JP2004088129A - Laser light generator - Google Patents

Abstract

An object of the present invention is to reduce radiation of unnecessary light, internally reflected light, and scattered light to the outside of a package. Control polarization etc. without increasing the number of parts.
A wavelength conversion element (3) is provided in a resonator of a solid-state laser oscillator excited by a semiconductor laser element (8), and high-efficiency, short-wavelength SHG is provided by strong solid-state laser oscillation light stored in the resonator. A small-sized integrated SHG laser light generator for obtaining laser light, which separates the outside and the inside of a package 1 of the device, and has an SHG laser provided on at least one surface of a light transmitting means (window 2) provided at an outlet of the SHG laser light. A wavelength separation film for separating only light having a predetermined wavelength from light is provided. The window 2 has a wedge shape, a lens effect, an element for temporally controlling polarization, frequency, phase, and the like, an aperture for passing only a main beam of laser light, a slit, and the like.
[Selection diagram] Fig. 1

Description

The present invention relates to a laser light generator, and more particularly, to a small integrated second harmonic generation (SHG) laser light generator for generating a second harmonic generation (SHG) laser light.

Conventionally, so-called SHG laser light generators that generate the second harmonic laser light include an external resonance type SHG laser light generator and an SHG laser light generator using a nonlinear optical element inside the resonator.

As a device for generating the SHG laser light, in particular, a small integrated SHG laser light generating device for generating an SHG laser light by a nonlinear optical element inside a resonator is another small laser module (for example, a semiconductor laser oscillator). Similarly to the above, a light-transmitting plate (hereinafter referred to as a window) provided with an anti-reflection coating for one wavelength on both sides is provided in the opening (laser light emission port) of the package, and the package is kept airtight as necessary. Output light (that is, laser light) is emitted to the outside.

JP-A-4-326339 JP-A-4-25083

In the other laser module, the light emitted inside the package is limited to a range near a certain wavelength (for example, 20 nm or less). The anti-reflection coat alone is sufficient.

However, in the small integrated type SHG laser light generator, in addition to the wavelength-converted light of the desired wavelength, the light of the pumping semiconductor laser and the solid-state laser light whose wavelength has not been converted are both transmitted through the window and out of the package. Often radiated. Therefore, there is a problem in application to, for example, an optical disk recording and / or reproducing apparatus, and also a problem in safety for the human body, particularly for the eyes.

Further, since the window provided in the package is usually a parallel plate, unless the window is arranged to be inclined with respect to the laser emission direction (that is, the window surface is not perpendicular to the laser emission direction). Tilt), the reflected light from the window surface (so-called return light) returns to the light source inside the package, and the operation becomes unstable. However, it is difficult to tilt the window bonding surface of the package due to recent demands for cost reduction and miniaturization and thinning of the configuration.

Further, in the conventional small-sized integrated SHG laser light generator, the polarization direction of the emitted light is determined by the orientation of the internal crystal and the waveguide. Therefore, in order to extract the polarization desired by the user, a wavelength plate is required separately from the window. Etc. are needed.

Furthermore, even if the light emitted from the small integrated type SHG laser light generator is light having a wavelength desired by the user, unnecessary internal reflected light or scattered light is emitted from the package at the same time as the emitted light. In such a case, the user has to remove it as necessary.

In the first place, the package of the small integrated SHG laser light generator is usually larger than the package of the conventional semiconductor laser oscillator, so in order to reduce the size of the system, the package of the small integrated SHG laser needs to be multifunctional. However, conventionally, it was considered only as a light source.

In view of the above, the present invention can reduce unnecessary light other than light of a desired wavelength or radiation of internally reflected light or scattered light of light of a desired wavelength to the outside of the package. It is an object of the present invention to provide a laser light generator capable of stabilizing the operation by reducing return light without increasing the size of the device, and controlling the polarization of emitted light without increasing the number of components.

The laser light generator of the present invention has been proposed in order to achieve the above-mentioned object. A wavelength separation film for separating only the light from the outside of the package is provided on at least one surface of the light transmitting means provided at the laser light emission port.

Here, the wavelength separation film is provided on the surface of the light transmission means corresponding to the inside of the package, and the antireflection film is provided on the surface of the light transmission means corresponding to the outside of the package.

The following light transmitting means is used. For example, a polarization direction control plate for controlling the polarization direction, or the optical axis of the reflected light of the wavelength-converted laser light from the light transmitting means is deflected with respect to the optical axis of the wavelength-converted laser light incident on the light transmitting means. A wedge-shaped one, a lens having a lens function for expanding the divergence angle of the wavelength-converted laser light, an aberration-correcting function for spatially changing the phase of the waveform of the wavelength-converted laser light to correct aberrations, Use a graphic lens. Further, the light transmitting means includes a polarization control element that changes the polarization of the wavelength-converted laser light with time by applying a voltage, a frequency control element that changes the frequency of the wavelength-converted laser light with time, It is also possible to use a phase control element that temporally changes the phase of the converted laser light or an intensity control element that temporally changes the intensity of the wavelength-converted laser light.

光 At least on one side or in the vicinity of the light transmitting means, there is provided a light passage restricting means for passing only a substantially main beam of the wavelength converted laser light.

According to the laser light generating device of the present invention, a wavelength separation film that separates only light having a predetermined wavelength from the wavelength-converted laser light is provided on at least one surface of a light transmitting unit that separates the outside and the inside of the package and is provided at an emission port of the laser light. By providing a light-passing restricting means for passing only the main beam of the wavelength-converted laser light at least on one side or in the vicinity of the light transmitting means, unnecessary light other than light of the desired wavelength or light of the desired wavelength is provided. This prevents internal reflected light and scattered light from radiating outside the package.

戻 り Also, the return light to the laser oscillator is reduced by making the light transmission means wedge-shaped.

Further, the light transmitting means is composed of a polarization direction control plate for controlling the polarization direction, one having a lens function for expanding the divergence angle of the wavelength-converted laser light, and spatially changing the phase of the waveform of the wavelength-converted laser light. It is multifunctional, having an aberration correction function for correcting aberration, a holographic lens, and a method of changing the polarization, frequency, phase, and intensity of the wavelength-converted laser light with application of voltage over time.

In the present invention, a wavelength separation film that separates only light of a predetermined wavelength from the wavelength-converted laser light is provided on at least one surface of a light transmitting unit that separates the outside and the inside of the package and that is provided at an emission port of the laser light. By providing a light passage restricting means on at least one side of the transmitting means or in the vicinity thereof, which transmits only a substantially main beam of the wavelength-converted laser light, unnecessary light other than light having a desired wavelength or internally reflected light of light having a desired wavelength, The radiation of the scattered light out of the package can be reduced.

(4) By making the light transmission means in a wedge shape, return light can be reduced and the operation of the laser oscillator can be stabilized without increasing the cost or increasing the size of the device.

Further, the light transmitting means is composed of a polarization direction control plate for controlling the polarization direction, one having a lens function for expanding the divergence angle of the wavelength-converted laser light, and spatially changing the phase of the waveform of the wavelength-converted laser light. A configuration having an aberration correction function for correcting aberration, a configuration including a holographic lens, and a configuration in which the polarization, frequency, phase, and intensity of the wavelength-converted laser light are temporally changed by applying a voltage to increase the configuration. It is possible to realize multi-function without using.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a small integrated SHG green laser light generator as a laser light generator according to an embodiment of the present invention. This small-sized integrated SHG laser light generator (SHG green laser light generator) is provided with a wavelength conversion element 3 in a resonator of a solid-state laser oscillator excited by a semiconductor laser element (semiconductor laser chip) 8. A high-efficiency short-wavelength light is obtained by the powerful solid-state laser oscillation light stored in the inside.

That is, in FIG. 1, in the small integrated type SHG laser light generator, the laser light from the semiconductor laser element 8 such as a laser diode whose temperature is compensated by the thermistor 9 is transmitted to the converging lens 7 and the 1/4 wavelength. The light enters the solid-state laser oscillator having the Nd: YAG laser medium 5 via the plate 6.

A wavelength conversion element 3 is provided in a resonator of the solid-state laser oscillator. The solid-state laser oscillator generates a second harmonic, that is, SHG laser light by causing laser oscillation light (fundamental wave laser light) from the laser medium 5 to pass through the wavelength conversion element 3 via the spacer 4 and resonate. Let me. In the present embodiment, a nonlinear optical crystal called, for example, KTP (KTiOPO ₄ ) is used as the wavelength conversion element 3, but another crystal, a synthesized material, or a waveguide may be used. In addition, the position where the wavelength conversion element 3 is provided is not limited to the inside of the resonator, but may be provided in a stage preceding the solid-state laser oscillator. In this case, the wavelength of the semiconductor laser light is directly converted. . In addition, the wavelength conversion is not limited to the method of halving the wavelength called SHG, but can be expanded to nonlinear optical phenomena such as sum frequency mixing, parametric oscillation, and difference frequency generation.

The small-sized integrated SHG laser light is reflected by the reflecting mirror 10 having a reflecting surface at an angle of 45 degrees with respect to the optical axis (that is, the optical axis is bent by 90 degrees). The light is emitted to the outside via light transmitting means (hereinafter, referred to as a window 2) provided in the package 1 of the generator (only the main beam 13 of the emitted light is shown in FIG. 1). .

The thermistor 9, the semiconductor laser element 8, the condensing lens 7, the 波長 wavelength plate 6, the laser medium 5, the wavelength conversion element 3, the reflection mirror 10, and the like are arranged on a substrate 12. The package 1 is attached to a lower portion of the inner surface of the package 1 via a TE cooler (electronic cooling / heating element) 11 provided at a lower portion of the package 1. For the TE cooler 11, for example, an electronic cooling / heating element based on the so-called Peltier effect can be used.

In such a small-sized integrated SHG laser light generator, in the conventional configuration, the emitted light is radiated from the inside of the package to the outside through a parallel-plated glass window having antireflection coating on both surfaces. It was made so.

On the other hand, in the first embodiment of the present invention, for example, a window having a polarization control function is used as the window 2. That is, as the window 2 (polarization direction control plate) having the polarization control function of the first embodiment, for example, as shown in FIG. 2, a window 21 composed of a half-wave plate can be exemplified. According to the window 21 made of a half-wave plate shown in FIG. 2, as the polarization control function, the polarization direction of the incident SHG laser light indicated by the arrow 41 in FIG. 2A or the arrow 43 in FIG. Can be rotated 90 degrees as shown by the arrow (polarization direction indicating symbol) 40 in FIG. 2A or the arrow 42 in FIG. 2B.

Here, as the material of the window having the polarization control function, that is, the polarization control element (polarization direction control plate), when the above-mentioned wavelength plate is used, quartz and other birefringent materials can be exemplified. It is also possible to use an analyzer as the above-mentioned polarization control element (polarization direction control plate). When this analyzer is used, the material may be a combination of quartz and calcite (so-called Wollaston prism, Glan-Thompson prism, etc.). ) Or other synthetic materials are conceivable. The use of these polarization control elements makes it possible to rotate the polarization direction with respect to the linearly polarized internal emission light determined by a crystal (non-linear optical crystal) or the like, as shown in the example of FIG. This is effective for extracting only a specific polarization component. Further, a quarter-wave plate can also be used as the polarization control element. According to this, linear polarization of the internal emission light can be changed to circular polarization.

Next, as the window 2 of the second embodiment, as shown in FIG. 3, for example, a window plate made of a glass plate having a surface (a surface corresponding to the inside of the package 1) coated with a wavelength separation film 24 may be used. it can. By providing the wavelength separation film 24, it is possible to prevent light of an unnecessary wavelength from leaking outside. Further, by providing the wavelength separation film 24, it is possible to prevent deterioration of optical performance due to mixing of light of different wavelength bands when a user applies the laser light generation device of this embodiment to an optical disk device or the like. This eliminates the need for the user to perform wavelength separation outside. FIG. 4 shows an example of spectral characteristics of the window 22 with the wavelength separation film 24 when the Nd: YAG laser medium 5 (semiconductor laser pumped Nd: YAG laser medium) is used as the laser medium of the solid-state laser oscillator. Show.

Here, the window 22 of the second embodiment is provided with the anti-reflection film 23 on the surface corresponding to the surface coated with the wavelength separation film 24 (the window surface corresponding to the outside of the package 1). I have. In the case where a wavelength separation film is provided on one side of the window and an anti-reflection film is provided on the corresponding surface (opposite surface), it is better to provide the wavelength separation film 24 on the surface corresponding to the inside of the package 1. This is advantageous for protecting the separation membrane 24. Providing the wavelength separation film 24 on the window surface corresponding to the inside of the package 1 is also advantageous when combined with a wedge-shaped window shown in FIG.

Next, as a third embodiment, a wedge-shaped window 31 as shown in FIG. 5 is used for the window 2 in FIG. 1 instead of a parallel plate.

5 By using the window 31 shown in FIG. 5, the optical path of the laser beam transmitted through the window 31 is deflected to the thicker side of the wedge as shown by the arrow 16. On the other hand, the reflected light reflected by both surfaces of the window 31 is indicated by arrows 17a (reflection on the surface corresponding to the inside of the package 1) and arrows 17b (reflection on the inner surface of the window corresponding to the outside of the package 1). Reflect in the direction.

In the window 31 of the third embodiment, the reflected light (return light) by the inner surface of the window 31 (the surface corresponding to the inside of the package 1) does not return to the laser oscillator side, and Even if the outer surface (surface corresponding to the outside of the package 1) is perpendicular to the optical axis inside the package 1, the optical axis is deflected by the inner surface of the window 31 (the surface corresponding to the inside of the package 1). Therefore, the light reflected from the outer surface is not specularly reflected and returned. Therefore, there is no return light to the laser oscillator side, and the stability of operation of the laser oscillator is not impaired.

If the window is not a wedge as in the third embodiment but a parallel flat plate, as shown in FIG. 6, the outer surface of the window (the surface corresponding to the outside of the package) is aligned with the optical axis inside the package. When it is perpendicular, the inside surface of the window (the surface corresponding to the inside of the package) is also perpendicular to the optical axis, so that the laser light is specularly reflected at the inside surface of the window and the reflected light (return light). Light) is incident on the laser oscillator. At this time, specular reflection also occurs on the inner surface of the window corresponding to the outer surface of the window. Therefore, the operation of the laser oscillator becomes unstable and the noise level easily rises.

The use of the window 31 of the third embodiment is particularly effective when the parallel plate window cannot be tilted because the window attachment surface of the package is thin as described above. However, assuming that the refractive index of the material of the window 31 is n and the angle of the wedge is α as shown in FIG. 5, the emitted light is accompanied by the deflection of the optical axis by the angle (n−1) α. The angle of the reflecting surface of the reflecting mirror 10 (the angle with respect to the optical axis) is changed in accordance with the angle of deflection, or the light emitted from the laser oscillator is previously changed by the angle corresponding to the angle of deflection in advance. It is desirable to tilt it.

Next, as a fourth embodiment, a window 32 having a lens effect is used as shown in FIG.

That is, in the case of a small integrated type SHG laser oscillator, especially when no waveguide is used, the divergence angle of emitted light is smaller than the divergence angle of a semiconductor laser oscillator. When the optical path is used by extending to the effective diameter in the above, it is desirable from the viewpoint of miniaturization that the divergence angle is once widened by using a lens or the like to shorten the optical path length.

Therefore, it is effective to provide the window 32 with a lens function as shown in FIG. That is, as shown in FIG. 7, the divergence angle of the emitted light is widened by the window 32 having the lens function as shown by the arrow 18 in the figure.

Here, the lens is usually made of a material having at least one surface having an aspherical shape including a spherical surface or a cylindrical shape and having a refractive index of 1 or more. In a small integrated type SHG laser light generator including an oscillator, since the wavelength shift amount is generally small, a so-called holographic lens is also suitable as a lens used for the window 32.

For example, in wavelength conversion of a semiconductor laser pumped Nd: YAG laser, the wavelength change due to mode hop is usually ± 0.1 nm or less, and the deviation of the focal point when the holographic lens is used is very small.

Also, by providing the window with a spatial phase distribution, aberration correction can be performed in addition to the lens effect. Further, the window may have a function of forming a part of the focus position detecting optical system or a function of forming a light amount distribution into a desired shape on an imaging plane or a Fourier transform plane.

Next, as a fifth embodiment, as shown in FIG. 8, a window having a temporal modulation function is used.

That is, when a resonator is used in a small integrated type SHG laser light generator, direct modulation at a high frequency is difficult. Therefore, it is possible to use, for the window 33, a modulation element that performs phase modulation that changes the phase over time, sidebands that change the frequency over time, or polarization modulation that changes the polarization over time. It is valid. It is also effective to use a modulation element for performing intensity modulation for the window 33 if possible. Incidentally, such as _{PLZT ((Pb 1-x La} x) (Zr y Ti 1-y) 1-x / 4 O 3) or an inorganic crystal is considered as the modulation element. Further, the modulation here includes modulation including time and space.

By applying a predetermined voltage from the voltage generator 50 to the window 33 with the modulation function and transmitting the SHG laser beam to the window 33, for example, a single mode as shown in FIG. (In FIG. 8A) becomes the outgoing light (laser light 13a in FIG. 8A) as shown in FIG. 9A.

Next, as a sixth embodiment, as shown in FIG. 10, the aperture 25 and the slit 27 are arranged on the window 2 or close to the window 2 (disposed on or near the window corresponding to the inside of the package 1). ), Unnecessary output light is removed and separated by these apertures 25 and slits 27.

That is, in the small integrated type SHG laser light generator, since a large number of components are used, there are many reflection surfaces by these many components, and these reflection surfaces generate some stray light in addition to the main beam. Further, the scattered light on the crystal (non-linear optical crystal 3), the inside and surface of the lens 7, and the surface of the reflection mirror 10 may spread to the background, which may be harmful to the intended use of the user.

In order to cope with such a case, in the sixth embodiment, an aperture 25 composed of a hole 29 and a light shielding plate as shown in FIG. A slit 27 composed of a slit hole 30 and a light shielding plate as shown in FIG. FIGS. 10B and 10C show the aperture 25 and the slit 27 viewed from the front.

迷 By using the aperture 25 and the slit 27, as shown in FIG. 10A, the stray light or the scattered light (background light) is reflected (arrow 14 in the figure) and does not emit to the outside.

As shown in FIG. 11 of the seventh embodiment, a reflective film 26 having the same function as the aperture 25 and the slit 27 of the sixth embodiment can be used. FIG. 11B is a front view of a window 34 coated with the reflective film 26.

That is, the same effect as in the sixth embodiment is realized by the window 34 coated with the reflection film 26 for the stray light and the background light portion and the anti-reflection film 29 as needed for the main beam 13 portion. it can. Further, if necessary, wavelength characteristics can be used. For example, it is a coating or the like that enables only the main beam 13 to emit light of two wavelengths. In addition, both a metal film and a dielectric multilayer film can be practically used for the reflection film 26.

By coating the reflective film 26 on the window 34, it is possible to prevent the stray light and the background light from being reflected (reflected light 15) and emitted to the outside as shown in FIG.

As described above, according to this embodiment, if the window is provided with a polarization control function, the polarization of the outgoing light determined by the orientation of the crystal and the waveguide inside the small integrated SHG laser light generator can be changed by the window. Control can be performed without increasing the number of parts, and if functions such as a lens, a phase plate, and a modulation element are provided, it is possible to suppress an unnecessary increase in the number of parts.

Also, it is possible to suppress the regular reflection, reduce the return light, and stabilize the operation of the laser oscillator without changing the direction of the emitted light from the window with a wedge or requiring a difficult inclination of the parallel plate cap material. Further, by coating the window with a wavelength separation film, it is possible to prevent light of a wavelength unnecessary for the user from being emitted to the outside, which is advantageous in terms of application and safety.

Furthermore, by forming a spatial filter such as an aperture or a slit on the window or disposing it near the window, it is possible to prevent light unnecessary for the user from being emitted out of the package.

In the example of FIG. 1, the optical axis is bent by 90 degrees by the reflection mirror 10 and then emitted through a window provided on the upper part of the package 1. Instead of providing the window, the window of the present embodiment described above may be provided in the laser emission direction of the solid-state laser oscillator, and the window may be emitted to the outside through the window.

FIG. 1 is a view including a partially broken cross-sectional view showing a schematic configuration of a small integrated type SHG green laser light generating device according to an embodiment of the present invention. It is a figure explaining the example which used the polarization direction control board for the window. FIG. 3 is a diagram illustrating an example in which a window is provided with a wavelength separation film. FIG. 4 is a characteristic diagram illustrating an example of spectral characteristics of a window with a wavelength separation film. It is a figure showing a wedge-shaped window. It is a figure which shows the window of a parallel plate. FIG. 3 is a diagram illustrating a window having a lens function. FIG. 4 is a diagram illustrating a window having a temporal modulation function. FIG. 7 is a diagram for explaining an example of a state of modulation of a window having a temporal modulation function. It is a figure showing the example which provided the aperture and the slit. FIG. 3 is a diagram illustrating an example in which a metal / dielectric film is provided.

Explanation of reference numerals

1 Package 2 Window 3 Wavelength conversion element 4 Spacer 5 Nd: YAG laser medium 6 1/4 Wave plate 7 Condensing lens 8 Semiconductor laser element 9 Thermistor 10 Reflecting mirror 11 TE cooler (electronic cooling / heating element)
12, a substrate 21, a half-wave plate 22, a wavelength separating film 23, an anti-reflection film 31, a wedge-shaped window 32, a window 33 having a lens function, ... Window with temporal modulation function

Claims (12)

A wavelength separation film that separates only light of a predetermined wavelength from the wavelength-converted laser light whose wavelength has been converted by causing the laser light incident on the wavelength conversion element to resonate is used to partition the outside and inside of the package and to provide light at the laser light emission port A laser light generator provided on at least one side of a transmission means. 2. The laser beam according to claim 1, wherein the wavelength separation film is provided on the surface of the light transmission means corresponding to the inside of the package, and the antireflection film is provided on the surface of the light transmission means corresponding to the outside of the package. Generator. The laser light generator according to claim 1, wherein the light transmission means comprises a polarization direction control plate for controlling a polarization direction. The light transmitting means has a wedge shape, and deflects the optical axis of the reflected light of the wavelength converted laser light from the light transmitting means with respect to the optical axis of the wavelength converted laser light incident on the light transmitting means. The laser light generator according to claim 1, wherein: The laser light generator according to claim 1, wherein the light transmitting means is a lens means having a lens function of expanding a divergence angle of the wavelength-converted laser light. 2. The laser light generating apparatus according to claim 1, wherein the light transmitting means is an aberration correcting means having an aberration correcting function of correcting an aberration by spatially changing a phase of a waveform of the wavelength-converted laser light. . 6. The laser beam generator according to claim 5, wherein said lens means comprises a holographic lens. The laser light generator according to claim 1, wherein the light transmission means comprises a polarization control element that changes the polarization of the wavelength-converted laser light with time by applying a voltage. The laser light generating device according to claim 1, wherein the light transmitting means comprises a frequency control element that changes the frequency of the wavelength-converted laser light with time by applying a voltage. 4. The laser light generator according to claim 1, wherein the light transmitting means comprises a phase control element that changes the phase of the wavelength-converted laser light with time by applying a voltage. 4. The laser light generator according to claim 1, wherein the light transmitting means comprises an intensity control element that changes the intensity of the wavelength-converted laser light with time by applying a voltage. 4. The laser light generator according to claim 1, wherein a light passage restricting means is provided on at least one side of or near the light transmitting means to pass only a substantially main beam of the wavelength-converted laser light.

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