JP2001183712A - Wavelength converting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wavelength converting device which uses TYPE1 CLBO crystal in which a shift from phase matching conditions is suppressed, decrease in the wavelength conversion efficiency is suppressed and high average UV rays can be emitted. SOLUTION: In the wavelength converting device which uses a TYPE1 CLBO crystal 1, one point in the front half of the crystal in the incident side of light (almost center in the horizontal direction) is pressurized. By this method, distribution of phase mismatching caused in the crystal can be suppressed. Even when the crystal generates heat itself, decrease in the wavelength conversion efficiency can be suppressed and high average UV rays can be emitted. The pressurizing point is preferably 0 to 1/3 length in the front half of the CLBO crystal in the incident side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION A processing laser device is used for processing such as drilling a via hole in a printed circuit board and cutting a film or metal. The present invention relates to a wavelength converter used for the above-mentioned processing laser device and the like, and more particularly, to CLBO (CsLiB ₆ O ₁₀ ) capable of outputting high average ultraviolet light.
The present invention relates to a wavelength converter using crystal TYPE1.

[0002]

2. Description of the Related Art FIG. 8 shows an example of an ultraviolet laser device which uses a nonlinear optical crystal as a wavelength conversion element and outputs a fourth harmonic (fourth harmonic) of a fundamental wave. Fundamental wave laser device (for example, Nd: YLF laser) which is a pulse laser device 11
From the first nonlinear optical crystal [LBO (LiB ₃ O ₅ )] through the condenser lens 12.
Crystal] 1-1, and the second harmonic (second harmonic: wavelength 52
3 nm). This second harmonic is collected by the condenser lens 1
3 through a second nonlinear optical crystal (CLBO crystal) 1-
2 and is wavelength-converted to the fourth harmonic (fourth harmonic: wavelength 262 nm). The fourth harmonic is condensed by the condenser lens 14 and radiated on the workpiece 15. Nonlinear optical crystal 1
1, 1-2 are heated by heaters 3-1 and 3-2, and the temperature is detected by thermocouple 17. The output of the thermocouple 17 is sent to a temperature controller (temperature controller) 16, and the temperature controller 16 controls each of the nonlinear optical crystals to have a constant temperature.

[0003]

As shown in FIG. 8, a non-linear optical crystal (CLBO crystal) is used to generate ultraviolet light by generating a harmonic or a sum frequency of a fundamental wave laser having a wavelength of 1 μm such as a Nd: YAG or Nd: YLF laser. If you want to get
Normally, a nonlinear optical crystal for wavelength conversion (CLBO crystal) absorbs ultraviolet light more than in the visible region, and therefore, when outputting a high average output, the crystal is self-heated by the generated ultraviolet light. Due to this self-heating, the phase matching condition of the crystal is disturbed, and there is a disadvantage that the output is greatly reduced. In particular, when using a long crystal of 7 to 8 mm or more with respect to the direction of the incident light, the temperature rise in the crystal due to self-heating of the crystal by the generated ultraviolet light may have a distribution in the direction in which the ultraviolet light propagates.
The measurement was made by the present inventors using a thermoviewer.

Normally, when the input to the crystal increases and the output of ultraviolet rays increases, the refractive index of the crystal has a distribution in the direction in which ultraviolet light propagates for the above-described reason. This means that the phase matching angle differs depending on the location of the crystal. Therefore, usually, the phase matching angle must be readjusted with an increase in temperature due to an increase in the input to the crystal. However, as described above, since the refractive index of the crystal has a distribution in the direction in which ultraviolet light propagates, the angle of the crystal is It was not possible to optimally correct the amount of phase mismatch in all parts of the crystal only by adjustment.

FIG. 2 shows a case where the second harmonic (wavelength 532 nm) of the fundamental wave output from the Nd: YAG laser device is input to the CLBO crystal of TYPE 1 to obtain the fourth harmonic (wavelength 266 nm), as described later. FIG. 3 is a diagram illustrating a relationship between input energy and output energy of a CLBO crystal. Since the refractive index of the crystal has a distribution in the direction in which the ultraviolet light propagates, as shown by -2 in FIG. 2, in the related art, there is a limit even if the angle of the crystal is readjusted. Efficiency was reduced, and the output energy did not increase as much as the input energy, as indicated by -1. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and an object of the present invention is to provide a wavelength conversion device using TYPE 1 of a CLBO crystal even if the crystal has self-heating even if the crystal has self-heating. It is an object of the present invention to provide a wavelength conversion device capable of suppressing the deviation from the conventional one more than before, suppressing a decrease in the wavelength conversion efficiency, and outputting a high average ultraviolet light.

[0006]

The temperature rise in the crystal due to the self-heating of the crystal by the generated ultraviolet light induces a refractive index distribution in the direction in which the ultraviolet light propagates. The amount of phase mismatch is Δk = 2
π (n3 / λ3-n2 / λ2-n1 / λ1). Here, ni is the refractive index at the wavelength λi. For this reason, in-crystal distribution occurs in the amount of phase mismatch due to self-heating due to absorption of ultraviolet light by the crystal. In order to suppress the distribution of the phase mismatch amount in the crystal, the present invention utilizes the photoelastic effect of a nonlinear optical crystal used for wavelength conversion. The photoelastic effect is a property in which when a pressure is applied to a nonlinear optical crystal, the refractive index of the nonlinear optical crystal under the influence of the pressure changes. According to various experiments by the present inventors, in a wavelength conversion apparatus using TYPE 1 of a CLBO crystal, phase mismatch was caused by applying pressure to a point (almost the center in the horizontal direction) of the first half of the crystal length on the light incident side. It has been found that the distribution of the amount in the crystal can be minimized. The pressure is preferably applied to the first half of 0 to 1/3 of the light incidence side of the crystal length.

Based on the above, the present invention solves the above-mentioned problems as follows. (1) When wavelength conversion is performed using TYPE 1 of a CLBO crystal, pressure is applied to the first half on the incident side of the CLBO crystal within a plane determined by the optical axis and the direction of incident light. (2) In the above (1), the pressure is applied to the first half of the crystal length up to 1/3 of the light incident side. In the present invention, pressure is applied to the first half of the CLBO crystal on the incident side as described above in a plane determined by the optical axis and the incident light beam direction.
In-crystal distribution of the amount of phase mismatch generated in the crystal can be suppressed. For this reason, even if there is self-heating of the crystal, it is possible to suppress a decrease in the wavelength conversion efficiency and to output high average ultraviolet light.

[0008]

FIG. 1 is a diagram showing an embodiment of the present invention. In this embodiment, the CLBO crystal 1 is used and the TY
When performing wavelength conversion by phase matching of PE1, as shown in FIG. 1, when the crystal length in the incident light beam direction is L, one point from the light incident side to (（) × L is the optical axis C. Pressure was applied in a direction parallel to the plane P determined by the incident light beam direction. Here, the figure shows the phase matching of TYPE1, in which the incident light has a polarization direction in the vertical direction, and the outgoing light has a polarization direction perpendicular to the polarization direction of the incident light.

FIG. 2 shows a second harmonic (wavelength 532n) of the fundamental wave (wavelength 1064nm) output from the Nd: YAG laser light source.
m) is input to a CLBO crystal (7 × 8 × 15 mm), and T
FIG. 9 is a diagram illustrating an example of an experimental result in a case where wavelength conversion is performed by phase matching of YPE1 to obtain a fourth harmonic (wavelength: 266 nm) of the fundamental wave. The figure shows the output energy and the conversion efficiency when no pressure is applied and when the pressure is applied to the CLBO crystal as shown in FIG. 1. The horizontal axis indicates the second harmonic of the incident light on the CLBO crystal. Input energy of laser light (mJ), left vertical axis is output energy (mJ) of fourth harmonic laser light emitted from CLBO crystal,
The right side of the vertical axis shows the conversion efficiency [output energy / input energy]
(%), Where -1 and -2 indicate the output energy and conversion efficiency when no pressure is applied to the CLBO crystal, and -1 and -2 indicate the conversion efficiency when the pressure is applied to the CLBO crystal. As shown in FIG. 2, when no pressure is applied to the CLBO crystal, the second harmonic energy maximum input (186 m
The fourth harmonic output energy at J) was 87.9 mJ and the conversion efficiency was 48.6%. On the other hand, when pressure is applied to the CLBO crystal even at the same maximum input, the fourth harmonic output energy increases to 121.9 mJ, and the conversion efficiency is 67.5%.
Increased.

Next, an experiment was conducted to determine how much pressure should be applied to the CLBO crystal. FIG. 3 shows the result. The horizontal axis in the figure is the pressure (k) applied to the CLBO crystal.
g / cm ² ), the left vertical axis indicates the fourth harmonic output energy (mJ) of the CLBO crystal, and the right vertical axis indicates the increase rate (%) of the output energy, and indicates the output energy. In the figure, as shown in FIG. 1, a pressure is applied to the CLBO crystal, and a second harmonic of Nd: YAG (wavelength 532 nm) is used.
The output of the CLBO crystal was examined by changing the pressure applied to the CLBO crystal while keeping the input constant at 186 mJ.
As is clear from FIG. 3, the increase in output is saturated around a pressure of about 20 kg / cm ² . That is, it is shown that the pressure applied to the CLBO crystal is preferably about 20 kg / cm ² .

Further, as another experimental example, as shown in FIG. 4, light having a wavelength of 1064 nm and light having a wavelength of 236 nm are incident on the CLBO crystal 1, and a wavelength of 19
The case where 3 nm light was generated was examined. CLBO
The size and location at which pressure is applied to crystal 1 are substantially the same as in FIG. In this case as well, Type 1 phase matching is performed as in FIG. 1, and two lights of the input wavelength of 1064 nm and the light of 236 nm are the same polarization direction as shown in FIG. Then, the polarization direction of the output light is in a direction perpendicular to the polarization direction of the input light (for example, parallel to the plane of the drawing as shown).

Wavelength 1064n input to CLBO crystal 1
Since the light of m and the light of 236 nm are supplied from independent laser oscillators, it is difficult to synchronize them, and it is difficult to obtain the numerical data shown in FIGS. Therefore, the change in output power between when the pressure was applied to the CLBO crystal 1 and when the pressure was not applied was examined, and both were compared. As a result, although the output power fluctuated greatly, the effect of increasing the output by applying the pressure of the CLBO crystal 1 could be clearly confirmed.

FIGS. 5 and 6 show the results of the above experiment. FIG. 5 shows a change in output power during a transition from no pressure to pressure application, FIG. 6 shows a change in output power during a transition from pressure to no pressure, the horizontal axis represents time (seconds), and the vertical axis represents time. Output power (mW). As is clear from FIGS. 5 and 6, the output is significantly improved by the application of the pressure. As can be seen from the figure, when no pressure is applied to the CLBO crystal, the output power is 3.6 as an average value.
The pressure was 7 mW, but when pressure was applied, an average value of 6.07 mW was obtained when pressure was applied. That is, the output was increased 1.65 times.

The reason why the output power is increased by the application of the pressure is due to the photoelastic effect that the refractive index of the crystal under the influence of the pressure changes when the pressure is applied to the crystal as described above. That is, it is considered that the application of pressure changes the refractive index of the portion, and cancels the intra-crystal distribution of the amount of phase mismatch generated in the crystal.
In the above embodiment, the case where pressure is applied to one point up to (１ ／) × L on the light incident side of the nonlinear optical crystal has been described, but if pressure is applied to the first half of the nonlinear optical crystal on the light incident side. It has been confirmed that similar effects can be obtained.

FIG. 7 is a diagram showing a specific configuration example of a wavelength converter according to the present invention. There are various methods for applying pressure to the CLBO crystal. Here, an example in which pressure is applied to the CLBO crystal using an electrostrictive element will be described. FIG.
In the figure, (a) is a cross-sectional view of the wavelength converter, (b)
Shows a front view, and (c) shows a configuration example of a control system. FIG.
As shown in (b), a nonlinear optical crystal (CLBO crystal)
1 is accommodated in a crystal holding container 2, and the crystal holding container 2 is provided with an entrance 2 a and an exit 2 b. Entrance 2a
Is incident on the nonlinear optical crystal 1 and wavelength-converted, and the wavelength-converted laser light is emitted from the emission port 2b.

An electrostrictive element 3 is fixed to the crystal holding container 2, and a driving end 3a of the electrostrictive element 3 is in contact with one point of the first half of the nonlinear optical crystal on the light incident side. When a voltage is applied to the electrostrictive element 3, the drive end 3a is displaced.
, The nonlinear optical crystal 1 is pressed and pressure is applied. The magnitude of the force pressing the nonlinear optical crystal 1 is determined by, for example, monitoring the output light emitted from the nonlinear optical crystal 1 by the power monitor 4 as shown in FIG. 5, the voltage applied to the electrostrictive element 3 may be controlled.

[0017]

As described above, in the present invention, when wavelength conversion is performed using TYPE 1 of a CLBO crystal, the first half of the CLBO crystal is positioned within a plane determined by the optical axis and the incident light direction. Since the pressure is applied, the distribution of the amount of phase mismatch generated in the crystal in the crystal can be suppressed, the decrease in the wavelength conversion efficiency can be suppressed, and high average ultraviolet light can be output.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an experimental example of a pressure effect in generating a fourth harmonic of an Nd: YAG laser.

FIG. 3 is a diagram showing a relationship among a pressure applied to a CLBO crystal, output energy, and conversion efficiency.

FIG. 4 is a diagram illustrating generation of 193 nm laser light by sum frequency mixing.

FIG. 5 is a diagram illustrating an output change during a transition from no pressure to pressure application when a 193 nm laser beam is generated by sum frequency mixing.

FIG. 6 is a diagram illustrating a change in output during a transition from pressure application to no pressure when a 193 nm laser beam is generated by sum frequency mixing.

FIG. 7 is a diagram illustrating a configuration example of a wavelength conversion device to which the present invention is applied;

FIG. 8 is a diagram illustrating a configuration example of an ultraviolet laser device using a nonlinear optical crystal as a wavelength conversion element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nonlinear optical crystal (CLBO crystal) 2 Crystal holding container 3 Electrostrictive element 4 Power monitor 5 Control device

Claims (2)

[Claims] 1. A wavelength conversion device for performing wavelength conversion using a CLBO crystal TYPE1, wherein a pressure is applied to a first half of the CLBO crystal on a light incident side in a plane determined by an optical axis and an incident light beam direction. A wavelength converter characterized by adding: 2. The pressure is １ ／ of the crystal length on the light incident side.
2. The wavelength conversion device according to claim 1, wherein the wavelength conversion device is added to the first half of the wavelength conversion device.