JPH0697563A - Solid laser equipment - Google Patents

Abstract

PURPOSE:To obtain a short wavelength light source of high efficiency wherein longitudinal mode spectrum is single, in a semiconductor laser pumped solid laser equipment. CONSTITUTION:The light radiated from a semiconductor laser 101 is collected on laser medium 104 composed of YVO of 0.5mm in thikness whose Nd concentration is 3%, by a a collimate lens 102 and a focusing lens 103. A resonator is formed between the laser medium 104 and an output mirror 107 having a carvature. A wavelength converting device 108 which is inserted in the resonator and constituted of KTP performs wavelength conversion, and harmonic light is outputted from an output mirror 107. Hence a short wavelength light source of high efficiency and of single longitudinal mode can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device used in the field of optical information processing or the field of measurement and control of optical applications, and a solid-state laser capable of emitting stable and highly efficient coherent light with a single longitudinal mode It relates to the device.

[0002]

2. Description of the Related Art Using a semiconductor laser as an excitation light source,
Obtaining near-infrared light or obtaining a green light source or a blue light source by highly efficient wavelength conversion using a nonlinear optical crystal is required in the optical information processing field, the optical applied measurement control field, and the like. In particular, a light source with a short wavelength is required for high density recording on an optical disk, image processing and the like.

The output light obtained here has a lateral mode of Gaussian and can be focused up to near the diffraction limit, has a single longitudinal mode, has an output of several mW, and is stable in frequency and time. Needed to be. In order to obtain a stable short-wavelength light source of mW (milliwatt) or more using a semiconductor laser as a light source for excitation, a wavelength conversion device made of a nonlinear optical material is inserted into the resonator of a solid-state laser device excited by a semiconductor laser to generate higher harmonics. The internal resonator type that obtains

FIG. 5 shows a schematic diagram of a semiconductor laser-excited internal cavity type solid-state laser device constituting a short-wavelength light source. In FIG. 5, the light emitted from the semiconductor laser 501 is converted into a parallel beam by the collimator lens 502 and focused on the laser medium 504 by the focusing lens 503. The laser medium 504 is
It is an inorganic optically active substance (crystal) made of YVO ₄ and having a thickness of 1.0 mm, doped with 2% of Nd.

The end face 505 of the laser medium 504 is coated with an anti-reflection (AR) coating for the wavelength (809 nm) of the semiconductor laser 501, and the oscillation wavelength (1.064).
μm) and the wavelength of the higher harmonic wave (532 nm) are coated with a high reflection (HR). Also, the laser medium 50
4 has an end face 506 of wavelength 1.064 μm and wavelength 5
AR coating is applied to 32 nm.

An output mirror (planar output mirror) 507 having an infinite curvature has an HR coating for a wavelength of 1.064 μm, and the output mirror 507 and the laser medium 504 are provided.
And the end face 505 of (1) form a resonator having a fundamental wave of 1.064 μm. The resonator length was 10 mm. Then, the nonlinear optical material KTP (KTiOP) inserted inside the resonator is used.
A harmonic wave (0.532 μm) wavelength-converted by the wavelength conversion device 508 made of O ₄ ) is obtained from the output mirror 507.

In fact, for the output light of 50 mW incident on the laser medium 504 from the semiconductor laser 501, 0.5 mW of green light was emitted through the output mirror 507. The emitted light (green light) at this time was a single mode in both the longitudinal mode and the transverse mode. Further, in the optical system of FIG. 5, only the curvature of the output mirror 507 is set to 5
50m when changed to 0mm to make a spherical output mirror
3 mW of green output light was obtained for W input laser light, and high efficiency could be achieved. The longitudinal mode of oscillation at this time was measured with a Fabry-Perot spectrum analyzer. The obtained longitudinal mode spectrum is shown in FIG.

The Fabry-Perot spectrum analyzer has a finesse (F) of 100 and a mutual spacing of resonance frequencies, that is, a free spectrum range (FSR · Δ).
v) is 300 GHz and FIG. 6 shows the same longitudinal mode spectrum separated by FSR. From FIG. 6, in the optical system of FIG. 5, when the curvature of the output mirror 507 is 50 mm, a small spectrum appears next to a large spectrum. Therefore, there are two longitudinal modes oscillating in this resonator. You can see that they are not unified.

Furthermore, YVO with an Nd doping amount of 2%
_{In the} laser medium 504 made of ₄ (inorganic optically active substance), when the thickness was reduced to 0.5 mm, the longitudinal mode was unified. However, at this time, only 2.0 mW of green output light was obtained for 50 mW of input laser light, and a 1.0 mm thick laser medium (Nd doping amount of 2% was used).
(Composed of YVO ₄ ) of which the efficiency was reduced.

[0010]

In the solid-state laser device, the method of unifying the longitudinal mode spectrum of the oscillated laser light is (1) shortening the cavity length to 1 mm or less, (2) using the output mirror 507. Make the curvature infinite,
(3) It is conceivable to reduce the thickness of the laser medium 504.

However, in the conventional solid-state laser device whose schematic configuration is shown in FIG. 5, the distance (resonator length) between the laser medium 504 and the output mirror 507 causes the wavelength conversion device 508 made of a non-linear optical material to resonate. Since it exists inside the container, it is impossible to make it less than 1 mm. On the other hand, if the output mirror 507 has an infinite curvature, the curvature will be 50 m.
Light confinement is weaker and efficiency is lower than in the case of a resonator using an output mirror of about m.

Further, if the thickness of the laser medium 504 is reduced to unify the longitudinal mode, the efficiency becomes low with a small Nd doping amount of about 2%. An object of the present invention is to provide a solid-state laser device capable of realizing a single longitudinal mode spectrum of oscillated laser light and realizing highly efficient oscillation or highly efficient wavelength conversion.

[0013]

A solid-state laser device according to claim 1 is a laser medium having an excitation semiconductor laser and an inorganic optically active substance doped with at least 3% by weight of a rare earth element and having a thickness of 0.5 mm or less. A resonator including an output mirror and an output mirror, and a coupling optical system that guides the light emitted from the excitation semiconductor laser to the end face of the laser medium.

According to a second aspect of the solid-state laser device, the semiconductor laser for excitation and the rare earth element are at least 3% by weight.
0.5m thick made of doped inorganic optically active substance
A wavelength conversion device having a resonator composed of a laser medium of m or less and an output mirror, a coupling optical system for guiding light emitted from a semiconductor laser for excitation to an end face of the laser medium, and a resonator made of a non-linear optical material. is doing.

According to a third aspect of the present invention, there is provided a solid-state laser device in which the inorganic optically active substance according to the first or second aspect is YVO.
₄ In the solid-state laser device according to claim 4, the rare earth element according to claim 1 or 2 is mainly composed of Nd or Nd. According to a fifth aspect of the solid-state laser device, the inorganic optically active substance according to the first or second aspect is YVO ₄ , and the rare earth element is Nd.

[0016]

According to the construction of the present invention, the laser medium made of an inorganic optically active substance such as YVO ₄ doped with Nd or a rare earth element mainly composed of Nd has a curvature of 0.5 mm or less. Even in the output mirror, the vertical mode can realize single mode oscillation. Therefore, highly efficient and stable laser light can be obtained. Further, by setting the doping amount of the rare earth element to 3% by weight or more, the absorption length can be shortened, and higher efficiency oscillation can be realized.

Further, by providing the wavelength conversion device in the resonator, the harmonic light can be efficiently obtained, and the short wavelength light source can be realized.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic configuration diagram of a semiconductor laser-excited internal cavity type solid-state laser device constituting a short wavelength light source. In FIG. 1, the light emitted from the semiconductor laser 101 is converted into a parallel beam by the collimator lens 102, and focused on the laser medium 104 by the focusing lens 103. The laser medium 104 is Y
A 0.5 mm-thick inorganic optically active substance (crystal) made of VO ₄ was doped with 3% of Nd. In particular,
The laser medium 104 is formed by substituting the yttrium (Y) of YVO ₄ which is the base material with Nd ³⁺ which is an element that emits fluorescence.

The end face 105 of the laser medium 104 is coated with an antireflection (AR) coating for the wavelength (809 nm) of the semiconductor laser 101, and the oscillation wavelength (1.064).
μm) and the wavelength of the higher harmonic wave (532 nm) are coated with a high reflection (HR). Also, the laser medium 10
4 has a wavelength of 1.064 μm and a wavelength of 5
AR coating is applied to 32 nm.

The spherical output mirror 107 having a curvature of 50 mm is HR coated for a wavelength of 1.064 μm, and the output mirror 107 and the end face 10 of the laser medium 104 are provided.
5 and 5 constitute a resonator having a fundamental wave of 1.064 μm.
The resonator length is 10 mm. Then, the harmonics (0.5%) wavelength-converted by the wavelength conversion device 108 made of the nonlinear optical material KTP (KTiOPO ₄ ) inserted in the resonator are used.
32 μm) is obtained from the output mirror 107.

Effectively, for the laser output light of 50 mW incident on the laser medium 104 from the semiconductor laser 101, a harmonic wave of 10 mW was obtained through the output mirror 107. FIG. 2 shows the harmonic output obtained for the laser output light incident on the laser medium 104. For comparison, YVO with a thickness of 0.5 mm doped with 2% of Nd
The oscillation characteristics when using ₄ are also shown in Fig. 2.

In FIG. 2, a curve A ₁ is an inorganic optically active substance (YVO ₄ ) doped with 3% of Nd and having a thickness of 0.5 mm.
2 shows the relationship between the incident laser light output and the harmonic output in a laser medium made of. Curve A ₂ has 3% Nd
Doped inorganic optically active substance with a thickness of 0.3 mm (YVO
₄ ) shows the relationship between the incident laser light output and the harmonic output in the laser medium composed of ₄ ). The curve A ₃ is a 0.5 mm thick inorganic optically active substance (Y
The relationship between the incident laser light output and the harmonic output in a laser medium made of VO ₄ ) is shown.

The oscillation efficiency in the single longitudinal mode of the solid-state laser device of this embodiment is higher than that of the conventional laser medium made of inorganic optically active substance (YVO ₄ ) doped with 2% of Nd and having a thickness of 0.5 mm. A value of about 5 times was obtained. The longitudinal mode of oscillation at this time was measured with a Fabry-Perot spectrum analyzer. The obtained longitudinal mode spectrum is shown in FIG. The Fabry-Perot spectrum analyzer has a finesse (F) of 100 and a mutual spacing of resonance frequencies, that is, a free spectrum range (FSR · Δ).
ν) is 300 GHz and FIG. 3 shows the same longitudinal mode spectrum separated by FSR.

For an optical system as shown in the schematic diagram of FIG.
The longitudinal mode spectrum was unified, and a highly efficient internal cavity type SHG (second harmonic) light source was obtained. Here, the points of the configuration of the solid-state laser device of the present invention will be described below as compared with the conventional laser device. (1) The longitudinal mode can be unified by reducing the thickness of the laser medium.

(2) To increase the efficiency by increasing the concentration of the rare earth element (eg Nd) in the laser medium.
First, the reason (1) will be described with reference to FIGS. 4A to 4D showing the relationship between the thickness of the laser medium and the longitudinal mode spectrum. Now, it is assumed that the resonator has a uniform gain. When only the standing wave having the intensity distribution (first mode) as shown in FIG. 7A exists, the population inversion becomes as shown in FIG. At this time, assuming that the material causes spatial hole burning, the gain distribution for the second mode having the intensity distribution as shown in FIG. 6C becomes as shown in FIG.

As can be seen from FIG. 4D, the gain of the second mode is eliminated by shortening the distance from the output mirror, that is, by reducing the thickness of the laser medium, and as a result, the longitudinal mode can be unified. . Therefore, by using a material having a short absorption length, the second mode oscillation can be suppressed and highly efficient oscillation becomes possible. Next, the reason (2) will be described.

Table 1 shows the absorption length (reciprocal of absorption coefficient) for a wavelength of 810 nm when the Nd doping amount of YVO ₄ used in this example was changed.

[0028]

[Table 1]

As can be seen from Table 1, when the Nd doping amount is increased, that is, the Nd doping amount is 2.0 at% from 1.1 at% (atomic%), and 3.0 from 2.0 at%.
At%, the absorption coefficient becomes larger and the absorption length becomes shorter.
Therefore, if YVO ₄ with a large Nd doping amount is used,
It is possible to suppress a decrease in oscillation efficiency caused by reducing the thickness of the laser medium.

The laser medium 104 containing YVO ₄ as the inorganic optically active substance used in the schematic diagram of FIG.
It can be understood from the above description that a laser crystal having an Nd concentration of 3% at 5 mm can realize a high efficiency single longitudinal mode solid-state laser and a short wavelength light source. In this embodiment, Nd
The crystal thickness of the laser medium made of YVO ₄ doped with is 0.5 mm, but as can be seen from the description of FIG. 4, a thinner laser medium is used to further stabilize the unification of the longitudinal modes. be able to. For example, the oscillation characteristic when the thickness is 0.3 mm is shown by the curve A ₂ in FIG. A harmonic output of 7 mW is obtained for an incident laser light output of 50 mW, and the oscillation efficiency is reduced by about 30% compared to when the thickness is 0.5 mm, but considering the stability of the single longitudinal mode, it is 0.3 mm thick. Seems to be more practical.

If the crystal thickness is further reduced, more stable single-mode oscillation can be obtained, but it is not practical because it is difficult to process the crystal thickness of 0.1 mm or less and the oscillation efficiency is lowered. Further, in this embodiment, YVO ₄ doped with 3% of Nd was used as the laser medium. However, if the doping amount is 3% or more, the absorption coefficient can be further improved, so that it is highly efficient and stable. It is possible to realize a single solid-state laser and a short-wavelength light source with a long vertical mode.

Further, in this embodiment, the laser medium is N
d-doped YVO_FourThe following crystals were laser
You may use it as a crystal. That is, used in the present invention
The laser medium used contains at least one rare earth element.
It consists of a doped inorganic optically active substance. Inorganic optical activity
As a substance, is it conventional in the field of solid-state laser devices?
Various known ones can be adopted. For example, crystal
Then, YAG, LiSrF, LiCaF, YLF, NA
B, KNP, LNP, NYNB, NPP, GGG, Ca
F₂, CaWO_Four, MgF₂Can be mentioned
Amorphous, such as glass, can be mentioned, but the above Y
VO _FourMaterials of the system are preferred.

On the other hand, the rare earth element is in the form of ions.
If written, Pr³⁺, Nd³⁺, Eu ³⁺, Ho³⁺, E
r³⁺, Tm³⁺, Yb³⁺, Sm²⁺, Dy²⁺, Tm²⁺, U³⁺
The laser medium is Nd.³⁺But
preferable. Although not particularly related to this embodiment,
As a punt, Cr³⁺, Ni²⁺, Co²⁺Iron group Io, etc.
There are also

As the constituent material of the laser medium,
Particularly preferred is the Nb-doped YVO described below._Foursystem
Is an inorganic optically active substance. This Nb-doped YVO_Foursystem
In the laser medium of, as the inorganic optically active substance,
YVO_FourAlone or YVO _Four10 as its main component
0 parts by weight of the other inorganic optically active substance as described above
0.001 to 20 parts by weight of at least one kind, preferably
It may be a mixture with 0.01 to 10 parts by weight.

The rare earth element used as the dopant may be Nb alone, or Nb may be used in combination with at least one other rare earth element. In the case of the combined system, the amount of the rare earth element is 0.001 to 2 per 100 parts by weight of Nb.
It is 0 part by weight, preferably 0.01 to 10 parts by weight. Whether YVO ₄ is used alone or in the form of a mixture, the ratio of Y and V does not necessarily have to be 1: 1. For example, V is 0.9 to 1.
It may be in the range of 5 mol, preferably 0.95 to 1.2 mol. The Nb-doped YVO ₄ type laser medium can be produced by a normal crystal growing method such as Bernoulli method, floating method, flux method, pulling method, etc., and generally has a crystallinity as high as possible. Is preferred. Currently, the flux method or the pulling method is used.

Nd-doped YVO_FourIs limited to advanced crystals
No Also, the crystal growth is Y₂O ₃(99.999
%) And V₂O_Five(99.99%) and Nd₂O₃(99.
999%), and V₂O_FiveIs decomposed
Evaporation is easy, so the molar ratio of V is Nd + Y and 1: 1
It may not be complete, but there is no particular problem. Les
Laser medium, so that it does not affect the characteristics of the laser
In some cases, impurities may be included.

By using the laser medium described above, it is possible to stably obtain near-infrared light in a single longitudinal mode and other visible light (red, blue, etc.) by wavelength conversion. Next, although KTP (KTiOPO ₄ ) was used as the wavelength conversion material constituting the wavelength conversion device in this embodiment, organic nonlinear optical materials and other inorganic nonlinear optical materials such as K
N (KNbO ₃ ), KAP (KAsOPO ₄ ), BB
O, LBO, and bulk type polarization inversion element (LiNb
O _3, LiTaO _3, etc.) may be used.

In the above embodiment, the wavelength conversion device is inserted in the resonator to perform the harmonic conversion. However, the present invention is also applied to a solid-state laser device having no wavelength conversion device. As a result, wavelength conversion is not performed, but it is possible to obtain the effect that the longitudinal mode spectrum of the oscillated laser light is made single and highly efficient oscillation is possible.

[0039]

According to the solid-state laser device of the present invention,
Since the rare earth element doped into the inorganic optically active substance is set to 3% by weight or more and the thickness of the laser medium made of the inorganic optically active substance doped to the rare earth element is set to 0.5 mm or less, high efficiency and a long longitudinal mode spectrum are obtained. It is possible to obtain a stable laser beam with high efficiency and to realize a stable light source with low noise required in the fields of optical information processing and optical measurement control.

Further, in the case where the resonator has the wavelength conversion device, the wavelength can be efficiently converted to obtain the harmonics, and the short wavelength light source can be easily obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of a solid-state laser device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the incident laser light intensity and the harmonic output intensity in the example.

FIG. 3 is a characteristic diagram showing a longitudinal mode spectrum of laser oscillation in an example.

FIG. 4 is a characteristic showing the relationship between the thickness of the laser medium and the longitudinal mode spectrum in the example.

FIG. 5 is a schematic diagram showing a configuration of a conventional solid-state laser device.

FIG. 6 is a characteristic diagram showing a longitudinal mode spectrum of laser oscillation in a conventional example.

[Explanation of symbols]

 101 Semiconductor Laser 102 Collimating Lens 103 Focusing Lens 104 Laser Medium 105 End Face 106 End Face 107 Output Mirror 108 Wavelength Converter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Taniguchi 8 Nishinomachi, Higashimukaijima, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Wire & Cable Co., Ltd.

Claims (5)

[Claims] 1. A pumping semiconductor laser, a resonator made of an inorganic optically active substance doped with at least 3% by weight of a rare earth element and having a thickness of 0.5 mm or less, and an output mirror, and the pumping semiconductor. A solid-state laser device comprising: a coupling optical system for guiding light emitted from a laser to an end face of the laser medium. 2. A pumping semiconductor laser, a resonator made of an inorganic optically active substance doped with at least 3% by weight of a rare earth element and having a thickness of 0.5 mm or less, and an output mirror, and the pumping semiconductor. A solid-state laser device comprising: a coupling optical system for guiding light emitted from a laser to an end face of the laser medium, and a wavelength conversion device in which the resonator is made of a non-linear optical material. 3. The solid-state laser device according to claim 1, wherein the inorganic optically active substance is YVO ₄ . 4. The solid-state laser device according to claim 1, wherein the rare earth element is mainly composed of Nd or Nd. 5. The solid-state laser device according to claim 1 or 2, wherein the inorganic optically active substance is YVO ₄ and the rare earth element is Nd.