JPH0669569A - Optical wavelength conversion apparatus - Google Patents

Abstract

PURPOSE:To oscillate the fundamental wave of a desired output light with simple constitution, by forming a solid laser crystal in a wedge type wherein an outer end surface and an inner end surface are intersecting. CONSTITUTION:An optical wavelength conversion apparatus 16 consists of the following; a wedge type Nd-doped YAG laser crystal 13 irradiated with pumping laser light, an output mirror 14 and an end surface mirror formed on the pumping laser light incidence end surface 13A whose mirrors resonate laser light, and a KNbO3 crystal 15 which outputs the second harmonic wave form the inputted fundamental wave. The inclination of a second end surface 13B to a path 21 is so adjusted that the angle of refraction of laser light whose wavelength is to be oscillated becomes equal to the wedge angle theta1 (crossing angle of a first end surface 13A and the second end surface 13B) of the YAG laser crystal 13. Thereby only the laser light of desired wavelength is normally reflected by the end surface mirror of the second end surface 13B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in various optical devices such as color printers and produces a light in a short wavelength region such as green or blue by using a solid laser crystal and a light wavelength conversion element. The present invention relates to an optical wavelength conversion device for improving the structure of a mirror portion of a laser resonator on the excitation light incident side.

[0002]

2. Description of the Related Art In the field of various optical devices such as color printers, it has become necessary to generate short wavelength light in the green and blue wavelength regions. As a technique for generating such short-wavelength light, for example, YA doped with Nd (neodymium) is used.
G laser crystal is excited by semiconductor laser light (809 nm),
As a result, 1064 nm or 94 emitted from the YAG laser crystal
Using 6nm infrared laser light as a fundamental wave through a nonlinear optical crystal such as KNbO ₃ crystal (hereinafter referred to as KN) to obtain laser light of 532nm (green) or 473nm (blue) which is the second harmonic of these It has been known.

It is also known that one of the two mirrors constituting the resonator, which is on the pumping light incident side, is formed by coating the end surface of the YAG laser crystal on the outside of the resonator.

That is, for example, as shown in FIG. 3, a laser beam having a wavelength of 809 nm outputted from a semiconductor laser light source 1 is made incident on a flat YAG laser crystal (Nd-doped) 3 through a focusing lens 2 to make the YAG laser crystal 3 an end face. The YAG laser crystal 3 is excited to output a plurality of laser beams having different wavelengths including a laser beam having a wavelength of 946 nm. The laser light having a wavelength of 946 nm is a light wavelength composed of a KNbO ₃ crystal (hereinafter referred to as KN) while being reflected back and forth between the incident side mirror 3A formed by coating the excitation light incident end face of the YAG laser crystal 3 and the output mirror 4. The conversion element 5 converts the wavelength into the second harmonic having a wavelength of 473 nm (blue). The laser light with a wavelength of 473 nm passes through the output mirror 4 and is output to the outside, whereby laser light in the blue region can be obtained.

[0005]

As described above, when laser light in the blue region (wavelength 473 nm) is obtained by the above technique, the wavelength from the Nd-doped YAG laser crystal 3 is obtained.
It is necessary to reflect the laser light of 946 nm back and forth inside the resonator, but the YAG laser crystal 3 outputs laser light of wavelength 1064 nm in addition to the wavelength of 946 nm.

This laser light having a wavelength of 1064 nm has the highest intensity among the lights outputted from the YAG laser crystal 3, and therefore, in order to oscillate the light having a wavelength of 946 nm, the coating of two reflection mirrors constituting a resonator is performed. Devise,
High reflectivity for light of wavelength 946 nm (reflectance of 10
(Close to 0%), and it is necessary to have low reflection (for example, a reflectance of 70% or less) for light with a wavelength of 1064 nm.

However, since the two wavelengths are extremely close to each other, it is difficult to form the coating film having the ideal characteristics as described above.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical wavelength conversion device capable of oscillating a desired fundamental wave of output light with a simple structure.

Further, in the case where the pumping light incident side mirror of the two mirrors constituting the resonator is formed by coating the pumping light incident side end face of the solid-state laser crystal as described above, this end facet It is necessary to devise a way to handle the reflected light of the pumping laser light from the above to prevent it from returning to the pumping laser light source and becoming a noise source.

In view of this, the present invention is capable of reflecting a desired fundamental wave of output light with a high reflectance with a simple structure and setting an optical wavelength converter capable of setting the pumping laser light so as not to return to the laser light source. It is intended to provide.

When the end face of the solid-state laser crystal on the pumping light incidence side constitutes one of the resonator mirrors, the laser light reciprocating in the resonator passes through the solid-state laser crystal. Therefore, in order to improve the oscillation efficiency, it is preferable to make the reflectance as small as possible when the light is incident on the end surface (reflection surface) of the solid-state laser crystal opposite to the end surface (reflection surface) on the excitation light incident side. It is possible to form an antireflection film on this end face, but this is not preferable because it increases the manufacturing cost.

Therefore, in the present invention, the reflectance of the laser light relating to the fundamental wave of the output light is made as small as possible on the end face of the solid-state laser crystal opposite to the end face on the pumping light incidence side without forming an antireflection film. It is an object of the present invention to provide an optical wavelength conversion device capable of performing the above.

[0013]

A first optical wavelength conversion device according to the present invention has an optical wavelength conversion element disposed between two mirrors forming a laser resonator of a solid-state laser.
Of the two mirrors, a mirror on the incident side of the excitation light beam is an optical wavelength conversion device formed by processing an end surface of a solid-state laser crystal on the outside of the cavity, wherein the solid-state laser crystal and the outer end surface are A fundamental wave of a desired output wave having a wedge shape in which an inner end surface facing the outer end surface intersects with each other, and an inclination of the solid-state laser crystal reciprocates between the two mirrors generated by the solid-state laser crystal. It is characterized in that the laser beam is adjusted so as to be specularly reflected inside the outer end face.

The above "intersection" includes the case where the extension surfaces of the two end surfaces intersect.

Further, the "fundamental wave" is a term corresponding to a higher harmonic wave, which is one that has not been wavelength-converted into a higher harmonic wave in the optical wavelength conversion element.

A second optical wavelength conversion device according to the present invention is the same as the first optical wavelength conversion device, except that the excitation light beam is inclined from a direction perpendicular to the outer end face to the outer side. The tilt of the solid-state laser crystal is adjusted so as to be incident on the end face.

A third optical wavelength conversion device according to the present invention is the same as the first or second optical wavelength conversion device, wherein the incident angle α of the fundamental laser beam with respect to the inner end face is α.
Is the Brewster angle, and the tilt of the solid-state laser crystal is adjusted so that the fundamental laser beam becomes P-polarized with respect to the inner end face.

Further, in a fourth optical wavelength conversion device according to the present invention, in the first optical wavelength conversion device, the solid-state laser crystal is a YAG laser crystal and the optical wavelength conversion element is a KNbO ₃ crystal. It is characterized by.

[0019]

According to the first optical wavelength conversion device described above, the solid-state laser crystal is formed in a wedge shape, and the fundamental wave laser beam having a desired output wave generated by the solid-state laser crystal is the solid-state laser crystal. The tilt of the solid-state laser crystal is adjusted so as to be specularly reflected inside the outer end face of the resonator.

That is, the laser light generated by the end face excitation of the solid-state laser crystal is reflected by the output mirror,
Re-enter the solid-state laser crystal. Since multiple laser lights with different wavelengths are output from the solid-state laser crystal, these multiple laser lights will re-enter the solid-state laser crystal. Since the size of the angle depends on the wavelength of the laser beam, when these laser beams pass through the solid-state laser crystal and reach the resonator outer end face, the incident angles at the outer end face must be different. become.

In order for the laser beam to oscillate in the resonator, it is necessary that the laser beam reflected by the outer end face travels backward in the incident optical path, that is, the outer end face is specularly reflected.

In the device of the present invention, the fundamental wave laser beam of the desired output wave is adjusted so as to be specularly reflected by this outer end face, so that the laser beams of other wavelengths are not specularly reflected, and therefore the desired wavelength is not desired. It becomes possible to oscillate only the fundamental wave laser beam of the output wave of 1) in the resonator.

After that, the oscillated fundamental wave laser beam of the desired output wave is converted into a desired output wave by the wavelength conversion element, and only this desired output wave is output to the outside from the output mirror.

Further, according to the second optical wavelength conversion device, the excitation light beam is incident on the outer end face of the solid-state laser crystal from a direction inclined with respect to a direction perpendicular to the outer end face of the resonator. Since it is adjusted, the reflection of the excitation light beam from the outer end face does not become a specular reflection, so that this reflected light can be prevented from returning to the excitation light source and causing noise.

Further, according to the third optical wavelength converter, the incident angle α of the fundamental wave laser beam of the desired output light with respect to the resonator inner end face of the solid-state laser crystal is set to be the Brewster angle. The fundamental wave laser beam is adjusted so as to be P-polarized with respect to the inner end face, and all of the fundamental wave laser beam enters from the inner end face,
Since it does not have a component that reflects, it is possible to make the reflectance at this inner end face substantially zero without forming an antireflection film on this inner end face.

Further, according to the fourth optical wavelength conversion device, the solid laser crystal is a YAG laser crystal and the optical wavelength conversion element is a KNbO ₃ crystal (KN element).

When the YAG laser crystal is excited with excitation light having a predetermined wavelength, laser light having a wavelength of 1064 nm, 946 nm or the like is generated. When this is passed through the KN element, second harmonics of 532 nm, 473 nm, etc. are output, and visible light of a short wavelength can be obtained by selectively extracting this from the output mirror. However, the light of 1064 nm and the light of 946 nm are close to each other in wavelength, and it is difficult to surely oscillate one of the desired ones by devising the coating on the mirror.

In the present apparatus, the solid-state laser crystal is formed in a wedge shape, and the inclination thereof is adjusted so that only the laser light of the desired wavelength is specularly reflected by the resonator outer end face of the solid-state laser crystal. As described above, even when a plurality of laser beams having wavelengths close to each other are generated, only the laser beam having the desired wavelength can be easily oscillated.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a laser oscillation device equipped with an optical wavelength conversion device according to an embodiment of the present invention.

This laser oscillator is a semiconductor laser (L
D) 11, a focusing rod lens 12 for focusing the excitation laser light (wavelength 809 nm) output from the semiconductor laser (LD) 11, and the focused excitation laser light, and the laser light is emitted. Is provided with an optical wavelength conversion device (resonator) 16 that outputs different desired short wavelength laser beams.

The optical wavelength converter 16 resonates the wedge-shaped Nd-doped YAG laser crystal 13 irradiated with the excitation laser light by the focusing rod lens 12 and the laser light output from the YAG laser crystal 13. The output mirror 14 and the end face mirror formed on the pumping laser light incident end face (hereinafter referred to as the first end face) 13A of the YAG laser crystal 13 and the fundamental wave are input and the second harmonic is output. KNbO ₃ crystal (hereinafter K
(Referred to as N element) 15.

The YAG laser crystal 13 is end-face excited by a laser beam for excitation having a wavelength of 809 nm, and has a wavelength of 1064 nm or 946 n.
Outputs multiple m laser beams. The plurality of output laser beams are reflected by the output mirror 14, and the wavelength between the output mirror 14 forming the resonator mirror and the end face mirror on the first end face 13A of the YAG laser crystal 13 is changed.
It is configured so that only the 946 nm laser beam oscillates.

The oscillated laser beam having a wavelength of 946 nm is used as the second incident light by the KN element arranged in the resonator 16.
It is converted to a laser beam with a wavelength of 473 nm, which is a harmonic wave.

Since the output mirror 14 is constructed to have a coating property of transmitting only light having a wavelength near 473 nm, only the laser beam having a wavelength of 473 nm is output from the output mirror 14.

By the way, in the apparatus of this embodiment, as described above, only the laser light of wavelength 946 nm out of the laser light of plural wavelengths outputted from the YAG laser crystal 13 oscillates. This principle will be described with reference to FIG. 2 showing an enlarged YAG laser crystal 13.

That is, in FIG. 2, a YAG laser crystal
A plurality of laser lights having different wavelengths, which are output from the output mirror 13 and reflected by the output mirror 14, pass through the path 21 or a path parallel to this path, and the inner end face (hereinafter referred to as the second end face) 13B to the YAG laser crystal. Reincident on 13.

The path 21 is inclined by an angle α with respect to the normal line 22 of the second end surface 13B. Therefore, the incident angle of the laser light when re-incident on the YAG laser crystal 13 is α.

As described above, the YAG laser crystal 13 is formed at the incident angle α.
Since the plurality of laser lights having different wavelengths incident on the laser light have different refractive indices depending on the wavelengths, they have different refraction angles.

On the other hand, light is emitted from the air into the YAG laser crystal 13
When incident on the inside, sin α = ns in θ (1) holds according to Snell's law.

(However, the refractive index of the YAG laser crystal 13 with respect to the incident light is n (a variable of the incident light wavelength), the incident angle is α,
Let the refraction angle be θ. ) Therefore, even if a plurality of laser beams having different wavelengths enter the YAG laser crystal 13 from the second end face 13B at the same incident angle α, the refractive index n of the YAG laser crystal 13 changes depending on the wavelength. θ (that is, the path of the laser beam after re-incident) is all different depending on the wavelength.

Here, in order for the laser light generated by the YAG laser crystal 13 to oscillate, it is necessary to satisfy the condition that at least mirrors at both ends of the resonator are specularly reflected. Of the incident laser light, only the laser light perpendicularly incident on the end face mirror of the first end face 13A oscillates.

Therefore, the refraction angle of the laser light of the wavelength to be oscillated (laser light of 946 nm in this embodiment) is the wedge angle of the YAG laser crystal 13 (intersection angle between the first end face 13A and the second end face 13B).
The second end face 13 with respect to the path 21 should be equal to θ _1.
By adjusting the inclination of B, only the laser light of the desired wavelength can be specularly reflected by the end face mirror of the second end face 13A, and this desired wavelength can be oscillated.

With the above-described structure, in the present embodiment, the return reflectance of the laser light having a wavelength of 1064 nm, which is extremely close to 946 nm in wavelength, is substantially reduced, so that the wavelength of 946 n
It is possible to oscillate m laser light.

Further, the YAG laser crystal shown in FIG.
By setting the incident angle α of the re-incident light on the second end face 13B of 13 at Brewster's angle, and adjusting the polarization so that the laser light with a wavelength of 946 nm becomes P-polarized with respect to this second end face 13B, This second end face 13B of this laser light of wavelength 946 nm
It is also possible to prevent reflections at. This eliminates the need to apply a thin film coating such as an antireflection film on the second end surface 13B.

On the other hand, in FIG. 2, a semiconductor laser (LD)
The excitation laser light from 11 passes through the path 24 and the first end face 13A
Then, it enters the YAG laser crystal 13. At this time, the laser light for excitation does not vertically enter the first end face 13A, but the position where the YAG laser crystal 13 is arranged may be adjusted so as to enter from the direction inclined from the normal 25 of the first end face 13A. It is possible.

As a result, the reflected light of the excitation laser light from the first end face 13A does not return to the incident path 24 as it is and is reflected in a different direction, so that this reflected light is emitted from the semiconductor laser (LD) 11 It is possible to prevent an increase in noise of the semiconductor laser (LD) 11 due to the returning light without the risk of returning to the above.

Since the beam spot of the laser light from the semiconductor laser is generally elliptical, it can be adjusted by adjusting the direction perpendicular to the plane of the paper of FIG. It is also possible to assist in shaping the spot shape of the excitation laser beam.

The optical wavelength conversion device of the present invention is not limited to the above-mentioned embodiment, but can be modified to various other modes.

For example, in the above-mentioned embodiments, the YAG laser crystal is used as the solid-state laser crystal and the KNbO ₃ crystal is used as the light wavelength conversion element, but instead of this, NVO-doped YVO ₄ or the like is used as the solid-state laser crystal. Other laser crystals, or as a light wavelength conversion element KT
Other optical wavelength conversion elements such as P, KDP, BBO, LBO, and UREA can be used.

Also, as the laser light to be oscillated, 946 nm
The wavelength is not limited to the above wavelength, and laser light of other wavelengths can of course be used.

Further, the incident angle of the excitation light beam to the solid-state laser crystal is defined as the Brewster angle with respect to this incident surface,
In addition, it is preferable that the excitation light beam is P-polarized on the incident surface because the reflectance on the incident surface can be substantially zero.

In the above-described embodiment, both the first end face 13A and the second end face 13B are tilted in the same direction with respect to the plane perpendicular to the excitation light beam.
Of course, it does not matter if the two end surfaces 13A and 13B are tilted in different directions with respect to the vertical surface.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example in which an optical wavelength conversion device according to an embodiment of the present invention is applied.

FIG. 2 is a schematic view showing an enlarged YAG laser crystal of the device shown in FIG.

FIG. 3 is a schematic diagram showing a conventional technique.

[Explanation of symbols]

 1,11 Semiconductor laser 3,13 YAG laser crystal 3A, 13A First end face 13B Second end face 4,14 Output mirror 5,15 KN element 16 Optical wavelength converter (resonator)

Claims (4)

[Claims] 1. A laser cavity 2 of a solid-state laser.
An optical wavelength conversion element is arranged between two mirrors, and an optical wavelength of the two optical mirrors is formed by processing the end face of the solid-state laser crystal on the outer side of the cavity of the pumping light beam incident side mirror. In the conversion device, the solid-state laser crystal has a wedge shape in which the outer end surface and an inner end surface facing the outer end surface intersect each other, and the inclination of the solid-state laser crystal is generated by the solid-state laser crystal. An optical wavelength conversion device, characterized in that a fundamental wave laser beam of a desired output wave that reciprocates between two mirrors is adjusted so as to be specularly reflected inside the outer end face. 2. The tilt of the solid-state laser crystal is adjusted so that the pumping light beam is incident on the outer end face from a direction inclined with respect to a direction perpendicular to the outer end face. The optical wavelength conversion device according to claim 1. 3. The solid-state laser crystal so that an incident angle α of the fundamental wave laser beam with respect to the inner end face becomes a Brewster angle and the fundamental wave laser beam becomes P-polarized with respect to the inner end face. The optical wavelength conversion device according to claim 1 or 2, wherein the inclination of is adjusted. 4. The solid-state laser crystal is a YAG laser crystal (Nd-doped), and the optical wavelength conversion element is KNbO.
The optical wavelength conversion device according to claim 1, wherein the optical wavelength conversion device is composed of _three crystals.