JP4109869B2 - Method for manufacturing wavelength conversion element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a wavelength conversion element.
[0002]
[Prior art]
In laser research 20 (1992) 200 published by the present inventors and other documents, when a crystal of KTP represented by KTiOPO ₄ is used for second harmonic generation and optical parametric oscillation of an Nd: YAG laser, It is disclosed that the generated green light causes crystal defects in the KTP and the output decreases with time.
[0003]
In addition, B. Boulanger, IEEE JQE 35 (1999) 281 reports a method for dealing with KTP crystals that is effective for slow repetition lasers, but reports on effective countermeasures for fast repetition lasers. Not.
[0004]
Japanese Patent Application Laid-Open No. 5-97599 describes that the output characteristics can be improved by annealing for 10 to 50 hours at 200 ° C. or higher in an oxygen atmosphere after KTP crystal growth.
[0005]
[Problems to be solved by the invention]
As for the problem of time-dependent decrease in the generated output in the wavelength conversion element made of KTP crystal, the conventional report has reported an effective countermeasure method for the slow repetition laser, but it is an effective countermeasure for the fast repetition laser. Has not been reported.
[0006]
The present invention intends to provide a method for manufacturing a wavelength conversion element capable of maintaining high output characteristics for a long time with respect to a high-speed repetitive laser.
[0007]
[Means for Solving the Problems]
Method for manufacturing a wavelength conversion element according to the present invention, the output of the wavelength conversion by the wavelength conversion element for the wavelength conversion element made of KTP crystal was reduced by 10% or more of the output of the initial use, the output deterioration with time Thereafter, annealing is performed for 1 hour or more at a temperature of 170 ° C. or higher in an atmosphere containing water vapor and oxygen .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the manufacturing method of the wavelength conversion element concerning the present invention is explained in detail.
[0009]
First, KTP crystals are grown by a hydrothermal synthesis method or a flux method. For example, the KTP crystal is incorporated as a wavelength conversion element in the laser light source shown in FIG. The crystal form of KTP used here may be a bulk crystal, a plurality of bulk crystals, or a domain-inverted structure.
[0010]
FIG. 1 shows a second harmonic generation (SHG) apparatus using an Nd: YAG laser as a laser light source. In this device, a fundamental wave is generated by a laser oscillator and a double harmonic is generated by wavelength conversion in the resonator. Between the first and second resonant mirrors 1 and 2, a third resonant mirror 3 that is inclined at an angle of 45 ° with respect to the optical path of the mirrors 1 and 2 is disposed. Since these resonator mirrors 1, 2, and 3 perform laser oscillation with a wavelength of 1.064 μm as a fundamental wave by driving an excitation module, which will be described later, the resonator mirrors 1, 2, and 3 have the fundamental wave. On the other hand, it has a characteristic of being highly reflective. Among these resonator mirrors 1, 2, and 3, the second resonant mirror 2 generates double harmonic light in the resonator by an SHG module, which will be described later, and outputs the second harmonic light (wavelength in order to output it outside the resonator). The third resonator mirror 3 also has a high transmission characteristic for the second harmonic light. The excitation module 4 is disposed in the optical path between the first and third resonant mirrors 1 and 3. The excitation module 4 includes an Nd: YAG oscillator and excitation means. The Q switch 5 is disposed between the excitation module 4 and the first resonance mirror 1. The SHG module 6 equipped with a wavelength conversion element made of KTP crystal is disposed in the optical path between the second and third resonant mirrors 2 and 3.
[0011]
In the SHG apparatus configured as described above, the oscillation of the fundamental wave is generated by oscillating the oscillator of the excitation module 4 and oscillating the Q switch 5 after performing laser oscillation with a wavelength of 1.064 μm as the fundamental wave by the excitation means. Light is pulsed and reflected between the first and second resonant mirrors 1 and 2. At this time, since the SHG module 6 equipped with a wavelength conversion element made of a KTP crystal is provided in the resonator, the fundamental wave generated in the resonator is converted into a second harmonic, and the third resonance. The second harmonic output 7 is output outside the resonator by the resonator mirror 3. That is, the fundamental wave having a wavelength of 1.064 μm generated by the laser oscillation of the excitation module 4 is converted to a second harmonic of a wavelength of 0.532 μm by the wavelength conversion element of the SHG module 6 and output outside the resonator.
[0012]
We reported in Laser Research 20 (1992) 200 by the inventors that the wavelength conversion element composed of the KTP crystal converts the fundamental wave with a wavelength of 1.064 μm into a double harmonic and outputs it continuously. Thus, the second harmonic output by the wavelength conversion element deteriorates with time. This is caused by the occurrence of crystal defects in the laser light path in the KTP crystal. In particular, the deterioration of output with time is remarkable in a Q-switched laser oscillator having a high peak value of oscillation output, and more remarkable in a high repetition pulse laser by a continuous excitation Q switch having a high repetition frequency.
[0013]
A wavelength conversion element made of a KTP crystal that has caused such output deterioration with time is annealed.
[0014]
The annealing is preferably performed at a temperature of 170 ° C. or higher in an atmosphere containing water vapor and oxygen such as an air atmosphere. When the annealing temperature is less than 170 ° C., it becomes difficult to obtain a wavelength conversion element that maintains high output characteristics for a long time with respect to a high-speed repetitive laser. The upper limit of the annealing temperature is preferably set below the temperature at which the KTP crystal melts.
[0015]
The annealing is preferably performed at a temperature of 170 ° C. or higher for 1 hour or longer. However, when the KTP crystal is grown by a hydrothermal synthesis method, annealing at the temperature may be performed for 1 hour or longer. However, when the KTP crystal is grown by a flux method, annealing at the temperature is performed. It is preferable to perform for 2 hours or more.
[0016]
The annealing is desirably performed when the output of the wavelength conversion element made of the KTP crystal is reduced by 10% or more, more preferably by 12% or more with respect to the initial use output of the wavelength conversion element during the conversion operation. . When annealing is performed at a time when the wavelength conversion element made of KTP crystal is not sufficiently deteriorated with time, that is, when the deterioration of the output characteristic in the initial stage of use is less than 10%, the high output characteristic over a long time with respect to the high-speed repetitive laser It is difficult to obtain a wavelength conversion element that maintains the above.
[0017]
As described above, according to the present invention, a wavelength conversion element made of a KTP crystal with improved output aging characteristics can be manufactured. That is, when a wavelength conversion element made of a KTP crystal is continuously operated as a wavelength conversion light source, for example, crystal defects occur in the optical path in the KTP crystal, and the conversion output decreases with time. By annealing the KTP crystal in which the output deterioration has occurred in an atmosphere containing water vapor and oxygen such as an air atmosphere, a wavelength conversion element made of a KTP crystal with improved output aging characteristics can be manufactured.
[0018]
Note that even when annealing is performed in a state where the wavelength conversion element made of the KTP crystal does not deteriorate with time, that is, in an initial state before use of the wavelength conversion element made of the KTP crystal, the output temporal characteristics are almost improved. By not performing the annealing on the wavelength conversion element made of the KTP crystal whose conversion output is deteriorated with time as in the present invention, the output temporal characteristics can be improved.
[0019]
In particular, the annealing temperature is regulated to 170 ° C. or more for 1 hour or more, and the output of the wavelength conversion element comprising the annealed KTP crystal is reduced by 10% or more, more preferably 12% or more with respect to the initial output. Sometimes, it is possible to manufacture a wavelength conversion element made of a KTP crystal with further improved output aging characteristics.
[0020]
【Example】
Hereinafter, a preferred embodiment will be described in detail with reference to FIG.
[0021]
(Example 1)
A wavelength conversion element comprising a KTP crystal obtained by the hydrothermal synthesis method was incorporated in the SHG module 6 of the SHG apparatus of FIG. 1 described above, and the second harmonic was intermittently output for 60 hours under the following conditions.
[0022]
<Output conditions>
-Spot diameter on wavelength conversion element; diameter 2mm,
・ Pulse frequency: 10 kHz
・ Green output: 60W
-Pulse width: 130 ns.
[0023]
FIG. 2 shows the relationship between time and output when such a double harmonic is intermittently output for 60 hours.
[0024]
As can be seen from FIG. 2, when a double harmonic is output by a wavelength conversion element made of a KTP crystal, the output decreases with time.
[0025]
A wavelength conversion element made of KTP crystal in which such output deterioration with time (output decreased by about 36% with respect to the initial output) was annealed at 170 ° C. for 3 hours in the air atmosphere. The annealed wavelength conversion element was incorporated in the SHG module 6 of the SHG apparatus of FIG. 1 described above, and the double harmonic was intermittently output for 60 hours under the same conditions as described above. The relationship between time and output at this time is shown in FIG.
[0026]
As is apparent from FIG. 3, the converted output is restored to the initial state by annealing the wavelength conversion element made of the KTP crystal whose output has deteriorated with time. It can be seen that there is a marked improvement.
[0027]
(Comparative Example 1)
A wavelength conversion element comprising a novel KTP crystal obtained by the hydrothermal synthesis method was annealed at 170 ° C. for 3 hours in the air atmosphere. The annealed wavelength conversion element was incorporated into the SHG module 6 of the SHG apparatus of FIG. 1 described above, and double harmonics were intermittently output for 60 hours under the same conditions as in Example 1. FIG. 4 shows the relationship between time and output at this time.
[0028]
As is clear from FIG. 4, the output of the wavelength conversion element of Comparative Example 1 decreases with time as compared with Example 1 (FIG. 3), and the output time-lapse characteristics even when the wavelength conversion element made of a novel KTP crystal is annealed. It can be seen that the improvement effect cannot be obtained.
[0029]
(Example 2)
A wavelength conversion element made of KTP crystal obtained by the flux method was incorporated in the SHG module 6 of the SHG apparatus of FIG. 1 described above, and double harmonics were intermittently output for 60 hours under the same conditions as in Example 1.
[0030]
FIG. 5 shows the relationship between time and output when such a double harmonic is intermittently output for 60 hours.
[0031]
As is apparent from FIG. 5, when a second harmonic is output from the wavelength conversion element made of KTP crystal grown by the flux method, the wavelength conversion element made of KTP crystal grown by the hydrothermal synthesis method as in Example 1 is used. In comparison, it can be seen that the output greatly decreases with time.
[0032]
The wavelength conversion element made of KTP crystal in which such output deterioration with time (output decreased by about 55% with respect to the initial output) was annealed at 170 ° C. for 4 hours in the air atmosphere. The annealed wavelength conversion element was incorporated in the SHG module 6 of the SHG apparatus of FIG. 1 described above, and the double harmonic was intermittently output for 60 hours under the same conditions as described above. FIG. 6 shows the relationship between time and output at this time.
[0033]
As apparent from FIG. 6, the converted output is restored to the initial state by annealing the wavelength conversion element made of the KTP crystal whose output is deteriorated with time, and the output is reduced slightly at first, but the output characteristics thereafter. It can be seen that the output aging characteristics are greatly improved.
[0034]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to maintain a high output characteristic for a long time with respect to a high-speed repetitive laser, and to provide a method for manufacturing a wavelength conversion element useful for a wavelength conversion light source or the like. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a second harmonic generation (SHG) apparatus incorporating a wavelength conversion element of the present invention.
FIG. 2 is a characteristic diagram showing the relationship between time and output when a double harmonic is intermittently output for 60 hours by a wavelength conversion element made of a KTP crystal grown by a hydrothermal synthesis method in Example 1 of the present invention. .
FIG. 3 is a characteristic diagram showing a relationship between time and output when a double harmonic is intermittently output for 60 hours by a wavelength conversion element made of an annealed KTP crystal in Example 1 of the present invention.
FIG. 4 shows the time and output when the second harmonic is intermittently output for 60 hours by the wavelength conversion element obtained by annealing the new KTP crystal grown by the hydrothermal synthesis method in Comparative Example 1. The characteristic view which shows a relationship.
FIG. 5 is a characteristic diagram showing a relationship between time and output when a double harmonic is intermittently output for 60 hours by a wavelength conversion element made of a KTP crystal grown by a flux method in Example 2 of the present invention.
FIG. 6 is a characteristic diagram showing a relationship between time and output when a double harmonic is intermittently output for 60 hours by a wavelength conversion element made of an annealed KTP crystal in Example 2 of the present invention.
[Explanation of symbols]
1, 2, 3 ... Resonant mirror,
4 ... Excitation module,
5 ... Q switch,
6 ... SHG module,
7 ... Double harmonic output.

Claims (4)

For the wavelength conversion element made of KTP crystals, reduced by 10% or more with respect to the output Output of the wavelength conversion by the wavelength conversion element of the initial use, after this output deterioration with time in an atmosphere containing water vapor and oxygen, A method for manufacturing a wavelength conversion element, comprising annealing at a temperature of 170 ° C. or higher for 1 hour or longer .   The method for manufacturing a wavelength conversion element according to claim 1, wherein the atmosphere containing water vapor and oxygen is an air atmosphere. The KTP crystal, the method for manufacturing a wavelength conversion element according to claim 1, wherein the grown by hydrothermal synthesis method.   2. The method for manufacturing a wavelength conversion element according to claim 1, wherein the KTP crystal is grown by a flux method, and the annealing is performed at a temperature of 170 [deg.] C. or more for 2 hours or more in an atmosphere containing water vapor and oxygen.

Images