JP3480946B2 - Laser light generator - Google Patents

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 for generating a laser light whose wavelength is converted by a nonlinear optical crystal element.

[0002]

2. Description of the Related Art A fundamental wave laser beam having a high power density generated in a laser resonator is used to efficiently perform wavelength conversion such as SHG (second harmonic generation) by a nonlinear optical effect of a nonlinear optical crystal element. As a result, a laser light generator for obtaining a short wavelength laser light is disclosed in, for example,
It is proposed in Japanese Patent No. 937845.

In order to use such an SHG laser light generator by incorporating it into various devices such as an optical disk reproducing device, the optical elements and the like required for generating the SHG laser light are housed in a small casing (package). Therefore, it is desired to make it easy to handle as a part.

[0004]

By the way, the SHG in which the SHG laser light generating optical system and the like are housed in a small housing is provided.
When incorporating the laser light generator into various devices such as an optical disk reproducing device, so-called optical axis alignment is required,
It is desired to facilitate this optical axis alignment work. This optical axis alignment is performed by finely moving in two orthogonal directions on a plane orthogonal to the optical axis.

However, the elements of the SHG laser light generating optical system are normally arranged in a direction parallel to the bottom surface (horizontal plane) of the housing, and the direction of the optical axis is parallel to the bottom surface (horizontal surface) of the housing. It is said that Since the bottom surface (horizontal surface) of the housing is generally used as a mounting surface of the laser light generator, the bottom surfaces (horizontal surfaces) are orthogonal to each other for the optical axis alignment.
One of the two directions is perpendicular to the mounting surface. Since such a movement in the vertical direction relative to the mounting surface is a movement that raises and lowers the bottom surface of the housing, the structure for fine adjustment of the optical axis alignment becomes complicated, the adjustment work is troublesome, and the accuracy can be improved. It has the drawback of being difficult.

The present invention has been made in view of the above circumstances, and in a laser light generating device constructed by housing each element for generating laser light in a housing (package), Easy fine adjustment for alignment,
It is an object of the present invention to provide a laser light generator that can improve accuracy.

[0007]

A laser light generator according to the present invention comprises an excitation light source element, a laser medium excited by a light beam from the excitation light source element, and an emission of the light beam from the excitation light source element. A non-linear optical crystal element arranged in an optical path, a reflection means constituting a laser resonator together with the laser medium and the non-linear optical crystal element, a temperature control for controlling the temperature of the pumping light source element and the non-linear optical crystal element Means, a deflection means for deflecting an optical path of a light beam emitted from the laser resonator, the excitation light source element,
The excitation light source element comprises the laser resonator, the deflection means, and a housing that houses the temperature control means, and the deflection means is provided on the mounting surface of the housing via the temperature control means. The laser resonator and the deflecting means are arranged, and the deflecting means deflects the optical path of the light beam in a direction substantially perpendicular to the mounting surface of the housing, thereby solving the above-mentioned problems. Solve.

A semiconductor laser element such as a laser diode is often used as the excitation light source element.
As the laser medium, Nd: YAG, Nd: YVO
₄ , Nd: BEL, LNP, etc. are used, and examples of the nonlinear optical crystal element include KTP, BBO, LN, L
BO or the like is used. The pumping light source element and the laser resonator are arranged such that their optical axes are parallel to, for example, the mounting surface (bottom surface) of the housing, and the deflecting means uses the optical axis of the resonator or the like as the housing. It is possible to use so-called rising mirrors which deflect in a direction perpendicular to the mounting surface of the body. The SHG emitted from the resonator (second
Generation of higher harmonics) The polarization direction of higher harmonics such as laser light is determined by the arrangement direction of the non-linear optical crystal element, and the non-linear optical system is adjusted so that the polarization direction is the S-polarization axis direction of the deflecting means such as a rising mirror. By disposing the crystal element, the reflectance of the deflecting means can be increased.

[0009]

Since the pumping light source element and the optical axis of the resonator arranged inside the housing are deflected by the deflecting means to extract the laser light to the outside of the housing, for example, in the direction perpendicular to the mounting surface of the housing. Laser light can be emitted, and the fine adjustment of the attachment position within the attachment surface can be easily performed, and the optical axis alignment and the like can be facilitated.

[0010]

1 is a schematic cross-sectional view showing a schematic structure of an embodiment of a laser light generator according to the present invention, and FIG. 2 is a schematic plan view (with a lid removed) of the embodiment. In these laser light generators shown in FIGS. 1 and 2, a semiconductor laser element 11 such as a laser diode serving as an excitation light source element.
Is mounted on the mounting table 12, and the lens 12 for condensing the light emitted from the semiconductor laser element 11 is mounted on the lens fixing block 14. Lens 1
The excitation laser light collected in 2 is incident on the laser medium (laser rod) 17 using Nd: YAG via the incident surface of the quarter-wave plate 15, for example. Quarter wave plate 15
The incident laser light (for example, the wavelength 810
wavelength of 10 nm generated by the laser medium 17
A reflecting surface (dichroic mirror) 16 having a wavelength selectivity for reflecting the fundamental wave laser light of 64 nm is formed (coated, for example). In this embodiment, the reflecting surface 16 is from the laser medium 17 side. It looks like a concave mirror. The second harmonic generation (SHG) is performed by the fundamental wave laser light generated in the laser medium 17 being incident on the nonlinear optical crystal element 18 made of KTP (KTiOPO 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. A reflection surface (dichroic mirror) 19 is formed. Therefore, the laser resonator 20 is provided between the reflection surface 16 of the quarter-wave plate 15 and the reflection surface 19 of the nonlinear optical crystal element 18.
Is configured.

The quarter-wave plate 15 is a birefringent element used in the laser light source proposed by the applicant of the present invention in Japanese Patent Laid-Open No. 1-220870.
This is for stabilizing the second harmonic laser light emitted as the output laser light. That is, the laser medium 15
When the second-harmonic laser light of type II is generated by causing the fundamental-wave laser light generated in 1 to resonate so as to pass through the nonlinear optical crystal element 18 provided in the resonator 20, By inserting a birefringent element such as a quarter-wave plate 15 into the inside and reciprocating the inside of the resonator 20 while rotating the polarization plane of the fundamental laser light, the two are orthogonal to each other.
The two eigenpolarizations are set as the fundamental wave mode, and the azimuth angle θ and the phase amount Δ of the quarter-wave plate 15 are set so that energy is not transferred between the two eigenpolarizations of the fundamental wave laser light through generation of the second harmonic. By selecting a proper value, the fundamental wave laser light can be stabilized, and thus the second harmonic laser light can be stabilized. Further, by integrally forming the quarter-wave plate 15, the laser medium 17, and the type II phase-matching nonlinear optical crystal element 18 in close contact with each other, the laser light generator can be downsized as a whole and the conversion efficiency can be improved. Can be increased.

A quarter-wave plate 15 constituting the resonator 20,
The opposing surfaces of the laser medium 17 and the respective elements of the nonlinear optical crystal element 18 are provided with, for example, a non-reflective coating, closely adhered and fixed, and mounted on the resonator fixing block 21. This resonator fixing block 21 is
For example, as shown in FIG. 3, a guide groove 2 having a V-shaped cross section is formed on the surface.
1 V is formed, and the laser medium 17 and the nonlinear optical crystal element 18 are guided and attached to the V-shaped guide groove 21 V. At this time, the nonlinear optical crystal element 18 is arranged so that the arrow Z direction in the figure is the optical axis direction and the polarization direction of the emitted second harmonic wave is the arrow S direction (arrow X direction) in the figure. Has been done. This is because when the above KTP is used as the nonlinear optical crystal element 18, the XZ plane is a plane including the a-axis and the b-axis of the crystal, and the Y-axis perpendicular to this is cut out so as to be the c-axis of the crystal. You can use it. This polarization direction is the S of the rising mirror 22 which is a deflection means.
It has a polarization direction.

That is, the second light emitted from the resonator 20
The harmonic laser light is vertically deflected by the 45 ° rising mirror 22 that is a deflecting means. The raising mirror 22, the resonator fixing block 21 to which the resonator 20 is attached, 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 the same base (base). ) 23 and mount them on a single temperature control means, the so-called TE
(Thermoelectric) Temperature control element 2 such as cooler
The temperature is controlled by 4. Further, a thermistor 25 as a temperature detecting means for detecting the temperature on the base 23 is attached to the mounting table 12, for example.

Each element for generating laser light as described above is housed in a package or a casing 31.
The bottom surface 32 of the housing 31 serves as a mounting surface, and as shown in FIG. 2, a mounting screw or the like can be inserted into a screw insertion hole 37 of a mounting flange piece 36 so as to be fixed by screwing. Each element 11, 13, 1 of the above optical system
5, 17, 18 and the like are bottom surfaces 32 which are the mounting surfaces.
The optical axis is arranged in the direction parallel to the
It is parallel to 2. When the laser light is taken out of the housing while being parallel to the bottom surface 32 of the housing, it is necessary to move the laser light in the horizontal and vertical directions in order to align the optical axis.
In particular, the structure for moving in the direction perpendicular to the mounting surface becomes complicated. Therefore, the laser light emitted from the resonator 20 is deflected in a direction perpendicular to the bottom surface 32 by using the 45 ° raising mirror 22, and the laser light is emitted through the emission hole 34 formed in the lid 33 of the housing 31. I take it out. 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 the mixed state containing the component and the 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 polarization direction of the SHG laser light emitted from the nonlinear optical crystal element 18 such as KTP is raised and the mirror 2 is raised.
The non-linear optical crystal element 18 so that the S polarization direction is 2
Is determined with respect to the outer shape (by setting the cut-out shape of the crystal) to coat the rising mirror 22 and the like, whereby the reflectance of S-polarized light is, for example, 99.9.
%, The power loss can be suppressed as much as possible, and the SHG laser light can be extracted vertically upward through the emission hole 34 of the upper lid 33 of the housing 31.

That is, in the small and compact SHG laser light generator as shown in FIGS. 1 and 2, the vertical and horizontal dimensions of the bottom surface of the housing (package) 31 (including the flange piece 36) are about 38 mm × 28 mm. The height is about 16 mm, and the laser diode 11 for the pumping light source is provided in this package without particularly providing a mutual adjusting mechanism.
The SHG laser resonator 20 (laser medium 17, non-linear optical crystal element 18, etc.), lens 13, temperature control element 24, etc. are arranged and fixed at a predetermined position, and only by supplying electric power from the outside. The SHG laser light can be emitted. Since this SHG laser light generator is shorter than the room temperature oscillation wavelength of the existing semiconductor laser, a stable short-wavelength laser can be obtained by supplying current in the same manner as the semiconductor laser, so that the utility value is high.

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. When the polarization direction of the emitted light is determined with respect to the package in this way, it can be easily handled as a component and incorporated into an optical disk reproducing device or the like.
Further, since the emitted light is taken out vertically upward (Y direction in the drawing), adjustment work such as so-called optical axis alignment is performed in two directions (X direction, Z direction in the drawing) on the mounting surface of the package.
It is a simple operation that requires only fine adjustments, and it is easy to improve accuracy.

Next, the temperature control element 24 such as a TE cooler will be described. In this embodiment, only one temperature control element (TE cooler) 24 is used for temperature control of both the wavelength control of the semiconductor laser element 11 such as a laser diode which is an excitation light source element and the stabilization of the SHG laser resonator 20. I am using. This is within the stable temperature range of the resonator 20 when the stable temperature range of the resonator 20 and the temperature range in which the pumping laser light is efficiently absorbed by the laser medium 17 exist separately and are narrow. It is necessary to select the semiconductor laser element 11 that can obtain a wavelength such that the effective absorption coefficient of the laser medium 17 such as Nd: YAG becomes a certain value or more. Conversely, it is also possible to select the resonator. Further, in order to expand the stable temperature range of the resonator, it is effective to shorten the length of the birefringent crystal whose phase delay amount has temperature dependence or to use a crystal having small temperature dependence.

A specific example will be described. When the SHG laser resonator 20 having a stable operating temperature range of 30 ° C. to 35 ° C. is used due to the temperature dependence of the phase delay amount of the nonlinear optical crystal element 18 such as KTP, this Laser medium (N
d: YAG) wavelength with high absorption efficiency (absorption line) about 809
It suffices to select the semiconductor laser device 11 having a wavelength of nm. The center wavelength is, for example, about 0.3 nm /
When a laser diode of multimode oscillation that changes with K is used, it is about 80 at 30 ° C to 35 ° C.
In order to obtain the center wavelength of 9 nm, it is sufficient to select the one having a center wavelength at 25 ° C. shorter than the above 809 nm by about 2.3 ± 0.7 nm. On the other hand, when the temperature tolerance of the laser diode with respect to the effective absorption coefficient of the Nd: YAG rod near the absorption line is about ± 1.3 ° C, the center wavelength of the laser diode is about 806.7 ± 25 ° C.
It may be 1.1 nm.

Since the temperature dependence of the change in the amount of phase delay of the nonlinear optical crystal is proportional to the crystal length, the shorter the crystal length, the smaller the temperature change rate of the phase change amount. The wavelength margin of the diode is wide.

As described above, since the single temperature control element (TE cooler) 24 adjusts the wavelength of the semiconductor laser element 11 to the absorption wavelength to perform the temperature control for stabilizing the laser resonator 20, the temperature control element is used. Since it is not necessary to separately provide each part, it is possible to solve all the problems such as the complicated structure and the difficulty of alignment due to the provision of two or more temperature control elements. Therefore, the number of parts and the cost can be reduced, the control unit including the circuit can be simplified and downsized, and the power consumption can be reduced.

The present invention is not limited to the above embodiment, and a laser resonator having the structure shown in FIG. 4 can be used, for example. In the example of FIG. 4, the laser light emitted from the laser diode 41, which is the excitation light source element, is condensed by the lens 42, and Nd: Y
It is incident on the laser medium 43 such as an AG rod. The incident surface of the laser medium 43 is similar to the reflecting surface 16 of the quarter-wave plate 15 described above, and the excitation laser light (for example, wavelength 8).
A reflection surface (dichroic mirror) 44 having a wavelength selectivity that allows a fundamental wave laser beam having a wavelength of 1064 nm generated in the laser medium 43 to pass therethrough is transmitted. The fundamental wave laser light generated in the laser medium 43 is incident on the nonlinear optical crystal element 45 made of KTP (KTiOPO ₄ ) and second harmonic generation (SHG) is performed. The concave mirror 46 has a wavelength-selective reflection 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 45. 46R is formed. The nonlinear optical crystal element 45 in this case is also arranged so that the polarization direction of the emitted SHG laser light is the S-polarized light of the rising mirror (not shown). Further, the temperature control of the laser diode 41 and the laser resonator (laser medium 43, nonlinear optical crystal element 45, etc.) is performed by the single temperature control element 47, and the temperature control element 47 is provided on the heat dissipation plate 48. There is. The operation and effect are similar to those of the above-described embodiment, and thus the description thereof will be omitted.

In addition, resonators having various structures such as a concave mirror provided on the incident surface side can be used. Further, the deflecting means is not limited to the 45 ° rising mirror, and a polarization beam splitter, a prism or the like may be used, and the laser medium or the nonlinear optical crystal element is not limited to Nd: YAG or KTP. is there.

[0024]

As is apparent from the above description, according to the laser light generator of the present invention, the optical axis of the pumping light source element and the laser resonator arranged inside the housing (package) is mirrored. Since the laser light is extracted by deflecting means such as a deflection device such as the outside of the housing, it is possible to emit the laser light in a direction perpendicular to the mounting surface of the housing, for example. Adjustment can be easily performed, and optical axis alignment and the like can be facilitated.

[Brief description of drawings]

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

FIG. 2 is a schematic plan view of the embodiment with the lid removed.

FIG. 3 is a perspective view showing a specific example of a resonator fixing block used in the embodiment.

FIG. 4 is a diagram showing a schematic configuration of another embodiment of the laser light generator according to the present invention.

[Explanation of symbols]

11 ... Semiconductor laser device 13 ... Lens 15 ... 1/4 wave plate 16, 19 ... Reflective surface 17 ... Laser medium 18: Non-linear optical crystal element 20: Laser resonator 21: Resonator fixing block 22 ... Launch mirror 23 ... Base 24: Temperature control element (TE cooler) 25: Thermistor (temperature detection means) 31 ... Housing (package) 32 ... Mounting surface of housing 34 ... Exit hole

Claims (3)

(57) [Claims] 1. A pumping light source element, a laser medium pumped by a light beam from the pumping light source element, a nonlinear optical crystal element arranged in an emission optical path of the light beam from the pumping light source element, The temperature of the laser medium and the reflection means constituting the laser resonator together with the nonlinear optical crystal element, the temperature of the pumping light source element and the nonlinear optical crystal element,
Temperature control means for controlling, deflection means for deflecting the optical path of the light beam emitted from the laser resonator, the excitation light source element, the laser resonator, the deflection means ,
And a housing for accommodating the temperature control means , wherein the deflection means includes the temperature control means on a mounting surface of the housing.
The excitation light source element, the laser resonator,
And a deflection means, wherein the deflection means deflects the optical path of the light beam in a direction substantially perpendicular to the mounting surface of the housing. 2. The laser light generator according to claim 1, wherein the polarization direction of the light beam incident on the light beam deflecting means is S-polarized with respect to the incident surface. 3. A temperature control element is provided inside the mounting surface of the housing, and the excitation light source element and the laser resonator are provided on the temperature control element with an optical axis parallel to the mounting surface of the housing. The laser light generator according to claim 1, wherein the laser light generator is arranged so that