JP3767318B2 - LD pumped solid state laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to output stabilization of an LD-pumped solid-state laser device.
[0002]
[Prior art]
Conventionally, output light from a semiconductor laser (hereinafter referred to as “LD light” as appropriate) is collected and irradiated onto a solid-state laser medium, and a fundamental wave guided and emitted from the solid-state laser medium is accommodated in an optical resonator. By irradiating the nonlinear optical crystal, second harmonics (hereinafter referred to as “SH waves” as appropriate) are generated, and the second harmonics are oscillated in the optical resonator and output to the outside through the output mirror. A wavelength conversion solid-state laser device is known.
[0003]
A specific example of this will be described with reference to FIGS. As shown in FIG. 3, the output light from the semiconductor laser 31 is applied to the solid-state laser medium (Nd: YAG) 33 through the collimator lens 32a and the focus lens 32b. A highly reflective coating that transmits LD light from the semiconductor laser 31 on one side of the solid laser medium 33 and reflects the fundamental wave and the SH wave that are stimulated and emitted from the solid laser medium 33 with high reflectivity. A film is formed, and an optical resonator is formed between the highly reflective coating film and the output mirror 36.
[0004]
A nonlinear optical element (hereinafter also referred to as “SHG”, for example, KNbO ₃ ) 35 for generating an SH wave is inserted inside the optical resonator, and a solid laser medium 33 is excited by output light from the semiconductor laser 31. By irradiating the nonlinear optical element 35 with the fundamental wave stimulated and emitted as a result, a second harmonic is generated. The output mirror 36 mainly transmits the SH wave, and therefore the SH wave is output to the outside of the optical resonator through the output mirror 36.
[0005]
A part of the SH wave output outside the optical resonator is separated as a monitor light Lm at a predetermined ratio by a beam sampler 37 disposed close to the output mirror 36 and guided to the photodetector 38. Intensity is detected. The detection result is fed back to the laser controller 39, and the LD current is controlled so as to keep the SH wave output constant. The main part of the apparatus is controlled to a predetermined temperature by a laser controller 39.
[0006]
[Problems to be solved by the invention]
In the above configuration, as shown in FIG. 4, there is a serious problem in the detection of monitor light incident on the photodetector 38. The light receiving surface 38a of the photodetector 38 is disposed in the casing 38b and is covered with the light receiving surface protecting resin 38c and the glass substrate 38d. However, the monitor light Lm is subjected to multiple reflection inside the protecting resin 38c and the glass substrate 38d. And a state of interference occurs. When the monitor light interferes, even if a slight temperature change of the resin for protecting the light receiving surface or the glass substrate or a slight change in the incident angle of the monitor light occurs, the interference condition until the monitor light enters the light receiving surface 38a Changes, and even if the output light intensity (Lo) is constant, the intensity Le of the effective monitor light incident on the PD light receiving surface 38a varies.
[0007]
Therefore, the ratio Le / Lo of the effective monitor light intensity Le to the laser output light intensity Lo varies, and the monitor light intensity detection value varies even when the laser output light intensity Lo is stable. When the monitor light intensity detection value fluctuates, the LD drive current is controlled by the laser controller 39 so as to keep it constant, and the monitor light is contrary to the original function, and the laser output Lo according to the influence of the light interference described above. This will result in a fluctuation of.
The present invention provides an LD-pumped solid-state laser device with a stable output, in which the ratio of the intensity of effective monitor light incident on the light-receiving surface of the photodetector does not fluctuate due to the influence of a slight temperature change of the protective resin or the glass substrate. The purpose is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an LD-pumped solid-state laser device of the present invention excites a solid-state laser medium with output light from a semiconductor laser, and installs a nonlinear optical element in an optical resonator including the solid-state laser medium. It is configured to output the second harmonic of the fundamental wave stimulated and emitted from the laser medium to the outside through the output mirror, and a predetermined part of the output is detected by the photodetector, and the detection output is constant. In the laser device that stabilizes the output by changing the drive current of the semiconductor laser so that the following is obtained, means for removing the interference of the monitor light incident on the light receiving surface is provided in front of the light receiving surface of the photodetector. Yes, as interference removal means, either one or both sides of the light-receiving surface protection resin or glass substrate are formed into a ground surface, and the monitor light is diffused, or the light-receiving surface protection resin or glass substrate is wedge-shaped. It is preferable to.
By the above means, the interference of the monitor light is eliminated, and the laser output does not fluctuate even when a slight temperature change of the resin for protecting the light receiving surface or the glass substrate and a slight change in the incident angle of the monitor light occur.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a system configuration diagram of an LD-pumped solid-state laser device according to an embodiment of the present invention, and FIGS. 2A, 2B, and 2C are detailed views of a part (PD) of FIG.
In FIG. 1, 1 is a semiconductor laser for exciting a solid laser medium, 2 (2a, 2b) is an optical system for irradiating the solid laser medium with light from the semiconductor laser 1, 2a is a collimator lens, 2b is It is a focus lens. 3 is a solid-state laser medium, for example, Nd: YAG is used. Reference numeral 5 denotes a non-linear optical element for generating an SH wave from the output of the solid laser medium 3, and for example, KNbO ₃ is used. 6 is an output mirror having the characteristic of transmitting the SH wave and reflecting the fundamental wave. The front end face of the solid laser medium 3 transmits the LD light from the semiconductor laser 1 and reflects the fundamental wave and the SH wave stimulated and emitted from the solid laser medium 3 with high reflectivity. A coating film 3a is formed. The high reflection coating film 3a and the output mirror 6 form an optical resonator for SH waves.
[0010]
A beam sampler 7 is arranged close to the output mirror 6, and the SH wave output L of the output mirror 6 is converted into an actual SH wave output (transmitted light) Lo and monitor light SH wave (reflected light) Lm at a predetermined ratio. To separate. 8 is a light detector for detecting the intensity of the monitor light Lm, and 9 is a laser controller for controlling the laser light output Lo to a predetermined level. The detection result of the light detector 8 is fed back to the driver 9, and the SH wave The LD current is controlled so as to keep the output Lo constant.
[0011]
In the system configuration described above, in the present invention, means for preventing the multiple reflection of the monitor light incident on the light receiving surface and removing the interference of the monitor light is provided upstream of the light receiving surface 8a of the photodetector 8. Specific embodiments of the monitor light interference removing means S (S1, S2, S3) are shown in FIGS. 2A, 2B, and 2C, respectively. (A) of FIG. 2 forms a slit surface (S1) in the glass substrate 8d which comprises the input surface of the photodetector 8. FIG. The slit surface S1 is desirably formed not only in the range facing the light receiving surface 8a but also on the entire surface of the glass substrate 8d. In addition, although the surface S1 is formed on the surface (incident surface) in the drawing, it may be formed on the inner surface (exiting surface) or both surfaces. Due to the slit surface S1, the monitor light Lm incident on the detector 8 becomes diffused light on the slit surface and reaches the light receiving surface 8a with a disparate phase, so that no interference occurs.
[0012]
FIG. 2B shows an optical interference removing means S provided on the input surface side of the photodetector 8, wherein the glass substrate 8 d constituting the input surface of the photodetector 8 is inclined S 2 with respect to the light receiving surface 38 a, and resin The layer and the glass substrate are formed in a wedge shape. With this wedge shape, the optical path length gradually changes every time the incident monitor light is reflected, and there is almost no possibility of causing interference. In this case, the inclination direction of the glass substrate 8d is desirably a direction approaching the monitor light Lm as shown in the figure, but may be configured to be inclined in a direction away from the monitor light Lm.
[0013]
FIG. 2C shows a light diffusing plate (S3) provided near the outside of the glass substrate 8d constituting the input surface of the photodetector 8 as the optical interference removing means S provided on the input surface side of the photodetector 8. It is a thing. The light diffusing plate S3 is provided in parallel to face the entire surface of the glass substrate 8d. However, in some cases, the light diffusing plate (S3) itself may be arranged in a slightly inclined shape in combination with the method of FIG. Good.
Although not the main point of the present invention, in this embodiment, the output wavelength of the semiconductor laser 1 is, for example, 809 nm, Nd: YAG is used for the solid laser medium 3, the laser fundamental wave is 946 nm, and the SH wave ( Nonlinear optical element: KNbO ₃ ) is 473 nm.
[0014]
In the above configuration, the focus lens 2b, the solid laser medium 3, the etalon, the nonlinear optical element 5, the output mirror 6, and the beam sampler 7 are fixed on a common base plate (not shown). A temperature sensor is embedded in the base plate, and a Peltier element for temperature adjustment, in which a heat radiating plate is thermally connected, is disposed on the lower surface side of the base plate. The temperature detection value K of the thermometer is fed back to the laser controller 9, and the drive current of the Peltier element is controlled so as to keep the temperature of the base plate, that is, the temperature of the nonlinear optical element 5 constant.
[0015]
Next, the operation of the device of the present invention will be described.
Output light from the semiconductor laser 1 is applied to the solid-state laser medium (Nd: YAG) 3 through the collimator lens 2a and the focus lens 2b. When the nonlinear optical element 5 is irradiated with the fundamental wave stimulated and emitted by exciting the solid laser medium 3 with the output light from the semiconductor laser 1, a second harmonic is generated. The output mirror 6 mainly transmits the SH wave. Therefore, the SH wave L is output to the outside of the optical resonator through the output mirror 6.
[0016]
The SH wave L output to the outside of the optical resonator is separated into the actual output light Lo and the monitor light Lm at a predetermined ratio by the beam sampler 7 disposed close to the output mirror 6, and the monitor light Lm It is guided to the detector 8 and its intensity is detected.
In the detection of the monitor Lm, means S, for example, a slit surface S1, for preventing multiple reflection of the monitor light incident on the light receiving surface and removing the interference of the monitor light is provided in the light detector 8 before the light receiving surface 8a. As a result, the monitor light Lm incident on the detector 8 becomes diffused light on the incident surface and reaches the light receiving surface 8a with a disparate phase, so that interference is prevented and effective monitor light for the laser output light intensity Lo is obtained. As long as the ratio Le / Lo of the intensity Le is maintained at a predetermined value and the laser output light intensity Lo is stable, the monitor light intensity detection value does not vary, and if the monitor light intensity detection value varies, it is held constant. As described above, the LD drive current is controlled by the controller 9, the monitor light performs its original function, and the laser output Lo is stably maintained.
[0017]
【The invention's effect】
As described above, according to the LD excitation wavelength conversion solid-state laser device of the present invention, the means for preventing the reflection of the monitor light and preventing the interference of the monitor light by preventing the reflection of the monitor light incident on the light receiving surface before the light receiving surface of the photodetector. By providing, interference due to multiple reflection does not occur inside the resin or glass substrate, so that the output of the PD does not fluctuate as long as the output is stable. Therefore, the laser output does not fluctuate even when there is a slight change in the temperature of the resin for protecting the light receiving surface, the glass substrate, or the change in the incident angle of the monitor light. Therefore, an LD-pumped solid-state laser device that is resistant to environmental temperature changes can be configured.
[Explanation of symbols]
LD: Semiconductor laser 2a: LD light collimator lens 2b: LD light condensing lens 3: Laser medium (Nd YAG crystal)
5: Non-linear crystal (KNbO ₃ crystal)
6: Output mirror 7: Beam sampler 8: Photo diode 9: Laser controller [Brief description of the drawings]
FIG. 1 is a schematic system configuration diagram of an LD-pumped solid state laser apparatus according to an embodiment of the present invention.
FIG. 2 shows an embodiment of the main part of the LD-excited solid-state laser device of the present invention.
FIG. 3 shows a configuration example of a conventional LD-pumped solid-state laser device.
FIG. 4 is a diagram for explaining the operation of a conventional LD-pumped solid-state laser device.

Claims (1)

  A solid-state laser medium is excited by output light from a semiconductor laser (LD), and a nonlinear optical element is installed in an optical resonator including the solid-state laser medium, and the second harmonic of the fundamental wave stimulated and emitted from the solid-state laser medium. Is output to the outside via an output mirror, the monitor light is detected by a photodetector, and the output of the semiconductor laser is changed so that the detection output is constant, thereby stabilizing the output. In the laser apparatus, means for removing interference of monitor light incident on the light receiving surface is provided in front of the light receiving surface of the photodetector, and the means for removing interference of the monitor light constitutes an input surface of the photodetector. An LD-pumped solid-state laser device comprising a groove surface formed on a glass substrate

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