JP2002050813A - Solid laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid laser device that can obtain a high-output laser beam and at the same time has less fluctuation in heat lens effect being generated by each stimulation medium. SOLUTION: The level of the heat lens effect being generated in each stimulation medium is measured with a current being supplied to an LD stack as a parameter, and a current value to be supplied based on the measurement result is set and adjusted for each LD stack.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device comprising a plurality of excitation media arranged in series.

[0002]

2. Description of the Related Art In order to obtain a high-power laser beam, a solid-state laser device having a plurality of excitation media has been developed. However, in the case of a solid-state laser device having a plurality of pumping media, since the magnitude of the thermal lens effect generated in each pumping media varies, it is difficult to obtain a stable oscillation mode and obtain good beam quality. Become. The thermal lens effect means that when the excitation medium is excited, a temperature distribution with the laser optical axis as a peak occurs in a plane perpendicular to the laser optical axis of the medium, and the laser optical axis is peaked. This is a phenomenon in which a refractive index distribution occurs and behaves optically equivalent to a thick lens. In order to reduce the variation in the magnitude of the thermal lens effect, it is conceivable to make the configurations for exciting the individual excitation media exactly the same and to make the power injection to the individual excitation sources equal. However, when a lamp is used as an excitation source, for example, the progress of deterioration differs for each lamp, so that the magnitude of the thermal lens effect, which was initially kept equal when the emission spectrum and luminous efficiency changed, was changed. Variations occur. Further, when a semiconductor laser is used as an excitation source, individual differences in excitation light power and center wavelength are large, so that even if the configuration for each excitation medium is equal, the magnitude of the thermal lens effect still varies. As a result, a stable oscillation mode cannot be obtained. Therefore,
In order to obtain a stable oscillation mode, it is necessary to frequently replace the lamp or to procure a semiconductor laser having the same performance.

In order to obtain good beam quality,
It is preferred that the spacing between the individual excitation media be as long as possible. However, when the interval between the excitation media is increased, a slight variation in the thermal lens effect in each excitation medium makes the oscillation mode unstable. Therefore, in order to obtain a stable oscillation mode, the interval between the excitation media is shortened to some extent, and the beam quality is sacrificed instead. As described above, in order to obtain a stable oscillation mode and good beam quality, it is assumed that variations in the thermal lens effect generated in each excitation medium are eliminated. Japanese Patent No. 27380 describes a method for reducing the variation of the thermal lens effect generated in each excitation medium.
As disclosed in JP-A-38, a flash lamp light source that excites at least one solid state element is turned on so that the average input power is constant, and a flash lamp light source that excites other solid state elements is desired. There has been proposed a solid-state laser device in which the input power is changed so that the laser output is obtained so as to be turned on, and the thermal lens value of at least one solid-state element is compensated as described above.

[0004]

However, in the case of this method, it is necessary to turn on at least one of the flash lamp light sources so that the average input power thereof is constant. The original purpose of a laser device having a medium cannot be achieved.
The present invention has been made in order to solve such a problem, and provides a solid-state laser device capable of obtaining high-power laser light and having a small variation in a thermal lens effect generated in each excitation medium. It is an object.

[0005]

According to the present invention, there are provided a plurality of excitation media arranged in series on an optical path, a plurality of semiconductor laser devices for irradiating the excitation medium with excitation light, and the semiconductor laser. In a solid-state laser device including a power supply for supplying power to the device and a resonator that resonates light generated by excitation of the excitation medium, the power supply has a value of a thermal lens effect generated in each of the excitation media. Wherein the power supplied to the semiconductor laser device is adjusted so that the values are equal. Also,
A plurality of excitation media arranged in series on the optical path, a plurality of excitation light sources for irradiating the excitation medium with excitation light, a power supply for supplying power to the excitation light source, and excitation of the excitation medium A solid-state laser device comprising: a resonator that resonates generated light; and a temperature adjusting unit that adjusts the temperature of the excitation light source so that a value of a thermal lens effect generated in each of the excitation media is equal. A solid-state laser device characterized by the above-mentioned. 3. The solid-state laser device according to claim 2, wherein said excitation light source is a semiconductor laser device. Further, a plurality of excitation media arranged in series on the optical path, a plurality of excitation light sources for irradiating the excitation medium with excitation light, a power supply for supplying power to the excitation light source, and A resonator that resonates light generated by excitation, in a solid-state laser device, a temperature adjustment for performing temperature adjustment for each of the excitation media so that the value of the thermal lens effect generated in each of the excitation media is equal. A solid-state laser device characterized by comprising means.

The laser device according to claim 4, wherein the excitation light source is a semiconductor laser device.

[0007]

(First Embodiment) FIG. 1 shows a configuration diagram of a solid-state laser device 10 according to a first embodiment of the present invention. This solid-state laser device 10 is a two-stage solid-state laser device 10 including an output mirror 12a and a high-reflection mirror 12b, which are optical resonators, and two pumping modules 20a and 20b in a gap therebetween. Each excitation module
A YAG rod 21, a flow tube 22 for storing the YAG rod 21, a cooler 23 for cooling the YAG rod 21, and three LD stacks 27, 28, for irradiating the YAG rod 21 with excitation light. 29 and L
An LD cooler 25 for cooling the D stacks 27, 28, and 29 and a power supply 26 for supplying power to the laser diodes incorporated in the LD stacks 27, 28, and 29 are provided. Hereinafter, each component will be described. The YAG rod 21 as an excitation medium is made of a YAG (yttrium-aluminum-garnet) crystal doped with 0.8 at% of Nd (neodymium). The YAG rod 21 has a cylindrical shape with a diameter of about 10 mm and a length of about 200 mm, and two YAG rods 21a and 21b are arranged in series on an optical path.

The flow tube 22 is a YAG rod 21
To store. On the outer surface of the flow tube 22, an anti-reflection film for preventing reflection of laser light emitted from the LD stack described later is formed. The inner surface of the flow tube 22 is provided with a high reflection coating so that the laser light is absorbed by the YAG rod 21 with high efficiency. The cooler 23 circulates cooling water for cooling the YAG rod 21 inside the flow tube 22.
The LD stacks 27, 28, and 29 serving as excitation sources irradiate the YAG rod 21 with excitation light having a main wavelength of 807 nm. As shown in FIG. 2, the LD stacks 27, 28 and 29 are formed by arranging laser diodes in a matrix and stacking them, and are arranged so as to irradiate the side surface of the YAG rod 21 with p-polarized light. . As shown in FIG. 3, three LD stacks 27, 28, and 29 are equally arranged every 120 degrees around one YAG rod 21 so that the excitation distribution in the YAG rod 21 is not biased. I have.
In addition, LD stack 27, 28, 29 and YAG rod 2
Collimator lenses 31, 32, 33 for collimating the excitation light are disposed between the two. In addition, the LD cooler 25 has a function of circulating cooling water inside a heat sink built in each LD stack in order to cool the LD stacks 27, 28, and 29.

The high-reflection mirror 12b and the output mirror 12a, which are optical resonators, are provided with two YAG rods 21a, 21 arranged in series so as to resonate light generated by excitation.
b. The power supply 26 supplies power to the laser diodes contained in the LD stacks 27, 28, 29. The power supply 26 is connected to the excitation modules 20a, 2
0Yb, YAG rods 21a, 21a
The current value supplied in advance is adjusted so that the variation of the thermal lens effect generated in b is reduced and equalized. The measurement of the value of the thermal lens effect and the setting of the current supplied by each power supply 26 are performed as follows. What is the thermal lens effect?
A phenomenon in which, when the excitation medium is excited, a refractive index distribution with the laser optical axis as a peak is formed in a plane perpendicular to the laser optical axis of the medium, and behaves optically equivalent to a thick lens. It is. In the solid-state laser device 10 according to the present embodiment, the magnitude of the thermal lens effect generated in the YAG rods 21a and 21b is measured in advance, and the YAG rods 21a and 21b are measured.
The variation of the thermal lens effect generated in b is reduced and equalized. The magnitude of the thermal lens effect is measured as follows.

The probe light is made incident on the YAG rod 21 in a state where the LD stacks 27, 28 and 29 are irradiated with the excitation light. Irradiation of the excitation light generates a refractive index distribution inside the YAG rod 21. Therefore, the probe light focuses on a position separated by a predetermined distance. This value of the back focal length is defined here as the value of the thermal lens effect. FIG. 4 shows a graph in which the horizontal axis represents the total current supplied to the laser diodes provided in each module, and the vertical axis represents the back focal length for each of the YAG rods 21a and 21b. The reason that the larger the current value is, the shorter the rear focal length is, because the larger the current output and the larger the energy output of the excitation light, the larger the bias of the refractive index distribution inside the excitation medium becomes, and the more the thermal lens effect occurs. It is. Also, the back focal length differs for each excitation medium even when the current value is the same because the main wavelength has a variation of about ± 3 nm for each laser diode, and the luminous efficiency has a variation of about 10 to 20% for each laser diode. It is caused by having. Now
The difference in current when the back focal lengths of the excitation media are equal is about 2A. Therefore, the current supplied to the laser diode provided in the excitation module 20a is supplied to the excitation module 20a.
The power supplies 26a and 26b are adjusted in advance so that the current supplied to the laser diode included in the laser diode b is increased by 2A.

The laser light emitted from the laser diode has a narrow spectral width of several nm and has a variation in the main wavelength of about ± 3 nm depending on the laser diode. The absorption efficiency of the YAG rod 21 as the excitation medium is several n.
The difference greatly depends on the difference in the wavelength of m. Further, the luminous efficiency of the laser diode has an individual difference of 10 to 20%. For this reason, even if the same current is supplied to excite the excitation medium, the magnitude of the thermal lens effect generated in the excitation medium differs. In addition, the thermal lens effect changes greatly with a slight change in current. According to the present invention, (1) the magnitude of the thermal lens effect generated in each excitation medium is different even when the same current is applied. (2) The magnitude of the thermal lens effect varies with the variation of the current. The power supplied to the laser diode is adjusted so that the values of the thermal lens effect generated in each excitation medium become equal. In order to realize such a configuration, the relationship between the value of the thermal lens effect generated for each excitation medium and the supplied current is measured in advance.
By doing so, it is possible to provide a high-output laser device with small variations in the thermal lens effect.

The excitation source may be another semiconductor laser light source such as a two-dimensional LD array laser. The excitation medium is N
d: Not only YAG but also other substances can be applied. The number of LD stacks 27, 28, 29 is not limited to three. For example, the LD stack and the YAG rod may be one-to-one. Also, the power supply 26 is an LD stack 27, 28,
29, and the supply current may be adjusted in consideration of the difference in output efficiency between the LD stacks 27, 28, and 29. Also, the number of excitation media is not limited to two, and for example, four YAG
The rods 21 may be arranged in series. Further, the excitation source does not necessarily need to be provided in one excitation medium unit, and for example, two excitation media may be irradiated with excitation light. In the present invention, “so that the value of the thermal lens effect in each excitation medium is equal” means that the difference in the value of the thermal lens effect in each excitation medium is small, and it is not necessarily the case that the thermal lens effect in each excitation medium is small. Does not mean that the values of Further, the value of the thermal lens effect is not limited to the method described in the present embodiment,
For example, the beam diameter of the probe light at a position separated by a predetermined distance may be measured, and the value of the beam diameter may be used as the value of the thermal lens effect. In addition, the present embodiment can be variously modified for the same purpose.

(Second Embodiment) The solid-state laser device 40 according to the second embodiment controls the temperature of the excitation source so that the thermal lens effect generated in each excitation medium becomes equal. It was made. That is, the difference from the first embodiment is that the current value supplied to the laser diode provided in each excitation module 43 is not changed for each excitation module, and the LD stacks 27 and 2 are not changed.
The temperature setting of the LD coolers 41a and 41b for cooling the cooling units 8 and 29 is adjusted and set for each excitation module, so that the thermal lens effect for each excitation medium becomes equal. Components having the same functions as those of the configuration of the solid-state laser device 40 according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the second embodiment, L is set for each of the excitation modules 42a and 42b.
Using the operating temperatures of the D stacks 27, 28, and 29 and the current supplied to the laser diodes as parameters, probe light is incident on the YAG rod 21 and the focal length is measured, as in the first embodiment. FIG. 6 shows the measurement results. The solid line indicates the back focal length for the excitation module 42a, and the dashed line indicates the back focal length for the excitation module 42b. L of the excitation module 42a
It can be seen that the rear focal length when the operating temperature of the D stack is 25 degrees and the rear focal length when the operating temperature of the LD stack of the excitation module 42b is 30 degrees. Therefore, the temperature of the cooling water for cooling the LD stack is set to 25 degrees in the excitation module 42a and 30 degrees in the excitation module 42b, and is set to 30 degrees.
By adjusting a and b, it is possible to make the magnitude of the thermal lens effect generated in each excitation medium substantially equal.

When a semiconductor laser light source is used as an excitation source,
The center wavelength of the excitation light from the semiconductor laser light source can be controlled by the operating temperature of the semiconductor laser light source. The wavelength of the semiconductor laser light source is about 807 nm and the excitation medium Y
There is an absorption peak on the AG rod, at which time the thermal lens effect of the excitation medium is maximized. In the solid-state laser device described in the present embodiment, the value of the thermal lens effect generated in each excitation medium is measured in advance for each operating temperature of the LD stack, and the temperature of each LD stack is adjusted based on the measurement result. Therefore, the variation in the magnitude of the thermal lens effect generated in each excitation medium can be reduced and made equal. Note that the cooling means is not limited to the present embodiment, and it is also possible to use a method using a cooling medium, an air cooling method, or another cooling method. The excitation light source is not limited to the semiconductor laser device, and a light source such as a flash lamp may be used. In addition, this embodiment can be variously modified in the same manner as shown in the first embodiment. (Third Embodiment) The solid-state laser device according to the third embodiment reduces the variation in the value of the thermal lens effect generated in each YAG rod by adjusting the temperature of the YAG rod as the excitation medium. It is for doing. That is, the back focal length of the probe light is measured using the cooling temperature of the YAG rod and the current flowing through the laser diode provided in the module as parameters, and the temperature of each excitation medium is adjusted based on the result. Specifically, the temperature of the YAG rod can be adjusted by adjusting the temperature of the cooling water circulating in the flow tube storing the YAG rod. Focusing on the fact that the magnitude of the thermal lens effect decreases as the temperature of the excitation medium decreases, the magnitude of the thermal lens effect for each temperature of the excitation medium was measured in advance, and the temperature was adjusted based on the measurement results. . Therefore, only by adjusting the temperature of the cooling water, variations in the magnitude of the thermal lens effect generated in each excitation medium can be reduced. Note that the present invention is not limited to the present embodiment, and can be variously modified in the same manner as shown in the above-described embodiment. Further, the above embodiments can be combined. For example, using the amount of power supplied to the excitation source, the operating temperature of the excitation source, and the cooling temperature of the excitation medium as parameters, the magnitude of the thermal lens effect generated in the excitation medium is measured, and each parameter is determined based on this result. It is also possible.

[0015]

According to the present invention, the magnitude of the thermal lens effect generated in each excitation medium is measured for each of various parameters, and the solid-state laser device is configured based on the measurement results, so that high-power laser light can be obtained. In addition, a solid-state laser device in which the thermal lens effect generated in each excitation medium is equal can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a solid-state laser device according to a first embodiment.

FIG. 2 is a diagram schematically showing an LD stack according to the first embodiment.

FIG. 3 is a diagram schematically showing that a YAG rod is irradiated with excitation light in the first embodiment.

FIG. 4 is a graph obtained by measuring the back focal length of each excitation medium for each current supplied to the excitation module in the first embodiment.

FIG. 5 is a diagram schematically showing a solid-state laser device according to a second embodiment.

FIG. 6 is a graph obtained by measuring a back focal length for each excitation medium for each operating temperature of an excitation source in the second embodiment.

[Explanation of symbols]

 10 solid-state laser device, 20a, 20b excitation module, 21a, 21b YAG rod, 25a, 25b LD cooler, 26a, 26b power supply.

Claims (5)

[Claims] 1. A plurality of excitation media arranged in series on an optical path, a plurality of semiconductor laser devices for irradiating the excitation medium with excitation light, and a power supply for supplying power to the semiconductor laser device. A resonator configured to resonate light generated by excitation of the excitation medium, wherein the power supply controls the semiconductor laser device so that a value of a thermal lens effect generated in each of the excitation media is equal. A solid-state laser device in which supplied power is adjusted. 2. A plurality of excitation media arranged in series on an optical path, a plurality of excitation light sources for irradiating the excitation medium with excitation light, a power supply for supplying power to the excitation light source, A resonator that resonates light generated by excitation of the excitation medium.In the solid-state laser device, the temperature adjustment is performed by adjusting the temperature of the excitation light source so that a value of a thermal lens effect generated in each of the excitation media becomes equal. A solid-state laser device characterized by comprising means. 3. The solid-state laser device according to claim 2, wherein said excitation light source is a semiconductor laser device. 4. A plurality of excitation media arranged in series on an optical path, a plurality of excitation light sources for irradiating the excitation medium with excitation light, a power supply for supplying power to the excitation light source, A resonator that resonates light generated by excitation of the excitation medium, wherein the excitation medium is provided for each of the excitation media so that the value of the thermal lens effect generated in each of the excitation media is equal. A solid-state laser device comprising a temperature adjusting means for adjusting the temperature of the solid-state laser. 5. The solid-state laser device according to claim 4, wherein said excitation light source is a semiconductor laser device.