JP2734934B2 - Solid state laser - Google Patents

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, and more particularly, to a solid-state laser in which a fundamental wave generated from a solid-state laser medium is wavelength-converted by a nonlinear optical element.

[0002]

2. Description of the Related Art FIG. 4 is a schematic configuration diagram showing the configuration of a conventional solid-state laser of this kind disclosed in Japanese Patent Application Laid-Open No. 2-247601. In the figure, reference numeral 13 denotes Nd-doped YAG (yttrium aluminum garnet)
The rod 14 is an anti-reflection film formed on both end surfaces of the YAG rod 13, the reference numeral 15 is an SHG (second harmonic generation) element made of KTP (KTiOPO ₄ ), 16, 17, and 1.
Numeral 8 denotes a TiO ₂ film, a ZrO ₂ film, and a SiO ₂ film, respectively, and 16 to 18 constitute an anti-reflection film. 19 is a first mirror for reflecting basic light, 20 is
This is a second mirror that reflects basic light and prevents reflection of SH (second harmonic) light.

In the solid-state laser shown in FIG.
The G rod 13 is optically excited, and the first and second mirrors 1
The fundamental wave 11 is oscillated using the optical resonators 9 and 20 as optical resonators. This fundamental wave 11 is generated by the SHG element 1 arranged in the optical resonator.
The wavelength is converted into a second harmonic 12 by the laser beam 5, and is output as a desired laser beam. In the solid-state laser proposed in Japanese Patent Application Laid-Open No. Hei 2-247601, a TiO ₂ film 16, a ZrO ₂ film 17,
_The antireflection film consisting of only three layers of the _two films 18 has a reflectance of 0.028% with respect to the fundamental wave 11 and a second harmonic 1
The ratio can be set to 0.025% with respect to 2, thereby realizing an extremely low-loss device.

As described above, in a conventional solid-state laser using a non-linear optical element, a solid-state laser medium and a non-linear optical element are arranged separately, but in a semiconductor laser, a non-linear optical element forming material is formed in a semiconductor active layer. A structure with a close contact has been proposed. FIG.
FIG. 5 is a perspective view of a semiconductor laser proposed in Japanese Patent No. 75286, and FIG. 5B is a conceptual diagram showing an oscillation state thereof. As shown in the figure, an active layer 21 made of GaAs is sandwiched between a cladding layer 22 made of AlGaAs on the upper and lower sides, and an SHG material layer 23 on the left and right sides. A multilayer film coat 26 is formed.

When a current is supplied from a power supply 25 via electrodes 24 arranged on the upper and lower surfaces, a fundamental wave 11 is generated in the active layer 21 using two multilayer coats 26 as optical resonators. The oscillation mode light intensity distribution 27 of the fundamental wave 11 is not limited to the inside of the active layer 21 but slightly spreads out into the SHG material layer 23. The second harmonic 12 is generated from the portion of the SHG material layer 23 that intersects the fundamental wave 11.

[0006]

The conventional solid-state laser shown in FIG. 4 has the following problems since each component is arranged separately. Since an antireflection film must be formed on the nonlinear optical element, materials other than those that can be formed by vapor deposition, sputtering, and the like cannot be used as materials for forming the nonlinear optical element. Was. For example,
An organic material such as DAN [4- (N, N-dimethylamino) -3-acetamidonitrobenzene] has high wavelength conversion efficiency and has desirable characteristics as a material for forming a nonlinear optical element, but has a melting point of 170 ° C. Therefore, it was difficult to perform vapor deposition, so that it could not be put to practical use. Since it is necessary to apply a multilayer coating such as an anti-reflection film or a reflection film to each component, a large number of manufacturing steps are required, and it has been difficult to reduce the cost. Since the size of the device is increased and the length of the resonator is increased, it is difficult to unify the transverse mode. Since the resonator is in contact with the outside air, dust scattered in the air tends to adhere to members in the resonator, which causes a reduction in the internal power of the fundamental wave.

On the other hand, although the conventional example shown in FIG. 5 is a semiconductor laser, some of the above-mentioned problems have been solved by bringing a nonlinear optical element forming material layer into close contact with a semiconductor active layer. . However, even in this conventional example, since a multilayer coating is required on both end surfaces of the nonlinear optical material layer, there is still a limitation in material selection. Further, in this conventional example, since the nonlinear optical material layer exists in the direction perpendicular to the optical axis of the optical resonator, the efficiency is inferior. That is, the internal power of the fundamental wave 11 is strong in the active layer 21, but is low in the nonlinear optical material layer located around the active layer 21 because of the Gaussian distribution, and the conversion efficiency is generally lower than the power density. Since it is proportional to the square, the decrease in wavelength conversion efficiency is remarkable, and the output of the second harmonic is extremely weak.

Therefore, an object of the present invention is, first, to alleviate the limitation on material selection so that a multilayer film is not required to be formed on a nonlinear optical element.
The goal is to realize a solid-state laser structure that does not require many multilayer coatings to reduce man-hours and reduce costs.
Fourth, it is to provide a downsized solid-state laser, and fourth, to provide a long-life solid-state laser which is hardly deteriorated.

[0009]

The solid-state laser of the present invention comprises:
In a solid-state laser in which a fundamental wave generated from a solid-state laser medium is wavelength-converted by a non-linear optical element, a non-linear optical element forming material layer forming the non-linear optical element is directly grown on the solid-state laser medium and is arranged. It is characterized by the following. A dichroic layer is formed on the surface of the solid-state laser medium on which the non-linear optical element forming material layer is not formed, and one surface of the transparent plate is formed on the surface of the non-linear optical element that is not in contact with the solid-state laser medium. The surface on the dichroic layer side of the mirror in which the dichroic layer is formed on the surface is optically contacted.

[0010]

In the conventional example, since the solid-state laser medium and the nonlinear optical element are formed separately, it is essential to form an antireflection film on the nonlinear optical element. This is because, when the antireflection film is not used, the light loss at the end face becomes 4% or more, and it is considered that oscillation cannot be performed. In the present invention, the above-mentioned difficulties are overcome by adopting a solid-state laser medium and a non-linear optical material having close refractive indexes to each other and bringing both materials into close contact with each other. For example, as a solid-state laser medium, Nd: YVO ₄
(Refractive index: n ₁ = 1.9) as D
When AN (refractive index: n ₂ = 1.8) is adopted, the reflectance R is R = (n ₁ −n ₂ ) ² / (n ₁ + n ₂ ) ² = 0.07%, which is the optical loss. However, oscillation is sufficiently possible with this level of light loss.

The significance of omitting the antireflection film is, first, that a highly efficient organic nonlinear optical material can be put to practical use. Organic nonlinear optical materials have attracted attention because of their higher wavelength conversion efficiency as compared with inorganic nonlinear optical materials. However, organic nonlinear optical materials generally have a low melting point (170 ° C. in the case of DAN) and have a weak crystal bonding force and are easily sublimated. However, it is not suitable for forming a vapor-deposited film that requires high-temperature heating in a vacuum, and has been difficult to put into practical use. The present invention opens the way to practical use of organic second harmonic generation materials, and the present invention makes it possible to provide a high-efficiency solid-state laser. The second significance of omitting the antireflection film is that the device can be downsized. In particular, when an organic second harmonic generation material is used, the resonator can be shortened and the device can be further miniaturized because of high conversion efficiency. Further, since the length of the resonator can be shortened, it becomes easy to unify the transverse mode.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a sectional view of a solid-state laser according to one embodiment of the present invention. In the figure, 1 is Nd: Y
The solid-state laser medium 2 composed of VO ₄ has a DAN [4-
(N, N-dimethylamino) -3-acetamidonitrobenzene], 3 is a quartz plate, 4 is a dichroic layer formed on one surface of the solid-state laser medium 1 and one surface of the quartz plate 3. .

Next, the manufacturing method of this embodiment will be described with reference to FIG. First, a solid laser medium 1 having a thickness of 0.7 mm is prepared, and a dichroic layer 4 is previously formed on one side thereof. Next, the glass container 5 is filled with a saturated solution 6 of DAN using acetone as a solvent. Then, the solid-state laser medium 1 is placed in a container with the surface on which the dichroic layer 4 is not formed facing up, and a seed crystal of DAN is placed on the solid-state laser medium 1. When the temperature of the solution 6 is gradually lowered, crystal growth of DAN on the solid-state laser medium 1 starts. At this time, the crystal axis of the growing CAN is arranged on the side surface of the container 5 and controlled by the electric field between the two electrodes 7 connected to the power supply 8.

After growing the DAN to a thickness of 1.3 mm, the sample is taken out of the container and the upper surface thereof is optically polished. On the other hand, after the surface of the quartz plate 3 is polished and sufficiently smooth, dichroic coating is performed. Finally, when the surface of the dichroic layer 4 of the quartz plate 3 is brought into optical contact with the nonlinear optical element 2, the solid-state laser of the present embodiment shown in FIG. 1A is obtained.

Next, the operation of this embodiment will be described.
The solid state laser medium is excited using a suitable excitation means, for example, a laser diode. The optical resonator is a solid-state laser medium 1
It is formed between the dichroic layers 4 provided on the respective surfaces of the quartz plate 3 and the quartz plate 3. The fundamental wave 11 undergoes multiple reflection in the optical resonator, that is, in the solid-state laser medium 1 and the nonlinear optical element 2. Then, a part of the fundamental wave 11 is wavelength-converted by the nonlinear optical element 2 and radiated as the second harmonic 12.

Next, a specific use example of this embodiment will be described. FIG. 2 is a cross-sectional view illustrating a configuration of a solid-state green laser using the present embodiment. The output light of the laser diode 10 is transmitted through the selfoc lens 9 to the solid-state laser medium 1.
Incident inside. The solid-state laser medium 1 generates a fundamental wave having a wavelength of 1.06 μm using the pair of dichroic layers 4 and 4 as optical resonators. A part of this fundamental wave is emitted to the outside after the wavelength is converted to 0.53 μm by the nonlinear optical element 2.

FIG. 3 is a cross-sectional view showing a configuration in which this embodiment is applied to a solid-state blue laser. In this example, the nonlinear optical element 2 is arranged so as to be on the laser diode 10 side. 0.81μ wavelength of laser diode 10
m infrared light is incident on the nonlinear optical element 2 and the solid-state laser medium 1 via the Selfoc lens 9. The solid-state laser medium 1 generates a fundamental wave having a wavelength of 1.06 μm using the pair of dichroic layers 4 and 4 as optical resonators. The nonlinear optical element 2 absorbs the fundamental wave and the infrared light of the laser diode and absorbs 0.459 μm corresponding to the sum of the energies of the two.
m sum frequency light is generated and emitted to the outside.

Although the preferred embodiment has been described above,
The present invention is not limited to the above embodiments, and various modifications are possible. For example, Pd: Y as a solid-state laser medium
Instead of _{VO 4 Pd: YAG, Pd:} YLF or the like can be used other media, also place the DAN [4- (N, N- dimethylamino) -3-acetamide-nitrobenzene] to form a nonlinear optical element Or other organic materials such as PCNB (propylcarbamic nitrobenzene, refractive index: 1.7 ) or KTP (KTiOPO ₄ , refractive index:
1.8) an inorganic material, or the like can be used. Flexion respectively
Ru can be combined with a material having close folding rate.

[0019]

As described above, according to the solid-state laser of the present invention, the non-linear optical element 2 is grown on the solid-state laser medium 1 so that the two components are brought into close contact with each other.
And the quartz plate 3 are optically polished and brought into optical contact with each other, so that the following effects can be obtained. It is not necessary to form an anti-reflection film on the nonlinear optical element, and the nonlinear optical element can be formed using a material that could not be used because a deposition film could not be formed even if the wavelength conversion efficiency was high. It can be formed. As a result, it is possible to increase the output of a solid-state laser using a nonlinear optical element. Further, in order to obtain the same output, the thickness of the nonlinear optical element can be reduced. The device can be made compact, and the length of the resonator can be reduced from the conventional 10 mm to 2 mm or less to 1/5.
The following configuration is possible. And, since the resonator length is shortened, it becomes easy to unify the transverse mode.

The inside of the laser resonator can be cut off from the outside air, and as a result, a decrease in power of the internal resonator due to adhesion of dust and dust scattered in the outside air can be suppressed, and the life of the solid-state laser can be extended. can do. In the conventional example, only two multi-layer coats, which are required six in the conventional example, need be formed, and a product can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention and a cross-sectional view for explaining a method for manufacturing the same.

FIG. 2 is a sectional view showing an application example of the embodiment of the present invention.

FIG. 3 is a sectional view showing an application example of the embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a configuration of a conventional solid-state laser.

FIG. 5 is a perspective view showing an example of a conventional semiconductor laser and its operation explanatory view.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Solid-state laser medium 2 Nonlinear optical element 3 Quartz plate 4 Dichroic layer 5 Container 6 Saturated solution of DAN 7 Electrode 8 Power supply 9 Selfoc lens 10 Laser diode 11 Fundamental wave 12 2nd harmonic 13 YAG rod 14 Anti-reflection film 15 SHG element Reference Signs List 16 TiO ₂ film 17 ZrO ₂ film 18 SiO ₂ film 19 First mirror 20 Second mirror 21 Active layer 22 Cladding layer 23 SHG material layer 24 Electrode 25 Power supply 26 Multi-layer coating 27 Light intensity distribution

Claims (3)

(57) [Claims] 1. A solid-state laser in which a fundamental wave generated from a solid-state laser medium is wavelength-converted by a nonlinear optical element.
The nonlinear optical element is bent over the solid-state laser medium.
By directly growing crystals using materials with similar bending ratios
A solid-state laser characterized by being formed . 2. A dichroic layer is formed on a surface of the solid-state laser medium that is not in contact with the nonlinear optical element,
The dichroic layer-side surface of a mirror having a dichroic layer formed on one surface of a transparent plate is in close contact with a surface of the non-linear optical element that is not in contact with the solid-state laser medium. Item 2. The solid-state laser according to Item 1. 3. The method according to claim 2, wherein the non-linear optical element is a DAN [4-
(N, N-dimethylamino) -3-acetamidonitrobenzene] (Refractive index at a wavelength of 1064 nm: 1.
8) PCNB (propyl carbamic nitrobenzene) (refractive index at a wavelength of 1064 nm: 1.7) or KTP (KTiOPO ₄ ) (a wavelength of 1064 nm )
2. The solid-state laser according to claim 1, wherein the solid-state laser is formed using a refractive index of 1.8) .