5-25 mm.

Typically, laser diode 2 generates radiation in the form of a strip with a thickness of about 1 μm. The radiation of a laser diode 2 of this geometry is focused into an optical fiber, and after passing through the fiber, the radiation uniformly fills the output section of the fiber. The reflection of radiation passes back through the fiber and enters in the form of a circle on the luminous region of the emitter 3. The attenuation of the intensity of the reflected radiation is equal to the ratio of the cross-sectional area of the fiber to the area of the luminous region of the diode 2.

Optical isolation is also ensured by focusing the pump radiation to a point on the optical axis that does not coincide with both surfaces of the active element 15. With this mismatch, the radiation reflected from the surface of the active element 15 will be weakened due to the lack of confocal focus of the emitting plane of the emitter 3 of the laser diode 2 and reflective surfaces active element 15.

Optical isolation is also ensured when the optical axis of the laser cavity is tilted to a certain angle with respect to the direction of the axis of propagation of the pump radiation. In this case, the reflected radiation returns at a certain angle to the incident one and focuses outside the emitting region of the laser diode 2 or only partially overlaps with it. If this angle is less than 2 °, then the back reflection is unacceptably large and leads to the destruction of the emitter of the diode. If the angle is greater than 10 °, then there is a case of longitudinal noncollinear pumping, in which the laser operation efficiency is unacceptably reduced. Optical isolation is also ensured if a Faraday cell is installed between lenses 10 and 12, which makes it possible to attenuate reflected radiation by a factor of 100 or more.

Optical isolation is also ensured if a polarizer and a quarter-wave plate are sequentially installed in the radiation path, and the polarizer is oriented to transmit linearly polarized pump radiation, and the quarter-wave plate is oriented so that it converts the linear polarization of the pump radiation into circular polarization. After reflection and passage of the quarter-wave plate in the opposite direction, the radiation acquires linear polarization, and its plane of polarization, crossed with the polarizer, is rotated 90 ° with respect to the incident radiation. As a result, the radiation is attenuated. Such a system can attenuate radiation tens of times.

Optical isolation is also ensured if a transparent optically inhomogeneous plate with dimensions of inhomogeneities much smaller than the transverse size of the pump radiation beam is installed in front of the active element 15 in the path of the pump radiation. In this case, the optical inhomogeneities provide a deviation of the radiation transmitted through it by a parallel beam at an angle of at least not greater than the numerical aperture of the focusing device. The pump radiation transmitted through this plate, due to optical inhomogeneities, partially deviates by a certain angle. The diameter of the pump beam in the active element 15 is practically unchanged. However, with the return pass of the reflected radiation, the beam deviates even more (its divergence increases). As a result, the reflected radiation returned to the diode 2 will be substantially attenuated.

Optical isolation is also provided if the focusing device uses lenses 10 and 12, which have sufficiently large optical aberrations. At large aberrations, the reflected radiation is focused in the plane of the emitting surface of the laser pump diode 2 in the form of a strip with a width much larger than the dimensions of the emitting region.

In the claimed invention, the active element 15 is made of a single-cation crystal (GdVO ₄ , YVO ₄ , LaVO ₄ ) or mixed (Gd _x Y _1-x VO ₄ , Gd _1-x La _x VO ₄ ,

Y _1-x La _x VO ₄ ) vanadate doped with Nd ³⁺ or Tm ³⁺ ions. These crystals in comparison with the known crystals (Y ₃ Al ₅ O ₁₂ , YAlO ₃ , LiYF ₄ ) have higher thermal conductivity and induced transition cross section, which makes it possible to realize highly efficient lasers with a high average output radiation power.

Mixed vanadate crystals allow you to change the laser properties of active elements by changing the concentration ratio of Gd, Y, La ions. In particular, in the mixed Nd ³⁺ : Gd _x Y _1-x VO ₄ vanadate, a change in x from 0 to 1 allows the generation wavelength to be tuned from 914 to 912 nm.

By installing an active element 15 made of a mixed vanadate crystal, with the possibility of moving across the optical axis of the resonator, it is possible to adjust the radiation frequency, since usually Gd, Y, and La are not uniformly distributed in the cross section of the active element 15. In this case, the movement of the active element 15 leads to the generation of various sections of the active element 15 with different concentrations of the components and, accordingly, provides a tuning of the radiation frequency. For example, you can use the active element 15, which has a gradient of the concentration of Gd, Y and La, which coincides with the direction of movement of the active element 15 in the transverse direction relative to the axis of the laser resonator.

The following are examples of specific implementation.

Example 1. As a laser diode 2, a SDL semiconductor laser was used with an output power of up to 4 W with an emitter 3 length of 100 μm. Lenses 10 and 12 of the focusing device were illuminated at a pump wavelength of 808 nm. Lenses 10 and 12 are made with a focal length of 7 mm. Active element 15 was made from a mixed vanadate crystal Gd _0.3 Y _0.7 VO ₄ activated by neodymium ions with a concentration of 1%. The active element 15 with a length of 2 mm was cut in the direction of the optical axis. The input and output surfaces of the active element 15 were illuminated at a wavelength of 913 nm generated by the quasi-three-level radiation generation scheme, a pump wavelength of 808 nm, and a wavelength of the most intense neodymium laser transition of 1.064 μm. Transparent cooling plates 14 and 16 1 mm thick, made of YAG crystal, had antireflection coatings similar to the active element. These plates were brought into contact with the input and output surfaces of the active element 15 using a special mechanical device. The pump radiation was focused inside the active element 15 at a distance of 0.6 mm from the input surface of the active element 15. The laser cavity was formed by the input mirror 13 and the output mirror 17. The mirror 13 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm. Mirror 17 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm, 2% for a wavelength of 456 nm.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 20% of the rise time of the pump current. In this case, the average laser output power was 200 mW. The emitter 3 of the laser diode 2 was destroyed by the reverse pump radiation at a radiation power density of the laser diode 2 of 260 W / mm ² .

Example 2. As a laser diode 2, a SDL semiconductor laser was used with an output power of up to 4 W with an emitter 3 length of 100 μm. The power supply of the semiconductor laser was modified by connecting in accordance with figure 1 of the microcontroller device 8. The lenses 10 and 12 of the focusing device were illuminated at a pump wavelength of 808 nm. An optical fiber with a core diameter of 100 μm and a length of 150 cm was used as an optical isolation device 11. Lenses 10 and 12 were made with a focal length of 7 mm.

Active element 15 was made from a mixed vanadate crystal Gd _0.3 Y _0.7 VO ₄ activated by neodymium ions with a concentration of 1%. The active element 15, 2 mm long, was cut in the direction of the optical axis. The input and output surfaces of the active element 15 were illuminated at a wavelength of 913 nm generated by the quasi-three-level radiation generation scheme, a pump wavelength of 808 nm, and a wavelength of the most intense neodymium laser transition of 1.064 μm. Transparent cooling plates 14 and 16 1 mm thick, made of YAG crystal, had antireflection coatings similar to the active element. These plates were brought into contact with the input and output surfaces of the active element 15 using a special mechanical device. The pump radiation was focused inside the active element 15 at a distance of 0.6 mm from the input surface of the active element 15. The laser cavity was formed by the input mirror 13 and the output mirror 17. The mirror 13 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm. Mirror 17 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm, 2% for a wavelength of 456 nm.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 460 mW.

Example 3. The same as in example 2, but in the laser cavity there is a frequency doubler 18 made of a KNbO ₃ nonlinear optical crystal with dimensions 3 × 3 × 2 mm and cut in the direction of synchronism of the second type of second harmonic generation. The surfaces of this crystal 18 were illuminated at all of the wavelengths listed above.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 456 nm was 210 mW.

Example 4. The same as in example 2, but the optical isolation device, including lenses 10 and 12, is absent, and the angle between the propagation axis of the laser diode and the optical axis of the laser cavity is 3 °.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 360 W / mm _{2, the} average laser power at a wavelength of 913 nm was 300 mW.

Example 5. The same as in example 3, but the angle between the propagation axis of the laser diode and the optical axis of the laser cavity is 6 °.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 360 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 240 mW.

Example 6. The same as in example 3, but the angle between the propagation axis of the laser diode and the optical axis of the laser cavity is 10 °.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 360 W / mm ^{2, the} average laser power was 200 mW.

Example 7. The same as in example 2, but the lenses 10 and 12 are absent, and the optical isolation device 11 is made in the form of a 45-degree Faraday cell at a wavelength of 808 nm from the laser diode 2.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 440 mW.

Example 8. The same as in example 6, but the optical isolation device 11 is made in the form of a polarizer and a quarter-wave plate, sequentially mounted on the propagation axis of the radiation of the laser diode 2.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 380 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 390 mW.

Example 9. The same as in example 2, but the optical isolation device 11 is made of fused quartz in the form of a transparent optically inhomogeneous plate with a thickness of 2 mm, providing irregular beam cross-sectional deviations of the radiation transmitted through it at an angle of 0.1 to 5 °.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 410 mW.

Example 10. The same as in example 2, but the optical isolation device 11 is missing, and the lenses 10 and 12 are made with optical spherical aberration 0.1 of the optical power of the focusing device.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 370 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 360 mW.

Example 11. The same as in example 10, but the lenses 10 and 12 are made with optical spherical aberration of 0.15 optical power of the focusing device.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 370 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 320 mW.

Example 12. The same as in example 10, but the lenses 10 and 12 are made with optical spherical aberration 0.2 of the optical power of the focusing device.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 370 W / mm ^{2, the} average laser power at a wavelength of 913 nm was 340 mW.

Example 13. The same as in example 2, but the active element 15 is made of a mixed vanadate crystal Gd _0.3 Y _0.7 VO ₄ activated by thulium ions with a concentration of 5%.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 1924 nm was 400 mW.

Example 14. The same as in example 13, but the active element 15 is made of a crystal of a single cationic vanadate GdVO ₄ activated by thulium ions with a concentration of 5%.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 1924 nm was 420 mW.

Example 15. The same as in example 13, but the active element 15 is made of a crystal of a single cationic vanadate YVO ₄ activated by thulium ions with a concentration of 5%.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 1924 nm was 440 mW.

Example 16. The same as in example 13, but the active element 15 is made of a single cationic vanadate crystal LaVO ₄ activated by thulium ions with a concentration of 5%.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 911 nm was 360 mW.

Example 17. The same as in example 13, but the active element 15 is made of a mixed vanadate crystal Gd _0.7 Y _0.3 VO ₄ activated by thulium ions with a concentration of 7%.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 912 nm was 330 mW.

Example 18. The same as in example 13, but the active element 15 is made of a crystal of mixed vanadate Gd _0.7 Y _0.3 VO ₄ activated by thulium ions with a concentration of 7%.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 912 nm was 320 mW.

Example 19. The same as in example 3, but the frequency doubler 18 is made of a non-linear optical crystal KTiOPO ₄ .

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 456 nm was 200 mW.

Example 20. The same as in example 19, but the frequency doubler 18 is made of a nonlinear optical crystal LiNbO ₃ .

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 456 nm was 180 mW.

Example 21. The same as in example 19, but the frequency doubler 18 is made of a nonlinear optical crystal LiJO ₃ .

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 456 nm was 380 mW.

Example 22. The same as in example 19, but the frequency doubler 18 is made of a non-linear optical crystal β-BaB ₂ O ₅ .

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power was 380 mW.

Example 23. The same as in example 19, but the frequency doubler 18 is made of a nonlinear optical crystal LiB ₃ O ₅ .

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 456 nm was 370 mW.

Example 24. In the specific embodiment (FIG. 3), the active element 20 of the laser source is made on the basis of an Nd: LiYF ₄ crystal with a radiation wavelength of 1.047 μm, and the active element 15 is made of crystal

Y _0.985 Nd _0.005 Sc _0.01 V _0.98 O _3.95 with a radiation wavelength of 0.9145 μm.

As laser diodes 2 and 27, a SDL semiconductor laser was used with an output power of up to 5 W with an emitter length of 3 and 26 of 100 μm. Lenses 10, 12, 23 and 24, made with a focal length of 7 mm, were illuminated at a pump wavelength of 808 nm. As an optical isolation device 11, an optical fiber with a core diameter of 100 μm and a length of 100 cm was used. The input and output surfaces of the active element 15 were illuminated at a wavelength of 0.9145 μm and a pump wavelength of 808 nm. The input and output surfaces of the active element 15 were illuminated at a wavelength of 1.047 μm and a pump wavelength of 808 nm. Mirror 13 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm. Mirror 17 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm, 2% for a wavelength of 456 nm. Mirror 22 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm. Mirror 23 had a radius of curvature of 50 mm and the following reflection coefficient values: 2% for a wavelength of 808 nm, 99.8% for a wavelength of 913 nm, 10% for a wavelength of 1064 nm, 2% for a wavelength of 456 nm.

A nonlinear optical frequency converter 18 is made in the laser cavity (Fig. 3), made of a non-linear optical KNbO ₃ crystal with dimensions 3 × 3 × 2 mm and cut in the synchronism direction to generate the second harmonic. The surfaces of this crystal 18 were illuminated at all of the wavelengths listed above. In front of the converter 18, a deflecting element 19 is installed, made in the form of a dichroic mirror, which is completely reflective for the radiation of the active element 15 and completely transmits for the radiation of the active element 21.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2 of} both active elements 15 and 23, the average laser power at a wavelength of 488 nm was 80 mW.

Example 25. The same as in example 24, but the deflecting element 19 is made in the form of a polarizer.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2 of} both active elements 15 and 23, the average laser power at a wavelength of 488 nm was 90 mW.

Example 26. The same as in example 2, but in the laser cavity between the active element 15 and the mirror 17 mounted Fabry-Perot interferometer, which allows you to tune the wavelength of the laser radiation.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 488 nm was 360 mW.

Example 27. The same as in example 26, but in the laser cavity between the active element 15 and the mirror 17 installed a Lyo filter, which allows you to tune the wavelength of the laser radiation.

Experience has shown that the wavelength of the laser diode radiation coincided with the center of the absorption line of the active element of the laser for 100% of the rise time of the pump current. At a pump radiation power density of 400 W / mm ^{2, the} average laser power at a wavelength of 488 nm was 360 mW.

The given examples of specific performance show that the task of increasing the reliability of the laser, increasing its operating life and increasing the average radiation power is achieved using the claimed invention.

Claims (34)

1. Quasi-three-level solid-state laser containing a laser diode for longitudinal pumping, an active element, a device for focusing the radiation of a laser diode into an active element and a laser resonator, the active element being configured to provide an even number of passes of the laser diode radiation through it, characterized in that it additionally contains a temperature sensor of the laser diode, a thermal stabilization unit, a control unit for current and temperature of the laser diode, electrically coupled to a laser diode, a thermostat unit stabilization and laser diode temperature sensor, wherein the current control unit and the temperature of the laser diode is configured to simultaneously varying the diode laser current and temperature. 2. The laser according to claim 1, characterized in that the control unit current and temperature of the laser diode is made on the basis of a microcontroller device. 3. The laser according to claim 1, characterized in that the angle between the axis of propagation of the radiation of the laser diode and the optical axis of the laser cavity is in the range from 1 to 10 °. 4. The laser according to claim 1, characterized in that it further comprises an optical isolation device installed between the laser diode and the active element, the optical isolation device configured to attenuate pump radiation reflected from the optical elements of the laser resonator. 5. The laser according to claim 4, characterized in that the optical isolation device is made in the form of a 45-degree Faraday cup at the wavelength of the radiation of the laser diode. 6. The laser according to claim 4, characterized in that the optical isolation device contains a polarizer and a quarter-wave plate, sequentially mounted on the propagation axis of the radiation of the laser diode. 7. The laser according to claim 4, characterized in that the optical isolation device is made in the form of a transparent optically inhomogeneous plate, providing irregular deviations of the radiation transmitted through it at an angle of not more than 5 ° over the beam cross section. 8. The laser according to claim 4, characterized in that the focusing device contains two lenses. 9. The laser of claim 8, characterized in that between the lenses there is a segment of optical fiber of length L satisfying the ratio L> 20 D, where D is the diameter of the optical fiber, with both ends of the fiber located in the foci of the lenses. 10. The laser of claim 8, characterized in that the lenses are made with optical spherical aberration in the range from 0.1 to 0.2 of the optical power of the device for focusing the radiation of a laser diode into an active element. 11. The laser according to claim 1, characterized in that the active element is mounted with the ability to move across the optical axis of the resonator. 12. The laser according to claim 1, characterized in that the active element contains at least one crystal of a single cation or mixed vanadate doped with Nd ³⁺ or Tm ³⁺ ions. 13. The laser according to claim 1, characterized in that it further comprises a Brewster plate mounted in the laser cavity. 14. The laser according to claim 1, characterized in that it further comprises a nonlinear optical frequency converter mounted in the laser cavity. 15. The laser according to 14, characterized in that the nonlinear optical frequency converter is made in the form of a frequency doubler. 16. The laser according to clause 15, wherein the frequency doubler is made of nonlinear optical crystals from the group of KTiOPO ₄ , KNbO ₃ , LiNbO ₃ , LiIO ₃ ,
β-BaB ₂ O ₄ , LiB ₃ O ₅ . 17. The laser according to 14, characterized in that it further comprises a deflecting element mounted in the laser cavity between the active element and the nonlinear optical frequency converter, and a laser source made in the form of a diode-pumped solid-state laser and containing an additional active element, moreover, the laser source is installed in such a way that its radiation and radiation at the output of the deflecting element propagate along the same direction. 18. The laser according to 17, characterized in that the deflecting element is made in the form of a dichroic mirror. 19. The laser according to 17, characterized in that the deflecting element is made in the form of a polarizer. 20. The laser according to clause 16, wherein the laser source is electrically connected to an additional power supply, an additional thermal stabilization unit, an additional control unit and an additional temperature sensor of the laser diode, as well as an additional active element, an additional device for focusing radiation of an additional laser diode into an additional active element and additional laser cavity. 21. The laser according to clause 16, wherein the active element contains a vanadate crystal, the additional active element contains a YLiF0 ₃ crystal doped with Nd ions, and the nonlinear optical frequency converter contains a KTiOPO ₄ crystal. 22. The laser according to claim 1, characterized in that a spectral selector is arranged in the laser cavity, configured to change the radiation wavelength. 23. The laser according to item 22, wherein the spectral selector is made in the form of a Fabry-Perot interferometer. 24. The laser according to item 22, wherein the spectral selector is made in the form of a Lyo filter. 25. The method of operation of a quasi-three-level solid-state laser with longitudinal diode pumping, during which a current is passed through a laser diode, the laser diode radiation is focused inside the active element located between the input and output mirrors, and then the radiation emitted by the active element is reflected from the output surface of the active element pass through the input and output surfaces of the active element, and the radiation incident on the output mirror of the resonator is partially passed through it, different In that they attenuate the laser diode radiation reflected from the laser elements, and during transients associated with turning on the laser diode or changing its radiation power, the current through the laser diode is changed so that the radiation wavelength of the laser diode coincides with the center of the absorption line active laser element. 26. The method according A.25, characterized in that before changing the current through the laser diode, measure the dependence of the radiation wavelength of the laser diode on the current passed through it, which is entered into the memory of the control unit of the current and temperature of the laser diode. 27. The method according A.25, characterized in that the plane of polarization of the radiation of the laser diode is rotated by 45 ° using a Faraday cell installed between the laser diode and the input mirror. 28. The method according A.25, characterized in that the radiation of the laser diode is converted into circularly polarized using a polarizer and a quarter-wave plate, sequentially installed between the laser diode and the input mirror. 29. The method according A.25, characterized in that the radiation of the laser diode is scattered using a transparent optically inhomogeneous plate mounted between the laser diode and the input mirror. 30. The method according A.25, characterized in that the intensity distribution of the radiation beam of the laser diode over its cross-sectional area is changed using a length of optical fiber between the laser diode and the input mirror of length L> 20 D, where D is the diameter of the optical fiber. 31. The method according A.25, characterized in that the intensity distribution of the radiation beam of the laser diode over its cross-sectional area is changed using a lens made with optical spherical aberration in the range from 0.1 to 0.2 of the optical power of the device for focusing the radiation of the laser diode in active element. 32. The method according A.25, characterized in that the radiation propagating inside the laser cavity is passed through a nonlinear optical frequency converter mounted in front of the output mirror. 33. The method according to p, characterized in that using a nonlinear optical frequency converter double the laser radiation frequency. 34. The method according to p. 33, characterized in that inside the nonlinear optical frequency converter, laser radiation with different wavelengths is mixed so that the laser emits radiation of the total frequency.

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