JPH06152014A - Laser light generator - Google Patents

Abstract

(57) [Summary] [Structure] A lens fixing block 1 for fixing the mounting table 12 to which the semiconductor laser element 11 is attached and the lens 13.
4 is mounted on the first base 23 to mount the first temperature control element 24.
The temperature of the semiconductor laser element 11 is controlled by the cavity fixing block 21 and the rising mirror for fixing the laser resonator 20 integrally formed by closely contacting the quarter-wave plate 15, the laser medium 17 and the nonlinear optical crystal element 18. 22 is mounted on the second base 25, and the temperature of the laser resonator 20 is controlled by the second temperature control element 26. [Effect] Laser light with high excitation efficiency and high output can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light generator, and more particularly to a laser light generator having a laser light source for generating high-order harmonic laser light using a nonlinear optical crystal element.

[0002]

2. Description of the Related Art It has hitherto been proposed to efficiently perform wavelength conversion by utilizing a high power density inside a laser resonator. For example, SHG (second harmonic) generated by a nonlinear optical crystal element inside the laser resonator has been proposed. Occurrence) etc. are being attempted.

Second harmonic generation (SHG) in laser resonator
As an example of the type of laser light generator, there is known a device in which a laser medium and a nonlinear optical crystal element are arranged between at least a pair of reflecting mirrors constituting a laser resonator.
In the case of this type of laser light generator, the nonlinear optical crystal element in the laser resonator efficiently phase-matches the second harmonic laser light with the fundamental laser light, thereby efficiently producing the second harmonic laser light. The light can be extracted.

[0004]

By the way, Nd: YA
In order to efficiently absorb the pumping light in the laser medium such as G, it is necessary to match the pumping light wavelength from the pumping light source element such as a laser diode that oscillates in multiple modes with the absorption wavelength of the laser medium. Since the light wavelength changes depending on the temperature of the excitation light source element such as a laser diode, it is necessary to control the temperature of the excitation light source element.

Further, in order to obtain stable emitted light with less noise from the laser medium, it is limited because of the temperature dependence of the phase delay amount of the nonlinear optical crystal element of the laser resonator and the deformation of the laser resonator. It is necessary to control the temperature within the specified temperature range.

As described above, in order to stably obtain highly efficient laser light in the SHG laser light generator, the pumping light source element and the laser are efficiently absorbed in the laser medium by the pumping light source element. Although it is necessary to control the temperature of the medium, there is a slight deviation between the peak of the absorption wavelength of the laser medium and the peak of the excitation light from the excitation light source element, so the excitation efficiency of the light emitted from the laser medium is high. When the value is improved, noise is generated, and when the noise is suppressed, the excitation efficiency is reduced.

Therefore, in order for the laser medium to efficiently absorb the pumping light from the pumping light source element, it is necessary to separately control the temperatures of the pumping light source element and the laser medium.

Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laser light generator capable of freely performing temperature control for increasing and stabilizing the efficiency of laser light generation. It is a thing.

[0009]

A laser light generator according to the present invention comprises at least a pumping light source element, a laser medium pumped by the laser light from the pumping light source element, and an incident laser beam to the laser medium. Reflecting means for generating emitted laser light by performing a resonant operation, a resonator fixing block for fixedly supporting the excitation light source element and the reflecting means, and the excitation light source element and the reflecting means for the excitation light source element and the reflecting means via the resonator fixing block. In a laser light generator having a temperature control element for adjusting temperature, a first temperature control element for controlling temperature so that an oscillation wavelength from an excitation light source element matches an absorption wavelength from a laser medium, and a laser resonance The problem described above is solved by including a second temperature control element for performing temperature control that suppresses noise of light emitted from the container.

[0010]

In the present invention, by separately controlling the temperature of the pumping light source element and the laser resonator, it is possible to obtain laser light having high pumping efficiency and high output.

[0011]

1 is a cross-sectional view showing a schematic structure of an SHG laser light generator which is an embodiment of a laser light generator according to the present invention, and FIG. It is a schematic plan view (in a state). In these laser light generators shown in FIGS. 1 and 2, a semiconductor laser element 11 such as a laser diode as an excitation light source element is mounted on a mounting table 12, and light emitted from this semiconductor laser element 11 is condensed. The lens 13 for fixing is the lens fixing block 1
It is attached to 4. The excitation laser light condensed by the lens 13 is passed through the incident surface of the quarter-wave plate 15 and the laser medium (laser rod) 1 using Nd: YAG is used.
It is incident on 7. The incident surface of the quarter-wave plate 15 has wavelength selectivity such that the excitation laser light (for example, 810 nm) is transmitted and the fundamental wave laser light having a wavelength of 1064 nm generated in the laser medium 17 is reflected. A reflection surface (dichroic mirror) 16 is formed (coated, for example), and in this embodiment, the reflection surface 16 is a concave mirror when viewed from the laser medium 17 side. The fundamental laser light generated by the laser medium 17 is KTP (KTiOP
The second harmonic generation (SHG) is performed by being incident on the nonlinear optical crystal element 18 made of O ₄ ). The emission surface of the nonlinear optical crystal element 18 has wavelength selectivity such that the fundamental wave laser light is reflected and the second harmonic laser light (wavelength 532 nm) generated by the nonlinear optical crystal element 18 is transmitted. Reflective surface held (dichroic mirror)
19 is formed. Therefore, the quarter wave plate 15
A laser resonator 20 is formed between the reflecting surface 16 of the non-linear optical crystal element 18 and the reflecting surface 19 of the nonlinear optical crystal element 18.

Here, the quarter-wave plate 15 is a birefringent element used in a laser light source, and is for stabilizing the second harmonic laser light emitted as output laser light. . That is, the fundamental wave laser light generated in the laser medium 15 is resonantly operated so as to pass through the nonlinear optical crystal element 18 provided in the laser resonator 20 to generate the type II second harmonic laser light. At this time, a birefringent element such as a quarter-wave plate 15 is inserted in the laser resonator 20 to reciprocate in the laser resonator 20 while rotating the polarization plane of the fundamental wave laser light, thereby making them orthogonal to each other. The two eigenpolarizations are set to the fundamental wave mode, and the azimuth angle θ and the phase amount Δ of the quarter-wave plate 15 do not cause energy transfer between the two eigenpolarizations of the fundamental wave laser light through generation of the second harmonic. By selecting such a value, it is possible to stabilize the fundamental wave laser light and thus the second harmonic laser light. Moreover, the conversion efficiency can be increased by integrally configuring the quarter-wave plate 15, the laser medium 17, and the type II phase matching type non-linear optical crystal element 18 so as to be in close contact with each other.

The opposing surfaces of the quarter-wave plate 15, the laser medium 17, and the nonlinear optical crystal element 18 constituting the laser resonator 20 are provided with, for example, a non-reflective coating and are closely adhered and fixed, Resonator fixing block 21
Is mounted on. This resonator fixing block 21
For example, as shown in FIG. 3, a guide groove 21V having a V-shaped cross section is formed on the surface, and the laser medium 17 and the nonlinear optical crystal element 18 are attached to the V-shaped guide groove 21V. At this time, the direction of the arrow Z in the figure is the optical axis direction, and the polarization direction of the emitted second harmonic is the direction of the arrow S (the direction of the arrow X) in the figure, and the nonlinear optical crystal element 18 is arranged.
Is provided. This is because when the above KTP is used as the nonlinear optical crystal element 18, the a
It is a plane including the axis and the b axis, and the Y axis perpendicular to this is the c of the crystal
What is cut out so as to form a shaft may be used. This polarization direction is the S polarization direction of the rising mirror 22 that is the deflecting means. That is, the second harmonic laser light emitted from the laser resonator 20 is 45 ° which is the deflection means.
It is vertically deflected by the rising mirror 22.

The lens fixing block 14 to which the lens 13 is attached and the mounting table 12 to which the semiconductor laser element 11 is attached are mounted on the first base (base) 23 so that the semiconductor laser element 11 is TE (thermo-electric). The temperature is controlled by the first temperature control element 24 formed by the cooler, and the resonator fixing block 21 to which the rising mirror 22 and the laser resonator 20 are attached is mounted on the second base 25 to cause laser resonance. The temperature of the container 20 is controlled by a second temperature control element 26 formed of a TE (thermo-electric) cooler.

Next, the TE cooler will be described. The TE cooler is also called an electronic cooling unit, and is a combination of semiconductor elements that can be freely cooled, heated, and temperature-controlled by a direct current. FIG. 4 is a circuit diagram showing the principle of temperature control of a semiconductor element. When two different P-type semiconductors 40 and N-type semiconductors 41 are joined with metals 42, 43 and 44 and a direct current is passed in the I direction, the joint 45 on the left side in the figure becomes a low temperature and the endotherm 45 absorbs heat. Q _ab occurs,
The joint 46 on the right side of the figure becomes hot, and heat Q ₀ is generated at this joint 46. The above phenomenon is called the Peltier effect, which is reversible, and when the current direction I is reversed, the heat absorption and heat generation of the respective junctions 45 and 46 are reversed. The Peltier effect is caused by the difference in energy level between the P-type semiconductor 40 and the N-type semiconductor 41. However, if the heat on the high temperature side is efficiently processed, the heat is continuously pumped from the low temperature side to the high temperature side. The electronic cooling unit in which a plurality of these semiconductor elements are combined functions as a heat pump (heat pump). In this embodiment, wavelength control of a semiconductor laser device 11 such as a laser diode, which is an excitation light source device, and S
The temperature control for stabilizing the HG laser resonator 20 is performed using the first and second temperature control elements (TE coolers) 24 and 26.

Each element for generating laser light as described above is housed in a package 31. The bottom surface 32 of the package 31 serves as a mounting surface, and as shown in FIG. 2, a screw insertion hole 37 of a flange piece 36 for mounting.
It can be fixed by inserting a mounting screw into the. Each element 11, 13, 15, 1 of the above optical system
7, 18 and the like are arranged in a direction parallel to the bottom surface 32 (horizontal plane) which is the mounting surface, and the optical axis is parallel to the bottom surface 32. When the laser light is taken out of the package 31 in the state of being parallel to the bottom surface 32, it is necessary to move the laser light in the horizontal and vertical directions in order to align the optical axis. The configuration for is complicated. Therefore, the laser light emitted from the laser resonator 20 is emitted from the bottom surface 3 by using the 45 ° rising mirror 22.
The light is deflected in a direction perpendicular to 2 and is taken out through the emission hole 34 formed in the lid 33 of the package 31. The exit hole 34 is closed by a transparent plate 35.

Here, the reflectance of the rising mirror 22 having an inclination angle of 45 ° can be easily increased for S-polarized light, but it is difficult to increase it for P-polarized light. In a mixed state containing a polarized component and a P-polarized component, the reflected light becomes elliptically polarized light due to the difference in reflectance between these polarized components, and the handling becomes troublesome. Therefore, in the present embodiment, the azimuth of the nonlinear optical crystal element 18 is set to the outer shape so that the polarization direction of the SHG laser light emitted from the nonlinear optical crystal element 18 such as KTP becomes the S polarization direction of the rising mirror 22. It is possible to increase the reflectance of S-polarized light to, for example, about 99.9% by coating the rising mirror 22 or the like according to the determination in advance, and to suppress the power loss as much as possible and to suppress the upper portion of the package 31. The SHG laser light can be taken out vertically upward through the emission hole 34 of the lid 33.

According to the SHG laser light generator of this embodiment, since the polarization direction of the nonlinear optical crystal element 18 is the S polarization direction of the rising mirror 22 which is the deflecting means, the S polarization of the rising mirror 22 is S polarization. The reflectance of the SHG laser light can be increased, and the SHG laser light reflected and taken out from the emission hole 34 is not elliptically polarized, and the polarization direction is fixed. In this way, if the polarization direction of the emission hole is determined with respect to the package 31, it is easy to handle as a component and to incorporate it in an optical disk reproducing device or the like. Further, since the emitted light is taken out vertically upward (Y direction in the figure), adjustment work such as so-called optical axis alignment is
Two directions on the mounting surface of the package (X direction in the figure, Z
It is a simple work of just adjusting the fine movement in the direction) and the accuracy is easy to improve.

The raising mirror 22 may not be used. For example, the SHG laser light may be taken out in the horizontal direction as in another embodiment shown in FIG. In the embodiment of FIG. 5, the laser light emitted from the laser diode 51, which is an excitation light source element, is condensed by the lens 52 and is incident on the laser medium 53 such as an Nd: YAG rod. The incident surface of the laser medium 53 is
Similar to the reflection surface 16 of the quarter-wave plate 15 described above, a wavelength that allows the excitation laser light (for example, a wavelength of 810 nm) to pass therethrough and reflects the fundamental wave laser light having a wavelength of 1064 nm generated in the laser medium 53. A reflective surface (dichroic mirror) 54 having selectivity is formed by coating. The fundamental laser light generated by the laser medium 53 is K
Nonlinear optical crystal element 5 made of TP (KTiOPO ₄ )
Then, the second harmonic wave is generated (SHG). The concave mirror 56 has a wavelength-selective reflecting surface (dichroic mirror) that reflects the fundamental laser light and transmits the second harmonic laser light (wavelength 532 nm) generated by the nonlinear optical crystal element 55. 56R is formed. Further, the first temperature control element 57 controls the temperature of the laser diode 51, the second temperature control element 58 controls the temperature of the laser resonator (laser medium 53, nonlinear optical crystal element 55, etc.). The temperature control elements 57 and 58 are provided on the heat dissipation plate 59. The operation and effect are similar to those of the above-described embodiment, and thus the description thereof will be omitted.

Next, the temperature control operation for maintaining the stability while increasing the efficiency of the SHG laser light generator will be described in detail. In the embodiment of the present invention, two temperature control elements (TE coolers) are used to separately control the temperature of the pumping light source element such as a laser diode and the SHG laser resonator, so that the noise can be reduced without reducing the power. A small amount of stable SHG laser light is generated.

The SHG laser resonator 20 as shown in FIGS. 1 and 2 includes a nonlinear optical crystal element 18 inside,
There is a stable operation region in a limited temperature range due to the temperature dependence of the phase delay amount and the deformation of the laser resonator. In order to expand the stable operating temperature range of the laser resonator 20, for example, it is effective to shorten the length of a birefringent crystal whose phase delay amount has temperature dependence or to use a crystal having small temperature dependence. is there.

FIG. 6 shows a solid-state laser medium Nd: YA.
It is a graph which shows the temperature dependence of the absorption coefficient of G. On the other hand, FIG. 7 shows a spectrum (wavelength distribution) of emitted light intensity when the temperature of the laser diode, which is the excitation light source element, is 23 ° C., and the wavelength is plotted on the horizontal axis. FIG. 8 shows that Nd: Y is changed by changing the temperature of such a laser diode.
It is the result of measuring the effective absorption coefficient of the excitation light absorbed by the AG rod (sample thickness: about 1 mm). In FIG. 8, the laser diode temperature range R _A is about 2.6 ° C. when it is desired to obtain efficiency such that the effective absorption coefficient is 90% or more of the peak of the effective absorption coefficient. Further, the temperature range R _B when the effective absorption coefficient is good at 70-80% of more than peak efficiency is about 6.7 ° C.

In this example, since the wavelength distribution of the laser diode is large (wide), the peak efficiency is low, but the allowable temperature range for keeping the efficiency above a certain level is wider than that of the laser diode operating in single mode oscillation. . Since the center frequency of the laser diode changes at about 0.3 nm / K even in the case of multimode oscillation, even if it deviates from the absorption line of Nd: YAG at room temperature or room temperature (for example, 25 ° C), The absorption efficiency can be increased by changing the temperature so as to match the absorption line of Nd: YAG.

In FIG. 9, a laser diode and an SHG laser resonator are mounted on a TE cooler which is one temperature control element, the laser diode is driven by a constant current, and the temperature is changed to output the SHG laser light. It is a plot of power (dashed line) and noise level (solid line). Here, the output power indicated by the broken line in the figure is mainly because the pump laser light of the laser diode is Nd: YA in the laser resonator.
It is determined by the ratio of absorption by G, that is, the effective absorption coefficient, and the noise level shown by the solid line in the figure is determined by the stability of the operation of the laser resonator. The temperature range R _X (from point a to point b) for keeping the output power above 80% of the maximum value is about 3 ° C., and the stable operating temperature range R _Y (point c To point d) is about 4.5 ° C. Therefore, the temperature of the laser diode by a temperature control element 24 in FIG. 1 range R _X
The efficiency is high (80% or more of the maximum power) and stable because the target temperature range for temperature control of the SHG laser resonator by the temperature control element 26 is set to the stable operation temperature range R _Y. An SHG laser light output having good properties can be obtained.

The present invention is not limited to the above embodiment, and a solid-state laser composed of a resonator composed of a pumping laser light source and a pair of reflecting mirrors sandwiching a laser medium may be used. . Further, the laser medium and the nonlinear optical crystal element are not limited to Nd: YAG and KTP, as a matter of course.

[0026]

As is clear from the above description, according to the laser light generator of the present invention, the first temperature control element for controlling the temperature of the excitation light source element and the temperature control of the laser resonator are controlled. By providing a second temperature control element for controlling the temperature of the pumping light source element and the laser resonator separately, laser light having an absorption wavelength that can be efficiently absorbed by the laser medium, Light can be emitted from the excitation light source element, and stable emission light with less noise can be obtained from the laser medium. Therefore, the excitation efficiency of the laser light is increased, and higher output of the laser light can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an embodiment of a laser light generator according to the present invention.

FIG. 2 is a front view showing a schematic configuration of the above embodiment with a lid removed.

FIG. 3 is a perspective view showing a schematic configuration of a resonator used in the above embodiment.

FIG. 4 is a circuit diagram showing the principle of temperature control of a semiconductor element.

FIG. 5 is a diagram showing a schematic configuration of another embodiment of the laser light generator according to the present invention.

FIG. 6 is a diagram showing an absorption coefficient of Nd: YAG which is a laser medium.

FIG. 7 is a diagram showing a wavelength distribution of relative intensity of laser light emitted from a laser diode.

FIG. 8: Nd: YAG of excitation light from laser diode
FIG. 3 is a diagram showing temperature characteristics of an effective absorption coefficient of the above.

FIG. 9 is a diagram showing temperature characteristics of laser light output power and noise level.

[Explanation of symbols]

 11 --- Semiconductor laser element 13 --- Lens 14 --- Lens fixing block 15 --- / 4 wave plate 16, 19 ...・ Reflecting surface 17 ・ ・ ・ ・ Laser medium 18 ・ ・ ・ ・ ・ ・ Nonlinear optical crystal element 20 ・ ・ ・ ・ ・ ・ Laser resonator 21 ・ ・ ・ ・ ・ ・ Resonator fixed block 22 ・・ ・ ・ Rising mirror 23 ・ ・ ・ ・ ・ First base (base) 24 ・ ・ ・ ・ ・ First temperature control element (TE cooler) 25 ・ ・ ・ ・ ・2 bases (base) 26 ... Second temperature control element (TE cooler) 31 ... Package 34 ...

Claims (3)

[Claims] 1. A pumping light source element, a laser medium pumped by a laser beam from the pumping light source element, and a reflection means for generating an emitted laser beam by resonating the laser beam incident on the laser medium. A laser light generator having a resonator fixing block for fixedly supporting the excitation light source element and the reflecting means, and a temperature control element for adjusting the temperature of the excitation light source element and the reflecting means via the resonator fixing block. In the above, the first temperature control element for controlling the temperature so that the oscillation wavelength from the pumping light source element matches the absorption wavelength from the laser medium, and the temperature control for suppressing the noise of the light emitted from the laser resonator are performed. And a second temperature control element for the laser beam generator. 2. The laser light generator according to claim 1, wherein a non-linear optical crystal element that generates a harmonic laser light of the laser light of the laser medium is provided in the reflecting means. 3. The laser light generator according to claim 1, wherein the temperature control element is a temperature control element utilizing a Peltier effect.