JP2000307180A - Semiconductor laser stimulating solid-state laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser stimulating solid-state laser which is capable of preventing its oscillation laser beam from being deformed in cross section by a method wherein an Nd:YVO4 crystal used as the solid-state laser is prescribed in Nd content. SOLUTION: A semiconductor laser stimulating solid-state laser is of c-axis absorption and c-axis oscillation type, where a laser crystal such as an Nd:YVO4 crystal of small thermal conductivity coefficient is used, a thermal lens effect is generated when an exciting power is increased, and an oscillation laser beam is deformed in cross section. Then, when Nd added to an Nd:YVO4 crystal is reduced to 0.7 at.% in content, the absorption coefficient of the laser crystal is reduced to below 28 cm-1, so that a thermal lens effect is restrained, and a laser beam emitted from the solidstate laser crystal is prevented from being deformed in cross section. A thermal lens effect can be more restrained with a reduction of an Nd content in an Nd:YVO4 crystal, but when a Nd content is smaller than 0.4 at.%, a single vertical mode is deteriorated, so that an Nd content is set larger than 0.4 at.%. Therefore, an Nd content is set more than 0.4 but below 0.7 at.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention, Nd as the solid laser medium: relates YVO ₄ laser diode pumped solid-state laser using the crystal, and more particularly to a beam cross section of oscillation light upon high output by the thermal lens effect The present invention relates to a semiconductor laser-excited solid-state laser whose shape is prevented from being deformed.

[0002]

2. Description of the Related Art As disclosed in, for example, JP-A-7-302946, a solid-state laser in which a solid-state laser crystal to which a rare earth element such as neodymium is added is excited by a semiconductor laser is known.

In this semiconductor laser pumped solid-state laser, an Nd: YVO ₄ crystal is often used as a solid-state laser crystal.
_{The four} crystals are arranged so that their c-axis is parallel to the direction of the linear polarization of the excitation light (so-called c-axis absorption), and the direction of the linear polarization of the solid-state laser oscillation light is set to the direction parallel to this c-axis (the so-called c-axis). c-axis oscillation).

That is, as shown in Table 1 below,
In the case of d: YVO ₄ crystal, the absorption coefficient of excitation light is larger in the case of c-axis absorption than in the case of a-axis absorption.
Inevitably, such a method has been adopted.

[0005]

[Table 1]

[0006]

However, this Nd:
C axis absorbed with YVO ₄ crystal, in the conventional semiconductor laser pumped solid state laser of c-axis oscillation excitation using a semiconductor laser of high output of about 1W~3W in order to meet the demand for higher output of the solid-state laser When the power is increased, there is a problem that the beam cross-sectional shape of the solid-state laser oscillation light is easily deformed into an elliptical shape or the like.

The present invention has been made in view of the above circumstances, and has been developed in consideration of Nd: YVO.
_An object of the present invention is to prevent a beam cross-sectional shape of oscillation light from being deformed in a semiconductor laser pumped solid-state laser using _four crystals.

[0008]

The semiconductor laser pumped solid-state laser according to the present invention is, as described above, a c-axis absorbing and c-axis oscillating semiconductor laser that excites a Nd: YVO ₄ crystal with a laser beam emitted from the semiconductor laser. In a pumped solid-state laser, Nd: YVO ₄
With an addition amount of 0.4 at% or more and less than 0.7 at%,
Particularly preferably, 0.5 at% is used.

The Nd: YVO ₄ crystal conventionally used as a laser medium has an Nd content of 1.0%.
The Nd: YVO ₄ crystal having a content of 0 at% or more and having a low added amount of Nd as in the present invention was not used.

The present invention is particularly effective when applied when the output of the semiconductor laser is 1 W or more and the thermal lens effect easily occurs as described above.

[0011]

According to the present invention, the problem of the conventional device that the beam cross-sectional shape of the solid-state laser oscillation light is deformed is as follows.
It has been found that, in a laser crystal having a small thermal conductivity coefficient, such as a Nd: YVO ₄ crystal, a higher excitation power causes a thermal lens effect.

Therefore, if the amount of Nd added to the Nd: YVO ₄ crystal is reduced to less than 0.7 at%, the absorption coefficient decreases to less than 28 cm ^{−1 as} is apparent from Table 1 above. The thermal lens effect is suppressed, and it is possible to prevent the beam cross-sectional shape of the solid-state laser oscillation light from being deformed.

For suppressing the thermal lens effect, Nd: Y
The smaller the amount of Nd added to the VO ₄ crystal, the better, but 0.4a
It has been found that when it is less than t%, the single longitudinal mode property is impaired. Therefore, in the present invention, most preferably, the amount of Nd added to the Nd: YVO ₄ crystal is 0.4 at%.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<First Embodiment> FIG. 1 shows a semiconductor laser-pumped solid-state laser according to a first embodiment of the present invention. This semiconductor laser pumped solid-state laser
A semiconductor laser 11 that emits a laser beam 10 as excitation light, a collimator lens 12 that parallelizes the laser beam 10 that is divergent light, and a condenser lens 13 that collects the laser beam 10 that has become parallel light. , Neodymium (N
d) A YVO ₄ crystal (Nd: YVO ₄ crystal) 14 which is a solid-state laser medium doped with, and a resonator mirror 15 disposed on the front side (right side in the figure) of the Nd: YVO ₄ crystal 14
And an etalon 18 disposed between the resonator mirror 15 and the Nd: YVO ₄ crystal 14.

The semiconductor laser 11 has an emission width of 200 μm.
With a power of 2 W and a wavelength of 80 emitted from it.
A 9 nm laser beam 10 is condensed by a condensing lens 13 and has a convergent beam diameter of 130 μm and is Nd: YVO.
₄ Excite the crystal 14.

On the other hand, the Nd: YVO ₄ crystal 14 has an Nd of 0.5
It is doped at at% and has a length of 3 mm × width of 3 mm × thickness of 1 mm. This Nd: YVO ₄ crystal 14
Emits light having a wavelength of 1064 nm when neodymium ions are excited by the laser beam 10. Laser oscillation is caused by the resonator constituted by the rear end face 14a of the Nd: YVO ₄ crystal 14 and the mirror face 15a of the resonator mirror 15, and a solid laser beam 20 having a wavelength of 1064 nm is obtained. This solid-state laser beam 20 is converted into a single longitudinal mode by the action of the etalon 18.

The c-axis of the Nd: YVO ₄ crystal 14 has the direction of linear polarization of the laser beam 10 (the direction parallel to the paper).
The semiconductor laser-excited solid-state laser has c-axis absorption and c-axis oscillation.

In this apparatus, since the Nd: YVO ₄ crystal 14 has a relatively small Nd doping amount of 0.5 at% and an absorption coefficient of 20 cm ⁻¹ , the thermal lens effect is suppressed. Become like Therefore, even if the output of the semiconductor laser 11 is relatively high as 2 W as described above,
The beam cross-sectional shape of the solid-state laser beam 20 can be prevented from being deformed into an elliptical shape or the like. The beam diameter of the solid laser beam 20 was about 200 μm. On the other hand, the solid-state laser output was sufficiently high at 600 mW, and a complete single longitudinal mode was realized.

<Second Embodiment> FIG. 2 shows a semiconductor laser pumped solid-state laser according to a second embodiment of the present invention. In FIG. 2, the same elements as those in FIG. 1 are denoted by the same reference numerals, and a duplicate description thereof will be omitted (the same applies hereinafter).

This semiconductor laser pumped solid-state laser
1 is different from the one shown in FIG. 1 in that an optical wavelength conversion element 16 is provided in a resonator constituted by a rear end face 14a of an Nd: YVO ₄ crystal 14 and a mirror surface 15a of a resonator mirror 15. Are fundamentally different. As an example, the light wavelength conversion element 16 in the present example is made of LiN doped with MgO.
The bO ₃ crystal is provided with a periodic domain inversion structure.

In this case, the solid-state laser beam 20 having a wavelength of 1064 nm enters the optical wavelength conversion element 16 and is converted into a second harmonic 21 having a wavelength of 1/2, that is, 532 nm. The coating applied to the mirror surface 15a of the resonator mirror 15 reflects the laser beam 10 and the solid-state laser beam 20 well, and partially transmits the second harmonic 21 having a wavelength of 532 nm. Almost only the second harmonic 21 is emitted from the resonator mirror 15.

Also in the second embodiment, the Nd: YVO ₄ crystal 14 is arranged in the same manner as in the first embodiment, so that the c-axis absorption and the c-axis oscillation also occur in this example. The Nd: YVO ₄ crystal 14 has an Nd doping amount of 0.5 at%.
Because it is small, the thermal lens effect is suppressed,
Beam cross-sectional shape of the solid-state laser beam 20, that is, the second
Deformation of the beam cross-sectional shape of the harmonic 21 can be prevented. In addition, a second harmonic output as high as 550 mW is obtained,
And the complete single longitudinal mode was realized.

<Third Embodiment> FIG. 3 shows a semiconductor laser pumped solid-state laser according to a third embodiment of the present invention. This semiconductor laser pumped solid-state laser
The difference from the one shown in FIG. 2 is that the Brewster plate 17 is further disposed inside the resonator.

The Brewster plate 17 as a polarizing element
Are arranged such that light linearly polarized in the c-axis direction of the Nd: YVO ₄ crystal 14 is incident as p-polarized light. As described above, by inserting the Brewster plate 17 for promoting the c-axis oscillation, the polarization ratio, that is, the intensity ratio between the a-axis oscillation light and the c-axis oscillation light, is about 1:50 in the case without the Brewster plate. To about 1: 1000.

Next, a description will be given of a semiconductor laser-excited solid-state laser according to a comparative example which was prepared to confirm the effects of the present invention.

<First Comparative Example> First, a semiconductor laser-pumped solid-state laser as a first comparative example has a Nd: YVO ₄ crystal 14 having an Nd doping amount of Nd: YVO ₄ crystal 14 as compared with the first embodiment shown in FIG. The difference is that 1 at% is used, and the other configuration is the same as that of the first embodiment.

The solid-state laser output in this case is 500 mW
However, the use of the Nd: YVO ₄ crystal 14 having a larger Nd doping amount than in the first embodiment causes a thermal lens effect, and the beam cross-sectional shape of the solid-state laser beam 20 having a beam diameter of about 200 μm Has become elliptical. In this example, the ratio of the minor axis to the major axis of the ellipse is 1: 1.1
Met.

<Second Comparative Example> A semiconductor laser pumped solid-state laser as a second comparative example is different from the first embodiment shown in FIG. 1 in that the Nd: YVO ₄ crystal 14 has an Nd doping amount of 2 at%. Is different from the first embodiment in that the second embodiment is the same as the first embodiment.

Also in this case, the thermal lens effect is produced by using the Nd: YVO ₄ crystal 14 having a large Nd doping amount of 2 at%, and the beam sectional shape of the solid-state laser beam 20 having a beam diameter of about 200 μm is made elliptical. did. In this case, the ratio of the minor axis to the major axis of the ellipse was 1: 1.15. The solid-state laser output was reduced to 400 mW.

<Third Comparative Example> A semiconductor laser-pumped solid-state laser as a third comparative example has an Nd: YVO ₄ crystal 14 having an Nd doping amount of 2 at% as compared with the second embodiment shown in FIG. Is different from that of the second embodiment.

Also in this case, the thermal lens effect is generated by using the Nd: YVO ₄ crystal 14 having a large Nd doping amount of 2 at%, and the beam cross-sectional shape of the solid-state laser beam 20, that is, the beam of the second harmonic 21 The cross-sectional shape has become elliptical. Then, the second harmonic output was reduced to 250 mW in the case of 2 W excitation.

The second harmonic 21 is composed of Nd: YVO ₄ crystal.
Although it is reflected between both end faces inside 14 (see FIG. 2),
Reflected second harmonic wave 21 whose wavefront is deformed by the generated thermal distortion
Interference occurs between the second harmonic 21 and the second harmonic 21 emitted forward from the Nd: YVO ₄ crystal 14, and the beam cross section of the second harmonic 21 is generated due to a synergistic effect of the interference and the beam shape deformation of the fundamental wave. The shape was greatly deformed.

As a result, the second harmonic 21 could not be completely made into a single transverse mode, and therefore, it could not be completely made into a single longitudinal mode. Therefore, noise occurred due to vertical mode competition.

<Fourth Comparative Example> A semiconductor laser-pumped solid-state laser as a fourth comparative example shown in FIG. 4 is different from the semiconductor laser 11 and Nd: Y in the second embodiment shown in FIG.
The arrangement relationship with the VO ₄ crystal 14 is different. That is, in this example, the Nd: YVO ₄ crystal 14 is arranged so that its a-axis is parallel to the linear polarization direction of the laser beam 10 (the direction perpendicular to the paper). Here, Nd: YVO ₄
The crystal 14 has a Nd doping amount of 2 at%.

In the fourth comparative example, a-axis absorption and a-axis oscillation are obtained. In this example, the thermal lens effect could be suppressed by using the a-axis absorption. However, since the a-axis oscillation was used, several oscillation spectra existed, and the second harmonic output was reduced in the second embodiment. 550mW,
It decreased to 200 mW.

The effects of the present invention are clear when compared with the results of the first to fourth comparative examples described above.

[Brief description of the drawings]

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

FIG. 2 is a side view showing a semiconductor laser pumped solid-state laser according to a second embodiment of the present invention;

FIG. 3 is a side view showing a semiconductor laser-pumped solid-state laser according to a third embodiment of the present invention;

FIG. 4 is a side view showing a semiconductor laser-pumped solid-state laser as a comparative example for confirming the effect of the present invention.

[Explanation of symbols]

10 Laser beam (excitation light) 11 Semiconductor laser 12 Collimator lens 13 Condensing lens 14 Nd: YVO ₄ crystal 15 Resonator mirror 16 Optical wavelength conversion element 17 Brewster plate 18 Etalon 20 Laser beam (Solid laser beam) 21 Second harmonic

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2K002 AB12 BA03 EA07 FA27 GA04 GA05 HA20 5F072 AB20 FF09 JJ20 KK01 KK06 KK08 KK12 PP07 QQ02 RR01 SS01

Claims (5)

[Claims] 1. A c-axis absorption, c-axis oscillating semiconductor laser-excited solid-state laser that excites a Nd: YVO ₄ crystal by a laser beam emitted from a semiconductor laser, wherein the amount of Nd added as the Nd: YVO ₄ crystal is 0.4
A semiconductor laser-excited solid-state laser, wherein at least less than 0.7 at% is used. 2. The semiconductor laser-excited solid-state laser according to claim 1, wherein the amount of Nd added is 0.5 at%. 3. The semiconductor laser pumped solid-state laser according to claim 1, wherein an output of said semiconductor laser is 1 W or more. 4. The semiconductor laser-excited solid laser according to claim 1, further comprising an optical wavelength conversion element for shortening the wavelength of the solid-state laser oscillation light. 5. The semiconductor laser-pumped solid-state laser according to claim 4, wherein said optical wavelength conversion element is made of a bulk crystal of a nonlinear optical material having a periodic domain inversion structure.