JP2012042808A - Laser wavelength converter and laser wavelength conversion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate for self-heating by a laser and improve a decrease in conversion efficiency at high intensity.
The wavelength conversion nonlinear crystal is driven by driving a first Peltier element based on a detection output from a temperature detector that detects an average temperature rise due to wavelength conversion in the wavelength conversion nonlinear crystal. The average temperature obtained by averaging the temperatures of the entire 10 crystals is controlled, and a drive current having a magnitude corresponding to the amount of the _second harmonic light (L ₂ ) emitted from the emission end face 10 B of the wavelength conversion nonlinear crystal 10 is set to a first value. The second Peltier element 31 generates a heat flow (HC2) that cancels out the temperature gradient in the wavelength converting nonlinear crystal 10 by flowing it through the second Peltier element 31 to control the temperature gradient, and the wavelength taking the phase matching of converting nonlinear crystal 10, the emitted second harmonic wave light (L ₂₎ light quantity of said frequency converting nonlinear crystal 10 to a temperature of maximum average temperature of the first of Controlled by Peltier elements 21.
[Selection] Figure 2

Description

  The present invention relates to a laser wavelength conversion apparatus and a laser wavelength conversion method for generating laser light having a wavelength different from a fundamental wave in a propagation direction by making laser light incident on a wavelength conversion nonlinear crystal having a periodic polarization structure.

  Coherent light sources are indispensable not only in the optical communication field, but also in the medical field and the measurement field such as a microscope. As for the wavelength of coherent light, various wavelengths are being used depending on the purpose in the medical field, for example.

  Various laser oscillators such as semiconductor lasers and solid-state lasers are known as light sources for coherent light, but there are some which cannot be obtained directly from the laser oscillator depending on the wavelength. In that case, a nonlinear wavelength conversion method is used to obtain a necessary wavelength.

  Second harmonic generation (SHG: Second Harmonic Generation), a second-order nonlinear optical effect that uses an existing long-wavelength (red) semiconductor laser as the fundamental wave and generates light with half the wavelength, realizes a short-wavelength laser light source It has been widely studied as a means to do this. In general, since crystals have a frequency dispersion in the refractive index, the fundamental wave and the second harmonic have different velocities. Therefore, there is a point where a second harmonic that cancels out with the second harmonic generated at a certain point is generated. For this reason, in order to generate the second harmonic efficiently, a phase matching condition is necessary. In general, there is a method of aligning the refractive indexes of the fundamental wave and the second harmonic by using a crystal having birefringence whose refractive index differs depending on polarization at each frequency. However, semiconductors and the like have a large second-order nonlinear optical susceptibility that determines the generation efficiency of second harmonics, but they do not have birefringence, so that second harmonic generation using birefringence cannot be used.

  On the other hand, in 1962, Armstrong et al. Proposed second harmonic generation by quasi phase matching (QPM). Quasi-phase matching means that the addition of the second harmonic generated at each point inverts the direction of the nonlinear polarization that causes the second harmonic for each crystal length that becomes the largest, thereby canceling the electric field oscillation that has been canceled until then. In this method, the second harmonic is changed in a direction in which the electric field is energized (or not canceled) to match the phases in a pseudo manner. Therefore, in this method, even a crystal having no birefringence such as a semiconductor can be used.

  Inside the nonlinear optical crystal that generates second harmonics, the nonlinear polarization induced by the strong photoelectric field of the laser beam causes the nonlinear polarization wave to propagate at the same speed as the fundamental phase velocity, and from the nonlinear polarization to the dipole radiation. The emitted second harmonic (SHG wave) propagates together.

  Here, if the phase velocity of the polarized wave and the SHG wave are the same, the propagating SHG wave and the dipole radiation generated at any point in the crystal have the same phase. Waves can be generated. Matching the phases of the polarization wave and the SHG wave in this way is called phase matching, and the condition for obtaining the maximum conversion efficiency is called the phase matching condition. This phase matching condition can be obtained by making the refractive index of the crystal equal to the refractive index of the SHG wave at the wavelength of the incident wave.

  In other words, when wavelength conversion is performed using the nonlinear optical effect, the nonlinear polarization induced by the input laser beam and the harmonics generated from the nonlinear polarization are usually out of phase and in phase mismatch, resulting in coherence. Since the maximum and minimum are periodically repeated for each length (distance where the fundamental wave and the harmonic phase are shifted by 180 °), phase matching conditions must be satisfied in order to perform wavelength conversion efficiently.

Conventionally, wavelength conversion with high efficiency of a CW laser has been performed by means of PPLT (periodically poled LiTaO ₃ ), PPKTP (Periodically Poled KTiOPO ₄ ), etc. having a periodic polarization structure (for example, see Non-Patent Document 1).

Wavelength conversion by quasi-phase matching of polarization inversion elements such as PPLT (periodically poled LiTaO ₃ ) and PPKTP (Periodically Poled KTiOPO ₄ ) having a periodically polarized structure has a relatively high wavelength conversion efficiency and is visible from 1 μm band to around 500 nm. It is widely used in SHG wavelength conversion to the optical band (see, for example, Patent Documents 1 and 2).

  Here, in the case of the second harmonic, when the laser intensity is low, it is converted by the square of the incident intensity. However, when the incident intensity exceeds 10 W, a non-uniform temperature distribution is generated in the crystal due to heating by the laser itself. it can. As a result, it is known that the phase matching condition is not the only condition, and the conversion efficiency is reduced (see, for example, Non-Patent Document 2). Non-Patent Document 2 describes this as thermal dephasing.

  It is also possible to increase the incident intensity by ignoring the decrease in conversion efficiency to a desired intensity, and 16 W of 0.5 μm light has already been generated (for example, see Non-Patent Document 3). However, the conversion efficiency has dropped to about 16%.

  On the other hand, it is as high as 32.5% using a crystal that maintains a low absorptivity with respect to the absorption characteristics when the second harmonic and the first and second order lasers coexist with high intensity and the light condensing characteristics to the crystal. Some have succeeded in obtaining an output of 9.6 W with conversion efficiency (see, for example, Non-Patent Document 4). However, here too, thermal dephasing has not been addressed, and the author has commented that if this is resolved, higher efficiency can be achieved.

JP 2006-208629 A JP 2008-40301 A

S.C.Kumar et al., OPTICS Express Vol.17, No.16, (2009) 13711 F.J.Kontur, et al., OPTICS EXPRESS, Vol.15, No.20 (2007) 12882 S.V.Tovstonog, OPTICS EXPRESS, Vol.16 (2008) 11294 G.K.Samanta, Opt. Lett., 34 (2009) 1561

  By the way, the temperature phase matching becomes important when the wavelength of laser light is converted by a nonlinear optical crystal. In particular, in a nonlinear optical crystal having a periodic polarization structure that can obtain high conversion efficiency even with a CW laser, quasi-phase matching can be achieved over a long distance, but temperature phase matching becomes more important.

  However, when the wavelength of a laser beam is converted using a wavelength conversion element made of a nonlinear optical crystal having a periodic polarization structure, the nonlinear optical crystal constituting the wavelength conversion element has a long periodic polarization structure. As the incident intensity increases, the crystal is heated by incident laser light and converted light, and the uniformity of the temperature distribution of the crystal cannot be maintained.

  That is, when the incident laser intensity is increased, absorption of the converted second harmonic, absorption of the fundamental wave with assistance of the second harmonic, and the like occur, and the temperature rises particularly in the downstream side in a long crystal. An increase in the temperature of the entire crystal can be dealt with by increasing the cooling capacity, but such a temperature distribution in the direction of the laser axis is a limiting factor in high-efficiency conversion because there is no method that can be compensated.

  Conventionally, the thermal dephasing problem has been summarized by ZM Liao et al. In JOSAB, Vol.21-12 (2004) 2191, etc. As described, only a method of changing the temperature distribution by opening the upper part of the crystal holder and providing two temperature controls in the upstream part and the downstream part has been proposed. In terms of control, it is difficult to find the optimal solution to control the output characteristics using the same quality of two temperatures.

  An object of the present invention is to provide a laser wavelength conversion apparatus and a laser wavelength conversion method that compensate for self-heating by a laser and improve a decrease in conversion efficiency at high intensity in view of the above-described conventional situation. It is in.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the embodiments described below with reference to the drawings.

  When generating laser light with a wavelength different from that of the fundamental wave in the propagation direction, there is not yet a technique for applying a thermal gradient from the outside in the direction of the laser, and in principle the flow itself that produces the temperature gradient is in the opposite direction. The idea of driving and compensating for the flow is better.

  In the present invention, a heat flow is generated by the Peltier element in the axial direction of the laser, and in parallel with the temperature control in the direction perpendicular to it, the self-heating by the laser is compensated and the reduction in conversion efficiency at high intensity is improved. .

  That is, the present invention is a laser wavelength conversion device, in which a basic laser beam is incident from an incident end face, a wavelength of the incident basic laser beam is converted into a harmonic wave, and a harmonic polarization is emitted from the emission end face A wavelength conversion nonlinear crystal having, a detection means for detecting a shift in temperature phase matching caused by heating of the crystal by wavelength-converted light in the wavelength conversion nonlinear crystal, and the wavelength based on the detection output by the detection means A first temperature control means for controlling an average temperature obtained by averaging the temperatures of the entire crystal of the non-linear crystal for conversion by a first Peltier element; and detecting the amount of harmonic light emitted from the emission end face of the non-linear crystal for wavelength conversion. And the wavelength conversion from the emission end face side to the incident end face side of the wavelength conversion nonlinear crystal based on the detection output by the light quantity detection means. A second temperature control means for controlling the temperature gradient by generating a heat flow that cancels out the temperature gradient in the nonlinear crystal by a second Peltier element, and the first temperature control means and the second temperature control means. By controlling the average temperature of the wavelength conversion nonlinear crystal and the temperature gradient in the wavelength conversion nonlinear crystal, the temperature phase matching of the wavelength conversion nonlinear crystal is optimally maintained.

  In the laser wavelength conversion device according to the present invention, the first temperature control means includes the wavelength conversion nonlinear crystal at a temperature at which the amount of second harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal is maximized. Is controlled by the first Peltier element, the light quantity of the second harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal is detected by the light quantity detection means, and the second temperature control means is The temperature gradient can be controlled by causing a current having a magnitude corresponding to the light quantity of the second harmonic light detected by the light quantity detection means to flow through the second Peltier element.

  In the laser wavelength conversion device according to the present invention, the first Peltier element is provided between the wavelength conversion nonlinear crystal and a heat sink, and the first temperature control means includes the wavelength conversion nonlinear crystal. The heat generated in the crystal is released to the heat sink via the first Peltier element, thereby controlling the average temperature of the wavelength conversion nonlinear crystal, and the second Peltier element is used for the wavelength conversion nonlinear crystal. Are provided between the other end faces of a pair of thermal circulation arms whose one end faces are in contact with the incident end face side face and the exit end face side face, and the first temperature control means is provided in the nonlinear crystal for wavelength conversion. The temperature gradient can be controlled by causing the second Peltier element to generate a heat flow that cancels the temperature gradient and flowing it through the pair of thermal circulation arms to the wavelength conversion nonlinear crystal. .

  The present invention also uses the wavelength conversion nonlinear crystal having a periodic polarization structure to convert the wavelength of the basic laser light incident on the wavelength conversion nonlinear crystal from the incident end face into the harmonic light, and emit the harmonic light from the emission end face. A laser wavelength conversion method in a laser wavelength conversion device, wherein the crystal of the nonlinear crystal for wavelength conversion is based on a detection output by a temperature detection means for detecting an average temperature rise due to wavelength conversion in the nonlinear crystal for wavelength conversion Based on the detection output by the light amount detecting means for controlling the average temperature obtained by averaging the entire temperatures by the first Peltier element and detecting the light amount of the harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal. By passing a current according to the amount of the second harmonic light detected by the detection means to the second Peltier element, the wavelength conversion non-wave The second Peltier element generates a heat flow that cancels the temperature gradient in the wavelength conversion nonlinear crystal from the emission end face side to the incident end face side of the shaped crystal to control the temperature gradient, and the wavelength conversion nonlinear crystal The phase temperature of the wavelength conversion nonlinear crystal is controlled by controlling the average temperature and the temperature gradient in the wavelength conversion nonlinear crystal, and the amount of the second harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal The average temperature of the wavelength conversion nonlinear crystal is controlled by the first Peltier element so that the temperature becomes the maximum.

  The present invention reduces the thermal dephasing in the laser axis direction due to self-heating when a long crystal such as a crystal having a periodically polarized structure is used and interacts with a high-intensity laser, resulting in high efficiency. Wavelength conversion can be performed.

  In the present invention, by controlling two independent elements of temperature and heat flow having orthogonality, stable and simple optimum condition control is possible when high temperature uniformity such as temperature phase matching is required. .

  In other words, in the present invention, the heat feedback type closed circuit using the heat flow proportional to the current generated by the Peltier device is controlled in parallel with the normal temperature control, thereby controlling two independent elements of the heat flow and the temperature. A laser wavelength conversion device and a laser wavelength conversion method that can determine the value, enable stable and simple optimum condition control, compensate for self-heating by the laser, and improve the decrease in conversion efficiency at high intensity. Can be provided.

It is a block diagram which shows the structure of the laser wavelength converter to which this invention is applied. It is principal part sectional drawing which shows typically the mode of the temperature control of the nonlinear optical crystal in the said laser wavelength converter. It is an external appearance perspective view which shows typically the shape of the nonlinear optical crystal in the said laser wavelength converter. In the said laser wavelength converter, it is a figure which shows typically a mode that non-converted light reduces by a nonlinear optical effect within a nonlinear optical crystal, and a 2nd harmonic light increases. In the laser wavelength conversion device, when the control of the average temperature of the nonlinear crystal for wavelength conversion by the first Peltier element and the control of the temperature gradient in the nonlinear crystal for wavelength conversion by the second Peltier element are performed. It is a figure which shows the typical measurement result of.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  The present invention is applied to, for example, a laser wavelength conversion apparatus 100 configured as shown in FIG.

The laser wavelength conversion device 100 generates a second harmonic light (L ₂ ) having a frequency twice that of the incident fundamental wave laser light (L _IN ) by performing wavelength conversion using a nonlinear optical effect. Nonlinear optical crystals such as PPLT (periodically poled LiTaO ₃ ) and PPKTP (Periodically Poled KTiOPO ₄ ) that function as a second harmonic generation (SHG) device and have a periodically polarized structure as the nonlinear optical crystal 10 for wavelength conversion. Is provided.

The nonlinear optical crystal for wavelength conversion 10 has a fundamental wave laser beam (CW laser beam (L _IN ) emitted from a laser light source (not shown) incident from the incident end face 10A and the incident fundamental wave laser beam (L _IN ). The wavelength is converted into _second harmonic light (L ₂ ) by the nonlinear optical effect and emitted from the emission end face 10 B. The emitted light (L _OUT ) emitted from the emission end face 10 B of the wavelength conversion nonlinear optical crystal 10 is shown in FIG. As shown in FIG. 2, non-converted light (L ₁ ) and second harmonic light (L ₂ ) are included.

Here, in the laser wavelength conversion device 100, as the wavelength conversion nonlinear optical crystal 10, for example, as shown in FIG. 3, a length T of 1 mm, a width W of 2 mm, and a length L of 20 mm are long. A rectangular parallelepiped type PPLT (periodically poled LiTaO ₃ ) was used.

The laser wavelength converter 100 reflects the non-converted light (L ₁ ) included in the outgoing light (L _OUT ) emitted from the outgoing end face 10B of the wavelength conversion nonlinear crystal 10 to reflect the second harmonic light (L ₂ ) is a first semi-transparent mirror 11 having wavelength selectivity to transmit, and second harmonic light (L ₂ ) transmitted through the first semi-transparent mirror 11 at a predetermined light quantity ratio. ₂₁ ) and (L ₂₂ ) are provided. Then, a photodetector 13 such as a photodiode serves as a light amount detecting means for detecting the light amount of the _second harmonic light (L ₂ ) included in the outgoing light emitted from the outgoing end face 10B of the wavelength conversion nonlinear crystal 10. The second harmonic light (L ₂₂ ) reflected by the second semi-transparent mirror 12 is provided so as to be received.

  Further, in this laser wavelength conversion device 100, the wavelength conversion nonlinear crystal 10 is installed on a heat sink 20 for heat dissipation via a first Peltier element 21. Further, the wavelength conversion nonlinear crystal 10 is provided with a pair of thermal circulation arms 30A and 30B each having one end face in contact with the incident end face side surface 11C and the emission end face side face 11D, and the pair of thermal circulation arms. A second Peltier element 31 is provided between the other end faces of 30A and 30B. Further, the wavelength conversion nonlinear crystal 10 is provided with a temperature detector 22 such as a thermocouple or a thermistor as detection means for detecting a temperature phase matching shift caused by heating due to wavelength conversion in the wavelength conversion nonlinear crystal 10. It has been.

  The temperature detector 22 detects a temperature phase matching shift caused by heating due to wavelength conversion by wavelength conversion in the wavelength conversion nonlinear crystal 10 as an average temperature rise of the wavelength conversion nonlinear crystal 10. The temperature detector 22 is connected to a temperature control circuit 23 that supplies a drive current to the first Peltier element 21. The photodetector 13 is connected to a temperature gradient control circuit 32 that supplies a drive current to the second Peltier element 31.

  That is, the laser wavelength conversion device 100 includes the first Peltier element 21 that controls the average temperature obtained by averaging the temperatures of the entire crystal of the wavelength conversion nonlinear crystal 10, the absolute value control of the temperature using the temperature measurement, and the wavelength conversion. A second Peltier element 31 for generating a heat flow in the laser axis direction of the nonlinear crystal 10 and a thermal circuit thereof.

In the long rectangular parallelepiped nonlinear optical crystal 10, when a fundamental laser beam (CW laser beam (L _IN ) is incident from the incident end face 10A, a fundamental laser beam (CW laser beam (L _IN ) is wavelength-converted to the _second harmonic light (L ₂ ), and as shown in FIG. 4, the non-converted light (L ₁ ) decreases as it approaches the exit end face 10B side from the entrance end face 10A side. Second harmonic light (L ₂ ) increases.

The temperature distribution in the nonlinear crystal 10 for wavelength conversion, which is a problem as thermal dephasing, is mainly determined by the intensity distribution of the _second harmonic light (L ₂ ). The temperature gradually increases toward the 10B side, generating a heat flow (HC1) in the opposite direction. The heat flow (HC1) generated by the temperature gradient in the wavelength conversion nonlinear crystal 10 flows through the heat circuit by driving the second Peltier element 31 attached to the upper part of the wavelength conversion nonlinear crystal 10 (HC2). To cancel and reduce the phase mismatch of the wavelength conversion nonlinear crystal 10. The temperature of the entire wavelength conversion nonlinear crystal 10 is determined by the first Peltier element 21 so that the amount of the _second harmonic light (L ₂ ) emitted from the emission end face 10B is maximized, and the second harmonic light. A temperature gradient in the wavelength conversion nonlinear crystal 10 is controlled by causing a drive current having a magnitude corresponding to the amount of light (L ₂ ) to flow through the second Peltier element 31.

  In the laser wavelength conversion device 100, the temperature control circuit 23 detects the output from the temperature detector 22 that detects an average temperature rise of the wavelength conversion nonlinear crystal 10 due to wavelength conversion in the wavelength conversion nonlinear crystal 10. Based on the above, the first Peltier element 21 is driven by supplying a drive current from the temperature control circuit 23, and the heat (H1) generated in the nonlinear crystal for wavelength conversion 10 as shown in FIG. Is allowed to escape to the heat sink 20 via the first Peltier element 21, thereby functioning as first temperature control means for controlling the temperature averaged over the entire crystal of the wavelength converting nonlinear crystal 10.

Further, the temperature gradient control circuit 32 is based on the detection output by the photodetector 13 that detects the light amount of the _second harmonic light (L ₂ ) emitted from the emission end face 10B of the wavelength conversion nonlinear crystal 10. As shown in FIG. 2, the wavelength conversion is performed by causing a driving current having a magnitude corresponding to the amount of the _second harmonic light (L ₂ ) detected by the photodetector 13 to flow through the second Peltier element 31. The second Peltier element 31 generates a heat flow (HC2) that cancels the temperature gradient in the wavelength conversion nonlinear crystal 10 from the emission end face 10B side to the incident end face 10A side of the nonlinear crystal 10 for use. It functions as a second temperature control means to control.

In the laser wavelength conversion device 100, the drive current is supplied from the temperature control circuit 23 based on the detection output from the temperature detector 22 that detects an average temperature rise due to wavelength conversion in the wavelength conversion nonlinear crystal 10. The first Peltier element 21 is driven by supplying the first Peltier element 21 to control the average temperature of the nonlinear crystal 10 for wavelength conversion, and second harmonic light emitted from the emission end face 10B of the nonlinear crystal 10 for wavelength conversion ( L ₂₎ quantity on the basis of the detection output of the photodetector 13 for detecting the magnitude of the driving current the temperature corresponding to the amount of the second harmonic light detected by the photodetector 13 (L ₂₎ By flowing from the gradient control circuit 32 to the second Peltier element 31, the wavelength conversion nonlinear crystal 10 is directed from the exit end face 10B side to the entrance end face 10A side. The second Peltier element 31 generates a heat flow (HC2) that cancels the temperature gradient in the wavelength conversion nonlinear crystal 10 to control the temperature gradient, and the average temperature and the wavelength of the wavelength conversion nonlinear crystal 10 are controlled. The temperature gradient in the conversion nonlinear crystal 10 is controlled to achieve phase matching of the wavelength conversion nonlinear crystal 10 and second harmonic light (L ₂ ) emitted from the emission end face 10 B of the wavelength conversion nonlinear crystal 10. The average temperature of the wavelength conversion nonlinear crystal 10 is controlled by the first Peltier element 21 to a temperature at which the amount of light becomes maximum.

  In the laser wavelength conversion device 100 having such a configuration, thermal dephasing in the laser axis direction due to self-heating when a long crystal such as a crystal having a periodically polarized structure is used and interacted with a high intensity laser (Thermal dephasing ), The SHG wavelength conversion from the 1 μm band to the visible light band near 500 nm can be performed with high efficiency, and a high-intensity DC green laser can be obtained. In addition, by controlling two independent elements of temperature and heat flow that are orthogonal to each other, stable and simple optimum condition control is possible when high temperature uniformity such as temperature phase matching is required. Therefore, it is possible to obtain high-intensity direct-current light of several W without the problem of thermal dephasing.

  Here, in the laser wavelength conversion device 100 configured as described above, the average temperature of the wavelength conversion nonlinear crystal 10 by the first Peltier element 21 and the wavelength conversion nonlinear crystal 10 by the second Peltier element 31 are controlled. FIG. 5 shows a typical result in the case of performing two controls of the temperature gradient control.

  That is, the measurement result of the conversion efficiency when the average temperature rise of the heating by the laser is not controlled by the first Peltier element 21 is indicated by white circles in FIG. The measurement result of the conversion efficiency when the average temperature of the crystal is controlled is indicated by a square ■ in FIG. 5, and the conversion efficiency is measured when the heat flow by the self-heating of the second Peltier element 31 is controlled. The result is shown in green diamond ◆. In the laser wavelength conversion device 100 having the above-described configuration, it can be seen that the thermal phase mismatching (Thermal dephasing) which has been said so far is greatly improved.

  In addition, this invention is not limited only to the above embodiment, Of course, a various change is possible in the range which does not deviate from the summary of this invention.

  DESCRIPTION OF SYMBOLS 10 Nonlinear optical crystal, 10A Incidence end surface, 10B Outgoing end surface, 11 1st semi-transparent mirror, 11C Incident end surface side surface, 11D Outgoing end surface side surface, 12 2nd semi-transparent mirror, 13 Photo detector, 20 Thermal sink, 21 1st 1 Peltier element, 22 Temperature detector, 23 Temperature control circuit, 30A, 30B Thermal circulation arm, 31 Second Peltier element, 32 Temperature gradient control circuit, 100 Laser wavelength converter

Claims (4)

A wavelength conversion nonlinear crystal having a periodic polarization structure in which the basic laser light is incident from the incident end face, wavelength-converted the incident basic laser light to harmonic light, and emits the harmonic light from the emission end face;
Detecting means for detecting a shift in temperature phase matching caused by heating of the crystal by wavelength-converted light in the wavelength conversion nonlinear crystal;
A first temperature control means for controlling an average temperature obtained by averaging the temperature of the whole crystal of the wavelength conversion nonlinear crystal by a first Peltier element based on the detection output by the detection means;
A light amount detection means for detecting the light amount of the harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal;
Based on the detection output by the light quantity detection means, a second Peltier element generates a heat flow that cancels the temperature gradient in the wavelength conversion nonlinear crystal from the emission end face side to the incident end face side of the wavelength conversion nonlinear crystal. And second temperature control means for controlling the temperature gradient.
By controlling the average temperature of the wavelength conversion nonlinear crystal and the temperature gradient in the wavelength conversion nonlinear crystal by the first temperature control means and the second temperature control means, the temperature phase of the wavelength conversion nonlinear crystal is controlled. A laser wavelength converter characterized by maintaining an optimum match. The first temperature control means sets the average temperature of the wavelength conversion nonlinear crystal to the temperature at which the amount of second harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal is maximized. Controlled by
The light amount of the second harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal is detected by the light amount detection means, and the second temperature control means is the second harmonic light detected by the light amount detection means. The laser wavelength converter according to claim 1, wherein the temperature gradient is controlled by causing a current corresponding to the amount of light to flow through the second Peltier element. The first Peltier element is provided between the wavelength conversion nonlinear crystal and a heat sink, and the first temperature control means transfers heat generated in the wavelength conversion nonlinear crystal to the first Peltier element. By controlling the average temperature of the nonlinear crystal for wavelength conversion by letting it escape to the heat sink via
The second Peltier element is provided between the other end faces of a pair of thermal circulation arms whose one end faces are in contact with the incident end face side face and the exit end face side face of the wavelength conversion nonlinear crystal, The temperature control means generates a heat flow that cancels out the temperature gradient in the wavelength conversion nonlinear crystal by the second Peltier element, and flows it to the wavelength conversion nonlinear crystal through the pair of thermal circulation arms. The laser wavelength converter according to any one of claims 1 and 2, wherein the temperature gradient is controlled. In a laser wavelength conversion device that converts wavelength of fundamental laser light incident on an input end face of the wavelength conversion nonlinear crystal into a harmonic light by a wavelength conversion nonlinear crystal having a periodic polarization structure, and emits the harmonic light from the output end face A laser wavelength conversion method comprising:
Based on the detection output of the temperature detecting means for detecting an average temperature rise due to wavelength conversion in the wavelength conversion nonlinear crystal, the average temperature obtained by averaging the temperature of the entire crystal of the wavelength conversion nonlinear crystal is a first Peltier element. Controlled by
Based on the detection output by the light quantity detection means for detecting the light quantity of the harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal, a current corresponding to the light quantity of the second harmonic light detected by the light quantity detection means is obtained. By flowing through the second Peltier element, the second Peltier element generates a heat flow that cancels out the temperature gradient in the wavelength conversion nonlinear crystal from the emission end face side to the incident end face side of the wavelength conversion nonlinear crystal. To control the above temperature gradient,
By controlling the average temperature of the wavelength conversion nonlinear crystal and the temperature gradient in the wavelength conversion nonlinear crystal, phase matching of the wavelength conversion nonlinear crystal is achieved,
The laser, wherein the first Peltier element controls the average temperature of the wavelength conversion nonlinear crystal to a temperature at which the amount of second harmonic light emitted from the emission end face of the wavelength conversion nonlinear crystal is maximized. Wavelength conversion method.

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