JP3338714B2 - Semiconductor laser pumped solid-state laser device - 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 device and, more particularly, to a semiconductor laser-excited solid-state laser device in which the output fluctuation of solid-state laser light is reduced.

[0002]

2. Description of the Related Art A semiconductor laser-excited solid-state laser device (hereinafter, referred to as a solid-state laser device) excites a solid-state laser medium with semiconductor laser light to cause laser oscillation. It has features such as high conversion efficiency and stable operation, and its use is expanding in various industrial fields. In recent years, attempts have been made actively to realize a green laser or a blue laser in the visible region by combining a nonlinear optical element and a solid-state laser.

FIG. 5 shows a cross section of a solid-state laser device. The solid-state laser medium 43 is made of Nd: YAG (neodymium: yttrium aluminum oxide), Nd: YVO
₄ , Nd: YLF (neodymium: yttrium lithium fluoride) or the like is used. The semiconductor laser 41 has an oscillation wavelength of 808 to 810 nm, which is the absorption wavelength range of the solid-state laser medium 43, and has an output of 100 mW or more.

The solid-state laser medium incident surface of the solid-state laser medium 43 and the concave surface of the output mirror 44 are connected to the fundamental wave 1 of the solid-state laser.
A coating having a high reflectivity for 053 to 1064 nm is formed to constitute a solid-state laser resonator (hereinafter referred to as a resonator). When the semiconductor laser light is condensed on the solid-state laser medium 43 by the condensing optical system 42, solid-state laser oscillation occurs in the resonator and a part thereof is emitted to the outside through the output mirror 44. When a nonlinear optical element is inserted into the resonator, the second harmonic or the third harmonic of the solid-state laser fundamental wave is generated by the interaction between the nonlinear optical element and the solid-state laser fundamental wave. By using a nonlinear optical element having a large second-order nonlinear optical effect, the second harmonic, that is, the solid-state laser fundamental wave 1
Attempts have been made to realize a laser having a wavelength of / 2.

In such a solid-state laser device, when an Nd: YVO ₄ crystal is used as the solid-state laser medium 43,
d: YVO4 crystal has an oscillation wavelength of 80 of the semiconductor laser.
The absorption coefficient in the range of 8 to 810 nm is about four times that of the Nd: YAG crystal, and the thermal conductivity is about 1 times that of the Nd: YAG crystal.
As a result, the temperature of the Nd: YVO ₄ crystal semiconductor laser pumping light absorbing portion rises, and the output of solid-state laser light fluctuates.

For example, when the power of the pumping light of the semiconductor laser is 50,
0 mW, excitation light spot size 100 μm, N
It is known that the temperature of the center of the pumping light spot on the surface of the semiconductor laser pumping light incident surface of the d: YVO4 crystal rises by about 40 degrees, and the output of the solid-state laser light decreases to one third with that. (IEICE Technical Study Group OQE91-
30P73-78)

3 mm × 3 mm × 1 mm Nd: YVO4
The crystal was fixed in an aluminum holder of 10 mm × 10 mm × 2 mm embedded with an adhesive, and the semiconductor laser oscillation wavelength was 809 nm and the semiconductor laser excitation light power was 200 m.
W, Nd: Y under the condition of an excitation light spot size of 100 μm
As a result of measuring the temperature change of the aluminum holder and the output change of the solid-state laser beam when the VO ₄ crystal was excited, the output change of the solid-state laser beam was ± 15%, which was substantially synchronized with the temperature change of the aluminum holder. I knew it was there.
This is presumably because the cycle of absorption of the semiconductor laser pumping light of the Nd: YVO ₄ crystal, increase in temperature, decrease in solid-state laser output, decrease in temperature, increase in absorption of semiconductor laser pumping light, and increase in temperature are repeated.

[0008]

[SUMMARY OF THE INVENTION An object of the present invention, the solid-state laser medium is Nd: suppress output variations of the solid-state laser device is YVO _4, it is intended to obtain a solid-state laser device of stable output .

[0009]

SUMMARY OF THE INVENTION The present invention provides a semiconductor laser chip, a metal block for supporting the semiconductor laser chip, an electronic cooling element joined to the metal block, a heat sink to which the electronic cooling element is fixed, Nd: Y arranged opposite to the laser excitation light emission surface of the semiconductor laser chip
A solid-state laser medium of a VO ₄ crystal, an output mirror disposed in front of a laser excitation light emission surface of the Nd: YVO ₄ crystal, an optical housing to which the output mirror is fixed, the semiconductor-laser-pumped solid-state laser apparatus with a fixed solid-state laser medium and the heat sink, the Nd: semiconductor laser pumping light incident surface der of YVO ₄ crystal
Thus, the surface excluding the incident portion of the semiconductor laser pumping light is A
u, Ag, Cu, Al at least one metal or alloy selected from the group consisting of one surface of the metal block and the N
d: The YVO ₄ crystal is characterized in that the opposing surface of the semiconductor laser excitation light incident surface of the YVO ₄ crystal is disposed in contact with the surface and the opposing surface is thermally coupled.

[0010]

In [act invention, Nd by absorbing semiconductor laser excitation light: YVO ₄ laser excitation light incident surface of most temperature in the crystal is increased, the metal block is controlled to a constant temperature by the electronic cooling element In contact with the surface. Therefore, the temperature of the Nd: YVO4 crystal semiconductor laser pumping light incident surface is equal to the temperature of the metal block, and is always controlled to a constant temperature by the electronic cooling element.

Therefore, the output fluctuation of the solid-state laser device based on the temperature change of the Nd: YVO ₄ crystal can be suppressed, and a solid-state laser device having a stable output can be obtained. Furthermore, N
d: The semiconductor laser pumping light incident surface of the YVO ₄ crystal, excluding the semiconductor laser pumping light incident portion, was Au,
When coated with at least one metal or alloy selected from Ag, Cu, and Al, the metal is rich in ductility,
d: The contact property between the semiconductor laser pumping light incident surface of the YVO ₄ crystal and the metal block is improved, and the above-mentioned action can be further ensured.

[0012]

FIG. 1 is a sectional view showing an embodiment of a solid-state laser device according to the present invention, in which a semiconductor laser chip 11, a metal block 12, an electronic cooling element 13, and a Nd: YVO ₄ crystal 1 are shown.
4, output mirror 15, optical housing 16, heat sink 1
7, a radiating fin 18 and a heat insulating member 19. As the semiconductor laser chip 11, a multimode oscillation semiconductor laser having a wavelength of 809 nm and an output of maximum 500 mW was used.

The semiconductor laser chip 11 is provided with a thermo-conductive adhesive through a copper metal block 12 and an electronic cooling element 13.
Of the metal block 12 using screws.
d: Optical housing 16 so as to make surface contact with YVO4 crystal 14
Fixed to. Nd: YVO ₄ crystal 14 is 3 × 3 × 1 m
m, and the semiconductor laser pumping light incident surface has a wavelength of 80
A coating was applied so as to have no reflection at 9 nm and high reflection at a wavelength of 1064 nm, and a resonator was formed between the coating and the concave surface of the output mirror 15.

The output mirror 15 has a diameter of φ15 × 5 mm and a radius of curvature of 50 mm. Each optical element of the Nd: YVO ₄ crystal 14 and the output mirror 15 was fixed to an aluminum optical housing 16 with screws while adjusting the position precisely. The heat sink 17 with the heat radiating fin 18 has a central portion joined to a heat radiating plate of the electronic cooling element 13 by a heat conductive adhesive, and a peripheral portion formed of an acrylic resin plastic through a tetrafluoroethylene resin (heat insulating member 19). Optical housing 1 with screws
6 was fixed.

In FIG. 2, the dotted line 31 shows the time change of the output of the solid-state laser device of this embodiment, and the output fluctuation was within ± 5%. The solid line 32 in FIG.
d: Time change of the output of the conventional solid-state laser device using the same optical system and optical element as in the present embodiment except that the YVO ₄ crystal 14 is not in contact, and the output fluctuation is ± 15%. .

In the solid-state laser device of the present embodiment, the semiconductor laser excitation light incident surface is in contact with the surface of the metal block 12 controlled to a constant temperature by the electronic cooling element 13, so that Nd: YVO ₄ The temperature of the semiconductor laser pumping light incident surface of the crystal 14 is equal to the temperature of the metal block 12 and is always controlled to a constant temperature by the thermoelectric cooler 13. It can be seen that it is suppressed to a factor of one.

FIG. 3 is an enlarged view of a main part according to another embodiment of the present invention.
2, the electron cooling element 13 and the Nd: YVO ₄ crystal 14 are shown. A solid-state laser in which a gold thin film 20 is applied to a thickness of 3 μm on the surface of the Nd: YVO ₄ crystal 14 on which the semiconductor laser pumping light is incident, excluding the portion where the semiconductor laser pumping light is incident, by a known sputtering method. It is an example of an apparatus.

The gold thin film 20 is coated to a thickness of 3 μm on the surface of the Nd: YVO ₄ crystal 14 on which the semiconductor laser excitation light is incident, excluding the semiconductor laser excitation light incidence portion, by a known technique of sputtering. I wore it. The gold thin film at the center of the semiconductor laser excitation light incident surface of the Nd: YVO ₄ crystal 14 on which the gold thin film 20 was adhered was removed by a well-known etching method into a circle having a diameter of 200 μm. The area of the gold thin film 20 to be removed is larger than the beam diameter of the incident semiconductor laser, and is preferably as small as possible. The stripe width of the active layer of the semiconductor laser used in the present embodiment is 100 μm, and the beam diameter of the solid-state laser fundamental wave to be emitted is determined by the radius of curvature of the concave surface of the output mirror 15 and the length of the resonator. Since the radius of curvature is 50 mm and the length of the resonator is 7 mm, it is 77 μm.

Therefore, in the present embodiment, the diameter of the gold thin film 20 to be removed is set to 200 μm in consideration of a margin for adjusting the position of the optical element. In FIG. 2, the solid line 33 shows the time change of the output of the solid-state laser device of the present embodiment, and the output fluctuation was within ± 3%. The semiconductor laser pumping light incident surface is in contact with the surface of the metal block 12, which is controlled to a constant temperature by the electronic cooling element 13, and Nd: YVO
4 A gold thin film 20 having a thickness of 3 μm was applied to the surface of the crystal 14 on the surface of the crystal 14 where the semiconductor laser pumping light was incident, excluding the portion where the semiconductor laser pumping light was incident. Improved contact with the surface and N
d: The temperature of the semiconductor laser excitation light incident surface of the YVO ₄ crystal 14 is more reliably controlled to a constant temperature by the thermoelectric cooler, and the time change of the output of the solid-state laser device is reduced to one-fifth as compared with the conventional example. It turns out that it is suppressed.

In the above embodiment, Nd: YVO
_Although an example in which gold is used as the metal coated on the semiconductor laser pumping light incident surface of the _four crystal 14 has been described, the present invention is not limited to this, and copper, silver, aluminum, etc. Can be used.

In the embodiment described above, the optical system for oscillating the fundamental wave of the solid-state laser is shown. However, the present invention is not limited to this, and KTiOPO ₄ (titanium phosphate) is contained in the solid-state laser resonator. A nonlinear optical element such as potassium) is inserted, and the second harmonic of the solid-state laser fundamental wave, that is, a laser having a wavelength of の of the solid-state laser fundamental wave is realized by the interaction between the nonlinear optical element and the solid-state laser fundamental wave. Can be. Since the output of the second harmonic is proportional to the square of the power of the fundamental wave in the resonator, the output fluctuation of the second harmonic has a magnitude in which the output fluctuation of the solid-state laser fundamental wave is amplified. Therefore, the present invention, which can stabilize the output of the solid-state laser fundamental wave, is particularly effective for the second harmonic generation solid-state laser device.

FIG. 4 is a cross-sectional view of a solid-state laser device according to another embodiment of the present invention. The solid-state laser oscillates a laser having the second harmonic of the solid-state laser fundamental wave, that is, a half wavelength of the solid-state laser fundamental wave. 2 shows a cross section of the device. In the solid-state laser device of this embodiment, KTiOPO ₄ is used as the nonlinear optical element.
Crystal 21 was used. KTiOPO ₄ crystal 21 is 3 × 3
The incident surface of the solid-state laser fundamental wave having a size of × 5 mm was polished to a flat surface and coated so as not to reflect the solid-state laser fundamental wave (λ = 1064 nm) and the second harmonic (λ = 532 nm). .

On the other hand, the emission surface of the solid-state laser fundamental wave is R = 5.
A spherical surface is polished to a convex surface of 0 mm, and a solid-state laser fundamental wave (λ = 1
064 nm), and the coating was applied so as not to reflect the second harmonic (λ = 532 nm). By doing so, the solid-state laser resonator is composed of the semiconductor laser pumping light incident surface of the Nd: YVO ₄ crystal 14 and the spherical surface of the KTiOPO ₄ crystal 21, so that the output mirror can be omitted and the solid-state laser fundamental wave can be eliminated. The second harmonic, that is, 1/2 of the solid-state laser fundamental wave
It is possible to reduce the size of a solid-state laser device that oscillates a laser having a wavelength of.

The output fluctuation of the solid-state laser device of this embodiment is ±
The output fluctuation of the conventional solid-state laser device using the same optical system and optical element as in the present embodiment except that the metal block 12 and the Nd: YVO ₄ crystal 14 are not in contact with each other is within ± 27%. %Met. It is clear that the present invention is particularly effective for the second harmonic generation solid-state laser device.

[0025]

The present invention as described above, according to the present invention, the solid-state laser medium is Nd: suppress output variations of the solid-state laser device is YVO _4, it is possible to obtain a solid-state laser device of stable output.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a solid-state laser device according to the present invention.

FIG. 2 is a characteristic diagram showing a time variation of the output of the solid-state laser device.

FIG. 3 is an enlarged view of a main part in another embodiment of the present invention.

FIG. 4 is a sectional view of a solid-state laser device according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional solid-state laser device.

[Explanation of symbols]

Reference Signs List 11 semiconductor laser chip 12 metal block 13 thermoelectric cooler 14 Nd: YVO ₄ crystal 15, 44 output mirror 16 optical housing 17 heat sink 18 radiating fin 19 heat insulating member 20 gold thin film 21 KTiOPO ₄ crystal 41 semiconductor laser 42 condensing optical system 43 Solid laser medium 45 Holder

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-1344891 (JP, A) JP-A-4-157777 (JP, A) JP-A-4-209581 (JP, A) JP-A-4-199 62880 (JP, A) JP-A-2-161786 (JP, A) JP-A-4-174577 (JP, A) JP-A-5-55670 (JP, A) JP-A-4-283977 (JP, A) JP-A-5-2999751 (JP, A) JP-A-4-97375 (JP, U) Tables of publication JP-A-3-505948 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/00-3/30

Claims (1)

(57) [Claims] 1. A semiconductor laser chip, a metal block supporting the semiconductor laser chip, an electronic cooling element bonded to the metal block, a heat sink to which the electronic cooling element is fixed, and laser excitation light of the semiconductor laser chip An Nd: YVO ₄ crystal solid laser medium facing the emission surface, an output mirror arranged in front of the laser excitation light emission surface of the Nd: YVO ₄ crystal, an optical housing to which the output mirror is fixed, and the optical the metal block in the housing, the laser-diode pumped solid-state laser device fixing the solid-state laser medium and the heat sink, the Nd: a semiconductor laser excitation light incident surface of the YVO ₄ crystal, the semiconductor laser excitation
The surface excluding the incident portion of the light Au, Ag, Cu, an Al
And coated with at least one metal or alloy selected, the one surface of the metal block Nd: Semiconductor YVO ₄ crystal
A semiconductor laser-excited solid-state laser device, characterized in that the laser excitation light incident surface and the opposing surface are arranged in contact with each other and the opposing surfaces are thermally coupled.