JP2002076476A - Solid-state laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent decline of the polarization rate of a laser beam passing through a cover member in a solid-state laser provided with a sealed container for housing at least a resonator part provided with an opening for passing the generated laser beam through and the cover member formed of a material for passing the laser beam through for closing the opening. SOLUTION: In this solid-state laser for housing the resonator part composed of an Nd:YAG crystal 14 and a resonator mirror 15 for instance in the sealed container composed of a package base 40 and a package cover 41, transmitting the generated laser beam (second higher harmonic) 21 through the cover member 43 formed of the material for transmitting the laser beam 21 for closing the opening 42 and emitting it to the outside of the container, the cover member 43 is formed of a uniaxial crystal and is disposed in a direction for not feeling the double refractivity of the laser beam 21 transmitted there.

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 having a resonator portion housed in a closed container.

[0002]

2. Description of the Related Art As disclosed in, for example, JP-A-5-283123, a solid-state laser in which a solid-state laser crystal to which a rare earth such as neodymium is added is excited by a semiconductor laser (laser diode) is known.

[0003] In this type of laser, high output,
In order to meet the demand for higher quality and higher reliability of output light, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-283123, from the viewpoints of reducing the influence of environmental fluctuations and preventing dust and moisture, at least its resonance is required. It is widely practiced to store the container portion in a closed container. Adopting such a structure not only prevents dust, but also prevents the condensation phenomenon due to humidity, and furthermore, by keeping the air density in the sealed container constant, the output fluctuation caused by the fluctuation of the environmental temperature Can also be suppressed.

[0004] The above-mentioned closed vessel is provided with an opening through which the generated laser beam (oscillation light of the solid-state laser itself or a wavelength-converted wave such as a second harmonic obtained by passing it through a nonlinear optical crystal) is passed. , And this opening,
In general, the cover is closed by a cover member formed of a material that transmits the laser beam.

[0005]

However, as described above, in the conventional solid-state laser in which at least the resonator portion is housed in a closed container, the laser beam generated in the closed container has a straight line having a large polarization ratio. Although the light is polarized, the laser beam emitted out of the closed container has a small polarization ratio, and in the worst case, may be elliptically polarized.

Conventionally, almost no countermeasures have been taken against such a problem. For example, a semiconductor laser, not a solid-state laser, often contains a laser diode chip in a package and outputs the laser beam through a cover glass that closes the package opening. Since it is relatively small from about 50: 1, almost no consideration has been given to elliptically polarized light caused by passing through a cover glass.

However, the characteristics of the solid-state laser and the equipment using the same have been improved, so that a higher degree of linear polarization is required for the laser beam. Since the cover member is made of birefringent sapphire or the like in order to increase the polarization ratio, the reduction of the polarization ratio due to the passage of the cover member is becoming a situation that cannot be ignored.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a solid-state laser in which at least a resonator portion is housed in a closed container, so as to prevent a decrease in a polarization ratio due to a laser beam passing through a cover member. With the goal.

[0009]

As described above, a first solid-state laser according to the present invention comprises a closed container containing at least a resonator portion and having an opening through which a generated laser beam passes, and In a solid-state laser having a cover member formed of a material to be transmitted and closing the opening, the cover member is formed of a material having no birefringence.

A second solid-state laser according to the present invention comprises:
In a solid-state laser having a closed container and a cover member similar to the above, the cover member is formed from a uniaxial crystal, and the laser beam passing therethrough is disposed in a direction in which birefringence is not felt. It is characterized by having.

The laser beam taken out of the closed vessel through the opening may be the oscillation light of a solid-state laser itself as described above, or the second harmonic obtained by passing it through a nonlinear optical crystal. Or the like.

[0012]

According to the first solid-state laser of the present invention, since the cover member for closing the opening of the closed container is made of a material having no birefringence, the linearly polarized laser beam generated in the closed container is generated. When transmitting through the cover member, it is possible to prevent the generation of polarization components orthogonal to each other due to the birefringence, and therefore, it is possible to reduce the polarization ratio of this laser beam, and furthermore, to make the laser beam elliptically polarized. It can be prevented.

In the second solid-state laser according to the present invention, the cover member is formed of a uniaxial crystal having birefringence. However, this cover member is such that a laser beam passing therethrough does not feel birefringence. Because it is arranged in the direction,
In this case, the same effect as above can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a partially broken side view of a solid-state laser according to an embodiment of the present invention.
This solid-state laser is, for example, a semiconductor laser-excited solid-state laser having a wavelength conversion function, and a semiconductor laser 11 that emits a laser beam 10 as excitation light and a refractive index that focuses the laser beam 10 that is divergent light. A condenser lens 13 composed of a distributed lens and a neodymium (N
Y) crystal (hereinafter, referred to as Nd: YAG crystal) 14 which is a solid laser medium doped with d), and Nd:
A resonator mirror 15 disposed on the front side (the right side in the figure) of the YAG crystal 14, an optical wavelength conversion element 16 disposed between the Nd: YAG crystal 14 and the resonator mirror 15, a Brewster plate 17 And etalon 18.

The elements 14 to 18 described above are adhesively fixed to a common holder 30 made of, for example, copper. This holder 30 is fixed on a Peltier element 31 constituting a temperature control means via a base plate 32. I have. The semiconductor laser 11 and the condenser lens 13 are also mounted on a holder 33 made of copper or the like, and this holder 33 is also fixed on the Peltier element 31 via a base plate 32.

A holder 30 and a front side of a resonator section consisting of elements 14 to 18 attached thereto are provided with a holder.
An APC section comprising a 35, a partial reflection mirror 36 attached to the 35, and a photodiode 37 is provided.
The holder 35 is fixed on the base plate 32.

The driving of the Peltier device 31 is controlled by a thermistor 34 attached to the holder 30 for detecting the temperature of the resonator and a temperature control circuit (not shown), and the semiconductor laser 11 and the solid-state laser resonator (described later) are controlled. As described above, the elements in the Nd: YAG crystal 14 and the resonator mirror 15) and the elements in the APC section are all controlled to a common predetermined temperature.

The Peltier device 31 is fixed on a package base 40, and a package cover 41 is attached to the package base 40. Thus, all components held on the base plate 32 are housed in a closed container (housing) composed of the package table 40 and the package cover 41. The package cover 41 has a second
An opening 42 through which the harmonics 21 pass is formed, and the opening 42 is covered by a cover member 43 that transmits the second harmonic 21.

The optical wavelength conversion element 16 is a device in which a periodic domain inversion structure is provided in a MgO-doped LiNbO ₃ crystal, which is a nonlinear optical material. Brewster plate 17 acts as a polarization control element,
Reference numeral 18 functions as a wavelength selection element for unifying the oscillation wavelength.

The semiconductor laser 11 emits a laser beam 10 having a center wavelength of 808 nm. N
d: The YAG crystal 14 has a wavelength of 946 nm when neodymium ions are excited by the laser beam 10.
Emits light. And the rear end face 14 of the Nd: YAG crystal 14
a and the mirror surface 15a of the resonator mirror 15 cause laser oscillation to cause a wavelength of 946 nm.
Is obtained. This laser beam 20 enters the optical wavelength conversion element 16 and is converted into a second harmonic 21 having a wavelength of 1/2, that is, 473 nm.

The back end face 14a of the Nd: YAG crystal 14 is coated so that the laser beam 10, which is the excitation light, is transmitted well, while the solid laser beam 20 and the second harmonic 21 are reflected with high reflectivity. Have been. The resonator mirror 15 is a concave mirror having a radius of curvature of 50 mm, and its mirror surface is
15a and the rear end face 14a of the Nd: YAG crystal 14 are arranged so as to be separated by about 10 mm on the optical axis.

On the mirror surface 15a of the resonator mirror 15,
The solid-state laser beam 20 is reflected with high reflectance, and the second harmonic
The portion 21 is provided with a coat for partially transmitting the light, so that the second harmonic 21 is emitted from the resonator mirror 15. Second
The harmonic 21 passes through the opening 42, passes through the cover member 43, and exits outside the package cover 41.

Next, APC (Automatic Power Control) for stabilizing the output of the second harmonic 21 will be described. In this example, a resonator mirror (output mirror) 15
From the second harmonic 21 with a wavelength of 473 nm and the laser beam 10 with a central wavelength of 808 nm leaking from the second harmonic 21
Are almost the same. This second harmonic 21
The light is reflected upward by the partial reflection mirror 36 in the portion C, and is detected by the photodiode 37.

The output signal S of the photodiode 37 is
The data is input to the APC circuit 38 provided outside the package cover 41. The APC circuit 38 lowers the drive current of the semiconductor laser 11 based on the output signal S indicating the light amount of the second harmonic 21 if the light amount value indicated by the signal S increases,
Conversely, if the light amount value indicated by the signal S decreases, control is performed so as to increase the amount, thereby making the output of the second harmonic 21 constant.

Next, a sealed container including the package table 40 and the package cover 41 will be described in detail. The package base 40 and the package cover 41 are made of Kovar. On the other hand, the cover member 43 is formed from a sapphire substrate obtained by cutting sapphire, which is a uniaxial crystal, on a plane perpendicular to the c-axis, and the cut surface, that is, the ± c plane is oriented so as to be a light passage surface, and the package cover 41 is formed. Is fixed by gold-tin brazing.

The uniaxial crystal sapphire, which is the material of the cover member 43, has birefringence. However, since it is cut out and fixed as described above, its c
The axis is aligned with the traveling direction of the second harmonic 21. The second harmonic 21 traveling in the same direction as the c-axis does not feel the birefringence of the cover member 43. 2nd harmonic
Originally, 21 is linearly polarized light having a polarization ratio of about 1000: 1. However, since the birefringence of the cover member 43 is not felt, the high polarization ratio of about 1000: 1 is maintained even after passing through the cover member 43. There is no elliptically polarized light.

As a comparative example, the same sapphire was cut out at random in the cutting direction with respect to the crystal axis, and a plurality of cover members having the same shape as the cover member 43 were formed. These cover members were attached to the package cover 41 instead of the cover member 43 in the configuration of FIG. 1, and the polarization state of the second harmonic 21 transmitted through the package cover 41 and emitted to the outside of the closed vessel was examined. In the worst case, it was reduced to about 50: 1.

Although the embodiment in which the cover member 43 is formed from sapphire, which is a uniaxial crystal, has been described above, the same effect as described above can be obtained by forming the cover member 43 from an isotropic material having no birefringence. Is obtained. In that case, it is not necessary to particularly consider the direction of cutting out the isotropic material and the direction of attachment to the package cover 41.

In the embodiment described above, the second harmonic 21 obtained by converting the wavelength of the solid-state laser beam 20 is used as the cover member.
It is configured to emit light through 43,
The present invention is similarly applicable to a solid-state laser in which the solid-state laser beam itself is emitted to the outside of the closed container through the cover member without performing wavelength conversion. The effect of preventing a decrease in the ratio and suppressing elliptically polarized light can be obtained.

[Brief description of the drawings]

FIG. 1 is a partially broken side view of a solid-state laser according to an embodiment of the present invention.

[Explanation of symbols]

 10 Laser beam (excitation light) 11 Semiconductor laser 13 Condensing lens 14 Nd: YAG crystal 15 Resonator mirror 16 Optical wavelength conversion element 17 Brewster plate 18 Etalon 20 Laser beam (solid laser beam) 21 Second harmonic 30, 33 , 35 Holder 31 Peltier device 32 Base plate 36 Partial reflection mirror 37 Photodiode 38 APC circuit 40 Package table 41 Package cover 42 Package cover opening 43 Cover member

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2K002 AB12 BA01 CA03 FA27 HA20 5F072 AB02 FF07 HH06 JJ20 KK01 KK08 KK12 KK30 PP07 TT13 TT14 TT15 TT16 TT28

Claims (4)

[Claims] 1. A solid-state laser having at least a resonator portion and having a closed container having an opening through which a generated laser beam passes, and a cover member formed of a material that transmits the laser beam and closing the opening. A solid-state laser, wherein the cover member is formed of a material having no birefringence. 2. A solid-state laser having at least a resonator portion and having a closed container having an opening through which a generated laser beam passes, and a cover member formed of a material that transmits the laser beam and closing the opening. A solid-state laser, wherein the cover member is formed of a uniaxial crystal, and the laser beam passing therethrough is arranged in a direction in which the laser beam does not feel birefringence. 3. The solid-state laser according to claim 2, wherein said cover member is formed of sapphire. 4. The solid-state laser according to claim 1, wherein the laser beam is a wavelength-converted wave obtained by passing solid-state laser oscillation light through a nonlinear optical crystal.