JP6248410B2 - Temperature control device for wavelength conversion element - Google Patents

Description

  The present invention relates to a temperature control device for a wavelength conversion element.

  As this type of conventional wavelength conversion element, in order to obtain laser light having a desired wavelength, an element having a periodically poled structure in which the polarization direction is periodically reversed inside the ferroelectric crystal substrate is used. . This wavelength conversion element outputs harmonic laser light by quasi-phase matching with the incident fundamental wave laser light.

  When using a wavelength conversion element, it is necessary to maintain the temperature of the wavelength conversion element at a phase matching temperature (a constant temperature) so as to satisfy the phase matching condition. In general, the Peltier element is brought into contact with a metal flat plate having a large heat capacity and good heat conduction, and the temperature of the wavelength conversion element is controlled by the Peltier element via the metal flat plate.

The temperature T (z) inside the wavelength conversion element is the amount of heat generated inside the wavelength conversion element Q (z), the thermal resistance of the wavelength conversion element is RLT, the thermal resistance of the metal flat plate is RM, and between the metal flat plate and the wavelength conversion element The thermal resistance of RI is RI, and the temperature of the surface in contact with the Peltier element of the metal plate is TB.
T (z) = Q (z) × (RLT + RM + RI) + TB.

As in the case of using the wavelength conversion element at a low output, when the amount of heat generated within the wavelength conversion element Q (z) is small, as shown in FIG. 5 (a), the wavelength conversion element 2 Temperature T ( z) can be kept uniform and can be substantially the same as the phase matching temperature. That is, in the low-power wavelength conversion, the absorption amount of the fundamental wave and the second harmonic is small and the internal heat generation is small, so that the temperature of the wavelength conversion element 2 can be kept uniform.

However, when the wavelength conversion element 2 is used with high output, the calorific value Q (z) has a large distribution in the Z direction, and the temperature of the wavelength conversion element 2 becomes non-uniform. In general, since the amount of absorption of the second harmonic is large, heat generation on the emission side is larger than that on the incident side. Specifically, since the output of the second harmonic increases as the light travels from the incident side to the emission side of the wavelength conversion element 2, heat generation on the emission side becomes larger than that on the incident side. For this reason, as shown to Fig.6 (a), the temperature of the wavelength conversion element 2 of the output side becomes higher than the incident side.

In this case, the temperature of the phase matching temperature and the wavelength converting element 2 as shown in FIG. 6 (a) is deviated, may not meet the phase matching condition by non-uniform temperature distribution, the second harmonic output is saturated Or stable output of the second harmonic.

  In addition, when the wavelength conversion element 2 and the metal flat plate 1A are in uniform contact (when RI does not have a distribution in the Z direction), non-uniformity according to the heat generation amount Q (z) of the wavelength conversion element 2 A temperature distribution occurs. As a method of suppressing this non-uniform temperature distribution, there is also a method of reducing the thermal resistance RI between the metal flat plate 1A and the wavelength conversion element 2 over the entire contact surface as much as possible. According to this, the heat absorption from the wavelength conversion element 2 to the metal flat plate 1A is increased, and the uneven temperature distribution is somewhat suppressed, but the effect of suppressing the uneven temperature distribution is not sufficient.

Therefore, in order to reduce the temperature difference between the emission side with high heat generation and high temperature and the incident side with low heat generation and low temperature, the heat absorption on the emission side with high temperature is different from the heat absorption on the incident side with low temperature. You should improve. In order to realize this, for example, as shown in FIG. 7 (b), an incident-side temperature adjustment device composed of a metal flat plate 1A and a Peltier element 3a, and a metal flat plate 1B and a Peltier element 3b. An apparatus provided with a temperature adjusting device on the emission side is known (Patent Document 1).

  According to this, by making the temperature of the emission-side Peltier element 3b lower than the temperature of the incident-side Peltier element 3a, the heat absorption on the emission side becomes larger than the incident side, so the temperature of the wavelength conversion element 2 The distribution is suppressed, and the temperature of the wavelength conversion element 2 approaches the phase matching temperature.

International Publication No. 2008-050802

  However, in the apparatus described in Patent Document 1, it is necessary to provide a plurality of temperature adjusting devices, and the configuration of the apparatus is complicated.

  An object of the present invention is to provide a temperature control device for a wavelength conversion element having a simple configuration that can suppress the saturation of the second harmonic output and stably output the second harmonic output in a high-power wavelength conversion element. There is.

In order to solve the above-described problem, the temperature control device according to the present invention converts a fundamental wave into a harmonic, and has a wavelength having an incident surface on which the fundamental wave is incident and an exit surface on which the harmonic is emitted. A conversion element; a flat plate-shaped holding member that holds the wavelength conversion element and has good heat conduction; and a temperature adjustment element that adjusts the temperature of the wavelength conversion element by heating and cooling the holding member, At least one of the holding member and the wavelength conversion element is configured such that the thermal resistance of the contact surface where the holding member and the wavelength conversion element are in contact varies and is distributed at least partially from the incident surface to the emission surface. It is characterized by being.

According to the present invention, at least one of the flat plate-shaped holding member and the wavelength conversion element has a fluctuation distribution in which the thermal resistance of the contact surface where the holding member and the wavelength conversion element are in contact is at least partially from the incident surface to the output surface. In the high-power wavelength conversion element, even when there is non-uniform heat generation inside the wavelength conversion element, the non-uniform temperature distribution can be suppressed and saturation of the second harmonic output is suppressed. It is possible to provide a temperature control device for a wavelength conversion element that can output the second harmonic output stably and has a simple configuration.

1 is a diagram illustrating a temperature control device for a wavelength conversion element of Example 1. FIG. It is a figure which shows the temperature control apparatus of the wavelength conversion element of Example 2. FIG. It is a figure which shows the temperature control apparatus of the wavelength conversion element of Example 3. FIG. It is a figure which shows the temperature control apparatus of the wavelength conversion element of Example 4. FIG. It is a figure which shows the temperature control apparatus of the wavelength conversion element of the prior art example 1. FIG. It is a figure which shows the temperature control apparatus of the wavelength conversion element of the prior art example 2. FIG. It is a figure which shows the temperature control apparatus of the wavelength conversion element of the prior art example 3.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a temperature control device for a wavelength conversion element according to the present invention will be described in detail based on the drawings.

  In the present invention, in order to suppress the temperature distribution of the wavelength conversion element generated at the time of high output of the wavelength conversion element with one temperature adjustment device, the thermal resistance of the surface where the metal flat plate and the wavelength conversion element are in contact is emitted from the incident side It is characterized by a distribution of changes between the sides. In this embodiment, the following three methods are adopted as this method.

  The first method changes the thermal resistance of the contact between the metal flat plate and the wavelength conversion element by changing the surface property of the metal flat plate. In the second method, the material of the metal flat plate is changed. The third method changes the surface property of the surface that contacts the metal flat plate of the wavelength conversion element.

  First, a specific example of the first method will be described. 1 is a diagram illustrating a temperature control device for a wavelength conversion element according to a first embodiment. In the temperature control device for a wavelength conversion element shown in FIG. 1B, the wavelength conversion element 2 converts a fundamental wave into a harmonic wave, an incident surface on which the fundamental wave is incident, and an emission surface from which the harmonic wave is emitted. Have

  The metal flat plate (holding member) 1 holds the wavelength conversion element 2 and has good heat conduction, and the thermal resistance of the contact surface where the metal flat plate 1 and the wavelength conversion element 2 are in contact varies from the incident surface to the output surface. Is configured to do. In this example, the metal flat plate (holding member) 1 has a fixed long groove portion 4 having a certain length of irregularities extending from the incident side I of the contact surface in contact with the wavelength conversion element 2 to the substantially central portion M. Is formed.

  The Peltier element (temperature adjustment element) 3 adjusts the temperature of the wavelength conversion element 2 by heating and cooling the metal flat plate 1.

  Thus, according to the temperature control device of the wavelength conversion element of Example 1 shown in FIG. 1, the metal flat plate 1 has a substantially central portion M from the incident side I of the contact surface in contact with the wavelength conversion element 2. Since the fixed long groove portion 4 is formed, the thermal resistance is increased by the fixed long groove portion 4.

  For this reason, as shown to Fig.1 (a), the temperature of the wavelength conversion element 2 rises rapidly from the incident side I to the approximate center part M. FIG. On the other hand, the temperature of the wavelength conversion element 2 gradually rises from approximately the center M to the emission side. For this reason, as shown in FIG. 1A, the temperature of the wavelength conversion element 2 comes close to the phase matching temperature, so that the phase matching condition can be satisfied.

  That is, in the high-power wavelength conversion element 2, even when there is non-uniform heat generation inside the wavelength conversion element, the non-uniform temperature distribution can be suppressed, the saturation of the second harmonic output is suppressed, and the second harmonic output is reduced. Stable output is possible. In addition, since one metal flat plate 1 is used without using a plurality of temperature adjusting devices shown in FIG. 8, a temperature control device for a wavelength conversion element having a simple configuration can be provided.

  In addition, as a method of changing the thermal resistance between the incident side I and the emission side, a method other than the method of forming irregularities on the incident side described in the first embodiment may be used. For example, the incident side surface is made rougher than the emission side surface. Alternatively, the contact pressure on the exit side is made larger than that on the entrance side. Alternatively, a film that further enhances heat transfer, such as a metal film or a conductive film, is formed on the emission side surface of the metal flat plate. As the metal film or the conductive film, a uniform film may be formed, and for example, patterning may be performed in a dot shape or a band shape. Alternatively, the area where the wavelength conversion element is in contact with the film that enhances heat transfer is increased as it proceeds from the incident side to the emission side. Alternatively, a film is formed on the incident surface of the metal flat plate so that the heat transfer is low.

  FIG. 2 is a diagram illustrating a temperature control device for a wavelength conversion element according to the second embodiment. In the second embodiment, the first method is adopted. In the temperature control device for a wavelength conversion element of Example 2 shown in FIG. 2B, the metal flat plate 1a is configured so that the thermal resistance on the incident surface side and the thermal resistance on the output surface side are continuously changed. Yes. In this example, the metal flat plate 1 a is provided with a concavo-convex portion in which the width of the groove gradually decreases from the incident side I to the output surface side of the contact surface in contact with the wavelength conversion element 2.

  Thus, according to the temperature control device for the wavelength conversion element of Example 2 shown in FIG. 2, the metal flat plate 1 a extends from the incident side I of the contact surface in contact with the wavelength conversion element 2 to the emission surface side. Since the concavo-convex portion in which the width of the groove is gradually narrowed is formed, the thermal resistance also changes continuously from the incident side I to the output surface side.

For this reason, as shown to Fig.2 (a), the temperature of a wavelength conversion element becomes uniform and smooth. Since the temperature of the wavelength conversion element is substantially equal to the phase matching temperature, Ru obtained same effect as in Example 1.

(Example 3)

FIG. 3 is a diagram illustrating a temperature control device for a wavelength conversion element according to a third embodiment. In the third embodiment, the second method is adopted. In Example 1 shown in FIG. 1, a fixed long groove portion 4 having a certain length of unevenness is formed on a metal flat plate 1 from the incident side I of the contact surface in contact with the wavelength conversion element 2 to the substantially central portion M. However, in Example 4 shown in FIG. 3 , the wavelength conversion element 2a has a certain length of irregularities extending from the incident side I of the contact surface in contact with the metal flat plate 1 to the substantially central portion M. The fixed long groove portion 4a is formed.

  Thus, even if the fixed long groove portion 4a is formed on the wavelength conversion element 2a from the incident side I of the contact surface in contact with the metal flat plate 1 to the substantially central portion M, the same operation as in the first embodiment is performed. Similar effects can be obtained.

In addition, as a method of changing the thermal resistance between the incident side I and the emission side, a method other than the method of forming irregularities on the incident side described in the first embodiment may be used. For example, the incident side surface is made rougher than the exit side surface. Alternatively, the contact pressure on the exit side is made larger than that on the entrance side. Alternatively, a film that further enhances heat transfer, such as a metal film or a conductive film, is formed on the emission side surface of the wavelength conversion element. As the metal film or the conductive film, a uniform film may be formed, and for example, patterning may be performed in a dot shape or a band shape. Alternatively, the area where the wavelength conversion element is in contact with the film that enhances heat transfer is increased as it proceeds from the incident side to the emission side. Alternatively, a film is formed on the incident side surface of the wavelength conversion element so as to reduce heat transfer.
Example 4

FIG. 4 is a diagram illustrating a temperature control device for a wavelength conversion element according to a fourth embodiment. In the fourth embodiment, the third method is adopted. In Example 2 shown in FIG. 2, the metal flat plate 1a is formed with an uneven portion in which the width of the groove gradually decreases from the incident side I to the output surface side of the contact surface in contact with the wavelength conversion element 2. However, in Example 4 shown in FIG. 4 , the wavelength conversion element 2 b is provided with a concavo-convex portion in which the width of the groove gradually decreases from the incident side I to the output surface side of the contact surface in contact with the metal flat plate 1. It is formed.

  In this way, even if the wavelength conversion element 2b is formed with an uneven portion in which the width of the groove gradually decreases from the incident side I to the output surface side of the contact surface in contact with the metal flat plate 1, Example 2 It operates in the same way as the above, and the same effect can be obtained.

In addition, this invention is not limited to the temperature control apparatus of the wavelength conversion element of Example 1 thru | or Example 4 mentioned above. That is, at least one of the metal flat plate 1 and the wavelength conversion element 2 is distributed so that the thermal resistance of the contact surface where the metal flat plate 1 and the wavelength conversion element 2 are in contact varies at least partially from the incident surface to the output surface. If configured, the same effects as those of the above-described embodiment can be obtained.

Also, any two or more wavelength conversion element temperature control devices of the wavelength conversion element temperature control devices of the first to fourth embodiments may be used in combination. This further increases the effect.

  The temperature control device for a wavelength conversion element according to the present invention can be used for a gas concentration analyzer and a fixed laser device.

1,1a, 10 Metal flat plate
2, 2a, 2b Wavelength conversion element 3 Peltier element 4, 4a Fixed long groove 5, 5a Variable length groove

Claims (5)

A wavelength conversion element that converts a fundamental wave into a harmonic and has an incident surface on which the fundamental wave is incident and an exit surface from which the harmonic is emitted;
A flat plate-shaped holding member that holds the wavelength conversion element and has good heat conduction;
A temperature adjusting element that adjusts the temperature of the wavelength conversion element by heating and cooling the holding member;
The wavelength conversion element is configured such that a thermal resistance of a contact surface where the holding member and the wavelength conversion element are in contact with each other varies at least partially from the incident surface to the emission surface. Temperature control device for wavelength conversion element. The temperature control device for a wavelength conversion element according to claim 1 , wherein the wavelength conversion element is configured such that a thermal resistance of the incident surface is larger than a thermal resistance of the emission surface.   The temperature control device for a wavelength conversion element according to claim 2, wherein at least one of the holding member and the wavelength conversion element is formed with irregularities on the incident surface side of the contact surface. 2. The temperature of the wavelength conversion element according to claim 1 , wherein the wavelength conversion element is configured such that a thermal resistance on the incident surface side and a thermal resistance on the emission surface side are continuously changed. Control device. The wavelength conversion element is characterized in that an uneven part is formed in which the width of the groove gradually decreases from the incident side to the output surface side of the contact surface in contact with the wavelength conversion element. 4. The temperature control device for a wavelength conversion element according to 4.

Images