JP4849417B2 - Wavelength conversion device and wavelength conversion laser device - Google Patents

Description

  The present invention relates to a wavelength conversion device that converts the wavelength of a laser using a nonlinear optical crystal, and a wavelength conversion laser device using the wavelength conversion device.

  A conventional wavelength conversion device includes a light source having a predetermined wavelength and two identical nonlinear optical crystals. In these two identical nonlinear optical crystals, the three crystal axis directions are exactly the same, and the c-axis of only one crystal is rotated 180 degrees around the light traveling direction (the direction in which phase matching is satisfied). It arrange | positions so that a state may be taken (for example, refer patent document 1).

  Further, another conventional wavelength conversion device processes a nonlinear optical material into a layer below an effective crystal with an orientation having a phase matching angle with respect to a laser wavelength to be used, and each layer is rotated 180 degrees with respect to the optical axis of incident laser light. The layers are laminated while being rotated and integrated (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 3-100630 JP-A-6-265950

However, the prior art has the following problems.
In such a conventional wavelength conversion device, as described above, two identical nonlinear optical crystals have the same three crystal axis directions, and only one crystal has the c axis as the center of the light traveling direction. It was arrange | positioned so that it might take the state rotated 180 degree. That is, the direction of the walk-off effect that occurs inside the nonlinear optical crystal is arranged in the opposite direction.

  Therefore, when a lens is disposed between two nonlinear optical crystals, the overlap between the fundamental laser beam and the harmonic laser beam generated in the preceding nonlinear optical crystal is reduced inside the latter nonlinear optical crystal. As a result, there has been a problem that the wavelength conversion efficiency in the preceding nonlinear optical crystal is lowered.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a wavelength conversion device and a wavelength conversion laser device that can obtain high wavelength conversion efficiency and a beam having a shape close to a circle. It is said.

  The wavelength conversion device according to the present invention has two nonlinear optical crystals for wavelength conversion and a lens disposed between the two nonlinear optical crystals, and generates a harmonic laser beam of the fundamental laser beam. In the conversion device, two nonlinear optical crystals are arranged in series, and the directions of the respective walk-offs generated in the two nonlinear optical crystals are the same as the optical axis of the fundamental laser beam, and are arranged in the subsequent stage. The optical crystal is arranged at a position away from the lens position from the focal length of the lens.

  According to the present invention, the two nonlinear optical crystals and the two nonlinear optics are increased so that the overlap between the fundamental laser beam and the harmonic laser beam generated in the preceding nonlinear optical crystal is increased in the latter nonlinear optical crystal. By devising the arrangement of the lenses between the crystals, it is possible to provide a wavelength conversion device that can obtain high wavelength conversion efficiency and a beam having a shape close to a circle.

  Hereinafter, preferred embodiments of a wavelength conversion device and a wavelength conversion laser device of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a side view of a wavelength conversion laser device including a wavelength conversion device and a laser light source according to Embodiment 1 of the present invention. Moreover, FIG. 2 is the elements on larger scale of the wavelength converter in Embodiment 1 of this invention. More specifically, FIGS. 2A, 2B, and 2C are enlarged views of the nonlinear optical crystal portion for wavelength conversion of the wavelength conversion device included in the wavelength conversion laser device of FIG. It is the top view, side view, and perspective view which show.

  The wavelength conversion laser device in FIG. 1 includes a laser light source 2 that generates a fundamental laser beam 3 and a wavelength conversion device. The wavelength conversion device reflects two wavelength conversion nonlinear optical crystals (hereinafter also referred to as wavelength conversion crystals) 1A and 1B, two lenses 6A and 6B, and the fundamental laser beam 3 arranged in series. And a separation mirror 8 that transmits the harmonic laser beam 3B.

  In such a wavelength conversion device, the laser beam is condensed on each of the two wavelength conversion crystals 1A and 1B by the lenses 6A and 6B, respectively, and wavelength-converted.

  The two wavelength conversion crystals 1A and 1B are arranged in series with respect to the optical axis of the laser light source 2 on the temperature controllers 4A and 4B, respectively. The two lenses 6A and 6B are disposed on the lens holders 7A and 7B, respectively. Further, the separation mirror 8 is disposed on the mirror holder 9. Further, the laser light source 2, the temperature controllers 4 </ b> A and 4 </ b> B, the lens holders 7 </ b> A and 7 </ b> B, and the mirror holder 9 are arranged on a common base 5.

The laser light source 2 uses, for example, Nd: YAG (Neodymium Yag) or Nd: YVO ₄ (Neodymium Wi-Fi) as an active medium, and generates a fundamental wave laser beam 3 having a wavelength of 1064 nm with linear polarization. The two wavelength conversion crystals 1A and 1B are made of nonlinear optical crystals such as lithium borate (chemical formula: LiB ₃ O ₅ , abbreviation: LBO), for example.

  Next, the operation of the wavelength conversion laser device shown in FIG. 1 will be described. A fundamental laser beam 3 generated from the laser light source 2 and serving as a fundamental wave for wavelength conversion is condensed by the lens 6A so as to have a beam waist inside the wavelength conversion crystal 1A with an appropriate beam diameter. Further, the condensed fundamental wave laser beam 3 is incident on the wavelength conversion crystal 1 </ b> A disposed in the preceding stage.

  By adjusting the temperature of the wavelength conversion crystal 1A by the temperature controller 4A, the fundamental wave laser beam 3 incident on the wavelength conversion crystal 1A satisfies the phase matching condition, and a part of the fundamental wave laser beam 3 is 2 It becomes a harmonic laser beam 3A composed of a double harmonic wave converted into a double harmonic wave.

  The fundamental laser beam 3 and the second harmonic laser beam 3A that have passed through the wavelength conversion crystal 1A are condensed by the lens 6B with an appropriate beam diameter so as to have a beam waist inside the wavelength conversion crystal 1B. Then, the condensed fundamental wave laser beam 3 and the second harmonic laser beam 3A are incident on the wavelength conversion crystal 1B disposed in the subsequent stage.

  By adjusting the temperature of the wavelength conversion crystal 1B by the temperature controller 4B, the fundamental wave laser beam 3 and the second harmonic laser beam 3A incident on the wavelength conversion crystal 1B satisfy the phase matching condition, and thus the fundamental wave laser. A part of the beam 3 and the second harmonic laser beam 3A become a harmonic laser beam 3B composed of the third harmonic converted into the sum frequency.

  The fundamental laser beam 3, the second harmonic laser beam 3A, and the third harmonic laser beam 3B that have passed through the wavelength conversion crystal 1B are incident on the separation mirror 8. Of the three incident beams, the fundamental laser beam 3 and the second harmonic laser beam 3A are reflected and incident on a damper or the like not shown in the figure, and only the third harmonic laser beam 3B is reflected. The light is transmitted and taken out of the wavelength conversion laser device.

  Next, the arrangement method of the wavelength conversion crystals 1A and 1B and the lens 6B and the propagation of the laser beam will be described in detail with reference to FIGS. Here, as the laser light source 2, an Nd: YAG (neodymium yag) laser that generates a fundamental laser beam 3 having a wavelength of 1064 nm and linearly polarized light is used.

Further, as the wavelength conversion crystal 1A, lithium borate (chemical formula: LiB ₃ O ₅ , abbreviation: LBO) that converts a part of the fundamental laser beam 3 into a second harmonic laser beam 3A having a wavelength of 532 nm by type 1 phase matching. ) Crystals were used. Further, as the wavelength conversion crystal 1B, a lithium borate that converts a part of the fundamental laser beam 3 and the second harmonic laser beam 3A into a third harmonic laser beam 3B having a wavelength of 355 nm by sum frequency by type 2 phase matching. Crystals were used.

  The fundamental wave laser beam 3 and the triple harmonic laser beam 3B have their optical paths indicated by the optical axes indicated by solid lines, and the double harmonic laser beam 3A has the optical path indicated by the optical axes indicated by broken lines. The wavelength conversion crystals 1A and 1B are arranged so as to be substantially perpendicularly incident on the fundamental laser beam 3.

  In this case, the angle φ from the dielectric principal axis X in the plane consisting of the dielectric principal axis X and the dielectric principal axis Y is perpendicular to the dielectric principal axis Z of the lithium borate crystal that is the wavelength conversion crystal 1A, in the direction of about 11.4 °. A linearly polarized fundamental laser beam 3 having a polarization direction in the direction of the dielectric principal axis Z is passed.

  Here, by adjusting the temperature of the wavelength conversion crystal 1A, the type 1 phase matching condition of the fundamental wave and the second harmonic is satisfied, and a part of the linearly polarized fundamental wave laser beam 3 is wavelength-converted to generate a dielectric. A linearly polarized second harmonic laser beam 3A having an in-plane polarization direction composed of the principal axis X and the dielectric principal axis Y is generated.

  At this time, the second harmonic laser beam 3A is generated within the wavelength conversion crystal 1A by the walk-off effect within the surface 10A where the walk-off effect including the dielectric principal axis X and the dielectric principal axis Y is generated. It occurs at an optical axis that is shifted from the optical axis in the direction of the dielectric principal axis Y. Since the wavefront of the second harmonic laser beam 3A is the same as that of the fundamental laser beam 3, it is stored outside the wavelength conversion crystal 1A. Propagates as an optical axis parallel to the optical axis.

  The fundamental laser beam 3 and the second harmonic laser beam 3A that have passed through the wavelength conversion crystal 1A are collected by the lens 6B and enter the wavelength conversion crystal 1B. The wavelength conversion crystal 1B has a focal length of the lens 6B from the lens 6B so that the laser beam having a beam waist inside the wavelength conversion crystal 1A has a beam waist inside the wavelength conversion crystal 1B again by the lens 6B. It is arranged at a position farther than.

  At this time, the optical axis of the second harmonic laser beam 3A is a fundamental laser beam in a plane composed of the dielectric principal axis X and the dielectric principal axis Y of the wavelength conversion crystal 1A at a position corresponding to the focal length of the lens 6B to the lens 6B. 3 intersects with the optical axis. As a result, the positional relationship between the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A is opposite between the positional relationship before incident on the lens 6B and the positional relationship after incident. It becomes.

  That is, the optical axis of the second harmonic laser beam 3A is on the side of the dielectric principal axis Y of the wavelength conversion crystal 1A from the optical axis of the fundamental laser beam 3 in the plane composed of the dielectric principal axis X and the dielectric principal axis Y of the wavelength conversion crystal 1A. The state where the optical axis of the second harmonic laser beam 3A is closer to the dielectric main axis X side of the wavelength conversion crystal 1A than the optical axis of the fundamental wave laser beam 3 (the positional relationship before incidence). (Positional relationship after incidence).

  Next, the dielectric principal axis X of the lithium borate crystal that is the wavelength conversion crystal 1B is arranged to be in the same direction as the dielectric principal axis Z of the lithium borate crystal that is the wavelength conversion crystal 1A. That is, the surface 10A where the walk-off effect of the wavelength conversion crystal 1A and the surface 10B where the walk-off effect of the wavelength conversion crystal 1B occurs are the same surface, and the direction where the walk-off effect of the wavelength conversion crystal 1A occurs and the wavelength conversion crystal 1B The direction in which the walk-off effect occurs is arranged in the same direction as viewed from the optical axis of the fundamental laser beam 3.

  Therefore, in the plane consisting of the dielectric principal axis Y and the dielectric principal axis Z of the wavelength conversion crystal 1B, the basic of linearly polarized light having the polarization direction of the dielectric principal axis X in the direction where the angle θ from the dielectric principal axis Z is about 42.5 °. The wave laser beam 3 and a linearly polarized second harmonic laser beam 3A having a polarization direction in the dielectric principal axis YZ plane are passed.

  Further, by adjusting the temperature of the wavelength conversion crystal 1B, the type 2 phase matching condition of the fundamental wave, the second harmonic, and the third harmonic is satisfied, so that the fundamental laser beam 3 and the second harmonic laser beam 3A are satisfied. Is partially wavelength-converted to generate a linearly polarized third-harmonic laser beam 3B having a polarization direction in the dielectric principal axis X direction.

  At this time, the second harmonic laser beam 3A has a fundamental wave laser beam 3 in the plane 10B where the walk-off effect consisting of the dielectric principal axis Y and the dielectric principal axis Z is generated inside the wavelength conversion crystal 1B due to the walk-off effect. Propagation along the optical axis deviated from the optical axis in the direction of the dielectric main axis Z. Note that the fundamental laser beam 3 and the third harmonic laser beam 3B do not receive the walk-off effect and propagate in the wavelength conversion crystal 1B coaxially.

  As described above, according to the first embodiment, the front-stage wavelength conversion crystal and the rear-stage wavelength conversion crystal are arranged so that the directions of the walk-off effect generated in the respective wavelength conversion crystals are the same direction. A lens is disposed between the wavelength conversion crystal and the latter wavelength conversion crystal, and the latter wavelength conversion crystal is disposed at a position farther from the lens position than the focal length of the lens.

  By adopting such an arrangement, the positional relationship of the optical axis of the second harmonic laser beam with respect to the optical axis of the fundamental laser beam at the time when the wavelength conversion crystal of the previous stage is emitted, and the incident light enters the wavelength conversion crystal of the subsequent stage. At this time, the positional relationship of the optical axis of the second harmonic laser beam with respect to the optical axis of the fundamental laser beam is reversed.

  Therefore, the optical axis of the second harmonic laser beam is shifted in the direction approaching the optical axis of the fundamental laser beam due to the walk-off effect when passing through the wavelength conversion crystal in the latter stage, and the fundamental harmonic laser beam and the second harmonic. The overlap with the laser beam is increased. As a result, high wavelength conversion efficiency can be obtained and a beam having a shape close to a circle can be obtained.

  In addition, the effect of the wavelength converter of this Embodiment 1 is demonstrated in more detail from the result of a specific experiment example. In the following description, the first experimental example and the second experimental example are shown under different conditions, and the comparison is made.

First Experimental Example The configuration of the first experimental example is the same as that of FIG. 2 described above, and includes an arrangement configuration that is a technical feature of the first embodiment of the present invention. In this first experimental example, an Nd: YAG (Neodymium Yag) laser that oscillates in a Q switch pulse and generates a fundamental laser beam 3 having a wavelength of 1064 nm and linearly polarized light is used as the laser light source 2. The conditions of the fundamental laser beam 3 were an average power of 81 W, a pulse repetition frequency of 50 kHz, a pulse width of 88 ns, and a beam quality M ² ≈1.2.

As the wavelength conversion crystal 1A, a lithium borate (chemical formula: LiB ₃ O ₅ ) crystal that generates a double harmonic by type 1 phase matching and has a length of 15 mm in the laser beam passing direction was used. As the wavelength conversion crystal 1B, a lithium borate (chemical formula: LiB ₃ O ₅ ) crystal that generates a third harmonic by type 2 phase matching and has a length in the laser beam passing direction of 18 mm was used. Furthermore, the dielectric principal axis Z of the wavelength conversion crystal 1A and the dielectric principal axis X of the wavelength conversion crystal 1B are arranged in the same direction.

As the lenses 6A and 6B, fused silica lenses having a focal length of 114.5 mm with respect to the fundamental laser beam 3 were used. The wavelength conversion crystal 1A was disposed at a position 118 mm away from the lens 6A, and the wavelength conversion crystal 1B was disposed at a position 266 mm away from the lens 6B. Further, the 1 / e ² waist radii of the fundamental wave laser beam 3 were 0.085 mm and 0.122 mm, respectively, so that the beam waist was inside the wavelength conversion crystals 1A and 1B.

  As the directions of the wavelength conversion crystals 1A and 1B, the dielectric principal axis Z of the lithium borate crystal which is the wavelength conversion crystal 1A and the dielectric principal axis X of the lithium borate crystal which is the wavelength conversion crystal 1B are in the same direction as shown in FIG. In this arrangement, 21 W was obtained as an average output of the third harmonic laser beam 3B after being separated from the fundamental laser beam 3 and the second harmonic laser beam 3A by the separation mirror 8. The roundness of the beam cross-sectional shape of the third harmonic laser beam 3B was 80% or more.

On the other hand, in the second experimental example, only the direction of the wavelength conversion crystal 1B is different from the first experimental example, and other conditions are the same. That is, the second experimental example corresponds to a case where the directions of the walk-offs generated in the two wavelength conversion crystals 1A and 1B are not the same direction with respect to the optical axis of the fundamental laser beam 3.

  FIG. 3 is a partially enlarged view of the wavelength conversion device in the second experimental example of the first embodiment of the present invention. More specifically, FIGS. 3A, 3 </ b> B, and 3 </ b> C each expand the nonlinear optical crystal portion for wavelength conversion of the wavelength conversion device included in the wavelength conversion laser device of FIG. 1. They are a top view, a side view, and a perspective view.

  As shown in FIG. 3, the dielectric principal axis Z of the wavelength conversion crystal 1A and the dielectric principal axis X of the wavelength conversion crystal 1B are 180 degrees centering on the optical axis of the fundamental laser beam 3 as in the conventional wavelength converter. When the wavelength conversion crystals 1A and 1B were arranged so as to be in the same different directions, the average output of the triple harmonic laser beam 3B was 2.7W. Compared with the results of the first experimental example, the average output obtained was about 87% lower. The roundness of the beam shape of the third harmonic laser beam 3B was 70% or less.

  From the result of the experimental example as described above, in particular, when a lens is arranged between two wavelength conversion crystals, the wavelength conversion device having the arrangement as shown in FIG. 2 described in the first embodiment is used. Thus, it became clear that a high-power wavelength-converted laser beam can be generated with high efficiency and high roundness.

  In the above experimental example, nonlinear optical crystals having a length of 15 mm and a length of 18 mm are used as the wavelength conversion crystal 1A and the wavelength conversion crystal 1B. However, the crystal length is not limited to this.

Embodiment 2. FIG.
In the second embodiment, a further effect will be described when the wavelength conversion crystal 1A arranged in the preceding stage is arranged to be inclined in the direction in which the walk-off occurs with respect to the optical axis of the fundamental wave laser beam 3.

  FIG. 4 is a partially enlarged view of the wavelength conversion device according to Embodiment 2 of the present invention. More specifically, FIGS. 4 (a), 4 (b), and 4 (c) respectively enlarge the nonlinear optical crystal portion for wavelength conversion of the wavelength conversion device included in the wavelength conversion laser device of FIG. They are a top view, a side view, and a perspective view.

  In the second embodiment, the wavelength conversion crystal 1A is disposed with the dielectric main axis Z as a rotation axis and tilted with respect to the optical axis of the fundamental laser beam 3 in a direction in which the walk-off effect occurs. Further, the wavelength conversion crystal 1B is disposed with the dielectric main axis X as a rotation axis and tilted in the direction in which the walk-off effect is generated with respect to the optical axis of the fundamental wave laser beam 3. Since other configurations are the same as those in the first embodiment, differences from the first embodiment will be mainly described below.

  The wavelength conversion crystal 1A is disposed with the dielectric main axis Z as a rotation axis and tilted in a direction in which a walk-off effect occurs with respect to the optical axis of the fundamental laser beam 3 (a direction inclined from the dielectric main axis X toward the dielectric main axis Y). is doing. Accordingly, due to refraction at the end face of the wavelength conversion crystal 1A, the fundamental wave laser beam 3 inside the wavelength conversion crystal 1A is shifted with respect to the optical axis of the fundamental wave laser beam 3 outside the wavelength conversion crystal 1A. Propagates in the direction in which the walk-off effect occurs.

  As a result, the fundamental wave laser beam 3 that has passed through the wavelength conversion crystal 1A and has exited the wavelength conversion crystal 1A has been refracted at the end face of the wavelength conversion crystal 1A, and thus has entered the wavelength conversion crystal 1A. It propagates along an optical axis parallel to the optical axis of the beam 3.

  Further, the second harmonic laser beam 3A inside the wavelength conversion crystal 1A is further in the direction of the dielectric principal axis Y from the optical axis of the fundamental laser beam 3 within the plane composed of the dielectric principal axis X and the dielectric principal axis Y due to the walk-off effect. It occurs with the optical axis deviated. Therefore, the second harmonic laser beam 3A exiting from the wavelength conversion crystal 1A is stored with the same wavefront as that of the fundamental laser beam 3, so that the fundamental laser beam 3 outside the wavelength conversion crystal 1A Propagates along an optical axis substantially parallel to the optical axis.

  As described above, according to the second embodiment, the wavelength conversion crystal in the previous stage is arranged with the dielectric main axis Z as the rotation axis and tilted in the direction in which the walk-off effect is generated with respect to the optical axis of the fundamental laser beam. ing. As a result, the amount of deviation between the optical axis of the fundamental laser beam that has passed through the wavelength conversion crystal in the previous stage and the optical axis of the second harmonic laser beam is the amount of deviation described in the first embodiment. (When the fundamental laser beam is perpendicularly incident on the previous wavelength conversion crystal, the optical axis of the fundamental laser beam and the second harmonic laser beam 3A that have passed through the previous wavelength conversion crystal and exited outside. This is smaller than the deviation from the optical axis.

  Therefore, the amount of deviation between the optical axis of the fundamental laser beam incident on the latter wavelength conversion crystal and the optical axis of the second harmonic laser beam is reduced, and twice that of the fundamental laser beam in the latter wavelength conversion crystal. The overlap of the harmonic laser beams is increased. For this reason, by arranging the wavelength conversion crystal arranged in the front stage to be inclined in the direction in which the walk-off occurs with respect to the optical axis of the fundamental laser beam, higher wavelength conversion efficiency can be obtained with the wavelength conversion crystal in the subsequent stage. In addition, an effect of obtaining a beam having a shape closer to a circle can be obtained.

  The effects of the wavelength converter according to the second embodiment will be described in more detail based on the results of specific experimental examples. In the following description, the third to fifth experimental examples are shown under different conditions, and comparisons are made.

Third Experimental Example The configuration of the third experimental example is the same as that of FIG. 4 described above, and includes an arrangement configuration that is a technical feature of the second embodiment of the present invention. The conditions of the laser light source 2 and the basic laser beam are the same as those in the first and second experimental examples.

As the wavelength conversion crystal 1A, a lithium borate (chemical formula: LiB ₃ O ₅ ) crystal that generates a double harmonic by type 1 phase matching and has a length of 15 mm in the laser beam passing direction was used. As the wavelength conversion crystal 1B, a lithium borate (chemical formula: LiB ₃ O ₅ ) crystal that generates a third harmonic by type 2 phase matching and has a length in the laser beam passing direction of 18 mm was used. Furthermore, the dielectric principal axis Z of the wavelength conversion crystal 1A and the dielectric principal axis X of the wavelength conversion crystal 1B are arranged in the same direction.

  Further, the wavelength conversion crystal 1A is disposed with an inclination of 20 degrees in the direction in which the walk-off effect occurs with respect to the optical axis of the fundamental laser beam 3 outside the wavelength conversion crystal 1A, with the dielectric main axis Z as the rotation axis. Furthermore, the wavelength conversion crystal 1B is disposed with an inclination of 20 degrees in the direction in which the walk-off effect occurs with respect to the optical axis of the fundamental laser beam 3 outside the wavelength conversion crystal 1B, with the dielectric main axis X as the rotation axis.

As the lenses 6A and 6B, fused silica lenses having a focal length of 114.5 mm with respect to the fundamental laser beam 3 were used. The wavelength conversion crystal 1A was disposed at a position 118 mm away from the lens 6A, and the wavelength conversion crystal 1B was disposed at a position 266 mm away from the lens 6B. Further, the 1 / e ² waist radii of the fundamental wave laser beam 3 were 0.085 mm and 0.122 mm, respectively, so that the beam waist was inside the wavelength conversion crystals 1A and 1B.

  The refractive index of the wavelength conversion crystal 1A is about 1.6, and the second harmonic laser beam 3A is generated by the walk-off effect in the wavelength conversion crystal 1A within the dielectric main axis XY plane. It is generated with an optical axis shifted from the optical axis by about 7.03 mrad (milliradian) in the dielectric principal axis Y direction. Therefore, at the emission end of the wavelength conversion crystal 1A, the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A are shifted by 0.1037 mm.

  When the fundamental laser beam 3 and the second harmonic laser beam 3A are passed through the lens 6B, the dielectric principal axis X and the dielectric of the wavelength conversion crystal 1A are located at a position at a focal distance of 114.5 mm from the lens 6B to the lens 6B. In the plane composed of the main axis Y, the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A intersect.

  As a result, the positional relationship between the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A is opposite between the positional relationship before incident on the lens 6B and the positional relationship after incident. It becomes. That is, the optical axis of the second harmonic laser beam 3A is closer to the dielectric principal axis Y side of the wavelength conversion crystal 1A than the optical axis of the fundamental laser beam 3 in the plane composed of the dielectric principal axis X and the dielectric principal axis Y of the wavelength conversion crystal 1A. The state is shifted from the close state to the state in which the optical axis of the second harmonic laser beam 3A is closer to the dielectric main axis X side of the wavelength conversion crystal 1A than the optical axis of the fundamental laser beam 3.

  At the incident end of the wavelength conversion crystal 1B, the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A are incident with a shift of 0.1372 mm. The refractive index of the wavelength conversion crystal 1B is about 1.6, and the second harmonic laser beam 3A is generated by the walk-off effect within the wavelength conversion crystal 1B due to the walk-off effect. Propagation takes place along the optical axis shifted from the optical axis in the direction of the dielectric principal axis Z by about 9.3 mrad. Therefore, in consideration of the beam diameter, the overlap between the optical axis of the fundamental laser beam 3 and the second harmonic laser beam 3A in the wavelength conversion crystal 1B was calculated to be 64.90%.

On the other hand, in the fourth experimental example, a case where only the direction of the wavelength conversion crystal 1A is different from the third experimental example will be described. That is, this fourth experimental example corresponds to the case where the wavelength conversion crystal 1A disposed in the previous stage is disposed in a direction opposite to the direction in which the walk-off occurs with respect to the optical axis of the fundamental laser beam 3. To do.

  FIG. 5 is a partially enlarged view of the wavelength conversion device in the fifth experimental example of Embodiment 2 of the present invention. More specifically, FIGS. 5 (a), 5 (b), and 5 (c) respectively enlarge the nonlinear optical crystal portion for wavelength conversion of the wavelength conversion device included in the wavelength conversion laser device of FIG. They are a top view, a side view, and a perspective view.

  The wavelength conversion crystal 1A is disposed with the dielectric main axis Z as a rotation axis and tilted by 20 degrees in the direction opposite to the direction in which the walk-off effect occurs with respect to the optical axis of the fundamental laser beam 3 outside the wavelength conversion crystal 1A. . Other configurations are the same as those in the first experimental example.

  In this case, at the emission end of the wavelength conversion crystal 1A, the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A are incident with a deviation of 0.1040 mm. At the incident end of the wavelength conversion crystal 1B, the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A are incident with a deviation of 0.1376 mm. From this, in consideration of the beam diameter, the overlap between the optical axis of the fundamental laser beam 3 and the second harmonic laser beam 3A in the wavelength conversion crystal 1B is calculated to be 64.76%. Compared with the experimental example 3, it was about 0.2% lower.

Fifth Experimental Example Further, as another fifth experimental example, as shown in FIG. 2, the wavelength conversion crystal 1A and the wavelength conversion crystal 1B are not inclined and are incident on the fundamental laser beam 3 substantially perpendicularly. The case of arrangement will be described, and a comparison is made with the case where the wavelength conversion crystal 1A arranged in the previous stage is arranged inclined with respect to the optical axis of the fundamental laser beam 3 in the direction in which the walk-off occurs.

  In the case of the fifth experimental example, at the emission end of the wavelength conversion crystal 1A, the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A are incident with a deviation of 0.1055 mm. At the incident end of the wavelength conversion crystal 1B, the optical axis of the fundamental laser beam 3 and the optical axis of the second harmonic laser beam 3A are incident with a deviation of 0.1395 mm. From this, in consideration of the beam diameter, the overlap between the optical axis of the fundamental laser beam 3 and the second harmonic laser beam 3A in the wavelength conversion crystal 1B is calculated to be 64.12%, Compared with the experimental example 3, it was about 1.2% lower.

  From the results of the experimental examples as described above, in particular, when a lens is arranged between two wavelength conversion crystals, the wavelength conversion device having the arrangement configuration shown in FIG. 4 described in the second embodiment is used. As a result, the overlap between the fundamental wave laser beam and the wavelength conversion laser beam inside the wavelength conversion crystal in the latter stage is increased. As a result, it became clear that a high-power wavelength-converted laser beam can be generated with higher efficiency and higher roundness.

  In the above experimental example, nonlinear optical crystals having a length of 15 mm and a length of 18 mm are used as the wavelength conversion crystal 1A and the wavelength conversion crystal 1B. However, the crystal length is not limited to this.

  In the first and second embodiments described above, the case where the fundamental laser beam 3 having linear polarization and a wavelength of 1064 nm is used has been described. However, the polarization and wavelength of the fundamental laser beam 3 are not limited to this, and for example, a randomly polarized fundamental laser beam 3 may be used.

  Further, as the wavelength conversion crystal 1A, a lithium borate crystal that converts a part of the fundamental laser beam 3 into a second harmonic laser beam 3A having a wavelength of 532 nm by type 1 phase matching is used. The case of using a lithium borate crystal that converts the fundamental laser beam 3 and a part of the second harmonic laser beam 3A into a third harmonic laser beam 3B having a wavelength of 355 nm by a sum frequency by two-phase matching is shown. However, the phase matching type, the wavelength of the harmonic laser beam, and the type of crystal are not limited thereto.

  For example, as the wavelength conversion crystal 1A and the wavelength conversion crystal 1B, the same wavelength using a lithium borate crystal that converts a part of the fundamental laser beam 3 into a second harmonic laser beam 3A having a wavelength of 532 nm by type 2 phase matching. The generated wavelength conversion crystal may be used.

  In short, the wavelength conversion crystal 1B is affected by the interaction of the incident two laser beams, and the direction of the walk-off effect generated in the wavelength conversion crystals 1A and 1B in the respective wavelength conversion crystals is on the optical axis. The lens 6B is disposed between the wavelength conversion crystals 1A and 1B, and the wavelength conversion crystal 1B is disposed at a position farther from the lens 6B than the focal length of the lens 6B. Thus, the same effect as in the first and second embodiments can be obtained.

It is a side view of the wavelength conversion laser apparatus provided with the wavelength conversion apparatus and laser light source in Embodiment 1 of this invention. It is the elements on larger scale of the wavelength converter in Embodiment 1 of this invention. It is the elements on larger scale of the wavelength converter in the 2nd experiment example of Embodiment 1 of this invention. It is the elements on larger scale of the wavelength converter in Embodiment 2 of this invention. It is the elements on larger scale of the wavelength converter in the 5th experiment example of Embodiment 2 of this invention.

Explanation of symbols

  1A, 1B nonlinear optical crystal (wavelength conversion crystal), 2 laser light source, 3 fundamental wave laser beam, 3A, 3B harmonic laser beam, 4A, 4B temperature controller, 5 base, 6A, 6B lens, 7A, 7B lens Holder, 8 Separating mirror, 9 Mirror holder, 10A, 10B Surface where walk-off effect occurs, X, Y, Z Dielectric principal axis of nonlinear optical crystal.

Claims (3)

In a wavelength conversion device that includes two nonlinear optical crystals for wavelength conversion and a lens disposed between the two nonlinear optical crystals, and generates a harmonic laser beam of a fundamental laser beam,
The two nonlinear optical crystals are arranged in series, and the walk-off directions generated by the two nonlinear optical crystals are set to the same direction with respect to the optical axis of the fundamental laser beam, and the nonlinear optics is arranged in the subsequent stage. A wavelength conversion device, wherein the crystal is disposed at a position away from a focal length of the lens from a position of the lens. In the wavelength converter of Claim 1,
A wavelength conversion device, wherein the nonlinear optical crystal disposed in the preceding stage is disposed so as to be inclined in a direction in which a walk-off occurs with respect to an optical axis of the fundamental laser beam. The wavelength converter according to claim 1 or 2,
A wavelength conversion laser device comprising: a light source that generates a fundamental laser beam supplied to the wavelength conversion device.

Images