JPH10209535A - Laser diode exciting solid laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the adjustment of oscillating characteristics by restricting the high ordering of lateral mode in a laser diode exciting solid laser and by suppressing the loss to a low level in a resonator. SOLUTION: In a laser diode exciting solid laser in which a solid laser crystal 13 is excited by a laser beam 10 focusing by a converging lens 12 generated from a laser diode 11, a slit plate 18 is provided which reduces the beam diameter only in the stripe width direction of the laser diode 11 in a light path of the solid laser beam 30 in a resonator, thereby restricting the high ordering of the lateral mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode-pumped solid-state laser in which a solid-state laser crystal is pumped by a laser diode (semiconductor laser), and more particularly, to a laser diode which suppresses higher-order transverse modes. It relates to a pumped solid-state laser.

[0002]

2. Description of the Related Art As disclosed in, for example, Japanese Patent Application Laid-Open No. 62-189773, a laser diode-pumped solid-state laser that excites a solid-state laser crystal doped with a rare earth element such as neodymium with light emitted from a laser diode is known. Has become. In this laser diode pumped solid-state laser, in order to obtain a shorter wavelength laser beam, an optical wavelength conversion element is arranged in the resonator,
The wavelength conversion of a solid-state laser beam to a second harmonic or the like is also widely performed.

[0003]

In this type of laser diode-pumped solid-state laser, there is a problem that the transverse mode is increased and the beam quality is likely to deteriorate. Also, especially if the wavelength conversion described above, the transverse mode is likely to higher order transverse mode competition i.e., alternately in higher mode and the time interval of μsec order, such as TEM ₀₀ mode and the TEM ₀₁ mode A standing phenomenon occurs.

In various conventional solid-state lasers, a pinhole plate for narrowing the beam diameter is provided in the optical path of the solid-state laser beam in the resonator in many cases in order to suppress the higher order of the transverse mode.

This pinhole plate is of course effective even if it is installed in a laser-diode-pumped solid-state laser. However, in that case, the loss in the resonator is large, and the oscillation characteristics are large before and after the pinhole plate is inserted. It has been recognized that it is difficult to adjust the oscillation characteristics because of the change. FIG. 8 shows an example of oscillation characteristics before and after the insertion of the pinhole plate. Here, the relationship between the cavity temperature, the laser output, and the oscillation wavelength is shown. The solid line in the figure shows the characteristics before the pinhole plate is inserted, and the broken line shows the characteristics after the pinhole plate is inserted.

Further, it is difficult to adjust the position of the pinhole plate so that the center of the pinhole coincides with the beam axis, so that it is not suitable for mass production of solid-state lasers.

The present invention has been made in view of the above circumstances, and can suppress the increase in the order of the transverse mode, can reduce the loss in the resonator, can easily adjust the oscillation characteristics, and can mass-produce. It is an object of the present invention to provide a laser diode-pumped solid state laser that is also suitable for:

[0008]

SUMMARY OF THE INVENTION A laser diode-pumped solid-state laser according to the present invention comprises a resonator, a solid-state laser crystal disposed in the resonator, and a laser diode for emitting a laser beam for exciting the solid-state laser crystal. And a condensing lens for converging the laser beam in or near the solid-state laser crystal. In the solid-state laser beam, the optical path of the solid-state laser beam in the resonator has a stripe width of the excitation laser diode. A slit plate is provided to reduce the beam diameter only in the direction and suppress higher order of the transverse mode.

[0009]

According to the present invention, when the laser beam as the excitation light emitted from the laser diode is converged by the condenser lens, the converged spot diameter is in the direction of the active layer (layer thickness direction).
Is relatively small, and becomes relatively large in the stripe width direction perpendicular to it. Further, the intensity distribution of the laser beam shows a tendency close to a Gaussian distribution in the direction of the active layer, but such a tendency is low in the direction of the stripe width.

Since the convergent spot diameter and the intensity distribution of the excitation light are different between the active layer direction and the stripe width direction, mode matching between the excitation light and the solid-state laser beam is good in the active layer direction. It is not good in the stripe width direction.

From the above, it is easy for the laser diode pumped solid-state laser to increase the order of the transverse mode because:
Generally, only in the stripe width direction, the tendency is much lower in the active layer direction. Therefore, as in the present invention, even when the beam diameter of the solid-state laser beam is reduced only in the stripe width direction of the laser diode using the slit plate, the effect of suppressing the higher order of the transverse mode can be sufficiently obtained. .

As described above, when the beam diameter of the solid-state laser beam is narrowed down one-dimensionally by using the slit plate, resonance is reduced as compared with the case where the beam diameter is narrowed down two-dimensionally by using the pinhole plate. Loss in the vessel can be reduced.

On the other hand, the problem of the conventional device that the oscillation characteristics change greatly before and after the insertion of the pinhole plate is caused by the fact that the temperature inside the resonator rises remarkably due to the large amount of reflected light from the pinhole plate. On the other hand, in the laser diode-pumped solid-state laser of the present invention, the beam diameter of the solid-state laser beam is narrowed down one-dimensionally by using a slit plate, so that the amount of light reflected by the slit plate is significantly reduced. Therefore, in the laser diode-pumped solid-state laser of the present invention, the oscillation characteristics do not significantly change before and after the slit plate is inserted, and the oscillation characteristics can be easily adjusted.

Since the intensity of the solid-state laser beam is more concentrated in the direction of the active layer than in the stripe width direction of the laser diode, the beam diameter is not reduced in the direction of the active layer. The effect of suppressing the loss of light and the effect of suppressing the amount of reflected light are particularly remarkable.

Further, the position adjustment of the slit plate with respect to the solid-state laser beam may be performed only in the stripe width direction, and the position adjustment in the active layer direction perpendicular to the stripe width is unnecessary. Therefore, the laser diode-pumped solid-state laser according to the present invention can easily adjust the position of the slit plate and is suitable for mass production.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a laser diode-pumped solid-state laser according to a first embodiment of the present invention. This laser diode pumped solid-state laser includes a laser diode (semiconductor laser) 11 that emits a laser beam 10 as excitation light, a condenser lens 12 that collects the laser beam 10 that is divergent light, and neodymium (Nd) doped. A solid-state laser medium YLF crystal (hereinafter, referred to as Nd: YLF crystal) 13;
A resonator mirror 14 arranged on the front side (right side in the figure) of the Nd: YLF crystal 13, and the resonator mirror 14 and the Nd: Y
And an optical wavelength conversion element 15 disposed between the LF crystal 13 and the LF crystal 13.

A Brewster plate 16 as a polarization control element, an etalon 17 as a wavelength selection element, and a slit plate 18 as a transverse mode control element are arranged between the optical wavelength conversion element 15 and the resonator mirror 14. Has been established. And N
d: A λ / 4 plate before and after the YLF crystal 13 for turning the oscillation mode into a twist mode to prevent hole burning.
19 and 20 are arranged.

The elements 13 to 20 described above are fixed to a resonator holder 21 made of Cu-Be or the like. The resonator holder 21 is fixed on the cooling surface of the Peltier element 22. In this embodiment, as described later, a λ / 4 plate
A Fabry-Perot resonator is constituted by 19 and the resonator mirror 14. The resonator is maintained at a predetermined temperature by driving and controlling the Peltier element 22 by a temperature control circuit (not shown).

The laser diode 11 has a wavelength of 797.
Those that emit a laser beam 10 of nm are used. The Nd: YLF crystal 13 excites neodymium ions by the incident laser beam 10 and emits light having a wavelength of 1314 nm. The excitation laser beam 10 having a wavelength of 797 nm is well transmitted to the end face 19a of the λ / 4 plate 19 on the side of the excitation light (transmission is 99% or more), and light having a wavelength of 1314 nm and the following wavelength of 657 nm is good. It is coated to reflect light (reflectance of 99.9% or more). On the other hand, the mirror surface 14a of the resonator mirror 14 is provided with a coating that favorably reflects light having a wavelength of 1314 nm and transmits light having a wavelength of 657 nm.

Therefore, the light having a wavelength of 1314 nm is applied to each of the above surfaces.
The laser beam 30 resonates between 19a and 14a to cause laser oscillation. The laser beam 30 thus generated is converted by the optical wavelength conversion element 15 into a second harmonic 31 having a wavelength of 1/2, that is, 657 nm. Wave 31 exits from resonator mirror 14. The light wavelength conversion element 15 is, for example, MgO
Can be used in which a periodic domain inversion structure is formed in a LiNbO ₃ crystal doped with.

FIG. 2 shows a relative positional relationship between the laser diode 11 and the slit plate 18. As shown in the figure, the slit plate 18 has a sufficiently long slit 18a in the direction of the active layer of the laser diode 11 (the thickness direction of the active layer 11a:
It is arranged in a direction extending in the direction of arrow Y). The beam diameter (1 / e ² diameter) of the laser beam 30 in the stripe width direction (arrow X direction) is about 200 μm, whereas the width of the slit 18a is about 440 μm. Therefore, the laser beam 30 is narrowed down by the slit plate 18 only in the stripe width direction of the laser diode 11.

FIGS. 3A and 3B respectively show N
d: The shapes of the excitation laser beam 10 and the laser beam 30 in the YLF crystal 13 are shown in the stripe width direction and the active layer direction. As shown, the divergence angle and spot diameter of the excitation laser beam 10 are relatively large in the stripe width direction and relatively small in the active layer direction. Therefore, the mode matching between the excitation laser beam 10 and the laser beam 30 is poor in the stripe width direction and good in the active layer direction.

FIGS. 4A and 4B show light intensity distributions of the laser beam 30 in the stripe width direction and the active layer direction when the slit plate 18 is not inserted. As is clear from this, it is only in the stripe width direction that the transverse mode tends to increase in order, and the tendency is low in the active layer direction. Therefore, just by narrowing the beam diameter of the laser beam 30 only in the stripe width direction as described above, the effect of suppressing the higher order of the transverse mode is sufficient, as in the case of narrowing down two-dimensionally using the pinhole plate. Is obtained.

In the present embodiment, the laser beam 30 is
Since the wavelength is converted to the harmonic 31, if the transverse mode becomes higher in order, the above-mentioned transverse mode competition may occur.However, by suppressing the higher order of the transverse mode, this transverse mode competition can also be suppressed. it can.

If the beam diameter of the laser beam 30 is narrowed down one-dimensionally, the loss in the resonator can be reduced as compared with the case where the laser beam 30 is narrowed down two-dimensionally using a pinhole plate.

Further, the position adjustment of the slit plate 18 with respect to the laser beam 30 may be performed only in the stripe width direction, and there is no need to adjust the position in the active layer direction perpendicular to the stripe width direction. Therefore, this laser diode pumped solid-state laser can easily adjust the position of the slit plate 18 and is suitable for mass production.

Further, since the beam diameter of the laser beam 30 is narrowed down only in the one-dimensional direction by the slit plate 18, the amount of light reflected by the slit plate 18 is significantly reduced.
Therefore, in the laser diode-pumped solid-state laser, the temperature inside the resonator does not greatly increase due to the insertion of the slit plate 18, so that it is possible to prevent the oscillation characteristics from largely changing before and after the slit plate is inserted.

Specifically, after arranging an aperture plate having a hole with a diameter of 1 mm in place of the slit plate 18 to adjust the oscillation characteristics, even if this aperture plate is replaced with the slit plate 18, the oscillation characteristics greatly change. I never did.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 5, elements that are the same as the elements in FIG. 1 are given the same reference numerals, and overlapping descriptions thereof will be omitted (hereinafter the same).

The laser-diode-pumped solid-state laser of the second embodiment is basically different from that of FIG. 1 in that the optical wavelength conversion element 15 is omitted. That is, in the second embodiment, the solid-state laser beam 30 is emitted from the resonator mirror 14 without being converted into the second harmonic. In this case as well, a Fabry-Perot resonator is constituted by the λ / 4 plate 19 and the resonator mirror 14, but the coating applied to the mirror surface 14a of the mirror 14 is a solid laser beam 30 having a wavelength of 1314 nm. Partially transmitted.

Also in the second embodiment, the slit plate
By 18, by narrowing the beam diameter of the laser beam 30 only in the stripe width direction of the laser diode 11, the same effect as that obtained in the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIG. The laser diode pumped solid-state laser of the third embodiment is basically different from that of FIG. 5 in that the Brewster plate 16, the etalon 17, the λ / 4 plates 19 and 20 are removed, and the position of the λ / 4 plate 19 is removed. A different point is that a flat plate-shaped resonator mirror 40 is provided. On the mirror surface 40a of the resonator mirror 40, the excitation laser beam 10 having a wavelength of 797 nm is transmitted well (transmittance of 99% or more), and the solid laser beam 30 having a wavelength of 1314 nm is reflected well (reflectance). 99.9% or more) Coat is applied.

In the third embodiment, the slit plate
By 18, by narrowing the beam diameter of the laser beam 30 only in the stripe width direction of the laser diode 11, the same effect as that obtained in the first and second embodiments can be obtained.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The laser-diode-pumped solid-state laser according to the fourth embodiment basically differs from that of FIG. 1 in that the Brewster plate 16, the λ / 4 plates 19 and 20 are removed, and the plate-like shape is formed at the position of the λ / 4 plate 19. Is different in that the resonator mirror 40 is disposed. And this resonator mirror
The laser beam 10 for excitation having a wavelength of 797 nm is transmitted through the mirror surface 40a of the 40 well (a transmittance of 99% or more), and the wavelength 13
The solid laser beam 30 having a wavelength of 14 nm and the second harmonic 31 having a wavelength of 657 nm are coated so as to reflect well (a reflectance of 99.9% or more).

Also in the fourth embodiment, the slit plate
By 18, by narrowing the beam diameter of the laser beam 30 only in the stripe width direction of the laser diode 11, the same effect as that obtained in the first, second, and third embodiments can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view illustrating a laser diode-pumped solid-state laser according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a part of the laser-diode-pumped solid-state laser of FIG. 1;

FIG. 3 is a schematic diagram showing shapes of an excitation laser beam and a solid-state laser beam in the laser diode-excited solid-state laser of FIG. 1 for each of a stripe width direction (a) and an active layer direction (b) of the excitation laser diode.

4 is a graph showing the light intensity distribution of a solid-state laser beam in the laser-diode-pumped solid-state laser shown in FIG. 1 for each of a stripe width direction (a) and an active layer direction (b) of the pumping laser diode.

FIG. 5 is a side view showing a laser diode-pumped solid-state laser according to a second embodiment of the present invention;

FIG. 6 is a side view showing a laser diode pumped solid state laser according to a third embodiment of the present invention.

FIG. 7 is a side view showing a laser-diode-pumped solid-state laser according to a fourth embodiment of the present invention;

FIG. 8 is a graph showing an example of a relationship between a resonator temperature, an output, and an oscillation wavelength in a laser diode-pumped solid-state laser.

[Explanation of symbols]

 10 Laser beam (excitation light) 11 Laser diode 12 Condenser lens 13 Nd: YLF crystal 14 Resonator mirror 15 Optical wavelength conversion element 16 Brewster plate 17 Etalon 18 Slit plate 19, 20 λ / 4 plate 21 Resonator holder 22 Peltier Element 30 Solid-state laser beam 31 Second harmonic 40 Resonator mirror

Claims (2)

[Claims] 1. A resonator, a solid-state laser crystal provided in the resonator, a laser diode for emitting a laser beam for exciting the solid-state laser crystal, and a laser beam in or in the solid-state laser crystal. A laser diode-pumped solid-state laser having a converging lens that converges the light in the vicinity, and increasing the transverse mode to the optical path of the solid-state laser beam in the resonator by narrowing the beam diameter only in the stripe width direction of the laser diode. A laser diode-pumped solid-state laser, characterized in that a slit plate is provided to suppress noise. 2. The laser diode-pumped solid-state laser according to claim 1, wherein an optical wavelength conversion element for converting the wavelength of the solid-state laser beam is provided in the resonator.