JP3329066B2 - Laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a laser light source for laser printers, optical disks, optical applied measurement, laser displays, etc., has a solid-state laser medium excited by a semiconductor laser, and has a wavelength inside a resonator. The present invention relates to a laser device having a conversion element.

[0002]

2. Description of the Related Art In recent years, a laser device including a wavelength conversion element (second harmonic generation (hereinafter abbreviated as SHG), light sum frequency generation, light difference frequency generation, etc.) using a second-order nonlinear optical material has been developed. It is actively studied as a light source for optical information processing (for example, an optical disk player or a laser printer), a light source for various measuring devices, and a light source for a laser display.

As a laser device including a wavelength conversion element,
It can be roughly divided into the following two types.

(1) The first method uses Nd: YAG or Nd:
A solid-state laser medium such as YVO ₄ is excited by a semiconductor laser,
A wavelength conversion element (mainly S
An HG element (Second Harmonic Generator) is arranged to generate the second harmonic (hereinafter abbreviated as SH wave).
An internal resonator type wavelength conversion element is used.

(2) The second method is a method in which a fundamental wave emitted from a semiconductor laser is directly incident on a wavelength conversion element to extract a second harmonic, and an external resonator type wavelength conversion element is used. A waveguide type wavelength conversion element is used.

[0006]

A first conventional method is as follows.
Wavelength conversion can be performed relatively easily. Further, a light source of a laser display requires an optical power of 1 W to several W, but a large power output can be obtained relatively easily with an internal resonator type SHG element. However, in the conventional Nd-based solid-state laser medium, the oscillation wavelength of the fundamental wave is around 1.06 μm, and the SH light becomes green light around 0.53 μm, so that it is impossible to obtain SH light of a shorter wavelength. The Nd: YAG crystal is capable of laser oscillation at 0.946 μm, but its oscillation efficiency is about one digit lower than that at 1.06 μm. Further, there is a problem that the oscillation efficiency greatly depends on the crystal temperature.

In recent years, Cr: Li using Cr as an active ion
CaAlF ₆ (hereinafter abbreviated as LiCAF), Cr: LiS
It has been reported that a laser medium such as rAlF ₆ (hereinafter abbreviated as LiSAF) oscillates efficiently in a wavelength range of 0.7 μm to 1.0 μm when excited by a semiconductor laser. However, when these laser crystals are used for an internal resonator type wavelength conversion element, it is necessary to select an oscillation wavelength with a birefringent filter or a grating, and there is a problem that the configuration of the optical resonator becomes complicated. Further, these are fluoride crystals, and have problems such as reaction with moisture in the air and difficulty in crystal growth. Further, since the fluorescence lifetime of these oxides and fluorides is about 100 μsec, laser light can be directly modulated only at about 10 kHz. In order to use it as a recording light source for an optical disc player or the like, it is necessary to modulate light to at least several MHz or more, and therefore, there is a problem that an external optical modulator utilizing an electro-optic effect or an acousto-optic effect is newly required. .

An internal resonator type wavelength conversion device using a semiconductor laser has also been proposed (for example, Harold D. et al .: IEE).
E J. Quantum Electronics Vol.QE6 (1970) pp356-36
0). However, ordinary semiconductor laser light has a narrow waveguide (0.
Light is emitted from a section of 1 μm × several μm square), and the emitted light has a large spread angle. Therefore, even if a lens or an output mirror is installed outside the semiconductor laser chip, only tens of percent of the light reflected by the output mirror returns to the semiconductor laser waveguide, and the fundamental wave intensity in the optical resonator increases. Can not. Therefore, there is a problem that a laser device having a high-efficiency wavelength conversion element cannot be realized.

In the second method, 0.4 μm band SH light can be obtained because the wavelength of the semiconductor laser light is directly converted. Further, CdZnSe, ZnSe, ZnMgS
SH light having a wavelength of 0.3 μm or less can be obtained by using light of a II-VI group semiconductor laser such as a Se-based laser as a fundamental wave. However, the external resonator type wavelength conversion element has a problem that a complicated wavelength control technique is required to make the wavelength of the semiconductor laser coincide with the resonance wavelength of the optical resonator. Further, when the wavelength conversion crystal itself is used as an optical resonator (for example, W. Le
nth et al .: Proceedings of SPIE Vol.1219 (1990) pp2
1-29, Japanese Patent Application Laid-Open No. 4-335586, etc.) There is a problem that a high-precision curved surface processing is required for the crystal end face, and the laser device becomes extremely expensive.

In the waveguide type wavelength conversion element, the cross-sectional area is several μm.
Since it is difficult to introduce high-power laser light into a waveguide of mx several μm or less, a light source for laser display cannot be realized. Further, it is difficult to efficiently and stably introduce the semiconductor laser light into the waveguide type wavelength conversion element. In addition, since a wavelength stabilizing mechanism is required to stabilize the wavelength of the semiconductor laser light, there is a problem similar to that of the external resonator type wavelength conversion element.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a laser device capable of obtaining a short-wavelength laser light source having a simple structure and a higher power which can be directly modulated. .

[0012]

The laser device according to the present invention comprises:
In a laser device including a semiconductor laser, a solid laser medium, an optical resonator, and a wavelength conversion element, a III-V semiconductor crystal or a II-VI semiconductor crystal is used as the solid laser medium.

In the above structure, the solid-state laser medium includes a GaAs crystal, which is a group III-V semiconductor crystal, and an AlG
at least one substance selected from an aAs crystal, an AlGaInP crystal, a mixed crystal thereof and a superlattice crystal, or
Group II-VI semiconductor crystals include CdS, CdSe, Zn
It is desirable that any one of S, ZnSe, ZnTe, a mixed crystal thereof and a superlattice crystal be used.

Further, a mirror made of a dielectric multilayer film is formed on at least one principal surface of the solid-state laser medium, and this end face is bonded to a sapphire substrate or a diamond substrate, or the solid-state laser medium has a heat conduction. Is preferable to be directly held by Au, Ag, Cu, Al, or an alloy containing these elements and having a thermal conductivity of 100 W · m ⁻¹ · K ⁻¹ or more.

More preferably, the pump power of the semiconductor laser and the generated second harmonic power are simultaneously monitored, and the temperature of the constituent optical components is more preferably controlled.

It is desirable that the diameter of the main surface of the portion contributing to light emission of the solid-state laser medium is substantially equal to the diameter of the semiconductor laser beam for excitation.

Further, it is preferable that a dielectric multilayer film for transmitting a fundamental wave and reflecting a higher harmonic wave is formed on the excitation-side main surface of the wavelength conversion element.

In the above structure, the wavelength conversion elements are KTiOPO ₄ (KTP), LiNbO ₃ (LN),
LiTaO ₃ (LT), KNbO ₃ (KN), LiI
O ₃ , β-BaB ₂ O ₄ (BBO), LiB ₃ O ₅ (LB
O) or at least one optical material for wavelength conversion selected from organic ion crystals.

In the above structure, it is preferable that the dielectric polarization of the nonlinear optical material for wavelength conversion is periodically inverted.

Further, it is preferable to use the laser device according to the present invention as a light source of a laser display.

[0021]

According to the structure of the present invention, the solid-state laser medium
By using a III-V semiconductor crystal or a II-VI group semiconductor crystal, it is possible to realize a laser device for a high-output short-wavelength light source that can be modulated.

That is, laser light having a wavelength of 0.9 μm to 0.6 μm is emitted from GaAs or AlGa as a solid-state laser medium.
Oscillation can be achieved by using a group III-V semiconductor crystal of As or AlGaInP system. At this time, efficient excitation can be achieved by setting the wavelength of the semiconductor laser light source for excitation (GaAs-based or AlGaInP-based semiconductor laser) shorter than the absorption edge wavelength of the semiconductor material used as the solid-state laser medium.

Since the internal cavity type wavelength conversion method is used as the wavelength conversion method, a simple structure of 0.9 μm to 0.6 μm
SH light having a half wavelength of the band can be obtained. The wavelength of the fundamental wave can be determined mainly by the composition of the semiconductor crystal used as the solid-state laser medium.

The laser light in the wavelength band of 0.5 μm to 0.4 μm is used as a solid-state laser medium by a C-II group semiconductor crystal.
dS, CdSe, ZnS, ZnSe, ZnTe, Mg
Any of S, MgSe, a mixed crystal thereof, and a superlattice crystal can be used.

As the semiconductor laser for excitation, for example, CdZ
II-VI group semiconductor lasers such as nSe, ZnSe, and ZnMgSSe can be used.

The fluorescence lifetime of these semiconductor crystals is on the order of several nsec, and it is possible to modulate at least to several hundred MHz by modulating the excitation light source. Therefore, there is a feature that a light modulator is not newly required as a light source for an optical disk, a laser display or the like. When an oxide crystal or a fluoride crystal is used as a solid-state laser medium, the modulation frequency is several tens of kHz. When a laser device using these crystals is used as a light source for an optical disk player or the like, a new optical modulator is required. Needed.

Next, the solid-state laser medium has a mirror made of a dielectric (or semiconductor) multilayer film formed on at least one principal surface of the solid-state laser medium or at least one main surface, and an output side on the opposite side. The mirror is located. Since the solid-state laser medium is bonded to a sapphire or diamond substrate or directly fixed to a base made of a material with good heat conductivity such as copper, the heat generated by the solid-state laser crystal can be efficiently extracted. I can do it. The laser device of this configuration is a photo-excitation type bulk laser device that does not use a waveguide structure. In the case of the wavelength conversion of the internal cavity type of the waveguide type semiconductor laser, the laser light which is a problem returns only to several tens% to the optical waveguide (the optical cavity loss is very large), and the fundamental wave intensity in the optical cavity is large. The problem of not being able to be solved can be solved.

By using the photo-excitation method, only the confinement of carriers generated by photo-excitation has to be considered.
There is no need to consider the confinement of the current and the reduction of the resistance for flowing the current, which are necessary for a normal semiconductor laser, and the element structure of the light emitting unit is simplified. Furthermore, since the beam quality (both vertical mode and horizontal mode) of the pumping semiconductor laser is not so required, a multi-mode high-power semiconductor laser can be used in both the vertical mode and the horizontal mode. Since the SHG output is proportional to the square of the incident power, the availability of such a high-power semiconductor laser is very effective in realizing a high-output SHG light source with high conversion efficiency. Usually 2
A high-power semiconductor laser of 00 mW or more has a wide waveguide width (several tens of μm or more), and a laser beam becomes multimode in both longitudinal and transverse modes, and cannot be used for a waveguide type or external resonator type SHG element.

As a nonlinear optical material, KTiOPO is used.
₄ (KTP), LiNbO ₃ (LN), LiTaO ₃ (L
T), KNbO ₃ (KN), and LiIO ₃ are effective because they exhibit relatively large nonlinear optical constants. β-BaB ₂ O ₄
(BBO) and LiB ₃ O ₅ (LBO) have an absorption edge wavelength of 0.1.
Since it is as short as 2 μm or less, it can be used up to generation of ultraviolet SH light, and a combination with II-VI group semiconductor crystal is particularly effective. Also K
TiOPO _4, LiNbO _3, when the nonlinear optical material such as LiTaO _3, it is possible to use a configuration of the material which dielectric polarization has been reversed periodically as the wavelength conversion element. In this case, by adjusting the inversion period of the dielectric polarization, phase matching at an arbitrary wavelength (so-called quasi-phase matching: for example, DHJund)
t et.al.:Apl.Phys.Lett Vol.59 pp2657-2659 (1991))
This is advantageous because it is not necessary to change the type of the wavelength conversion material. An organic ionic crystal is a kind of organic nonlinear optical material and can be expected to have a very large nonlinear optical constant, so that it is effective for low-output wavelength conversion.

Further, by using the laser device according to the present invention as a light source for a laser display, it is possible to realize a very small, highly efficient and inexpensive laser display as compared with a laser display using a gas laser which has been attempted in the past. Becomes

[0031]

EXAMPLES The present invention will be described more specifically with reference to the following examples.

The present invention uses a semiconductor crystal (a group III-V semiconductor crystal, a group II-VI semiconductor crystal) as a solid-state laser medium to provide a fundamental wavelength of 0.9 μm to 0.6 μm and 0.5 μm to 0.5 μm. A laser device that obtains light in the 0.4 μm band and generates short-wavelength laser light having a half wavelength using the internal resonator type wavelength conversion element is realized.

When a semiconductor crystal is used as the solid-state laser medium, the photoexcited carriers disappear not only at the excitation site but also by diffusion and non-radiative recombination on the crystal surface, so that the carrier density immediately decreases. Providing a blocking layer for confining excited carriers at a specific location is effective for confining carriers. Further, it is preferable because the carrier does not diffuse to the crystal surface containing many non-radiative recombination components. The carrier confinement structure can be realized by covering the excited portion with a material having a larger energy gap than the photoexcited location (and thus the light emitting location).

For example, a GaAs crystal can be used as a solid laser medium in the 0.8 μm band, and AlGaAs can be used as a material having a large band gap for confining carriers. Since the absorption coefficient differs depending on the wavelength of the semiconductor laser light for excitation, it is sufficient if the crystal thickness is large enough to absorb the excitation light. Usually, the thickness of the GaAs crystal may be several μm to several tens μm or less. In the simplest case, the GaAs substrate has a thickness of several μm by using mechanochemical polishing and wet etching.
A thin plate crystal of about m to several tens of μm can be obtained. Another method for obtaining a thin plate crystal having a thickness of about several μm to several tens μm is to grow AlGaAs on a GaAs substrate to 0.2 μm,
Next, GaAs is grown to several μm to several tens μm, and then AlGaAs is grown.
s is grown by 0.2 μm. Next, the GaAs substrate may be polished to a thickness of about several tens μm or less, and finally the GaAs substrate remaining by selective etching may be completely removed. In this case, a thin GaAs crystal having a thickness of several μm to several tens of μm sandwiched between AlGaAs having a thickness of 0.2 μm can be obtained. A GaAs-AlGaAs multi-quantum well thin plate crystal may be used as the light emitting layer in order to increase the luminous efficiency as the solid-state laser medium. Next, the thin plate crystal is bonded onto sapphire or diamond crystal. As a joining method, for example, an appropriate organic adhesive may be used,
Optical contact, anodizing (eg Bertil Hok
et al .: Appl. Phys. Lett. Vol 43 (1983) pp. 267-269) is desirable from the viewpoint of heat radiation and reliability.
Further, a sapphire substrate or a diamond substrate is made of Ag, Cu, Au, A having a thermal conductivity of 100 W · m ⁻¹ · K ⁻¹ or more.
The heat generated from the solid-state laser medium can be efficiently radiated by being held in a material made of 1 or an alloy thereof with a heat conductive paste, a screw, solder, or the like. The solid-state laser medium may be directly fixed to a table having good heat conduction.

Next, using a photo process and an etching process, the substrate is processed into a disk shape so that the diameter is substantially equal to the beam diameter of the semiconductor laser beam for excitation. For example, the peripheral portion may be removed so as to have a diameter of about several μm to 20 μmφ. Also, for wavelength conversion of a large power of 1 W to several W, 100 to 1000 which is almost the same as the beam diameter of the semiconductor laser for excitation.
The peripheral portion is removed so as to be about μmφ. In order to further suppress the diffusion of the carrier to the crystal surface, AlGaAs (for example, Al _0.3 Ga _0.7 As) may be epitaxially grown on the crystal surface. Next, an optical resonator is formed between one main surface of the semiconductor crystal and an output mirror arranged on the opposite side. Instead of using the semiconductor crystal main surface as one mirror of the optical resonator, a mirror in which a dielectric multilayer film is deposited on an optical glass substrate may be used separately. As the light source for light excitation, a semiconductor laser having a high conversion efficiency from electricity to light is used.
As a semiconductor laser, an AlGaAs semiconductor laser (wavelength 0.8 μm band) or an AlGaInP semiconductor laser (wavelength 0.6 μm band) can be used.

As a nonlinear optical material, KTiOPO is used.
₄ (KTP), LiNbO ₃ (LN), LiTaO ₃ (L
T), KNbO ₃ (KN), LiIO ₃ , etc. can be used. For LiIO ₃ , up to the fundamental wavelength of about 0.6 μm,
Also, KN allows phase matching up to a fundamental wave wavelength of about 0.84 μm. Examples of organic ionic crystals include, for example, Japanese Patent Application No.
As shown in -61680, sodium p-nitrophenoxyacetate and the like can be used. KT
In a bulk crystal of P and LN, phase matching is not performed at a fundamental wavelength of 1 μm or less. Further, LT has a small amount of birefringence and does not phase-match at all in a bulk crystal. Therefore, it is necessary to take what is called pseudo phase matching. As a method for quasi-phase matching, an ion diffusion method such as Rb is mainly used in KTP. In LN and LT, a comb-shaped electrode is formed and polling is performed in a high electric field. Alternatively, an element such as yttrium is added at the time of crystal growth, and the crystal is periodically pulled up by a method such as pulling up the crystal under a growth temperature condition that is periodically fluctuated several to several tens of times per minute (Czochralski method). An inverted crystal can be obtained.

By arranging a wavelength conversion element formed using the above-described nonlinear optical material in an optical resonator of the laser device, a laser device of an internal resonator type wavelength conversion system is realized. The wavelength conversion element and / or each optical component may be temperature controlled as needed. This configuration is an internal resonator type wavelength conversion system, and can efficiently perform wavelength conversion with a simple configuration. Therefore, complicated wavelength stabilization control and complicated processing of the wavelength conversion crystal, which are problems when using an external resonator type wavelength conversion element or a waveguide type wavelength conversion element, are hardly required.

When a group II-VI semiconductor crystal is used as a laser medium, for example, ZnSe is epitaxially grown on a GaAs substrate, and then only the substrate is removed by polishing and etching to obtain a ZnSe thin crystal. As the semiconductor laser for excitation, for example, CdZnS
A group II-VI semiconductor laser such as e, ZnSe, ZnMgSSe or the like can be used. BBO or LBO is used as the nonlinear optical material for wavelength conversion. Other than the above, a short wavelength laser device can be realized with the same configuration.

Further, when it is necessary to make the oscillation spectrum a single mode for stabilizing the SH light intensity, an etalon plate is provided in the optical resonator, and when it is necessary to control the polarization, a polarization control such as a Brewster plate is performed. This can be realized by disposing the element in the optical resonator. In addition, the power of the semiconductor laser for excitation and the output of the SHG are simultaneously monitored, and the temperature of the main components of the laser device is kept constant, so that a more stable SH can be obtained.
G output light can be obtained.

The present invention will be described in more detail with reference to specific examples. (Embodiment 1) FIG. 2 schematically shows a laser apparatus according to the present invention. 780 nm wavelength as the pumping semiconductor laser light source 20
AlGaAs semiconductor laser was used. Light emitted from the semiconductor laser 20 is condensed through a lens system 21 to a light emitting unit 22. FIG. 1 shows the structure of the light emitting section 22. Ga
The thickness of the As crystal 12 is 2 μm. The light absorption coefficient of a GaAs crystal at a wavelength of 780 nm is about 1.4 × 10
^{Since it is 4} (cm ^-1 ), 94% or more of the excitation light is absorbed when the crystal thickness is 2 μm. An antireflection coating made of a dielectric multilayer film 11 is deposited on the main surface of the crystal on the output mirror side. Ti as a high refractive material as a dielectric material
O ₂ , CeO _{2, and the} like, and SiO ₂ or M
By using gF ₂ or the like, light having a wavelength of 0.88 μm
An anti-reflection coat transmitting 9% or more is realized.

The excitation wavelength 0.78 μm is applied to the main surface of the crystal on the excitation side.
A dielectric multilayer mirror 13 is formed that transmits 99 m of light and reflects 99% or more of light of 0.88 μm, which is the fundamental wavelength. The dielectric mirror 13 is bonded to a sapphire (Al ₂ O ₃ ) substrate 14 by optical contact. A portion composed of GaAs and a dielectric multilayer film fixed to a sapphire substrate was processed to a diameter of 10 μmφ using a photo process and a dry etching technique. On the excitation light incident side of the sapphire substrate, a non-reflection coating made of a dielectric multilayer film 15 is formed so that light having a wavelength of 0.78 μm is transmitted efficiently. The light emitting section 22 is fixed to a copper holder so that heat is efficiently radiated. The output mirror is 99% of the 0.88 μm wavelength light, which is the fundamental wave.
The light having a wavelength of 0.44 μm which is reflected as SH light is 95%
As described above, a transparent dielectric multilayer film is formed. The light emitting section 22 excited by the excitation semiconductor laser 20 has a wavelength of 0.8
The light of 8 μm oscillates by repeatedly reciprocating between the excitation side mirror 13 and the output mirror 24 of the optical resonator. The light of the semiconductor laser for excitation is focused on the GaAs crystal part of the light emitting layer 12 to a beam diameter of about 10 μm. Since the light of 0.88 μm as the fundamental wave is confined in the optical resonator, the light intensity of the fundamental wave in the optical resonator increases. LiIO ₃ was used as a crystal for a wavelength conversion element. LiIO ₃
The crystal is cut out at an angle of phase matching at a wavelength of 0.88 μm. Further, light having a wavelength of 0.88 μm is transmitted to the light emitting portion side 23A of the crystal surface, and the SH light having a wavelength of 0.4A is transmitted.
A dielectric multilayer film that reflects light of 4 μm is formed.
Also, the surface of the wavelength conversion element on the output mirror side 23B has a thickness of 0.1 mm.
A dielectric multilayer film is formed for transmitting light of both the wavelengths of 88 μm and 0.44 μm. Therefore, this LiI
By disposing the wavelength conversion element made of O ₃ in the optical resonator, the wavelength 0.88 having a large light intensity in the optical resonator is obtained.
The output mirror 24 outputs 0.44 μm light, which is SH light of μm.
Can be taken out efficiently through. By using the laser device of this configuration, the semiconductor laser power for excitation 2
At 00 mW, SH light having a wavelength of 440 nm of 1 mW can be obtained.

Further, by modulating the pumping power of the pumping semiconductor laser having a wavelength of 780 nm, the fundamental
It was confirmed that SH light with a wavelength of 440 nm, which can be modulated up to 500 MHz and was further modulated up to 500 MHz. The modulation frequency (500 MHz) is due to the limitation of the drive circuit of the semiconductor laser for excitation, and can be modulated to a higher frequency.

(Embodiment 2) A case where a group II-VI semiconductor thin film crystal is used as a light emitting portion will be described with reference to FIG.
50 μm in thickness reduced in advance by polishing and etching
Is used. On top of this, ZnSe 92 is 0.2 μm as a blocking layer, and Zn _0.7 C is used as a light emitting layer.
d _0.3 Se93 is 2 μm, and ZnSe94 is 0.2 μm as a blocking layer, which is grown by MBE. Next, the GaAs substrate is completely removed using selective etching. Thereafter, one of the thin film crystals has a wavelength of 530 nm.
A dielectric multilayer film 91 that transmits light at a wavelength of 480 nm for excitation and reflects 99% or more of light having a wavelength of 530 nm, which is a fundamental wave, on the opposite surface.
Is deposited. The obtained crystal is bonded to a sapphire substrate 96 by using an optical contact method. On the sapphire substrate 96, a dielectric multilayer film 97 through which light having a wavelength of 480 nm for excitation is transmitted is deposited. The laser medium having this configuration is evaluated using the same optical system as in the first embodiment. However, the pumping semiconductor laser is a ZnSe-based semiconductor laser cooled to the temperature of liquid nitrogen, and is pumped at a wavelength of 480 nm. The laser output mirror is changed to a mirror that reflects 99% or more of the fundamental wave wavelength of 530 nm and transmits 265 nm of the SH light of 95% or more. Further, a BBO crystal is used as the wavelength conversion element. Other configurations of the optical system are the same as in the first embodiment.
0.1 mW when the semiconductor laser power for excitation is 100 mW
UV light having a wavelength of 265 nm can be obtained.

Further, by modulating the pumping power of the pumping semiconductor laser having a wavelength of 480 nm, SH light having a wavelength of 265 nm modulated to 500 MHz can be confirmed.

(Embodiment 3) Wavelength 440n according to the present invention
A specific example of the small laser device for m will be described with reference to FIG.

FIG. 3A is a top view schematically showing the configuration of the laser device, and FIG. 3B is a side view. An Si block 38 is used as a table on which the laser device is arranged. Where Si
The block is used because the thermal conductivity of Si is 168 W · m
^-1・ K ^-1 and a coefficient of linear expansion of 2.4 × 10 ^-6 ℃
^{- 1} and the optical axis deviation of the resonator for about one order of magnitude smaller than the ordinary metal is to become smaller.

The semiconductor laser chip 30 was mounted on a heat sink and fixed on the Si block 38. Example 1
Light-emitting part 35 similar to that (however, the diameter of the light-emitting part is 30 μm
(φ) bonded to a sapphire substrate 36 is fixed to a Si block 38 using solder or the like. Here, a sapphire substrate was used in which a metal such as gold was deposited on a portion fixed to the Si block 38 so as to be wet with solder.

The light emitted from the semiconductor laser chip excites the light emitting section 35 without passing through the lens. The same wavelength conversion element 33 and output mirror as those in the first embodiment were used. The wavelength conversion element 33 is fixed using an adhesive having good heat conductivity. Finally, the output mirror 34 was fixed using solder while adjusting the fundamental wave having a wavelength of 880 nm to stably oscillate and the output of SH light to be maximum while driving the semiconductor laser chip. Semiconductor excitation power 200
In the case of mW, SH light having a wavelength of 440 nm of 0.7 mW can be obtained.

(Embodiment 4) Wavelength 440n according to the present invention
A second specific example of the small laser device for m will be described with reference to FIG.

FIG. 4A is a top view schematically showing the configuration of the laser device, and FIG. 4B is a side view. A copper block 48 is used as a table on which the laser device is arranged. Here, a copper block is used because the thermal conductivity of copper is 400 W · m ⁻¹ · K.
^This is because it is as good as ^-1 . Although copper is used in this specific example, an alloy having a high thermal conductivity, such as Au, Ag, or Al, may be used. The semiconductor laser chip 40 was mounted on a heat sink, which was fixed on a copper block. Example3
In the same manner as described above, the light emitting section 45 joined to the sapphire substrate 46 is fixed to the copper block 48 using solder or the like.

Here, the semiconductor laser side of the sapphire substrate is inclined at an angle of about 5 to 15 degrees from the vertical in order to prevent reflected light from returning to the excitation side semiconductor laser. This is because the sapphire substrate is coated with an anti-reflection coating, but the slightly reflected light is not returned to the semiconductor laser.

Thereafter, assembly was performed in the same manner as in Example 3.
Using this apparatus, SH light having a wavelength of 440 nm and a wavelength of 0.8 mW can be obtained when the excitation power of the semiconductor laser is 200 mW. Further, since the return light reflected from the sapphire substrate does not return to the semiconductor laser, SH
G light can be obtained.

(Embodiment 5) In order to further increase the efficiency and output of the laser device of the present invention, it is necessary to further improve the efficiency of confining the carrier of the light emitting section and further improve the heat extraction. It is valid. Hereinafter, a configuration and a manufacturing process of the light emitting unit for improving the carrier confinement efficiency of the light emitting unit and improving heat extraction will be described with reference to FIG.

As shown in FIG. 5A, the GaAs substrate 50
l _0.3 Ga _0.7 As layer 51 is 0.2 μm, and GaAs layer 52 is
Is 2 μm, and the Al _0.3 Ga _0.7 As layer 53 is _0.2 μm
Grow using E method. Next, a SiO ₂ film is formed, and a circular mask having approximately the same area as a desired light emitting portion is formed by photolithography.

As shown in FIG. 5B, a columnar shape to be a light emitting layer is formed by dry etching and wet etching.

[0056] As shown in FIG. 5 (c), the blocking layer for confining carrier and (Al _0.3 Ga _{0. 7} As layer 55) is grown 0.5 to 2 [mu] m. Next, the substrate is polished to about 50μ.
m, and damage by polishing is removed by wet etching.

As shown in FIG. 5D, a circular pattern slightly larger than the effective area of the light emitting portion is formed on the photoresist.

As shown in FIG. 5E, the substrate 50 is
Selective etching with H ₄ OH: H ₂ O ₂ (= 1: 20).

As shown in FIG. 5F, dielectric multilayer films 57 and 58 are formed on the light excitation side and the side opposite to the excitation. Here, an excitation wavelength of 0.78 μm is applied to the dielectric multilayer film 58 on the excitation side main surface.
The light of m is transmitted and 99% or more is reflected with respect to the light of 0.88 μm which is the fundamental wavelength. The dielectric multilayer film 57 on the main surface of the crystal on the output mirror side is realized as a non-reflection coating through which 99% or more of light having a wavelength of 0.88 μm is transmitted.

(Embodiment 6) Next, an example of a small laser device using a semiconductor crystal having the same configuration as that of FIG. 5 (f) will be described with reference to FIGS. 6 and 7. FIG. FIG. 6 is a diagram showing the same mounting method of the light emitting unit 69 as shown in FIG. The light emitting section 69 is a copper plate 66 having a through hole through which the fundamental wave passes.
Is fixed with solder or the like. Further, the plate 66 is fixed to a copper block 68. Therefore, heat generated as a non-light-emitting component in the light-emitting portion can be efficiently released to the copper block. It is directly excited (not through a lens) by the light of the semiconductor laser chip 60 attached to the same copper block.

FIG. 7 is a diagram showing the overall configuration of a small laser device according to the present invention. Here, KNbO ₃ was used as a crystal for the wavelength conversion element 73. Further, photodiodes 80 and 81 for monitoring the power of the semiconductor laser for excitation and the SHG output are arranged. Further, the temperature of the entire optical system is controlled by the Peltier element 83 with an accuracy of ± 0.02 ° C. The entire laser device is composed of cases 84 and 8
5 completely sealed in a dry nitrogen atmosphere.

In this laser device, SH light of 3 mW can be obtained when the pumping semiconductor laser power is 200 mW. Further, the stability of the laser is such that the power fluctuation per hour is within ± 2%. This is because feedback control can be performed while monitoring output light.

(Embodiment 7) The same light emitting portion and K
Using the NbO ₃ crystal, an optical system similar to that of FIG. 2 was created to realize a high-power laser device. The effective diameter of the light emitting part is 50
0 μm. In addition, a multi-mode excitation semiconductor laser having a stripe width of 500 μm was used for both the longitudinal mode and the transverse mode. The temperature of the wavelength conversion element using the KNbO ₃ crystal is controlled by a Peltier element with an accuracy of ± 0.02 ° C. In the laser device having this configuration, SH light with a wavelength of 440 nm of 2 W can be obtained when the excitation power is 4 W. This laser device can be used as a light source of a laser display.

Embodiment 8 An example of a laser display according to the present invention will be described with reference to FIG. Red light source 801
Used was an internal resonator type second harmonic of an Nd: YAG laser oscillating at a wavelength of 1320 nm excited by a semiconductor laser. Using a vertical / horizontal multi-mode semiconductor laser with an excitation power of 5 W, a red SHG output of 2 W having a wavelength of 660 nm is obtained. As the green light source 802, an Nd: YVO ₄ laser oscillating at a wavelength of 1064 nm excited by a semiconductor laser is used. When the excitation power of the semiconductor laser is 3 W, green light of 532 nm wavelength of 1.6 W can be obtained.

As the blue light source 803, the laser light source of the sixth embodiment was used. Light emitted from these light sources is respectively modulated by modulators 805 to 807 using an acousto-optic effect. Here, the reason why the external modulator 807 is used is that the modulation characteristics of the used high-power excitation semiconductor laser are not good, and there is no need to use a semiconductor laser having good modulation characteristics. As described above, the red and green light sources need an external modulator in principle. Light transmitted through the external modulator is transmitted to ND filters 815 to 815
The light amount is adjusted by the dichroic mirrors 810 to 812 so that the light amount is improved by 17 so that the color reproducibility is improved. This light is totally reflected by the mirror 81
8, the light path is adjusted, the light is reflected by a polygon mirror 825 for horizontal light search, and further reflected by the vertical search mirror 820.
Reach 30. As a result of shooting an image having a screen size of 30 inches on the screen, an image having the same image quality as that of a normal NTSC system was obtained.

Although an example has been disclosed for the search type laser display, it can also be used as a light source for a projection type liquid crystal display. In this case, light adjusted to the same optical axis from the light source is used by expanding the screen size of the liquid crystal module using a beam expander. Also, an external modulator using an acousto-optic element is not required. When speckle noise occurs in an image projected on a screen, it can be avoided by disposing a random phase plate, a diffraction element, and the like in an optical system. When a laser light source is used, almost perfect parallel light can be easily obtained, and only light having a desired wavelength is generated, so that the light use efficiency is extremely high. When a normal lamp light source is used, unnecessary light such as infrared light or ultraviolet light becomes heat, and heat generation of the liquid crystal module becomes a problem. However, when a laser light source is used, this problem can be avoided. .

As described above, in the embodiment according to the present invention, an example of the laser device utilizing the second harmonic generation has been described.
The present invention can be applied to a laser device utilizing light sum frequency generation or light difference frequency generation.

Further, the above description relates to an embodiment of the present invention. A person skilled in the art can consider various modifications of the present invention, and they are all technical modifications of the present invention. Included in the range.

[0069]

As described above, according to the laser apparatus of the present invention, the following effects can be obtained, and its industrial value is extremely large. (1) By using a III-V semiconductor crystal or a II-VI group semiconductor crystal as a solid-state laser medium, a laser device for a short wavelength light source that can be directly modulated with a simple configuration can be realized. (2) By using the photo-excitation method, it is not necessary to consider only the confinement of carriers generated by photo-excitation (considering only the confinement of carriers generated by photo-excitation) and to reduce the resistance required for flowing the current, which is necessary for a normal semiconductor laser. The element structure of the light emitting section is simplified. (3) Since the quality of the beam of the semiconductor laser for pumping (both vertical mode and horizontal mode) is not so required, a multi-mode high power semiconductor laser can be used in both the vertical mode and the horizontal mode. Since the SHG output is proportional to the square of the incident power, the availability of such a high-power semiconductor laser is very effective in realizing a high-output SHG light source with high conversion efficiency. (4) By using the laser device according to the present invention as a light source for a laser display, it becomes possible to realize a very small, highly efficient and inexpensive laser display as compared with a laser display using a gas laser which has been attempted in the past. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a light emitting unit according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a laser device using the light emitting unit 22 of FIG. 1 according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a small laser device according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a small laser device according to a fourth embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration and a creation process of a light emitting unit according to a fifth embodiment of the invention.

FIG. 6 is a diagram illustrating a fixing portion of a light emitting unit according to a sixth embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration of a laser device according to a sixth embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a laser display using a light source according to the present invention.

FIG. 9 is a diagram illustrating a configuration of a light emitting unit according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Dielectric multilayer film 12 Solid-state laser medium 13 Dielectric multilayer film 14 Sapphire substrate 15 Dielectric multilayer film 20 Semiconductor laser for excitation 21 Optical system for condensing 22 Light-emitting part 23 Wavelength conversion element 24 Output mirror 801 Using SHG Red laser light source 802 Green laser light source using SHG 803 Blue laser light source using SHG 805, 806, 807 External modulation elements 810, 811, 812 Dichroic mirrors 815, 816, 817 Light amount adjusting filter 818 Total reflection mirror 820 Vertical scanning Mirror 825 for horizontal scanning polygon mirror

Continuation of the front page (56) References JP-A-56-93386 (JP, A) JP-A-4-148578 (JP, A) JP-A-4-335586 (JP, A) US Patent 5,253,258 (US, A) U.S. Pat. No. 5,341,390 (US, A) U.S. Pat. No. 5,381,429 (US, A) Applied Physics Letters, 1991, Vol. 59, p. 2657-2659 Applied Physics Letters, 1983, Vol. 43, p. 267-269 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 3/109 G02F 1/37 H01S 3/094 H01S 5/00-5/50

Claims (11)

(57) [Claims] A semiconductor laser, a solid-state laser medium excited by the semiconductor laser, a wavelength conversion element for converting a wavelength of laser light emitted from the solid-state laser medium, and an amplifier for amplifying laser light emitted from the solid-state laser. An excitation light from the semiconductor laser is applied to one main surface of the solid-state laser medium, and the optical resonator has an output disposed on an opposite side to the main surface. A mirror, wherein the wavelength conversion element is disposed between the optical resonators, and a III-V group semiconductor crystal or I as the solid-state laser medium.
A laser device using a group I-VI semiconductor crystal. 2. A GaAs crystal, A
at least one substance selected from the group consisting of lGaAs crystal, GaInP crystal, a mixed crystal thereof and a superlattice crystal, or CdS, CdSe, ZnS, ZnSe, ZnT
2. The laser device according to claim 1, wherein at least one substance selected from the group consisting of e, MgS, MgSe, and mixed crystals and superlattice crystals thereof is used. 3. The laser device according to claim 1, further comprising a monitor photodiode for monitoring a pump power of the semiconductor laser and a generated second harmonic power. 4. The laser device according to claim 1, wherein the optical components are temperature-controlled. 5. The laser device according to claim 1, wherein a diameter of a main surface of a portion contributing to light emission of the solid-state laser medium is substantially equal to a diameter of the semiconductor laser beam for excitation. 6. A mirror made of a dielectric multilayer film is formed on one main surface of the solid-state laser medium, said mirror transmitting excitation light emitted from a semiconductor laser and efficiently transmitting a fundamental wave. 3. The laser device according to claim 1, wherein the laser device has a reflecting function, and the main surface is bonded to a sapphire substrate or a diamond substrate. 7. The method according to claim 7, wherein the solid-state laser medium is directly Au, Ag, Cu,
Al or thermal conductivity including these elements is 100 W
The laser device according to claim 1, wherein the laser device is held in an alloy of m ⁻¹ · K ⁻¹ or more. 8. A sapphire substrate or a diamond substrate is held by a material made of Au, Ag, Cu, Al or an alloy containing these elements and having a thermal conductivity of 100 W · m ⁻¹ · K ⁻¹ or more. 7. The laser device according to claim 6, wherein: 9. The laser device according to claim 1, wherein a dielectric multilayer film that transmits a fundamental wave and reflects a harmonic is formed on a main surface on an excitation side of the wavelength conversion element. 10. A wavelength conversion element comprising: KTiOPO ₄ , Li
NbO ₃ , LiTaO ₃ , LiIO ₃ , β-BaB ₂ O ₄ ,
10. The laser device according to claim 1, wherein the laser device is made of at least one nonlinear optical material for wavelength conversion selected from LiB ₃ O ₅ or an organic ionic crystal. 11. The method according to claim 1, wherein the dielectric polarization of the nonlinear optical material for wavelength conversion is periodically inverted.
Or the laser device according to any one of 9 above.