JP2754991B2 - Wavelength converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength converter for stably generating a wavelength-converted laser beam.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a conventional laser beam wavelength converter disclosed in, for example, Japanese Patent Application Laid-Open No. 2-7487. In the figure, reference numerals 1 and 3 denote reflection mirrors, and wavelength-selective optical thin films 10 and 3 whose operation will be described later.
0 is provided. Reference numeral 4 denotes a laser medium, which is a solid-state Nd: YAG (YttriumAluminum Garnet) element, taking a yag laser as an example.
Is a wavelength conversion element, for example, a solid-state element exhibiting a non-linear effect on incident light. For example, when applied to a yag laser, for example, KTP (Potassium Titanyl Phosphate), and 7 is a laser resonance A laser beam generated in the vessel, 8 is an excitation light source for exciting the solid-state element 4 to be a laser medium, for example, a semiconductor laser mainly containing GaAlAs, 80 is excitation light generated from the excitation light source 8, and 9 is excitation light. A condenser lens for condensing the excitation light 80 and guiding it into the solid-state device 4;
Reference numeral 0 denotes a wavelength-selective optical thin film that transmits most of the excitation light 80 and reflects most of the laser beam 7, and 30 transmits most of the harmonic laser beam 70 of the laser beam 7 whose wavelength has been converted by the wavelength conversion element 5. On the other hand, a wavelength-selective optical thin film that reflects most of the fundamental laser beam 7, a wavelength-converted laser beam 70 extracted outside, and an optical substrate 100.

A conventional laser beam wavelength conversion device is configured as described above, and a laser beam generated by a laser medium generated in a solid-state element 4 by an excitation light source 8 is converted into a resonator formed by mirrors 1 and 3. Trapped inside
A high-intensity laser beam 7 is generated in the resonator, the high-intensity laser beam is wavelength-converted by the wavelength conversion element 5 in the resonator, and most of the wavelength-converted laser beam is resonated by the action of the wavelength-selective optical thin film 30. The laser beam 70 is extracted from the mirror 3 to the outside.
It is known that, in order to perform efficient wavelength conversion, it is necessary that the traveling speed of the fundamental laser beam and the wavelength-converted harmonic laser beam in the wavelength conversion element, that is, the phase speed match. , It is expressed that phase matching has been achieved when the condition is satisfied. The phase matching in the wavelength conversion element 5 is performed by using the birefringence of the wavelength conversion element 5, and for example, in the example of FIG.
, And is converted into a harmonic laser beam.

Further, the conventional laser beam wavelength converter is characterized in that a plurality of wavelength conversion elements are used.
The birefringence of the wavelength conversion element is used to achieve phase matching. Such a wavelength conversion element exhibits birefringence in which the refractive index in the direction perpendicular to the crystal axis C1 and the refractive index in the horizontal direction are different.
In this case, the polarization state of the fundamental laser beam is changed by passing through the wavelength conversion element 5. For example, even if the laser beam is incident as linearly polarized light, it is emitted as elliptically polarized light. Fluctuations appear as time fluctuations and unstable operation of the harmonic laser beam. In the above-mentioned conventional example, the crystal axis C2 of the second wavelength conversion element 5 is rotated and arranged, and the two wavelength conversion elements 5
However, the influence of the optical path difference on the laser beam 70 having the polarization components in the vertical direction and the horizontal direction on the paper is canceled.

[0005]

In the conventional laser beam wavelength converter as described above, a change in the polarization state of the fundamental laser beam is prevented by a combination of wavelength conversion elements whose crystal axes are orthogonal to each other. However, in such a configuration, the polarization direction of the harmonic laser beam is not stable, and it is not suitable for the application of the harmonic laser beam that requires a stable linearly polarized laser beam. Referring to FIG. The upper part in FIG. 7 shows the central part of the conventional device, and the lower part shows the polarization state of the laser beam at the locations indicated by A, B, C, and D in the upper part. The fundamental wave laser beam (w) is aligned with the crystal optical axis of the left wavelength
Incline at an angle. The harmonic laser beam (2 w ₁ ) whose wavelength has been converted by the left wavelength conversion element 5 is generated in the direction perpendicular to the crystal axis, that is, in the direction perpendicular to the paper. On the other hand, in the wavelength conversion element 5 on the right side, the crystal axis forms 90 degrees with respect to the wavelength conversion element 5 on the left side, so that the wavelength-converted laser beam (2 w ₂ ) is generated in a direction parallel to the paper surface. . The harmonic laser beam generated in this manner is synthesized at point D and emitted to the outside as elliptically polarized light. The degree of the elliptically polarized light depends on the phase difference between the two, but since the phase difference is affected by the temperature of the wavelength conversion element 5, particularly the temperature, the polarization direction of the harmonic laser beam fluctuates due to the temperature change of the device. There was a problem that it was not stable.

The present invention has been made to solve such a problem, and has as its object to obtain a wavelength-converted laser beam having a stable polarization direction.

[0007]

A wavelength converter according to the present invention arranges the crystal axes of at least one set of wavelength conversion elements in a mutually twisted relationship with respect to the optical axis, and further comprises: A wavelength plate is arranged to rotate the polarization direction of a harmonic laser beam generated by wavelength conversion by one wavelength conversion element and to align the polarization direction by wavelength conversion by the other wavelength conversion element.

Further, it is preferable to provide a polarizing element on the optical path of the laser beam in the laser resonator, for defining the polarization direction of the fundamental laser beam generated from the laser medium.

Further, the laser medium may be constituted by a solid element having a crystal axis.

[0010]

The wavelength plate in the wavelength converter constructed as described above rotates the polarization direction of the harmonic laser beam generated by wavelength conversion by one wavelength conversion element and wavelength conversion by the other wavelength conversion element. Since the polarization direction is generated as a result, a wavelength-converted laser beam with a uniform polarization direction is generated, and a stable laser beam with little fluctuation in the polarization direction can be obtained even when the temperature of the apparatus changes.

Further, if a polarization element for defining the polarization direction of the fundamental wave laser beam generated from the laser medium is provided on the optical path of the laser beam in the laser resonator, the linearly polarized fundamental wave laser beam can be used. Thus, a harmonic laser beam in a linearly polarized state can be obtained more stably.

Further, by using a solid-state device having a crystal axis as a laser medium, a linearly-polarized laser beam is generated from the solid-state device having a crystal axis, and the generated polarization direction of the fundamental laser beam is further stabilized. As a result, A stable harmonic laser beam can be obtained.

[0013]

[Embodiment 1] FIG. 1 is a block diagram showing an embodiment of the present invention, wherein 1, 3, 4, 5, 7, 8, 9, 10, 3
Reference numerals 0, 70, 80, and 100 are exactly the same as those of the above-described conventional apparatus. 2 is a half-wavelength wave plate.

In the laser beam wavelength converter configured as described above, the laser beam generated by the laser medium generated in the solid-state element 4 by the excitation light source 8 is
The laser beam is confined in a resonator constituted by the mirror 1 and the mirror 3, generates a high-intensity laser beam 7 in the resonator, and the high-intensity laser beam is wavelength-converted by the wavelength conversion element 5 in the resonator. Most of the laser beam obtained is taken out of the resonator mirror 3 as a laser beam 70 by the action of the wavelength-selective optical thin film 30. It is known that, in order to perform efficient wavelength conversion, it is necessary that the traveling speed of the fundamental laser beam and the wavelength-converted harmonic laser beam in the wavelength conversion element, that is, the phase speed match. , It is expressed that phase matching has been achieved when the condition is satisfied.
The phase matching in the wavelength conversion element is performed by utilizing the birefringence of the wavelength conversion element. For example, in the example of FIG. 1, the polarization component inclined by 45 degrees with respect to the crystal axis C1 is mainly the wavelength conversion element 5.
, And is converted into a harmonic laser beam. Such a wavelength conversion element 5 exhibits a so-called birefringence in which the refractive index for the polarization component in the direction perpendicular to the crystal axis C1 is different from that for the polarization component in the horizontal direction. In this case, the polarization state of the fundamental laser beam changes as it passes through the wavelength conversion element 5, and for example, even if the laser beam enters as linearly polarized light, it is emitted as elliptically polarized light. Such a change in the polarization state appears as a time change and unstable operation of the harmonic laser beam. In the present invention, as in the prior art, the crystal axis C2 of the second wavelength conversion element is arranged by rotating it by 90 degrees,
The optical path difference is canceled by the difference in the refractive index between the vertical direction and the horizontal direction of the drawing given to the laser beam 70 by the two wavelength conversion elements 5.

Further, in the present invention, the wave plate 2 rotates the polarization direction of the harmonic laser beam generated from the wavelength conversion element 5 on the left side in FIG. The beam is aligned with the polarization direction of the beam so that a linearly polarized harmonic laser beam 70 is generated outside. FIG. 2 will be described. The upper part in the figure is a drawing of the central part of the present invention, and the lower part is A, B, C, D in the upper part.
Represents the polarization state of the laser beam at the location indicated by. The fundamental laser beam (w) is incident at a point A at an angle of 45 degrees with the crystal optical axis of the wavelength conversion element 5 on the left side. The laser beam (2 w ₁₎
Occurs in a direction perpendicular to the crystal axis, that is, in a direction perpendicular to the plane of the paper. The crystal axis of the wave plate 2 is set to the polarization direction of the fundamental laser beam that has passed through the wavelength conversion element 5. Therefore, the fundamental laser beam is not disturbed by the wave plate 2 and its polarization direction is hardly disturbed. The light enters the wavelength conversion element 5. On the other hand, the harmonic laser beam has a polarization direction inclined by 45 degrees with respect to the fundamental laser beam, and is incident on the wave plate 2 in a polarization direction inclined by 45 degrees with respect to the crystal axis of the wave plate 2. The light is rotated in the direction, and enters the wavelength conversion element 5 on the right side with a polarization component parallel to the paper surface. In the wavelength converter 5 on the right side, the crystal axis is the wavelength converter 5 on the left side.
Wavelength-converted laser beam (2 w ₂ ) is generated in the direction parallel to the plane of the drawing in the same direction as the polarization direction of the harmonic laser beam generated by the left wavelength conversion element 5. The harmonic laser beams generated from each wavelength conversion element 5 in this manner are combined at point D and emitted to the outside as linearly polarized light.

Embodiment 2 FIG. When the combination of the wavelength conversion element 5 and the wavelength plate 2 is installed in a resonator as shown in FIG. 1, the polarization direction of the fundamental wave laser beam incident on the wavelength conversion element 5 is changed as shown in FIG. Conversion elements 5 and 45
If the polarizing element 6 made of glass set in the degree direction, for example, Brewster angle is set in the resonator, the operation is stabilized.

Embodiment 3 FIG. In the above embodiment, the solid-state element 4 serving as the laser medium is assumed to be isotropic, and no particular assumption of the crystal axis is made. However, if a solid-state element having a crystal axis, for example, YLF (Yttrium Lithium Fluoride) is used, Thus, a linearly polarized fundamental laser beam is stably generated, and as a result, a stable harmonic laser beam is obtained.

Embodiment 4 FIG. In the above embodiment, an example in which two wavelength conversion elements 5 are used has been described. However, for example, as shown in FIG.

Embodiment 5 FIG. When the wavelength conversion element 5 and the wavelength plate 2 are bonded to each other as shown in FIG. 5, the temperatures of the elements become the same, and the operation with respect to the temperature change becomes more stable.

Embodiment 6 FIG. In the above embodiment, the plurality of wavelength conversion elements 5 are described as having a crystal axis of 90 degrees with each other. However, the invention is not limited to 90 degrees, and an effect is obtained if the crystal axes are twisted with each other.

Although not particularly described in any of the above embodiments, a non-reflective thin film as in a normal optical element is applied to a part of the optical element, which is not particularly indicated, and a part through which a laser beam passes, as in the case of an ordinary optical element. If done, the loss in the resonator will decrease,
Efficient wavelength conversion can be realized.

[0022]

As described above, according to the present invention, the crystal axes of at least one set of wavelength conversion elements are arranged in a twisted relationship with respect to the optical axis, and one wavelength conversion element is disposed between the wavelength conversion elements. A wavelength plate is arranged so as to rotate the polarization direction of the harmonic laser beam generated by the wavelength conversion by the conversion element and to make the polarization direction generated by the wavelength conversion by the other wavelength conversion element. The polarization directions of the harmonic laser beams are uniform, and there is an effect that a stable laser beam is obtained with little change in the polarization direction even if the temperature of the apparatus changes.

Further, by providing a polarizing element on the optical path of the laser beam in the laser resonator for defining the polarization direction of the fundamental laser beam generated from the laser medium, the harmonic laser beam in a linearly polarized state can be stably formed. Obtainable.

Further, when the laser medium is constituted by a solid-state element having a crystal axis, the generated polarization direction of the fundamental laser beam is further stabilized, and as a result, a stable harmonic laser beam can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an operation of the wavelength conversion device according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram showing a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram showing a conventional wavelength converter.

FIG. 7 is an explanatory diagram showing an operation of a conventional wavelength converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reflection mirror 2 Wave plate 3 Reflection mirror 4 Solid-state element 5 Wavelength conversion element 6 Polarization element 7 Laser beam 70 Laser beam

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuki Kuba 8-1-1, Tsukaguchi-Honmachi, Amagasaki City Mitsubishi Electric Corporation Central Research Laboratory (58) Field surveyed (Int. Cl. ⁶ , DB name) H01S 3 / 109

Claims (3)

(57) [Claims] 1. A device for generating a harmonic laser beam by arranging a plurality of wavelength converting elements in a laser resonator constituted by a combination of a laser medium and a laser mirror, wherein at least one set of the wavelength converting elements is used. The crystal axes are arranged in a twisted relationship with respect to the optical axis, and the polarization direction of a harmonic laser beam generated by wavelength conversion by one of the wavelength conversion elements is rotated between the wavelength conversion elements. And a wavelength conversion device, wherein a wavelength plate is provided which is aligned in a polarization direction generated by wavelength conversion by the other wavelength conversion element. 2. A wavelength conversion device according to claim 1, wherein a polarization element for defining a polarization direction of a fundamental wave laser beam generated from a laser medium is provided on an optical path of the laser beam in the laser resonator. . 3. The wavelength conversion device according to claim 1, wherein the laser medium comprises a solid-state element having a crystal axis.