CN107425407B - Tunable blue light radiation source based on inner cavity self-frequency multiplication and implementation method - Google Patents

Abstract

The invention belongs to the field of nonlinear optics and aims to realize blue light output with continuously tunable wavelength. It has high technical performance such as high conversion efficiency, simple structure, low price and miniaturization, and has practical and industrial value. To this end, the technical solution adopted by the present invention is a tunable blue light radiation source based on intracavity self-frequency doubling and an implementation method, which includes the following steps: using an Nd:YAG (neodymium-doped garnet) Q-switched laser to generate a polarization direction along the vertical direction The 1064nm linearly polarized light in the direction is condensed by the focusing lens group, and the laser polarization state is adjusted through the 1064nm half-wave plate strip and incident on the frequency-doubled KTP crystal that meets the type II phase matching conditions. After frequency-doubling, the polarization state is generated along the vertical direction. The 532nm laser enters the OPO system after being reflected by a 45° high-reflection mirror, and pumps the KTP crystal in the OPO cavity controlled by an electric galvanometer rotating platform. The invention is mainly used in the design and manufacture of tunable blue light radiation sources.

Description

Tunable blue light radiation source based on intracavity self-frequency doubling and its implementation method

Technical field

The invention relates to the field of nonlinear optics, specifically, to a tunable blue light radiation source based on intracavity self-frequency doubling and an implementation method.

Background technique

Blue light refers to electromagnetic waves with wavelengths between 400-480nm. With its unique physical properties, blue light has huge application potential in many practical fields. First of all, blue light is one of the three primary colors. High-brightness blue laser can effectively improve the color range and brightness of color displays, and has the ability to improve color display effects; secondly, blue light has a shorter wavelength than red light, so it has diffraction It has the characteristics of small effect, high resolution, small focused spot size, etc. These characteristics allow it to increase the information capacity by nearly an order of magnitude in the fields of high-density optical storage and digital video technology; blue laser is the window for ocean transmission, and the attenuation coefficient Small, strong anti-interference ability, suitable for underwater communication and sensing ocean information; in addition, blue laser can be used to capture and dampen the thermal vibration of cesium atoms, eliminate Doppler broadening caused by thermal vibration, and provide accurate measurement of spectral lines Guaranteed; in addition, blue laser also has important applications in fields such as medical testing and laser entertainment. Blue laser has huge advantages in the above fields, but compared with the mature 532nm green laser technology, blue laser lacks effective acquisition methods and its application cost is high.

At present, the main means to obtain all-solid-state blue lasers mainly include: (1) semiconductor lasers that use semiconductor materials such as GaN (gallium nitride) to directly realize blue-band laser output. This method has the advantages of small size and high efficiency, but the spot quality is poor. Poor; (2) Frequency doubling of infrared semiconductor lasers based on single frequency and high beam quality produces blue lasers, but the output power is low; (3) Blue lasers based on upconversion materials as gain media, but the stability of the output blue light is relatively low Poor; (4) Blue laser is generated based on nonlinear optical frequency conversion methods such as frequency doubling and frequency doubling and frequency tripling of solid lasers, but involves many nonlinear processes and low conversion efficiency. In addition, there is a frequency-doubled blue light generation concept based on periodic polarization crystals. All the above solutions can obtain blue laser output of a single wavelength. The above processes are currently the most efficient acquisition methods in the field of blue laser. Chinese invention patent 201510923025.3 discloses a tunable blue light radiation source based on a sector-shaped periodic polarization crystal. The light source includes a wavelength-tunable infrared semiconductor laser; a collimation focusing system and a sector-shaped periodic polarization crystal. The sector periodic polarization As a frequency doubling crystal for infrared pump light, the crystal period can be adjusted for different infrared wavelengths to achieve tunable blue light output. The disadvantage of this system is that the tuning range of the tunable red light semiconductor laser is small, resulting in a limited blue light tuning range. At the same time, the production of periodic polarized crystals is difficult and the damage threshold is low, which limits the practicality and output power of the tunable blue light system. Currently, there are few methods to achieve tunable blue light, and the technology is not mature.

Laser self-frequency doubling crystal refers to a crystal that simultaneously serves as a laser gain medium and a nonlinear optical frequency doubling crystal. Frequency-doubled laser output can be directly achieved based on self-frequency doubling crystals, and the system structure is compact. However, laser tuning characteristics based on laser self-frequency doubling crystals are limited and there are few types of crystals. Compared with laser crystals, nonlinear optical parametric gain crystals are more flexible in application and have more types. If the nonlinear optical parametric gain crystals work as frequency doubling crystals at the same time, nonlinear optical self-frequency doubling crystals can be realized.

Inorganic crystals, such as KTP (potassium titanyl phosphate) crystal, BBO (barium metaborate) crystal and PPLN (periodic polarized lithium niobate) crystal, etc., rely on their large nonlinear coefficient, small absorption coefficient and phase coordination. Condition, is a very commonly used crystal in nonlinear frequency transformation. Among them, KTP crystal is a typical crystal. KTP crystal is the abbreviation of KTiOPO ₄ (potassium titanyl phosphate) crystal. It belongs to the orthorhombic crystal system, space group Pna21, point group mm2. It has a large nonlinear coefficient, a wide allowable temperature and allowable angle, and a high Damage threshold, wide light transmission range, good physical, chemical and mechanical properties. Due to the birefringence characteristics of KTP crystals, the angular phase matching technology based on KTP crystals is relatively mature and is suitable for various nonlinear optical frequency conversion methods such as frequency doubling (SHG), sum frequency (SFG), and optical parametric oscillation (OPO). Under the appropriate cutting angle of the KTP crystal, multiple phase matching processes can be satisfied simultaneously in the KTP crystal, and multiple nonlinear frequency conversion processes can be realized. If the crystal cutting angle and laser wavelength can be designed so that a KTP crystal can satisfy the OPO process, SHG process and SFG process at the same time, even if the KTP crystal becomes a nonlinear self-frequency doubling crystal, tunable multi-wavelength laser output can be obtained. In fact, the parameters of the crystal can be designed according to the wavelength requirements of the blue laser, so that a KTP crystal can be used as an OPO crystal and simultaneously as an SHG and SFG crystal, achieving self-frequency doubling in the OPO cavity to obtain multi-wavelength tunable blue light output.

Contents of the invention

In order to overcome the shortcomings of the existing technology, the present invention aims to propose a method and device for obtaining a blue light radiation source with continuously tunable wavelength, so as to achieve blue light output with continuously tunable wavelength. This blue light acquisition method has high technical performance such as high conversion efficiency, simple structure, low price, and miniaturization, making it more practical and industrialized. To this end, the technical solution adopted by the present invention is to implement a tunable blue light radiation source based on intracavity self-frequency doubling, which includes the following steps: using an Nd:YAG (neodymium-doped garnet) Q-switched laser to generate a polarization direction along the vertical direction The 1064nm linearly polarized light shrinks through the focusing lens group, adjusts the laser polarization state through the 1064nm half-wave plate strip, and is incident into the frequency-doubled KTP crystal that meets the type II phase matching conditions. After frequency-doubling, the polarization state is generated along the vertical direction. The 532nm laser enters the OPO system after being reflected by a 45° high-reflection mirror, and pumps the OPO inner-cavity KTP crystal controlled by an electric galvanometer rotating platform. The inner-cavity KTP crystal serves as a parametric gain crystal and can produce a beam of polarization state with a wavelength near 1.3 μm. Tunable idler light along the vertical direction and a corresponding tunable signal light with a polarization state of 700-900nm along the horizontal direction. The front and rear cavity mirrors of the OPO system are coated to ensure that the signal light oscillates in the cavity to improve the cavity. The power density of the internal signal light, the high power density signal light oscillated in the cavity, simultaneously meets the Class I phase matching conditions required for frequency multiplication in the intra-cavity parametric gain KTP crystal, that is, the intra-cavity KTP crystal simultaneously functions as a parametric gain crystal and frequency multiplication The function of the crystal is to finally obtain the tunable blue light output generated by the frequency doubling of the tunable signal light, and the polarization state of the blue light is linearly polarized light along the vertical direction. At the same time, combined with the angle phase matching of the KTP crystal, the galvanometer rotation system is controlled by the computer. The voltage on the cavity changes the angle of the KTP crystal in the cavity, thereby achieving blue light output with rapidly tunable wavelength.

Place another parametric gain KTP crystal in the resonant cavity. All parameters are the same as the previously placed self-frequency doubling KTP crystal. By controlling the rotation angles of the two crystals through the galvanometer rotation system 10, three wavelengths of tunable blue light can be obtained at the same time. The wavelength component of color laser comes from the frequency doubling process of the two wavelength signal lights oscillating in the cavity and the sum frequency process between the two wavelengths.

The cutting angle of the self-frequency doubling KTP crystal satisfies the optical parametric oscillation type II phase matching conditions, that is:

ν _532nm ＝ν _signal +ν _idler

Among them, υ _532nm , υ _signal and υ _idler represent the frequency of 532nm laser, signal light and idler light in the parametric oscillation process, n ⁺ _532nm , n ^- _signal and n ⁺ _idler respectively represent the vertically polarized 532nm laser, horizontal The refractive index of the polarized signal light and the vertically polarized idler light in the KTP crystal. λ _signal and λ _idler respectively represent the wavelengths of signal light and idler light.

Under the 532nm green light pump, a linearly polarized signal light of about 800nm oscillating in the cavity with the same polarization state as the 532nm green light is generated, as well as an idler light of about 1300nm with a polarization state orthogonal to it. At the same time, the intracavity oscillation The signal light also satisfies the type I phase matching condition of frequency doubling in the self-frequency doubling KTP crystal 8, that is:

2×ν _signal =ν _blue

Among them, υ _blue represents the frequency of signal light and blue light respectively; n ⁺ _blue represents the refractive index of vertically polarized blue light in the KTP crystal; λ _blue represents the wavelength of blue light.

Produce a blue laser whose polarization state is orthogonal to the signal light. This blue laser is collinearly transmitted with the idle frequency light generated by the previous nonlinear process. After being filtered by a 45° high-reflection mirror, the blue laser output can be obtained. .

By changing the voltage applied to the galvanometer rotating platform system through the computer, the phase matching angle of the self-frequency doubling KTP crystal is controlled, and then the signal light of the tuned intracavity oscillation can be obtained. The signal light of different wavelengths can be controlled by the self-frequency doubling KTP crystal. The frequency doubling process occurs in the process, thereby obtaining a blue laser output with a continuously tunable wavelength; the thickness L of the self-frequency doubling KTP crystal in the beam propagation direction is 1 to 2 mm.

The tunable blue light radiation source is based on the self-frequency doubling of the inner cavity. The structure is: the pump source uses an Nd:YAG Q-switched laser; the pump light frequency doubling crystal uses a KTP crystal, and the cutting angle of the frequency doubling crystal meets the Class II phase matching conditions; OPO System, the system is equipped with a KTP crystal inside, and the cutting angle is θ = 65.2°, The side is optically polished and specially coated. The inner cavity KTP crystal is placed on a rotatable galvanometer platform. The rotatable galvanometer platform is connected to a computer and uses computer control to change its external machine voltage to achieve the rotation angle.

Specifically, the laser is a neodymium-doped yttrium aluminum garnet Nd:YAG Q-switched laser, the output wavelength is 1064nm, the pulse width is in the order of ns, and the polarization state is linearly polarized light polarized along the vertical direction; it also includes receiving The laser emitted light is composed of a focusing lens group composed of a focusing convex lens and a focusing concave lens. The 1064nm half-wave plate is installed after the focusing lens group and is used to adjust the polarization state of the 1064nm laser to meet the Class II phase matching conditions in the frequency-doubled KTP crystal. ; The size of the self-frequency doubling KTP crystal in the OPO cavity is 10×10×2mm ^3. The sides are optically polished and specially coated to meet the high transmittance of 400~532nm, 700~900nm and 1300~1500nm bands. The crystal angle is rotated through the galvanometer rotating platform. The phase matching conditions of the crystal can be changed to achieve wavelength tuning;.

The frequency-doubled KTP crystal has a cutting angle of θ=90°. Size 15×15×10mm ³ is used to frequency-double the 1064nm laser to generate high-energy 532nm laser. The generated 532nm laser is linearly polarized light polarized in the vertical direction. It enters the OPO system after being reflected by a 45° high-reflective mirror and pumps the OPO system. ; The 45° high reflective mirror 6 is specially coated to meet the high reflection of 532nm and 1300~1500nm, and the high transmittance of 400~500nm and 1064nm. The remaining 1064nm fundamental frequency light is absorbed by the absorber.

The OPO system includes a front cavity mirror, a rotating galvanometer system and a rear cavity mirror that are arranged in sequence and form a straight cavity optical path together with the intracavity self-frequency doubling KTP crystal. The front cavity mirror 7 serves as the 532nm pump light input mirror and The tunable blue light output mirror has special coating requirements for high transparency in the 400-532nm and 1300-1500nm bands, and high reflection in the 700-900nm band. The rear cavity mirror 9 is used as a total reflective mirror, and the coating requirements are high reflection in the entire band.

The characteristics and beneficial effects of the present invention are:

The present invention utilizes the nonlinear optical properties of the KTP crystal, the tunable properties of the OPO, and the high power density properties of the inner cavity to obtain tunable blue light, achieving high conversion efficiency, room temperature operation, fast tuning speed, and outputting blue light polarization, which can be used in Blue light of any wavelength can be obtained within a certain wavelength range, and multi-wavelength tunable blue light can be obtained simultaneously through optimization. At the same time, this method also provides a feasible solution for obtaining arbitrary wavelength output based on self-frequency doubling of the OPO cavity.

Picture description:

Figure 1 shows a fast tunable blue light radiation source device based on intracavity self-frequency doubling according to the present invention. In the picture:

1 is the laser, 2 is the focusing convex lens, 3 is the focusing concave lens, 4 is the 1064nm half-wave plate, 5 is the frequency doubling KTP crystal, 6 is the high reflection mirror, 7 is the front cavity mirror, 8 is the intracavity self-frequency doubling KTP crystal, 9 is the back cavity mirror, 10 is the rotating galvanometer system, 11 is the computer, and 12 is the absorber.

Figure 2 is a parameter diagram of the inner-cavity self-frequency doubling KTP crystal in the present invention.

Figure 3 is a schematic structural diagram of a device that can be used as a multi-wavelength tunable blue light radiation source according to the present invention.

Detailed ways

The purpose of the present invention is to provide a method and device for obtaining a blue light radiation source with continuously tunable wavelength. The KTP crystal in the OPO is designed as a nonlinear optical self-frequency doubling crystal, that is, it can be used as a parametric gain crystal and a frequency doubling crystal at the same time. Continuously tunable blue light output. This blue light acquisition method has high technical performance such as high conversion efficiency, simple structure, low price, and miniaturization, making it more practical and industrialized.

The method and device of a fast tunable blue light radiation source based on intracavity self-frequency doubling of the present invention will be described in detail below with reference to the embodiments and drawings.

The fast tunable blue light radiation source method and device based on intracavity self-frequency doubling of the present invention can efficiently obtain linearly polarized blue laser with tunable wavelength, has fast wavelength tuning speed, and has the advantage of operating under room temperature conditions. In the fast tunable blue light radiation source device based on self-frequency doubling of the inner cavity of the present invention, the pump source adopts Nd:YAG Q-switched laser; the frequency doubling crystal of pump light adopts KTP crystal, and the cutting angle of the frequency doubling crystal meets the Class II phase matching conditions. . The self-frequency doubling crystal in the parametric oscillator cavity is a KTP crystal, and the crystal cutting angle is θ = 65.2°. The side is optically polished and specially coated. The crystal is placed on a rotatable galvanometer platform and connected to a computer. Computer control is used to change the external machine voltage to achieve the rotation angle.

As shown in Figure 1, the fast tunable blue light radiation source device based on intracavity self-frequency doubling of the present invention specifically includes a laser 1 and a focusing lens group composed of a focusing convex lens 2 and a focusing concave lens 3 that receives the light emitted from the laser 1. The laser 1 is a neodymium-doped yttrium aluminum garnet Nd:YAG Q-switched laser, with an output wavelength of 1064 nm, a pulse width of the order of ns, and a polarization state of linearly polarized light polarized along the vertical direction. Also set:

The OPO internal cavity self-frequency doubling KTP crystal 8, as shown in Figure 2, serves as both a parametric gain crystal and an internal cavity frequency doubling crystal in an optical parametric oscillator. The crystal cutting angle is θ=65.2°, The size is 10×10×2mm ^3. The sides are optically polished and specially coated to meet the high transmittance of 400~532nm, 700~900nm and 1300~1500nm bands. The phase matching conditions of the crystal can be changed by rotating the crystal angle through the galvanometer rotating platform 10. This enables wavelength tuning.

The 1064nm half-wave plate 4 is installed after the focusing lens group and is used to adjust the polarization state of the 1064nm laser to meet the Class II phase matching conditions in the frequency-doubled KTP crystal 5.

Frequency doubling KTP crystal 5, the cutting angle is θ=90°, Size 15×15×10mm ³ is used to frequency-double the 1064nm laser to generate high-energy 532nm laser. The generated 532nm laser is linearly polarized light polarized in the vertical direction. The generated green light is reflected by the 45° high-reflective mirror 6 and enters the OPO system. , pump OPO system. The 45° high reflective mirror 6 is specially coated to meet the high reflection of 532nm and 1300~1500nm, and the high transmittance of 400~500nm and 1064nm. The remaining 1064nm fundamental frequency light is absorbed by the absorber 12.

The OPO self-frequency doubling system is used to output a wavelength-tunable linearly polarized blue laser from the internal cavity self-frequency doubling KTP crystal 8. It includes a front cavity that is arranged in sequence and forms a straight cavity optical path together with the internal cavity self-frequency doubling KTP crystal 8. Mirror 7, rotating galvanometer system 10 and back cavity mirror 9. Among them, the front cavity mirror 7 and the rear cavity mirror 9 need to be specially coated respectively. The front cavity mirror 7 is used as a 532nm pump light input mirror and a tunable blue light output mirror. The special coating requirements are high transmittance in the 400~532nm and 1300-1500nm bands, 700 ~900nm band high reflection, the rear cavity mirror 9 is used as a total reflection mirror, and the coating is required to be full band high reflection.

The computer 11 is connected to the galvanometer rotating platform through a data acquisition card and is used to control the voltage on the galvanometer rotating platform 10 to change the rotation angle of the self-frequency doubling KTP crystal 8, thereby changing the wavelength of the self-doubling intracavity oscillation signal light. Finally, the tuning of blue light wavelength is achieved.

The method of the present invention for a fast tunable blue light radiation source device based on intracavity self-frequency doubling is achieved by self-doubling the frequency of a single-resonance OPO parametric gain crystal, including the following processes: using an Nd:YAG Q-switched laser to generate the polarization direction The 1064nm linearly polarized light along the vertical direction shrinks through the focusing lens group, adjusts the laser polarization state through the 1064nm half-wave plate strip, and is incident into the frequency-doubled KTP crystal that meets the type II phase matching conditions. After frequency doubling, the polarization state along the The 532nm laser in the vertical direction enters the OPO system after being reflected by a 45° high-reflection mirror. The pump cavity is placed on the KTP crystal on the electric galvanometer rotating platform. As a parametric gain crystal, the crystal can produce a beam with a wavelength of 1.3 μm. The nearby tunable idler light with a polarization state along the vertical direction and a corresponding tunable signal light with a polarization state near 700-900nm along the horizontal direction. The front and rear cavity mirrors of the OPO system are coated to ensure that the signal light is in the cavity Internal oscillation to increase the power density of the signal light in the cavity. The high-power-density signal light oscillated in the cavity simultaneously satisfies the Class I phase matching conditions required for frequency doubling in the intra-cavity parametric gain KTP crystal. That is, the intra-cavity KTP crystal simultaneously functions as a parametric gain crystal and a frequency doubling crystal. The final result is obtained by The tunable signal light frequency doubling produces tunable blue light output, and the blue light polarization state is linearly polarized light along the vertical direction. At the same time, combined with the angle phase matching of the KTP crystal, the voltage on the galvanometer rotation system 10 is controlled by the computer to change the angle of the KTP crystal in the cavity, thereby achieving fast and tunable blue light output.

The specific implementation of the fast tunable blue light radiation source device based on internal cavity self-frequency doubling of the present invention is embodied in the fast tunable blue light radiation source device based on internal cavity self-frequency doubling as shown in FIG. 1 . Using the device shown in Figure 1, the cutting angle of the parametric gain crystal in the cavity is specially designed, and the OPO cavity mirror is specially coated to meet the self-frequency doubling conditions of the cavity. At the same time, combined with the galvanometer rotation system, rapid Tunable blue light output.

In another use embodiment of the present invention, please refer to Figure 3. Another parametric gain KTP crystal is placed in the resonant cavity. All parameters are the same as the self-frequency multiplication KTP crystal 8. The two parameters are controlled by the galvanometer rotation system 10. By adjusting the rotation angle of the block crystal, three wavelengths of tunable blue laser can be obtained at the same time. The wavelength components are derived from the frequency doubling process of the two wavelength signal lights oscillating in the cavity and the sum frequency process between the two wavelengths.

This invention uses the principle of nonlinear optical frequency conversion to place the KTP crystal with a special cut angle in the resonant cavity, so that it can simultaneously meet the Class II phase matching conditions of the OPO process and the Class I phase matching conditions of the frequency doubling process, thereby oscillating in the OPO cavity. The high power density signal light undergoes a frequency doubling process, and finally a fast tunable blue laser is obtained. By changing the voltage applied to the high-precision galvanometer, the KTP crystal can be rotated with high precision to achieve the continuously tunable wavelength characteristics of blue light. The device of the invention has the advantages of compact and flexible structure, tunability, and good light spot quality, and can be used in fields such as marine communications and marine information detection.

The structure of the device of the present invention is shown in Figure 1. When the linearly polarized high-energy 532nm green light is reflected by the 45° high-reflection mirror 6, it enters the front cavity mirror 7, the self-frequency doubling KTP crystal 8 and the rear cavity mirror which are specially coated respectively. A resonant cavity composed of 9, in which the self-frequency doubling KTP crystal 8 is placed on the high-precision galvanometer rotating platform 10, and the cutting angle of the self-frequency doubling KTP crystal 8 meets the optical parametric oscillation type II phase matching conditions.

Right now

ν _532nm ＝ν _signal +ν _idler

Under the 532nm green light pump, a linearly polarized signal light of about 800nm oscillating in the cavity with the same polarization state as the 532nm green light is generated, as well as an idler light of about 1300nm with a polarization state orthogonal to it. At the same time, the intracavity oscillation The signal light also satisfies the Class I phase matching condition of frequency doubling in the self-frequency doubling KTP crystal 8.

Right now

2×ν _signal =ν _blue

Produce a blue laser whose polarization state is orthogonal to the signal light. This blue laser is collinearly transmitted with the idle frequency light generated by the previous nonlinear process. After being filtered by a 45° high-reflection mirror, the blue laser output can be obtained. . On this basis, by changing the voltage V applied to the galvanometer rotating platform 10 system through the computer 11, the phase matching angle of the self-frequency doubling KTP crystal 8 can be precisely controlled, and then the signal light of the tuned intracavity oscillation can be obtained. Different The signal light of any wavelength can undergo a frequency doubling process in the self-frequency doubling KTP crystal 8, so that a blue laser output with continuously tunable wavelength can be obtained. The thickness L of the self-frequency doubling KTP crystal 8 in the beam propagation direction also needs to be optimized and designed (L=1~2mm in the present invention).

In another embodiment of the present invention, the high power density in the cavity is used to realize multiple nonlinear processes in the cavity and simultaneously obtain multi-wavelength fast tunable blue light output.

Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still make various modifications to the foregoing aspects. The technical solutions described in the embodiments may be modified, or some of the technical features may be equivalently substituted. However, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the present invention. within the scope of protection.

Claims (9)

1. The realization method of the tunable blue light radiation source based on the inner cavity self-frequency multiplication is characterized by comprising the following steps: YAG Q-switched laser generates 1064nm linear polarized light with polarization direction along vertical direction, beam shrinking is carried out through a focusing lens group, laser polarization state is regulated through 1064nm half-wave plate strips and is incident into frequency multiplication KTP crystals meeting II-type phase matching conditions, 532nm laser with polarization state along vertical direction is generated through frequency multiplication, the laser enters an OPO system through reflection of a 45 DEG high-reflection mirror, the pumping cavity is placed on the KTP crystals on an electric vibrating mirror rotating platform, the cavity KTP crystals serve as parametric gain crystals and can generate tunable idle frequency light with polarization state near 1.3 mu m along vertical direction and tunable signal light with polarization state corresponding to the tunable idle frequency light along horizontal direction, the front cavity mirror and the rear cavity mirror of the OPO system are coated to ensure that the signal light oscillates in the cavity to improve power density of the signal light in the cavity, the high-power density signal light oscillated in the cavity meets the I-type phase matching conditions at the same time in the cavity parametric gain KTP crystals, namely the cavity KTP crystals are simultaneously realized to serve as the KTP crystals, the function of frequency multiplication can be simultaneously realized, the tunable idle frequency conversion function of the KTP crystals can be realized, the blue crystal can be simultaneously, the blue crystal can be controlled to output through the rotation of the phase gain crystal can be controlled, and the blue crystal can be simultaneously, and the blue crystal can be output through the phase-switched to achieve the combination, and the blue crystal can be output, and the blue crystal can reach the function, and the phase can reach the function.

2. The method for realizing the tunable blue light radiation source based on the inner cavity self-frequency multiplication according to claim 1, wherein a piece of parametric gain KTP crystal is placed in the resonant cavity, all parameters are the same as those of the self-frequency multiplication KTP crystal placed in the prior art, the rotation angles of the two crystals are respectively controlled through a vibrating mirror rotation system (10), and then three blue lasers with tunable wavelengths are obtained simultaneously, and wavelength components of the blue lasers are derived from respective frequency multiplication processes of two wavelength signal lights oscillated in the cavity and a sum frequency process between the two wavelengths.

3. The method for realizing the tunable blue light radiation source based on the inner cavity self-frequency multiplication as claimed in claim 1, wherein the self-frequency multiplication KTP crystal cut angle meets the optical parameter oscillation class II phase matching condition, namely:

ν _532nm ＝ν _signal +ν _idler

wherein v _532nm 、υ _signal And v _idler Representing the frequencies of 532nm laser, signal light and idler light in the process of parametric oscillation, n ⁺ _532nm 、n ^- _signal N is as follows ⁺ _idler 532nm laser and water respectively representing vertical polarization statesRefractive index of signal light in flat polarization state and idler light in vertical polarization state in KTP crystal, lambda _signal Lambda of _idler The wavelengths of the signal light and the idler light are shown, respectively.

4. The method for realizing the tunable blue light radiation source based on the inner cavity self-frequency multiplication according to claim 1, wherein a beam of signal light which is linearly polarized and has the same polarization state as 532nm green light and oscillates in a cavity around 800nm and idler light which has the polarization state orthogonal to the signal light is generated under the pumping of 532nm green light, and meanwhile, the signal light which oscillates in the cavity also meets the frequency multiplication I phase matching condition in the self-frequency multiplication KTP crystal (8), namely:

2×ν _signal ＝ν _blue

wherein v _signal And v _blue Respectively representing the frequencies of the signal light and the blue light; n is n ⁺ _blue Representing the refractive index of blue light of vertical polarization in the KTP crystal; lambda (lambda) _blue Represents blue wavelengths;

and generating a beam of blue laser with polarization state orthogonal to the signal light, wherein the beam of blue laser and the idle frequency light generated in the former nonlinear process are transmitted in a collinear manner, and the blue laser output can be obtained through filtering by a 45-degree high-reflection mirror.

5. The method for realizing the tunable blue light radiation source based on the inner cavity self-frequency multiplication according to claim 1, wherein the voltage applied to the vibrating mirror rotating platform system is changed through a computer, the phase matching angle of the self-frequency multiplication KTP crystal is controlled, so that tuned signal light oscillating in the cavity can be obtained, the signal light with different wavelengths can generate frequency multiplication in the self-frequency multiplication KTP crystal, and further, blue laser output with continuously tunable wavelength can be obtained; the thickness L of the self-frequency doubling KTP crystal in the light beam propagation direction is 1-2 mm.

6. The utility model provides a tunable blue light radiation source based on inner chamber is from doubling of frequency which characterized in that, the structure is: the pumping source adopts a Nd-YAG Q-switched laser; the pump light frequency doubling crystal adopts a KTP crystal, and the cut angle of the frequency doubling crystal meets the II-class phase matching condition; an OPO system, wherein KTP crystals are arranged in the system, the cutting angle is theta=65.2 degrees,and (3) carrying out optical polishing and special coating on the side surface, wherein the KTP crystal is arranged on a rotatable galvanometer platform which is connected with a computer, and the external voltage of the KTP crystal is changed by adopting computer control so as to realize the rotation angle, wherein:

neodymium doped garnet Nd: YAG Q-switched laser generates 1064nm linear polarized light with polarization direction along vertical direction, beam shrinking is carried out through a focusing lens group, laser polarization state is regulated through a 1064nm half-wave plate strip and is incident into frequency multiplication KTP crystals meeting II-type phase matching conditions, 532nm laser with polarization state along vertical direction is generated through frequency multiplication, the laser enters an OPO system through reflection of a 45 DEG high-reflection mirror, the pumping cavity is placed on the KTP crystals on an electric vibrating mirror rotating platform, the cavity KTP crystals are used as parametric gain crystals and can generate a beam of tunable idler light with polarization state near 1.3 mu m along vertical direction and a beam of tunable signal light with polarization state corresponding to 700-900nm along horizontal direction, the front and rear cavity mirrors of the OPO system are coated with films to ensure that signal light oscillates in a cavity to improve the power density of the signal light in the cavity, the high-power density signal light oscillated in the cavity simultaneously meets I-type phase matching conditions required by frequency multiplication in cavity reference gain KTP crystals, namely the cavity KTP crystals simultaneously realize functions of parametric gain crystals and frequency multiplication crystals, tunable blue light output generated by frequency multiplication of tunable signal light is finally obtained, the polarization state of the blue light is linear polarized light along the vertical direction, and meanwhile, the angle phase matching of the KTP crystals is combined, the voltage on a vibrating mirror rotating system is controlled through a computer, and the angle of the cavity KTP crystals is changed, so that the blue light output with the wavelength capable of being tuned rapidly is realized.

7. The substrate according to claim 6The tunable blue light radiation source with self-frequency doubling in the inner cavity is characterized in that the laser is specifically a neodymium-doped yttrium aluminum garnet Nd, namely a YAG Q-switched laser, the output wavelength is 1064nm, the pulse width is ns magnitude, and the polarization state is linearly polarized light polarized along the vertical direction; the laser also comprises a focusing lens group which is used for receiving the emergent light of the laser and consists of a focusing convex lens and a focusing concave lens, a 1064nm half-wave plate, the lens is arranged behind the focusing lens group and used for adjusting the polarization state of 1064nm laser to meet the II-type phase matching condition in the frequency doubling KTP crystal; OPO inner cavity self-frequency doubling KTP crystal size is 10 multiplied by 2mm ³ The opposite side is optically polished and special coating is carried out to meet the high transmittance of the wave bands of 400-532 nm, 700-900nm and 1300-1500nm, and the phase matching condition of the crystal can be changed by rotating the crystal angle of the vibrating mirror rotating platform, so that the wavelength tuning is realized.

8. The tunable blue radiation source based on inner cavity self-frequency doubling according to claim 6, wherein the KTP crystal has a cut angle θ=90°,size 15X 10mm ³ The laser frequency doubling device is used for generating high-energy 532nm laser for frequency doubling 1064nm laser, the generated 532nm laser is linearly polarized light polarized along the vertical direction, and the linearly polarized light is reflected by a 45-degree high-reflection mirror to enter an OPO system so as to pump the OPO system; the 45 DEG high reflection mirror (6) is specially coated to meet the high reflection between 532nm and 1300-1500nm, and the residual 1064nm fundamental frequency light with high transmission between 400-500 nm and 1064nm is absorbed by an absorber.

9. The tunable blue light radiation source based on inner cavity self-frequency doubling as claimed in claim 6, wherein the OPO system comprises a front cavity mirror, a rotary galvanometer system and a rear cavity mirror which are sequentially arranged and form a straight cavity light path together with the inner cavity self-frequency doubling KTP crystal, wherein the front cavity mirror (7) is used as a 532nm pump light input mirror and a tunable blue light output mirror, the special coating requirements are 400-532 nm and 1300-1500nm wave band high transmittance, the 700-900nm wave band high reflectance is achieved, the rear cavity mirror (9) is used as a full reflectance mirror, and the coating requirements are all wave band high reflectance.