JPH0697545A - Solid laser equipment - Google Patents

Abstract

PURPOSE:To provide a solid laser equipment which outputs second harmonic laser light of low noise. CONSTITUTION:The equipment is constituted of the following; a semiconductor laser device 1 for pumping, a solid laser rod 5 which generates fundamental light by the laser light for pumping which the laser device 1 outputs, a wavelength converting element 6 which converts the fundamental light to second harmonic light, and a resonating means which resonates the fundamental light passing the laser rod 5 and the wavelength converting element 6. Further, in a solid laser equipment which outputs the second harmonic light from the resonating means, the laser light for pumping enters obliquely one end surface 5a of the solid laser rod 5.

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 in which a solid-state laser rod and a wavelength conversion element are combined.

[0002]

2. Description of the Related Art In recent years, densification of information has become active, and researches for shortening the wavelength of coherent light used in optical information devices, optical sensors, etc. are being actively conducted.

As a method of obtaining short wavelength coherent light,
Research on generating second harmonic light using a non-linear optical material has been actively conducted. For example, Asahi Glass Research Report, 40
[1] (1991) pp. 85-94 describes a solid-state laser device combined with a solid-state laser rod.

FIG. 7 shows a schematic view of a conventional solid-state laser device. Wavelength output from semiconductor laser device 51 is 809 nm
Of the laser light of wavelength 809 nm on the solid-state laser rod 52 made of Nd-doped YAG crystal.
%, And is vertically incident from one end surface 52a coated with an optical film that reflects approximately 100% of light having a wavelength of 1064 nm,
After passing through the inside of the solid-state laser rod 52, light having a wavelength of 1064 nm, which is the fundamental wave light, is output from the other end surface 52b.
This fundamental wave light is a nonlinear optical crystal KTP (KTiOP
Output mirror 5 through the wavelength conversion element 53 composed of O ₄ ).
4 is reflected by one end surface 54a coated with a reflectance of 99% with respect to light having a wavelength of 1064 nm, passes through the wavelength conversion element 53 and the solid-state laser rod 52 again, and one end surface of the rod 52 is reflected. It is reflected again at 52a.

In this way, the fundamental wave light resonates between the one end face 52a of the solid-state laser rod 52 serving as a resonator and the one end face 54a of the output mirror 54. In this resonator, the fundamental wave light is efficiently converted into light having a wavelength of 532 nm, which is the second harmonic light, by repeatedly moving back and forth through the wavelength conversion element 53, and is output from the other end surface 54b of the output mirror 54.

However, the conventional solid-state laser device has a problem that the SN ratio is deteriorated because noise is generated in the second harmonic light.

By the way, the above-mentioned document describes that this noise can be reduced by using a quarter-wave plate, but in such a method, by using a quarter-wave plate,
There is a problem that the device becomes large and fine alignment adjustment is necessary for the quarter wavelength plate.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and can be downsized, and the second
An object of the present invention is to provide a solid-state laser device that can reduce noise of harmonic light.

[0009]

A solid-state laser device according to the present invention comprises a pumping laser device, a solid-state laser rod for generating a fundamental wave light by the pumping laser light output from the laser device, and a second fundamental wave light. In the solid-state laser device for outputting the second harmonic light, the pumping method comprises: a wavelength conversion element for converting into the harmonic light; and means for causing the fundamental wave light to resonate through the solid-state laser rod and the wavelength conversion element. The laser light for use is obliquely incident on one end face of the solid-state laser rod.

The solid-state laser rod is Nd-doped YV.
It is preferably an O ₄ crystal, and in particular, one end face of this solid-state laser rod is preferably a (100) face.

Further, the pumping laser light has an angle of 4 ° to 1 with respect to the normal direction of the one end face of the solid-state laser rod.
Incident at 0 ° is preferable.

[0012]

In the above structure of the present invention, the pumping laser light for optically exciting the solid-state laser rod is obliquely incident on the one end face of the solid-state laser rod, so that the second harmonic light output from the solid-state laser device is generated. Noise can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state laser device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing this solid-state laser device. Note that <a> and <b in the figure
>, <C> are a, b, and y of the YVO ₄ single crystal described below.
c shows the crystal axis direction.

In FIG. 1, reference numeral 1 denotes a wavelength of 809 nm and an output of 100.
A pumping semiconductor laser device that outputs a laser beam for solid-state laser pumping of mW, linearly polarized light (TE mode), and single mode. Reference numeral 2 is a collimator lens (for example, numerical aperture NA = 0.6) that makes the laser light output from the semiconductor laser device 1 parallel light, and 3 is an anammory that corrects the beam diameter of the laser light into a circular shape. The Fick prism pair 4 is a condenser lens (for example, numerical aperture NA = 0.3) that condenses this parallel light.

Reference numeral 5 denotes Y doped with Nd (for example, 1 to 3 at.%) Arranged in front of the semiconductor laser device 1.
With a solid-state laser rod made of a VO ₄ single crystal, the pumping laser light condensed by the condenser lens 4 is output so that the linear polarization direction thereof coincides with the c-axis direction of the YVO ₄ single crystal, and is output below. In order to reduce the noise of the generated second harmonic light, one end surface (flat surface) 5 of this solid-state laser rod is
obliquely to a, that is, the angle θ formed by the laser beam and the normal direction of the end surface 5a (preferably θ ≧ 4 °, more preferably θ)
= 4 to 10 °), the Nd (neodymium) atom is photoexcited by the laser beam, and TE ₀₀ mode fundamental wave light having a wavelength of 1064 nm having linearly polarized light parallel to the c-axis direction is output. The solid-state laser rod 5 has a plate shape having a length of 10 mm, a width of 10 mm, and a thickness of, for example, 1 mm to the extent that self-absorption of the fundamental wave light does not increase, and the pumping laser light incident side one end surface 5a is ( The 100) plane, which is the so-called a-plane, is created by polishing after cutting.

Reference numeral 6 denotes a wavelength conversion element made of KTiOPO ₄ (KTP) single crystal (non-linear optical material) disposed in front of the solid-state laser rod 5 and having a rectangular or cubic shape, for converting the fundamental wave light having the wavelength of 1064 nm. Wavelength 532
The wavelength is converted to the second harmonic light of nm. The wavelength conversion element 6 has, for example, a length of 3 mm, a width of 3 mm, and a thickness of 3 to 7 mm. The KTP single crystal is arranged such that the fundamental wave light of the TE ₀₀ mode and the second harmonic light are cut so as to be capable of type II (type two) phase matching.

Reference numeral 7 denotes an output mirror which is arranged in front of the wavelength conversion element 6 and has a concave surface 7a having a radius of curvature of 40 mm on the element 6 side and a diameter of 10 mmφ.

The one end face 5a of the solid-state laser rod 5 satisfactorily transmits the pumping laser light (for example, a transmittance of 95%), satisfactorily reflects the fundamental wave light (a reflectance of 99% or more), and A coating for reflecting the second harmonic light well (reflectance 99% or more) is applied, and the other end face 5b is so-called AR (Anti -Reflectin
g) The coat is coated.

The one end face 6a of the wavelength conversion element 6 on the solid-state laser rod 5 side and the other one end face 6b are provided with an AR coat for favorably transmitting the fundamental wave light (transmittance of 99% or more) and second harmonic light. Is coated (for example, light loss is 8% or less).

Further, on the concave surface 7a of the output mirror 7,
A coating is provided that reflects the fundamental wave light well (reflectance 99% or more) and transmits the second harmonic light well (for example, optical loss 20% or less).

Accordingly, the fundamental wave light output from the solid-state laser rod 5 is confined between the one end surface 5a of the solid-state laser rod 5 serving as a resonator and the concave surface 7a of the output mirror 7 to resonate, and the fundamental-wave laser light is emitted. Occurs. This fundamental wave laser light is efficiently wavelength-converted into second harmonic light in the wavelength conversion element 6, and coherent second harmonic light is output from the output mirror 7.

In this embodiment, the distance between the other end surface 5b of the solid-state laser rod 5 and the one end surface 6a of the wavelength conversion element 6 is, for example, 1 mm, and the other end surface 6b of the wavelength conversion element 6 and the concave surface of the output mirror 7 are set. The distance between 7a is 20 mm, for example, and the distance between the other end surface 5a of the solid-state laser rod 5 and the concave surface 7a of the output mirror 7 is selected so that the fundamental wave light can resonate. Further, the distance between the semiconductor laser device 1 and the solid-state laser rod 5 can be appropriately selected.

Hereinafter, as shown in FIG. 2, a polarization beam splitter 20 is disposed between the anamorphic prism pair 3 and the condenser lens 4, and a photodetector 21 such as a photodiode is arranged on the side of the splitter 20. The TM mode component of the popping laser light output from the semiconductor laser 1 was detected, and a photodetector 22 such as a photodiode was arranged in front of the output mirror 7 to detect the second harmonic light. still,
In this system, the solid laser rod 5, the wavelength conversion element 6, and the output mirror 7 are integrally rotated to rotate the rotary stage 2.
3, the angle θ between the normal direction of the one end surface 5a of the solid-state laser rod 5 and the incident direction of the pumping laser light can be arbitrarily set, and the condenser lens 4 is moved in the optical axis direction by a driving mechanism (not shown). It is possible.

FIG. 3 shows the SN ratio and output of the second harmonic light measured in the system shown in FIG. 2 and the angle θ between the normal direction of the one end surface 5a of the solid-state laser rod 5 and the incident direction of the pumping laser light. Show the relationship. The pumping laser light was set so as to be focused on the surface of the end face 5a, and the SN ratio was measured at a frequency of 1 MHz.

From FIG. 3, it can be seen that when the angle θ is 4 ° or more, the SN ratio becomes larger than when the angle θ = 0 °. When the angle θ is 4 ° to 10 °, the SN ratio has a value larger than about 82 dB, and the output has a value larger than about 2.2 mW.
Is a better value than 0 °. In particular, the angle θ is 6
It can be seen that the SN ratio and the output have large values in the range of 9 ° to 9 °. From this, the angle θ is preferably 4 ° or more in order to obtain the second harmonic light with less noise.
Then, the output is sufficient and desirable, and it is understood that 6 ° to 9 ° is particularly preferable.

Further, in FIG. 4, the SN ratio and the output of the TM mode component of the pumping laser light measured simultaneously with FIG.
The relationship between the normal direction of the one end surface 5a of the solid-state laser rod 5 and the angle θ formed by the incident direction of the pumping laser light is shown.

From this FIG. 4, TM of the pumping laser light is shown.
It is considered that there is a correlation between the SN ratio of the mode component and the SN ratio of the second harmonic light shown in FIG. 3, and it is presumed that the noise of the second harmonic light is caused by the optical noise returned to the semiconductor laser device 1. .

In FIG. 5, the position of the condenser lens 4 in FIG. 2 is moved in the optical axis direction to change the focus position (condensing state) of the pumping laser light on the one end surface 5a of the solid-state laser rod 5. FIG. 6 shows the SN ratio and output of the second harmonic light in this case, and FIG. 6 shows the SN ratio and output of the TM mode component of the pumping laser light measured simultaneously with FIG. Incidentally, here, the angle θ is 0 °, and when the collecting point position in the figure is 0 mm, the end surface 5
It is in a state where the focus is on a.

From FIGS. 5 and 6, there is a correlation between the SN ratio and the output of the pumping laser light and the second harmonic light.
It is considered that the change in the SN ratio of the second harmonic light therein is caused by the return light noise to the semiconductor laser device 1, and this noise can also be reduced by changing the condensing state.

Therefore, the one end surface 5a of the solid-state laser rod 5 is
When the laser light for pumping is incident at an angle with respect to
By changing the condensing state of the pumping laser light on the end face 5a, it is possible to further reduce the noise of the second harmonic light as compared with the case where the end face 5a is focused as described above.

However, when the pumping laser light is obliquely incident, the amount of noise with respect to the incident angle θ changes continuously. Therefore, the noise is reduced by changing the condensing state of the pumping laser light. Is easier to adjust than.

The anamorphic prism pair 3 used in the above embodiment may be omitted, and the collimator lens 2 may be omitted.
May be omitted, and it is also effective to omit both the collimating metal lens 2 and the condenser lens 4, and it is also effective to omit both the collimating metal lens 2, the anamorphic prism pair 3, and the condenser lens 4.

Further, in the above description, Nd-doped YVO ₄ is used for the solid-state laser rod 5, and its end face 5a is (100).
Although the surface is used, even if a surface other than this surface is used, the pumping laser light is obliquely incident on the surface, so that the second
Other solid-state laser rods such as Nd-doped YAG single crystal having the effect of reducing the noise of higher harmonic light may be used. Further, as the wavelength conversion element 6, another non-linear optical material capable of phase matching with the fundamental wave light output from the solid-state laser rod 5 may be used.

In the above description, the c-axis direction of the YVO ₄ single crystal and the linear polarization direction of the pumping laser light are made to coincide with each other.
Although the output of the second harmonic light is reduced, it is also effective when the angles are different from each other. Furthermore, although the linearly polarized pumping laser light is used in the above description, the same effect can be obtained with circularly polarized light or elliptically polarized light, and also with multimode.

[0035]

According to the solid-state laser device of the present invention, pumping laser light for optically exciting the solid-state laser rod is obliquely incident on one end face of the solid-state laser rod, so that the return light to the pumping laser device is emitted. It is considered possible to reduce the noise, and as a result, the noise of the second harmonic light output from this solid-state laser device can be reduced. Further, since it is not necessary to use an optical element such as a quarter wavelength plate to reduce the noise, the solid-state laser device can be downsized.
Furthermore, since the amount of noise changes continuously with respect to the incident angle of the pumping laser light, adjustment is easy.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of a measurement system for measuring the characteristics of the solid-state laser device.

FIG. 3 is a diagram showing the relationship between the incident angle θ of the pumping laser light of the solid-state laser device of the above-described embodiment, the output of the second harmonic, and the SN ratio.

FIG. 4 is a diagram showing a relationship between an incident angle θ of pumping laser light of the solid-state laser device of the above embodiment, an output of the laser light, and an SN ratio.

FIG. 5 is a diagram showing a relationship between a condensed state of pumping laser light of a solid-state laser device, an output of a second harmonic, and an SN ratio.

FIG. 6 is a diagram showing a relationship between a condensed state of pumping laser light of a solid-state laser device, an output of the laser light, and an SN ratio.

FIG. 7 is a schematic view of a conventional solid-state laser device.

[Explanation of symbols]

 1 semiconductor laser device for pumping 5 solid-state laser rod 6 wavelength conversion element 7 output mirror

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuharu Matsumoto 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Hideyuki Nonaka 2-18 Keiyo Hon-dori, Moriguchi City, Osaka Sanyo Denki Within the corporation

Claims (4)

[Claims] 1. A pumping laser device, a solid-state laser rod that generates a fundamental wave light by the pumping laser light output from the laser device, a wavelength conversion element that converts the fundamental wave light into a second harmonic light, and In the solid-state laser device, which comprises a resonance means for causing wave light to resonate through the inside of the solid-state laser rod and the inside of the wavelength conversion element, and which outputs the second harmonic light from the resonance means, wherein the pumping laser light is the solid-state laser rod. Solid-state laser device characterized in that it is obliquely incident on one end face of the. 2. The solid laser rod is Nd-doped Y
The solid-state laser device according to claim 1, which is made of a VO ₄ crystal. 3. The one end surface of the solid-state laser rod is (10
The solid-state laser device according to claim 2, wherein the solid-state laser device is a (0) plane. 4. The pumping laser light has an angle of 4 ° to 10 ° with respect to the normal direction of the one end surface of the solid-state laser rod.
The solid-state laser device according to claim 1, 2, or 3, wherein