JP3634164B2 - Multipath wavelength conversion method and apparatus for laser light - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength conversion method for efficiently converting wavelengths of various lasers used for excitation light sources such as tunable lasers and ultrashort pulse lasers, laser processing, etc. into wavelengths according to the purpose of use using a nonlinear crystal. And the apparatus.
[0002]
[Prior art]
In the conventional wavelength conversion method, laser light is incident on the nonlinear crystal only once, and the laser light that has been wavelength-converted and the laser light that has not been converted are separated by an optical system such as a prism or a separator (dichroic mirror). The unconverted laser light is not used thereafter. In general, in order to increase the wavelength conversion efficiency, the incident laser light is condensed by a lens or the like to increase its intensity and enter the nonlinear crystal. However, the conversion efficiency depends on beam quality such as laser beam mode, beam spread, wavelength width, pulse time waveform, and nonlinear crystal constants, crystal quality, crystal length, and other conditions. Even so, the conversion efficiency is saturated to some extent.
[0003]
As a method for increasing the conversion efficiency, it is also conceivable to separate the laser light that has not been converted and then perform wavelength conversion using another nonlinear crystal. However, in this case, a plurality of nonlinear crystals are required. Furthermore, since the converted laser beams become separate beams, it is necessary to combine these laser beams that have undergone wavelength conversion in order to obtain a single beam. However, it is impossible with the current technology to combine these wavelength-converted laser beams into a single beam with the same polarization and no loss.
[0004]
Furthermore, a method of using a resonator to resonate the incident laser light with this resonator and increasing the conversion efficiency is also conceivable. However, in this method, the laser light wavelength that can resonate with the resonator is a single wavelength and the beam quality is low. A good laser beam and a feedback device to keep the resonance state are required.
[0005]
[Problems to be solved by the invention]
In the conventional wavelength conversion method, there is a limit to the conversion efficiency in order to obtain wavelength-converted laser light as a single beam with the polarizations aligned. In addition, depending on the system, the applicable range is limited, such as requiring a system such as a feedback device or being largely dependent on the beam quality of incident laser light.
[0006]
The present invention provides a wavelength conversion method and apparatus for performing wavelength conversion with higher efficiency than those of the conventional wavelength conversion methods with a simple apparatus configuration using a commercially available optical system.
[0007]
[Means for Solving the Problems]
The above-mentioned problems include a step of wavelength-converting incident laser light with a type I nonlinear crystal, a step of separating the laser light wavelength-converted and the laser light not wavelength-converted in the wavelength conversion step, and the separation The laser light which has not been wavelength-converted is re-incident on the same type I nonlinear crystal once from the oblique direction with respect to the incident laser light, and the incident laser light and the type I nonlinear crystal are obliquely directed. In the type I nonlinear crystal, the size of the incident and re-incident laser light on the refractive index curved surface is the same, and the incident and re-incident laser A vector represented by a perpendicular from the origin on the refraction surface with respect to a line connecting the tips of the respective vectors of light is the wavelength. Is solved by the multi-pass wavelength conversion method of the laser light and having a conversion is vector become conditions on the refractive index curved surface of the laser beam.
[0008]
The above-described problem also includes a type I nonlinear crystal that converts the wavelength of incident laser light, means for separating laser light that has not been wavelength-converted in the nonlinear crystal from laser light that has undergone wavelength conversion, and means for separating the laser light. The laser light that has not been wavelength-converted and is re-incident on the same type I nonlinear crystal once from the oblique direction with respect to the incident laser light, and in the incident laser light and the type I nonlinear crystal. The type I nonlinear crystal has the same size on the refractive index curved surface of the incident and re-incident laser light, and the incident and re-incident laser light. A vector represented by a perpendicular from the origin on the refraction surface with respect to a line connecting the tips of the vectors is converted to the wavelength-converted laser beam. Is solved by the multi-pass wavelength converter of the laser light and having a condition which is a vector on the refractive index curved surface of over light.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0010]
FIG. 1 shows an embodiment of a preferred system using the wavelength conversion method of the present invention. FIG. 2 is a view of the light axis direction (that is, crystal axis) direction of the nonlinear crystal and the polarization of the fundamental wave laser beam and the second harmonic laser beam from the incident direction in the system shown in FIG. In the system shown in FIG. 1, a type II crystal is used as the nonlinear crystal, and the fundamental laser beam of the laser is wavelength-converted to the second harmonic in two passes. In the case of using a type II crystal, the polarization of the fundamental wave laser beam is converted by combining two laser beams perpendicular to each other in the normal ray axis and the extraordinary ray axis direction of the non-linear crystal. Is incident with a single laser beam tilted at 45 ° with respect to the nonlinear ray axis. When the components of polarized light in the normal ray axis direction and extraordinary ray axis direction are divided, it is utilized that it is equivalent to a combination of two laser beams having mutually perpendicular polarized light.
[0011]
In FIG. 1, reference numeral 10 indicates a laser beam multipath wavelength converter according to an embodiment of the present invention. The multipath wavelength converter 10 includes a polarizer 12 to which the laser beam emitted from the laser device 100 is incident, a nonlinear crystal 14 that converts the laser beam that has passed through the polarizer 12 to a second harmonic, and the nonlinear crystal 14. Separator 16 that separates the fundamental laser beam that has not been converted and the second harmonic laser beam that has been converted, and the fundamental laser beam separated by the separator 16 is made into a laser beam having a predetermined polarization and is incident on polarizer 12. A 45 ° incidence mirror 18, a λ / 4 wavelength plate 20, a λ / 2 wavelength plate 22, and a 45 ° incidence mirror 24.
[0012]
The operation of the laser beam multipath wavelength converter 10 shown in FIG. 1 will be described with reference to FIGS. The vertically polarized beam (fundamental laser beam) 30 emitted from the laser device 100 passes through the polarizer 12 as it is (see 32a in FIG. 1). The polarizer 12 also has a role for combining the horizontally polarized fundamental wave laser beam 32 b that has not been wavelength-converted in the first pass and re-entering the nonlinear crystal 14. The ordinary ray axis o and the extraordinary ray axis e of the nonlinear crystal 14 are arranged so as to be inclined by 45 ° with respect to the polarization direction of the fundamental laser beam. As described above, the relationship between the polarization and the nonlinear ray axis is shown in FIG. 2, which is a view seen from the incident direction of the laser beam. The fundamental wave incident laser beam 32a and the reentered fundamental wave laser beam 32b are converted into the second harmonic by the nonlinear crystal 14, respectively, while the second harmonic laser beam 34 is as shown in FIGS. Both are polarized in the direction of the extraordinary ray axis e of the nonlinear crystal 14. The fundamental wave that has passed through the nonlinear crystal 14 becomes elliptically polarized light 36 as shown in FIG. 1 due to the difference in phase velocity between the ordinary ray axis o and the extraordinary ray axis e of the nonlinear crystal 14. The separator 16 separates the second harmonic laser light 34 and the fundamental wave laser light 36 that has not been wavelength-converted. The second harmonic laser light 38 travels straight as one beam, and the fundamental laser light 36 is separated from the separator 16. 16 is reflected. The reflected fundamental laser beam 40 is turned back by the 45 ° incidence mirror 18 and then corrected to the linearly polarized light 42 by the incoming quarter-wave plate 20. However, since the polarization direction is inclined, the fundamental laser beam that has been further rotated by the input / 2 wavelength plate 22 and not wavelength-converted in the first pass was not wavelength-converted in the horizontal direction 44a even in the second pass. The fundamental laser beam is a laser beam polarized in the vertical direction 44b. Further, the fundamental laser light reflected by the 45 ° incidence mirror 24 is combined with the fundamental incident laser light 30 by the polarizer 12, and the laser light of the horizontally polarized light 46 a that has not been wavelength-converted in the first pass is combined with the nonlinear crystal 14. Re-incident with an angular relationship as shown in FIG. The fundamental laser beam of the vertically polarized light 46b that has not been wavelength-converted even in the second pass passes through the polarizer 12 and becomes a laser beam 48 that is not used.
[0013]
Referring again to FIG. 2, the fundamental laser beams 32 a and 32 b are polarized at 45 ° with respect to the optical axis of the nonlinear crystal 14. The wavelength-converted second harmonic laser beam 34 is all polarized in the direction of the extraordinary ray axis e of the nonlinear crystal, and is obtained as a single beam with uniform polarization.
[0014]
An example implemented using the wavelength conversion system shown in FIG. 1 will be described below. In this example, a KTP type II crystal was used as the nonlinear crystal 14, and an Nd: YAG laser having a fundamental wavelength of 1064 nm was used for the laser device 100. FIG. 3 shows the wavelength conversion characteristics measured using this system. When the output of the fundamental wave incident laser light is increased, the second harmonic obtained also increases. However, when the incident laser light output exceeds 9 mJ, the wavelength conversion efficiency in one pass is almost saturated at about 26%. . On the other hand, when the wavelength conversion is performed with two passes, the conversion efficiency can be improved up to about 37%, and the conversion efficiency is improved by about 1.4 times. This confirmed the effectiveness of the wavelength conversion method of the present invention.
[0015]
Next, another preferred embodiment of the laser beam multipath conversion apparatus of the present invention will be described below with reference to FIG. FIG. 4 shows an example of 4-pass wavelength conversion as another configuration example. In this example, a type II nonlinear crystal is used as the nonlinear crystal. In addition, the feature of this configuration is that the optical axis can be easily adjusted because the laser light is folded back on the same axis. In FIG. 4, the laser beam path 200 is on a straight line, but is divided in the middle due to the size of the drawing. In FIG. 4, reference numeral 50 denotes a laser beam multipath wavelength conversion device according to another embodiment of the present invention. The multipath wavelength converter 50 includes a polarizer 52 to which the fundamental laser beam emitted from the laser device 100 is incident, a Faraday rotator 54 that rotates the polarization of the fundamental laser beam that has passed through the polarizer 52, and the Faraday rotator 54. Λ / 2 wavelength plate 56 for further correcting the polarization of the fundamental laser beam from the polarizer, the polarizer 58 that passes the fundamental laser beam from the λ / 2 wavelength plate 56, and the polarization of the fundamental laser beam from the polarizer 58 A Faraday rotator 60 that rotates the separator, a separator 62 that passes the fundamental laser light from the Faraday rotator 60 and reflects the second harmonic laser light, and converts the fundamental laser light that has passed through the separator 62 into the second harmonic. Nonlinear crystal 64, for polarization correction of fundamental laser beam A λ / 4 wavelength plate 66, a separator 68 that separates the fundamental laser light that has not been converted by the nonlinear crystal 64 and the converted second harmonic laser light, and 0 ° that reflects the fundamental laser light that has not been converted. An incident mirror 70 is included.
[0016]
The operation of the laser beam multipath wavelength converter 50 shown in FIG. 4 will be described with reference to FIGS. FIG. 5 is a view of the direction of the light axis of the nonlinear crystal (that is, the crystal axis) and the polarization of the fundamental laser beam and the second harmonic laser beam as seen from the incident direction. Vertically polarized fundamental wave incident laser light 72 emitted from the laser device 100 passes through a polarizer 52 and a Faraday rotator 54. Since the fundamental laser beam simply passes through the polarizer 52, the fundamental laser beam remains the vertically polarized light 74. The polarization of the fundamental laser beam is rotated by 45 ° by the Faraday rotator 54 (see 76 in FIG. 4), and this is corrected to the vertical polarization 78 by the input / 2 wavelength plate 56. Further, the fundamental laser beam passes through the polarizer 58, the Faraday rotator 60, and the separator 62 that reflects the second harmonic laser beam. At this time, since the fundamental laser beam 78 simply passes through the polarizer 58, the polarization of the fundamental laser beam at the exit of the polarizer 58 remains the vertically polarized light 80. In the Faraday rotator 60, the polarization of the fundamental laser beam is rotated by 45 °, and in the direction indicated by reference numeral 82 in FIG. Since the fundamental laser beam simply passes through the separator 62, it is incident on the nonlinear crystal 64 at the polarization direction indicated by reference numeral 82, that is, the angle of the fundamental laser beam polarization in the first pass shown in FIG. The wavelength is converted into second harmonic laser light. As described above, since the polarization of the fundamental laser beam is rotated 45 ° by the Faraday rotator 60, the ordinary ray axis o and the extraordinary ray axis e of the nonlinear crystal 64 are set to 45 ° with respect to the polarization of the fundamental laser beam. Arrange so that The second harmonic laser light wavelength-converted in the first pass is obtained as a beam 84 polarized in the direction of the extraordinary ray axis e after passing through the fundamental wave laser input quarter-wave plate 66 and the separator 68. On the other hand, the fundamental laser light that has not been wavelength-converted is reflected back by the separator 68 and is incident on the nonlinear crystal 64 again. Since the polarization of the fundamental laser beam is elliptically polarized by the nonlinear crystal 64, the input / 4 wavelength plate 66 in the meantime is used for polarization correction for returning to the original polarization after passing through the folded nonlinear crystal. is there.
[0017]
The angle relationship between the polarization of the folded fundamental wave laser beam, that is, the second-pass fundamental laser beam and each beam axis of the nonlinear crystal 64 is as shown in FIG. Although the wavelength conversion is again performed by the nonlinear crystal 64, the second harmonic laser beam wavelength-converted in the second pass is opposite to the propagation direction of the second harmonic laser beam in the first pass. The second harmonic laser beam is folded and reflected coaxially by the separator 62 and guided toward the second harmonic laser beam 84 in the first pass. The fundamental laser light that has not been wavelength-converted even in the second pass passes through the separator 62 and the Faraday rotator 60. The Faraday rotator 60 turns the polarized light into a horizontally polarized light 86 rotated by 90 ° with respect to the vertical polarization of the incident laser light. And reflected by the polarizer 58 in the direction of the 0 ° incident mirror 70. The fundamental laser beam 88 reflected by the polarizer 58 is reflected back by the 0 ° incidence mirror 70, reflected again by the polarizer 58, and guided to the Faraday rotator 60. The fundamental laser beam that has passed through the Faraday rotator 60 is rotated by 45 ° as in the first pass, but is polarized by 90 ° with respect to the polarization of the incident laser beam (see 90 in FIG. 4). Three times, that is, the third-pass fundamental laser light is incident on the nonlinear crystal 64 and wavelength-converted as shown in FIG. 5 in terms of the angular relationship between the polarization and each ray axis of the nonlinear crystal 64. The second harmonic laser light wavelength-converted in the third pass is emitted from the separator 68 as in the first pass. The fundamental laser beam that has not been wavelength-converted even in the third pass is folded back by the separator 68 as in the first pass, and further wavelength-converted by the nonlinear crystal 64. Note that the angular relationship between the fundamental laser beam that has not been wavelength-converted even in the third pass, that is, the fundamental laser beam in the fourth pass and the beam axis of the nonlinear crystal 64 is as shown in FIG. Accordingly, the second harmonic converted in wavelength in the fourth pass is reflected by the separator 62 as in the second pass, and is emitted from the separator 68 as in the first pass. Fundamental laser light that has not undergone wavelength conversion in the nonlinear crystal 64 even in the fourth pass passes through the Faraday rotator 60 to become vertically polarized light 80, and passes through the polarizer 58, the input / 2 wavelength plate 56, and the Faraday rotator 54. The fundamental laser beam that has passed through the Faraday rotator 54 becomes horizontal polarized light 92, is reflected by the polarizer 52, and becomes a fundamental laser beam 94 that is not used.
[0018]
Referring back to FIG. 5, each fundamental laser beam is polarized at 45 ° with respect to the ray axis of the nonlinear crystal 64. The second harmonic laser light whose wavelength has been converted is all polarized in the direction of the extraordinary ray axis e of the nonlinear crystal, and is obtained as a single beam with uniform polarization.
[0019]
The present invention is not limited to the type II nonlinear crystal and can be applied to type I. FIG. 6 schematically shows a preferred embodiment of a laser multipath wavelength conversion apparatus of the present invention when using type I as a nonlinear crystal. In FIG. 6, reference numeral 200 indicates a laser beam multipath wavelength converter according to an embodiment of the present invention. The multi-pass wavelength converter 200 for laser light includes a non-linear crystal 202 using Type I, mirrors 204 and 206 for guiding the fundamental wave laser light not converted in the first pass to re-enter the non-linear crystal 202, 208 and 210, and a beam damper 212 for receiving the fundamental laser beam that has not been converted in the second pass.
[0020]
In the type I crystal, the polarization of the fundamental laser beam must be polarized in the normal ray axis o (or extraordinary ray axis e) direction of the crystal, but the two beams cannot be coaxially combined with each other. Therefore, in the present embodiment, it is necessary to make the first-pass fundamental laser beam and the second-pass fundamental laser beam incident obliquely to each other. The matching conditions in this case will be described with reference to FIG. FIG. 7 is a diagram for explaining the matching condition in the type I crystal. In the figure, reference numeral 250 indicates the refractive index surface of the extraordinary ray of the second harmonic and has an elliptical shape, and reference numeral 252 indicates the basic. It shows the refractive index surface of the ordinary ray of the wave and has a circular shape. The normal matching method in the type I nonlinear crystal is indicated by the reference numeral 254 in FIG. 7 in the direction in which the refractive index surface 250 of the extraordinary ray of the second harmonic intersects the refractive index surface 252 of the ordinary ray of the fundamental wave. So that the laser beam is incident in the direction. This is because when the laser light is incident in this way, the phase velocity directions of the fundamental laser beam and the second harmonic laser beam coincide. However, in the present invention, as described above, two laser beams cannot be combined on the same axis with the same polarization, and two fundamental laser beams (incident fundamental laser beam, re-incident fundamental laser beam) It is necessary to generate the second harmonic by crossing from the diagonal direction. The matching conditions when the fundamental laser beam is polarized on the ordinary ray axis o and the second harmonic is polarized on the extraordinary ray axis e are as follows. That is, in FIG. 7, the tip of the vector 256 indicating the emission direction of the second harmonic needs to be on the extraordinary ray refractive index surface (ellipse) 250. 7 indicates the incident direction of the first-pass incident fundamental laser beam, vector 260 indicates the incident direction of the second-pass (ie, re-incident) fundamental laser beam, and these two vectors 258. , 260 are on the ordinary refractive index surface (circle) 252. One pass so that the vector 256 is perpendicular to the line connecting the leading ends of the vectors from the origin O to the isosceles triangle formed by the vectors 258, 260 and the lines connecting the leading ends of the vectors. The incident fundamental laser beam of the eye and the second pass (that is, re-incidence) fundamental laser beam may be incident on the nonlinear crystal 202.
[0021]
First-pass fundamental laser light 220 (vector 258 in FIG. 7) and second-pass (re-incident) fundamental laser light 222 (vector 260 in FIG. 7) from the laser device 100 shown in FIG. In order that the ternary relationship with the second harmonic laser beam 224 (vector 256 in FIG. 7) converted and emitted by the type I nonlinear crystal 202 satisfies the above matching condition described with reference to FIG. The mirrors 204, 206, 208 and 210 are arranged.
[0022]
The operation of the laser beam multipath wavelength converter 200 in which the mirrors are arranged in this way will be described. The fundamental laser beam 220 of the first pass from the laser device 100 is incident on the type I nonlinear crystal 202 in the direction of the vector 258 in FIG. The nonlinear crystal 202 converts the incident first-pass fundamental laser light and emits the second harmonic 224 in the direction of the vector 256 in FIG. The fundamental laser beam 226 that has not been converted by the nonlinear crystal 202 is reflected by the mirrors 204, 206, 208, and 210 and reenters the nonlinear crystal 202 in the direction of the vector 260 in FIG. 7. In the non-linear crystal 202, the fundamental laser beam 222 of the first pass and the fundamental laser beam 222 of the second pass incident again are overlapped, and the second crystal 225 is superposed in the same direction as the direction of 224, that is, the direction of the vector 254 in FIG. The second harmonic is emitted. The second-pass fundamental laser beam 228 that has not been converted by the nonlinear crystal 202 is received by the beam damper 212.
[0023]
As can be easily understood from the preferred embodiments of the present invention described above, the basic principle of the present invention is to separate the laser light wavelength-converted from the nonlinear crystal and the laser light not wavelength-converted, and not wavelength-converted. The laser beam is combined with the incident laser beam and re-enters the same non-linear crystal for re-conversion, so that the wavelength conversion efficiency can be increased. In the wavelength conversion method and apparatus of the present invention, the longitudinal mode of the incident laser light may be single mode or multimode, does not require a resonator, does not require a feedback device, and does not need to further add a nonlinear crystal, Since the wavelength-converted laser light is obtained as a single beam with uniform polarization, it is not necessary to combine the wavelength-converted laser beams. In particular, even if the longitudinal mode is a multimode laser beam, the overall wavelength conversion efficiency is improved, and the fact that one wavelength-converted laser beam with uniform polarization is obtained is a remarkable effect of the present invention.
[0024]
In addition, since the laser light that has not been wavelength-converted is re-incident (multipath wavelength conversion) once or more in the same nonlinear crystal, high wavelength conversion efficiency can be expected. Also, if the conversion efficiency in the nonlinear crystal fluctuates and the wavelength conversion efficiency decreases, the laser light that is not wavelength-converted increases, but by returning it to the nonlinear crystal, the fundamental wave laser light output in the crystal is reduced. Increase by minutes. As a result, there is a feedback effect that fluctuations in the output of the laser light subjected to wavelength conversion can be suppressed. That is, the fluctuation of the conversion efficiency is suppressed by the feedback effect, and the wavelength-converted laser light output becomes stable.
[0025]
Further, when the laser beam intensity is not uniform (that is, the intensity of light per unit area on the surface perpendicular to the beam direction is positionally nonuniform), the fundamental laser beam that has not been converted is inverted or By rotating and re-entering the nonlinear crystal and averaging and correcting the laser light intensity distribution in the crystal, it is possible to obtain wavelength-converted laser light having a uniform intensity distribution. That is, laser light with a non-uniform intensity distribution is averaged, and the wavelength-converted laser beam can be made uniform. The means and method for reversing and rotating the beam are well known in the art, and any known beam reversal or rotation technique for reversing or rotating the fundamental laser beam in the present invention. Can be used. For example, in the configuration shown in FIG. 1, in order to invert the beam, the laser beam cross-sectional image inversion means shown in FIG. 8 is used between the separator 16 and the mirror 18, between the mirror 18 and the mirror 24, and between the mirror 24 and the polarizer 12. What is necessary is just to insert between either. The beam reversing means shown in FIG. 8 includes two lenses 300 and 302, and when the laser beam passes, the cross-sectional image is reversed as shown in the figure.
[0026]
Further, for example, in the configuration shown in FIG. 1, in order to rotate the beam, a system for returning the fundamental wave laser beam that is not converted between the separator 16 and the polarizer 12 may be configured as shown in FIG. In FIG. 9, the components with the same reference numerals as those in FIG. 1 are the same as those in FIG. 1, and the description of the functions and the like will not be repeated. In FIG. 9, the mirrors 310, 312, and 314 are arranged such that the fundamental laser beam 320 and the unconverted fundamental laser beam 322 are not on the same plane but are twisted. With this arrangement, the beam cross-sectional image of the fundamental laser beam that has not been converted rotates between the separator 16 and the polarizer 12 while passing through the mirrors 310, 312, and 314. Depending on how the mirrors 310, 312 and 314 are arranged, any desired rotation, such as 90 °, can be obtained.
[0027]
In the configuration of FIG. 4, for example, in order to invert the beam, the configuration shown in FIG. 10 may be used instead of the 0 ° incidence mirror 70 of FIG. In FIG. 4, reference numeral 58 indicates the polarizer 58 of FIG. 4. From the polarizer 58, the Faraday rotator 400, the λ / 2 wave plate 402, the polarizer 404, and the 45 ° incidence mirror 406 are arranged linearly in this order. A pair of lenses 408 and 410 and a 45 ° incidence mirror 412 follow in a perpendicular direction, and λ / 2 wave plates 414 and 45 in a direction perpendicular to a line connecting the 45 ° incidence mirror 406 and the 45 ° incidence mirror 412. An incident mirror 416 is arranged to follow. In FIG. 10, the fundamental laser beam that has returned without being converted enters and reflects from the right side of the polarizer 58 and is reflected toward the Faraday rotator 400. 406 passes through a pair of lenses 408 and 410, a 45 ° incident mirror 412, a λ / 2 wavelength plate 414, and a 45 ° incident mirror 416, and is incident again on the polarizer 404 to be reflected, and the λ / 2 wavelength plate 402 and the Faraday Return to the polarizer 58 through the rotator 400. The reversal of the lens beam cross-sectional image is performed by a pair of lenses 408 and 410 as in FIG. 8, and the polarization of the fundamental laser light entering and returning from the Faraday rotator 400 is shown in FIG. As shown, the Faraday rotator 400 and the λ / 2 wave plates 402 and 414 are provided to be the same.
[Brief description of the drawings]
FIG. 1 shows an embodiment of a preferred system using the wavelength conversion method of the present invention.
FIG. 2 is a view of the light axis direction (ie crystal axis) direction of the nonlinear crystal and the polarization of the fundamental wave laser beam and the second harmonic laser beam as seen from the incident direction in the system shown in FIG.
FIG. 3 is a measurement example of wavelength conversion characteristics implemented using the system shown in FIG. 1 and shows second harmonic output and wavelength conversion efficiency with respect to incident laser light output.
FIG. 4 shows another preferred embodiment of the laser beam multipath conversion apparatus of the present invention.
5 is a view of the direction of the light axis (that is, the crystal axis) of the nonlinear crystal and the polarization of the fundamental laser light and the second harmonic laser light from the incident direction in the system shown in FIG.
FIG. 6 shows still another preferred embodiment of the laser beam multipath conversion apparatus of the present invention.
7 is a diagram for explaining matching conditions in the type I nonlinear crystal of FIG. 6; FIG.
8 is a diagram showing a configuration for inverting fundamental wave laser light that has not been converted in the configuration shown in FIG. 1; FIG.
9 is a diagram showing a configuration for rotating fundamental wave laser light that has not been converted in the configuration shown in FIG. 1; FIG.
10 is a diagram showing a configuration for inverting fundamental wave laser light that has not been converted in the configuration shown in FIG. 4; FIG.
[Explanation of symbols]
10, 50, 200 Laser path multipath wavelength converter
12, 52, 58, 404 Polarizer
14, 64, 202 Nonlinear crystal
16, 62, 68 Separator
18, 24 45 ° incidence mirror
20, 66 λ / 4 wave plate
22, 56, 402, 414 λ / 2 wave plate
54, 60, 400 Faraday rotator
70 ° incidence mirror
100 laser equipment
204, 206, 208, 210, 310, 312, 314 Mirror
212 Beam damper
300, 302, 408, 410 Lens
406, 412, 416 Mirror

Claims (2)

Wavelength converting incident laser light with a type I nonlinear crystal;
Separating the wavelength-converted laser beam and the wavelength-converted laser beam in the wavelength converting step;
The separated laser light which has not been wavelength-converted is re-incident on the same type I nonlinear crystal once from the oblique direction with respect to the incident laser light, and the incident laser light and the type I nonlinear crystal And a step of wavelength conversion by intersecting from the diagonal direction,
In the type I nonlinear crystal, the size of the incident and re-incident laser light on the refractive index curved surface is the same, and the line with respect to the line connecting the tips of the respective vectors of the incident and re-incident laser light A multi-pass wavelength conversion method for laser light, characterized in that a vector represented by a perpendicular from an origin on a refractive curved surface is a vector on a refractive index curved surface of the wavelength-converted laser light. A type I nonlinear crystal that converts the wavelength of the incident laser light;
Means for separating laser light that has not been wavelength-converted in the nonlinear crystal from wavelength-converted laser light;
The laser light separated by the separating means and not wavelength-converted is re-incident on the same type I non-linear crystal once obliquely with respect to the incident laser light, and the incident laser light and the type I Means for crossing in an oblique direction in the nonlinear crystal,
In the type I nonlinear crystal, the size of the incident and re-incident laser light on the refractive index curved surface is the same, and the line with respect to the line connecting the tips of the respective vectors of the incident and re-incident laser light A multi-pass wavelength conversion apparatus for laser light, characterized in that a vector represented by a perpendicular line from the origin on the refractive surface is a vector on a refractive index curved surface of the wavelength-converted laser light.

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