JP4114260B2 - Solid state laser equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state laser device used in various fields such as various measuring instruments, laser printers, medical equipment, and optical modeling.
[0002]
[Prior art]
A solid-state laser device condenses and irradiates a solid-state laser medium (for example, a YAG crystal) placed in an optical resonator with a laser beam output from an excitation source such as a semiconductor laser, thereby exciting the solid-state laser medium. By doing so, a laser oscillation is caused in an optical resonator (hereinafter referred to as a resonator), and a SHG (Second Harmonic Generation) element of a nonlinear optical crystal is arranged in the resonator to generate a second harmonic. Solid state laser.
[0003]
As shown in FIG. 10, the conventional solid-state laser device includes a semiconductor laser (LD) 1 for outputting excitation light, lenses 2 and 3 forming an excitation light coupling system for condensing the excitation light, and a solid state. A resonator 18 that generates a fundamental wave and a second harmonic laser beam composed of the laser medium 4, the SHG element 5, and the output mirror 6, and a temperature detector 24 through the resonator 18 via the temperature control input / output line 15. The SHG wave is made up of a resonator temperature adjuster 17 for controlling the temperature of the temperature control element 23 so that the detected temperature coincides with a set value, a beam splitter 7, a photodiode 8, a blue laser light monitor line 12, and an LD driver 16. The APC (Auto Power Control) mechanism 19 to be described later is held.
[0004]
In such a semiconductor laser excitation type solid-state laser device, it is difficult to dispose a temperature detector 24 such as a thermistor on the optical axis of the SHG element 5, and it is usually relatively distant as shown in FIG. Installed. The temperature control of the resonator 18 generally employs a method of keeping the control temperature constant at the installation point of the temperature detector 24 as a reference. This method is also used for the pumping semiconductor laser 1.
[0005]
[Problems to be solved by the invention]
The conventional solid-state laser device is configured as described above, but the SHG element has a narrower temperature tolerance than a solid-state laser medium having a large temperature tolerance, and the control temperature at the installation point of the resonator temperature detector is constant. However, there is a problem that a temperature gradient is generated in the resonator due to the environmental temperature, and a crystal such as an SHG element is affected by the environmental temperature. The arrangement relationship between the SHG element (crystal) 5 and the temperature control element 23 and the temperature detector 24 shown in FIG. 10 shows an example, but generally, as shown in FIG. It is installed at a position indicated by crystal A or crystal B. In FIG. 4, the center position of the temperature detector 24 is set at a distance m from the center positions of the crystal B21 and the temperature control element 23, and the center positions of the crystals A20 and B21 are set apart by a distance n.
[0006]
In FIG. 4, since the temperature adjustment is performed based on the temperature measured by the temperature detector 24, the temperature in the vicinity of the temperature detector 24 is constant without being affected by changes in the environmental temperature. When the temperature in the vicinity of the temperature detector 24 is controlled at 25 ° C. and the environmental temperature is 5 ° C., for example, the metal plate 22 in the figure has a temperature control element 23 as shown in FIG. A temperature gradient is generated in which the temperature decreases as the distance from the center increases. Therefore, in order to control the vicinity of the temperature detector 24 so that the temperature is 25 ° C., which is the same as the set temperature, it is necessary to heat the temperature control element 23 to a set temperature or higher. As a result, as shown in FIG. 5A, the crystal B reaches a temperature Th higher than the set temperature, and the crystal A has a low temperature Tl. Further, when the environmental temperature becomes 45 ° C., for example, a reverse temperature gradient occurs, and the crystal A reaches a temperature Th higher than the set temperature as shown in FIG. Such temperatures Th and Tl are determined by the control temperature, the environmental temperature, and the installation position.
[0007]
FIG. 6 shows the temperature change of crystal A and crystal B when the control temperature, that is, the temperature in the vicinity of the temperature detector 24 (FIG. 4) is constant at 25 ° C. and the environmental temperature changes with time. As shown in the figure, as the difference between the environmental temperature and the control temperature (25 ° C.) increases, the difference between the actual temperature of the crystals A and B and the control temperature (25 ° C.) increases.
The temperature change of the crystal in such a solid-state laser device causes a difference between the actual temperature of the crystal and the phase matching temperature, and there is a problem that the oscillation state becomes unstable and the performance is deteriorated.
[0008]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a solid-state laser device capable of obtaining a stable output with respect to a change in environmental temperature.
[0009]
[Means for Solving the Problems]
To achieve the above object, the present invention includes a semiconductor laser, is excited by the output light from the semiconductor laser, a solid-state laser medium you stimulated emission the fundamental, to generate a second harmonic wave of the fundamental wave and a non-linear optical crystal, the houses a nonlinear optical crystal, and the solid-state laser medium, the second harmonic optical resonator and an output mirror for outputting to the outside, the second harmonic output to the external APC mechanism for controlling the drive current of the semiconductor laser to be constant, a metal plate holding the optical resonator and the nonlinear optical crystal, a Peltier element and a temperature measuring element disposed on the metal plate, Environmental temperature measuring means for measuring the environmental temperature, and the metal plate has a temperature detected by the temperature measuring element arranged on the metal plate so that the temperature is proportional to the temperature detected by the environmental temperature measuring means. Arranged By controlling the Peltier element, characterized by further comprising a temperature control means to maintain the actual temperature of the nonlinear optical crystal constant. In addition, a stem for holding the semiconductor laser, and a Peltier element and a temperature measuring element disposed on the stem, the temperature detected by the temperature measuring element disposed on the stem is detected by the environmental temperature measuring means. It further has a temperature control means for controlling the Peltier element arranged in the stem so as to be a temperature proportional to the temperature so as to keep the actual temperature of the semiconductor laser constant. Further, the environmental temperature measuring means measures the environmental temperature by detecting a driving current of the Peltier element.
[0010]
The solid-state laser device of the present invention is configured as described above, and the temperature of the crystal A or B is made constant by changing the control temperature as shown by the dotted line in FIG. Thus, a solid-state laser device which is not affected by the environmental temperature with respect to the crystal arrangement position can be obtained.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a solid-state laser device of the semiconductor laser excitation system of the present invention will be described with reference to FIG. This apparatus includes a semiconductor laser (LD) 1 for outputting pumping light, lenses 2 and 3 forming a pumping light coupling system for collecting pumping light, a solid-state laser medium 4, an SHG element 5, and an output. A resonator 18 that generates a fundamental wave and a second harmonic laser beam composed of a mirror 6, and this resonator 18 is connected to a thermistor 17 e that measures a detection temperature and an environmental temperature of the thermistor 10 via a temperature control input / output line 15. A resonator temperature controller 17 that adjusts the temperature of the Peltier element 9 so that the proportional set temperatures coincide with each other, a beam splitter 7, a photodiode 8, a blue laser light monitor line 12, and an LD driver 16, and keeps the SHG wave constant. The APC (Auto Power Control) mechanism 19 is provided.
[0012]
An Nd: YAG crystal is used for the solid-state laser medium 4 in the resonator 18, a nonlinear crystal of KNbO 3 is used for the SHG element 5, and a basic surface of 946 nm is formed on the excitation light incident end face 4 a of the solid-state laser medium 4 and the concave surface of the output mirror 6. A dielectric multilayer film having high reflectivity with respect to the wave and the SHG wave is coated.
[0013]
In this solid-state laser device, the excitation light generated from the semiconductor laser 1 is collimated by the lens 2 and then converged by the lens 3 to excite the solid-state laser medium 4. The solid-state laser medium 4 is disposed in a resonator 18 including the excitation light incident end face 4a and the output mirror 6 and causes laser oscillation. At this time, a second harmonic is similarly generated in the SHG element 5 disposed in the resonator, and a 473 nm blue laser beam, which is a second harmonic of the Nd: YAG946 nm laser beam, is generated. As a result, wavelength conversion is performed, and the laser beam having a shorter wavelength passes through the output mirror 6 and is output to the outside.
Note that other stimulated emission light such as 1.06 μm and 1.3 μm is also emitted from the solid-state laser medium 4, but the reflectivity at the output mirror 6 and the excitation light incident end face is low, so that the resonator passes through these. Only the fundamental wave of 946 nm and the second harmonic are confined in the resonator 18 and laser oscillation is performed and amplified to a large power light.
[0014]
The APC mechanism 19 separates a part of the blue laser light into the actual blue laser light and the monitor laser light by the beam splitter 7, and the monitor laser light is guided to the photodiode 8 to detect its intensity. Is done. The detected intensity signal is fed back to the LD driver 16 that outputs a drive current for adjusting the excitation light intensity of the semiconductor laser 1, and the drive current from the LD driver is adjusted so that the blue laser light intensity becomes a constant value. Be controlled.
[0015]
The nonlinear crystal KNbO3 used in the SHG element 5 performs wavelength conversion efficiently, but its temperature tolerance is narrow, and in order to perform stable wavelength conversion operation, it is necessary to accurately control the temperature during operation. .
[0016]
The present invention is characterized in that the control temperature in the vicinity of the thermistor 10 is changed in accordance with the environmental temperature. FIG. 2 shows the configuration of an embodiment of the resonator temperature controller in which the temperature set value is changed in accordance with the environmental temperature. The temperature regulator 17 includes resistors R1 and R2, a bridge circuit 17a having four sides of a thermistor 17e that measures the ambient temperature outside the resonator 18 and the surrounding temperature of the control temperature detection thermistor 10, and the bridge. The controller 17 includes an adjusting unit 17 b that receives the deviation voltage of the circuit 17 a and outputs a control signal to the Peltier element 9.
[0017]
A variable resistor (Vr) 17c is connected in parallel to the thermistor 17e, and the adjusting portion 17b works so that the combined resistance and the resistance value of the control temperature detecting thermistor 10 are equal to balance the bridge circuit 17a. For example, assuming that R1 = R2 and the resistance value of the variable resistor 17c is 1/9 that of the thermistor 17e, the resistance value of the thermistor 10 is 1/10 of the resistance value of the thermistor 17e. That is, the resistance ratio of the thermistor 17e and the thermistor 10 is 10: 1, but this ratio can be changed by adjusting the resistance value of the variable resistor 17c. Since the resistance value of the thermistor 17e changes depending on the environmental temperature and the resistance value of the thermistor 10 changes depending on the control temperature, the control temperature corresponding to the change of the environmental temperature is adjusted as shown in FIG. 7 by adjusting the resistance value of the variable resistor 17c. Can be changed as shown.
[0018]
As previously shown in FIG. 6, when the control temperature is controlled at 25 ° C., the temperature of the crystal B is 25 ° C. or higher when the environmental temperature is 25 ° C. or lower, and 25 when the environmental temperature is 25 ° C. or higher. The temperature difference is proportional to the difference between the environmental temperature and the control temperature (the temperature of the thermistor 10).
As shown in FIG. 7, the control temperature is 25 ° C. or lower when the environmental temperature is 25 ° C. or lower, and 25 ° C. or higher when the environmental temperature is 25 ° C. or higher. The deviation from 0 ° C. is compensated, and the actual temperature of the crystal B is kept at about 25 ° C.
[0019]
Further, in the bridge circuit 17a of FIG. 2, the control temperature with respect to the change of the environmental temperature can be changed as shown in FIG. 8 by switching the resistor R1 and the thermistor 10, and as a result, the crystal A shown in FIG. The deviation from 25 ° C. can be compensated by the control temperature of FIG. 8, and the actual temperature of the crystal A can be maintained at about 25 ° C.
[0020]
FIG. 3 shows a configuration of another embodiment of the resonator temperature controller in which the temperature set value is changed in accordance with the environmental temperature. This temperature controller 17 utilizes the fact that the drive current of the Peltier element used for temperature control of the semiconductor laser 1 is proportional to the environmental temperature as shown in FIG. 9, and is set in proportion to the drive current of the Peltier element. A variable resistor 17c for obtaining a voltage, a thermistor 10 for generating a feedback voltage proportional to the control temperature by flowing a current from a constant current source 17d, and the set voltage and the feedback voltage are differentially coupled. The adjustment unit 17b is configured to input the obtained deviation voltage and output a control signal to the temperature control element 9.
[0021]
By changing the variable resistor 17c, the voltage at both ends thereof, that is, the control temperature setting voltage changes, so that the control temperature can be changed at a constant ratio with respect to the Peltier element driving current that changes in accordance with the environmental temperature. According to this method, it is not necessary to use the thermistor 17e for environmental temperature measurement as shown in FIG. 2, and it is effective when there is no place for the thermistor, and the temperature control system is configured with a simple configuration. Can do.
As described above, the actual temperature of the crystal can be kept constant by changing the control temperature at a constant ratio with respect to the environmental temperature change according to the positional relationship between the thermistor and the crystal, and a wide operating temperature range. A stable laser output can be obtained.
[0022]
On the other hand, the temperature of the semiconductor laser 1 is also controlled by the LD driver 16 and the temperature control input / output line 14, but it is difficult to attach the control temperature detection thermistor to the chip of the semiconductor laser. Indirect temperature control is used. Therefore, if there is a difference between the control temperature and the environmental temperature, a temperature difference occurs between the thermistor mounting position and the semiconductor center position. Even in such a case, changing the control temperature in the vicinity of the thermistor according to the environmental temperature is an effective measure. For example, the resonator temperature control is used in the method of FIG. 2 using the ambient temperature measurement thermistor 17e, and the temperature control of the semiconductor laser 1 is proportional to the drive current of the Peltier element 9 in proportion to the Peltier element drive current of FIG. By using the current, the influence of the environmental temperature on the resonator 18 and the semiconductor laser 1 can be eliminated.
[0023]
In addition, a temperature control element and a temperature detector are not limited to the said implementation side, For example, a ceramic heater can be used as a temperature control element, a temperature sensitive resistor etc. can be used as a temperature detector.
[0024]
【The invention's effect】
The solid-state laser device of the present invention is configured as described above, and by changing the control temperature of the resonator and the semiconductor laser in accordance with the environmental temperature, the temperature of the crystal in the resonator and the semiconductor laser is changed according to the environmental temperature. The fluctuation can be prevented, and a stable laser output can be obtained in a wide temperature range.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a semiconductor laser excitation type solid-state laser device of the present invention.
FIG. 2 is a schematic configuration diagram showing an embodiment of a resonator temperature adjustment mechanism in which a temperature set value is changed according to an environmental temperature.
FIG. 3 is a schematic configuration diagram showing another embodiment of the resonator temperature adjusting mechanism in which the temperature set value is changed in accordance with the environmental temperature.
FIG. 4 is a component arrangement diagram showing the relationship between the temperature adjusting component of the resonator and the crystal arrangement position.
FIG. 5 is a temperature change diagram showing the relationship between the crystal arrangement and the temperature when the environmental temperature is low and high with respect to the set value of the temperature control.
FIG. 6 is a crystal temperature change diagram when the set temperature control value is constant and the environmental temperature is changed with time.
FIG. 7 is a temperature change diagram of crystal B when the control temperature is changed with respect to the environmental temperature.
FIG. 8 is a temperature change diagram of crystal A when the control temperature is changed with respect to the environmental temperature.
FIG. 9 is an environment temperature vs. Peltier device drive current characteristic diagram.
FIG. 10 is a configuration diagram of a conventional semiconductor laser excitation type solid-state laser device.
[Explanation of symbols]
1. Semiconductor laser (LD)
2, 3 ... Lens 4 ... Solid laser medium 4a ... Excitation light incident end face 5 ... SHG element 6 ... Output mirror 7 ... Beam splitter 8 ... Photo diode 9 ... Peltier elements 10, 17e ... thermistors 11, 22 ... metal plate 12 ... blue laser light monitor line 13 ... LD drive current lines 14, 15 ... temperature control input / output line 16 ... LD driver 17... Resonator temperature controller 17a... Bridge circuit 17b... Adjustment unit 17c... Variable resistor 17d... Constant current source 18. ..Crystal A
21 ... Crystal B
23 ... Temperature control element 24 ... Temperature detector

Claims (2)

A semiconductor laser;
A solid-state laser medium that is excited by output light from the semiconductor laser and stimulates and emits a fundamental wave;
A nonlinear optical crystal that generates a second harmonic of the fundamental wave;
An optical resonator containing the nonlinear optical crystal and including the solid-state laser medium and an output mirror that outputs the second harmonic to the outside;
An APC mechanism for controlling the drive current of the semiconductor laser so that the second harmonic output to the outside is constant;
A metal plate holding the optical resonator and the nonlinear optical crystal;
A Peltier element and a temperature measuring element disposed on the metal plate;
Environmental temperature measuring means for measuring the environmental temperature,
By controlling the Peltier element arranged on the metal plate so that the temperature detected by the temperature measuring element arranged on the metal plate becomes a temperature proportional to the temperature detected by the environmental temperature measuring means, the nonlinear optical A solid-state laser device further comprising temperature control means for keeping the actual temperature of the crystal constant. A stem for holding the semiconductor laser;
Having a Peltier element and a temperature measuring element disposed on the stem;
By controlling the Peltier element arranged in the stem so that the temperature detected by the temperature measuring element arranged in the stem becomes a temperature proportional to the temperature detected by the environmental temperature measuring means, 2. The solid state laser device according to claim 1, further comprising temperature control means for keeping the temperature constant.

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