JPH01128484A - High-efficiency second harmonic generating laser oscillator - Google Patents

Abstract

PURPOSE:To enable a high conversion efficiency and an improved laser beam to be obtained by providing an angular phase conformity type non-linear optical crystal as the second harmonic generating element and by providing an adjusting system of the diameter of laser beam and the length of non-linear optical crystal. CONSTITUTION:By allowing a laser beam generated from an oscillator to incide the second harmonic generating element formed from a non-linear optical crystal body, a laser beam wavelength is converted. In this case, an angular phase conformity type crystal is used as a non-linear optical crystal body. A crystal such as KTiOPO4 and beta-BaB2O4 can be used. By using a non-linear optical crystal body of angular phase conformity type to adjust the length of laser beam diameter and that of this crystal body, the second higher harmonic of higher efficiency can be generated. A laser oscillator has for example a laser oscillating element 1, an output mirror 2, and a plain all-reflection mirror 3 and a collimater lens for collecting light 4 and the second higher harmonic generating element 5 using a non-linear optical crystal are provided between this output mirror 2 and the plane total-reflection mirror 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a highly efficient second harmonic generation laser oscillator. More specifically, the present invention relates to a device that efficiently converts a fundamental laser beam into a second harmonic and oscillates a laser beam having half the wavelength.

(Background Art) In recent years, the application of laser light to various fields has become more and more popular, and with the expansion of this application, attempts have been made to convert the wavelength of laser light. . For example, when using a YAG laser device, which is a typical solid-state laser oscillation device, for processing, the shorter the wavelength, the higher the processing accuracy, so a second harmonic generation element is used. In many cases, the wavelength is halved and used. The second harmonic generation element used for converting the wavelength of this YAG laser beam includes Li I O, KT
i OP O,i (KTP) etc. are known,
Devices using these elements are already commercially available.

Generally, the conversion efficiency of such a second harmonic generation element increases in proportion to the intensity of the incident laser beam, so in order to increase the conversion efficiency, it is necessary to increase the output level of the laser beam. It will have to be done. For this reason, conventionally, a Q-switch is used to increase the peak output of the laser beam, or a lens with a short focal length is used to focus the laser beam strongly, and then the second harmonic generation element is The output of the laser light that is converted and output is increased.

However, when the peak output of laser light is large, as in the case of a pulse output laser oscillator using a Q switch, it is possible to obtain high conversion efficiency relatively easily, but continuous wave oscillation laser oscillators In the case of 'If!', the output level is 'If!' compared to the pulsed laser. Because it is low at the end,
It is known that high conversion efficiency cannot be obtained.

In order to deal with such problems, attempts have been made to increase the conversion efficiency by installing a nonlinear optical element inside the resonator and repeatedly passing the fundamental wave through the nonlinear optical element. For example, BNN (
A high conversion efficiency of 100% has also been obtained using Ba 2Na Nb 5015).

However, such attempts also had limitations. In the case of this BNN, a method called so-called 90 degree phase matching is adopted, and high conversion efficiency is obtained.
In the case of using the angular phase matching method, the conversion efficiency cannot be increased due to a factor called the so-called walk-off effect, and conventionally, a conversion efficiency of about 20% at most has been obtained. Since the method using angular phase matching is a very important method from a practical standpoint, it has been desired to achieve wavelength conversion of laser light with high conversion efficiency using this method.

(Purpose of the invention) This invention was made based on the above-mentioned circumstances, and it is possible to improve the drawbacks of the conventional method, obtain high conversion efficiency, and obtain a high-quality laser beam. It is an object of the present invention to provide a laser oscillation device including a second harmonic generation element.

(Disclosure of the Invention) In order to achieve the above object, the present invention provides a second harmonic generation element formed from a nonlinear optical crystal inside a resonator to generate a laser beam having a wavelength half that of the fundamental wave. A laser oscillator that generates an angularly phased nonlinear optical crystal as a second harmonic generating element, and an adjustment system for adjusting the diameter of the laser beam and the length of the nonlinear optical crystal. A highly efficient second harmonic generation laser oscillator using an angular phase matching method is provided.

In the laser oscillator of the present invention, the wavelength of the laser light is converted by making the laser light generated from the resonator enter the second harmonic generation element formed from a nonlinear optical crystal.
As the nonlinear optical crystal in this case, an angular phase matching crystal is used. Such crystals include, for example, K
Ti OPO4 (KTP), β-Ba B2O4 (B
Crystals such as BO), KDP, KD''P, ADP, and RDP can be used.

Highly efficient second harmonic generation is achieved by adjusting the beam diameter of the laser beam and the length of this crystal using an angular phase matching type nonlinear optical crystal. Unlike the case of 90 degree phase matching, it is necessary to take into consideration the so-called walk-off effect.

That is, a nonlinear optical crystal is a birefringent crystal, but in such a crystal, the traveling direction of an equiphase wavefront generally does not match the direction of a light beam in which energy propagates, and a shift occurs. This is called the walk-off effect, and when this effect occurs, the nonlinear optical crystal will only have an effect over a certain specified length, and the efficiency will not improve even if a long single crystal is used as a nonlinear optical element. .

In the present invention, the diameter of the laser beam and the length of the angle phase matching type nonlinear crystal are adjusted in consideration of such a walk-off effect so as to obtain the highest conversion efficiency.

More specifically, the adjustment is performed using, for example, a collimating lens system for condensing light.

In this case, the following formula (a) is applied. Make sure you get the right diameter of light. Note that A is a constant specific to the laser oscillator, for example, 2.8xlO in the case of a YAG laser.
', and about 2.9xlO' with an argon laser. Under these conditions, the length of the nonlinear optical crystal and the diameter of the laser beam in the nonlinear optical crystal are determined according to the relationship expressed by the following equation (b). and can be adjusted.

In relation to the above formulas (a) and (b), ρ (walk-off angle)
, d (nonlinear constant), and n (refractive index) are shown in the following table.

The laser oscillator of the present invention can have a configuration as shown in FIG. 1 of the attached drawings. For example, as shown in FIG. 1, it has a laser oscillation element (1), an output mirror (2), and a flat total reflection mirror (3), and this output mirror (2) and the flat total reflection mirror (3) A condensing collimating lens (4) and a second harmonic generation element (5) using a nonlinear optical crystal can be provided between the two.

In addition, as a collimating lens system, Fig. 2 (a) (b)
) (c) can also be used. That is, (a) a convex lens and a concave lens are placed in front of the output mirror.

<b> A convex lens is placed in front of the output mirror.

(c) Place two concave mirrors in front of the output mirror.

Next, an embodiment of the laser oscillator of the present invention will be described with reference to FIG.

Example 1 In the configuration of the apparatus shown in FIG. 1, a BBO was used as the second harmonic generation element, and a YAG rod was used as the laser oscillation element.

The diameter (D>) of the laser beam in this YAG rod is D≧9, assuming that the constant (A) of the device is 2.8x 10'.
It becomes the second issue. Under this condition, in order to obtain the highest conversion efficiency, L=152Do/D according to equation (b) above.
It is sufficient to satisfy the relationship.

Therefore, along this L=152Do/D, the length (L) of the nonlinear optical crystal and the diameter (Do) of the laser beam in the nonlinear optical crystal were adjusted using a collimating lens. Conversion efficiency was 100%.

Example 2 KTP was used as a nonlinear optical crystal. Similarly to Example 1, the diameter (D) of the laser beam in the YAG rod is D
≧O, 44n+n.

The conditions for obtaining the highest conversion efficiency under this article are as follows:
L=22.3Do/D.

Using a collimating lens, set the length (L) of the nonlinear optical crystal and the diameter (D.) of the laser beam in this crystal according to this relationship! I've adjusted it. A high conversion efficiency of over 80% was obtained. This efficiency is as high as 513 compared to the conventional one.

(Effects of the Invention) With this invention, as explained in detail above, resonance? By providing an element made of an angle phase matching type nonlinear optical crystal inside the laser beam and adjusting the diameter of the laser beam and the length of the nonlinear optical crystal, the second harmonic can be realized with high conversion efficiency.

In the academic world, such laser oscillation devices are used as light sources for spectroscopy and photochemical reactions, which are mainly used in fields such as biology and chemistry, and in the industrial world, they are used as light sources for precision processing and precision measurement. It is extremely useful as a light source.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the configuration of an apparatus according to the present invention. FIGS. 2(a), 2(b), and 2(c) are layout diagrams each showing an example of a collimating lens system. 1...Laser oscillation element 2...Output mirror 3...Flat total reflection mirror 4...Collimating lens for focusing 5...Second harmonic generation element Patent attorney Toshi Nishizawa Otsutsu 2 Figure

Claims (3)

[Claims] (1) In a laser oscillator in which a second harmonic generating element formed of a nonlinear optical crystal is provided inside a resonator to generate laser light having a wavelength half that of the fundamental wave, the second harmonic generating element is A highly efficient second harmonic generation laser oscillator using an angular phase matching method, comprising a phase matching nonlinear optical crystal and an adjustment system for adjusting the diameter of the laser beam and the length of the nonlinear optical crystal. (2) A highly efficient second harmonic generation laser oscillator according to claim (1), which uses β-BaB_2O_4 or KTiOPO_4 crystal as the nonlinear optical crystal. (3) A highly efficient second harmonic generation laser oscillator according to claim (1), which uses a collimating lens for condensing light.