JP2004294738A - Solid state laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress optical noise produced in the vicinity of a relaxation oscillation frequency fk of a solid state laser device. <P>SOLUTION: A phase shifting circuit (9c) to advance a phase in the vicinity of the relaxation oscillation frequency of the solid state laser device is mounted on output control circuits (9, 10). Thereby, summing up phase shifting transmission characteristics of the phase shifting circuit and phase transmission characteristics of a nonlinear optical element and a microchip laser crystal, a delayed phase in the vicinity of the relaxation oscillation frequency turns out to be 0° and the optical noise is suppressed by feedback control with the output control circuits. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid-state laser device, and more particularly, to a solid-state laser device capable of suppressing optical noise generated near a relaxation oscillation frequency of the solid-state laser device.
[0002]
[Prior art]
Conventionally, a semiconductor laser that generates laser light, a non-linear optical element that emits a harmonic when laser light from the semiconductor laser is incident, and a monitoring light detection unit that detects the intensity of light emitted from the non-linear optical element, 2. Description of the Related Art A solid-state laser device including an output control circuit that drives a semiconductor laser so that the light intensity becomes a predetermined value is known (for example, see Patent Document 1).
There is also known a solid-state laser device in which a microchip laser crystal, which is a crystal excited by laser light from a semiconductor laser and forms an optical resonator with a coating applied to a crystal end face, is provided in front of a nonlinear optical element. (For example, see Patent Document 2).
[0003]
[Patent Document 1]
JP-A-7-106682 [Patent Document 2]
Japanese Patent Publication No. Hei 4-503429
[Problems to be solved by the invention]
FIG. 4 shows an actual measurement example of gain transfer characteristics and phase transfer characteristics of a nonlinear optical element and a microchip laser crystal in an example of a conventional solid-state laser device.
In the example of FIG. 4, a gain peak appears at about 11 MHz. This peak frequency is called the relaxation oscillation frequency fk of the solid-state laser device. In the example of FIG. 4, the phase is delayed by about 90 ° near the relaxation oscillation frequency fk.
[0005]
FIG. 5 shows an actual measurement example of an optical noise waveform of the solid-state laser device.
In the example of FIG. 5, the oscillation frequency of the optical noise is about 11 MHz, which coincides with the relaxation oscillation frequency fk in FIG.
That is, it is considered that the optical noise occurs near the relaxation oscillation frequency fk, and a phase delay of about 90 ° occurs.
[0006]
In the solid-state laser device having the phase transfer characteristic shown in FIG. 4, output fluctuation (noise) is suppressed by feedback control by an output control circuit. In the feedback control by this output control circuit, there is a limit in suppressing noise because of a phase delay of about 90 °.
Accordingly, an object of the present invention is to provide a solid-state laser device that can suppress optical noise generated near the relaxation oscillation frequency fk.
[0007]
[Means for Solving the Problems]
In a first aspect, the present invention provides a semiconductor laser that generates a laser beam, and a microchip that is a crystal excited by the laser beam from the semiconductor laser and that forms an optical resonator with a coating applied to a crystal end face. A laser crystal, a non-linear optical element into which laser light from the microchip laser crystal is incident and emits harmonics, a monitoring light detecting means for detecting the intensity of light emitted from the non-linear optical element, An output control circuit for driving the semiconductor laser so that the intensity becomes a predetermined value, wherein a phase shift circuit for advancing a phase near a relaxation oscillation frequency of the solid-state laser device is provided in the output control circuit. A solid-state laser device is provided.
In the solid-state laser device according to the first aspect, a phase-shifting circuit for advancing the phase near the relaxation oscillation frequency of the solid-state laser device is provided. By adding the phase transfer characteristics of the crystal, the lag phase near the relaxation oscillation frequency becomes 0 °, and optical noise can be suppressed by feedback control by the output control circuit.
[0008]
In a second aspect, the present invention provides a semiconductor laser that generates laser light, a non-linear optical element into which laser light from the semiconductor laser is incident and emits harmonics, and an intensity of light emitted from the non-linear optical element. And a power control circuit for driving the semiconductor laser so that the intensity of the light becomes a predetermined value, a phase near the relaxation oscillation frequency of the solid-state laser device. Provided in the output control circuit is a solid-state laser device.
In the solid-state laser device according to the second aspect, a phase shift circuit for advancing the phase near the relaxation oscillation frequency of the solid-state laser device is provided. The phase shift transfer characteristic of this phase shift circuit and the phase transfer characteristic of the nonlinear optical element are provided. Is added, the lag phase near the relaxation oscillation frequency becomes 0 °, and optical noise can be suppressed by feedback control by the output control circuit.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention shown in the drawings will be described. Note that the present invention is not limited by this.
[0010]
-1st Embodiment-
FIG. 1 is a configuration diagram illustrating a solid-state laser device 100 according to the first embodiment. The solid-state laser device 100 includes a semiconductor laser 1 for generating laser light, a condensing lens system 2 for condensing laser light, and a crystal that is excited by the condensed laser light and is applied to a crystal end face. A microchip laser crystal 3 constituting an optical resonator by coating; a non-linear optical element 4 into which laser light from the microchip laser crystal 3 is incident to emit harmonics; and an intensity of light emitted from the non-linear optical element 4. A splitter 5, an optical filter 6, and a photodiode 7 for detection; a low-speed APC (Auto Power Control) circuit 8 for outputting a control signal L so that the intensity of light detected by the photodiode 7 becomes a predetermined value; A high-speed APC circuit 9 for outputting a control signal H so that a noise component of light detected by the diode 7 becomes 0; It is provided with a supply LD driving circuit 10 and a drive current based on the control signal H to the semiconductor laser 1.
[0011]
The low-speed APC circuit 8 includes a signal amplification circuit 8b and a signal inversion amplification circuit 8d.
The high-speed APC circuit 9 includes a coupling capacitor 9a, a signal amplification circuit 9b, a phase shift circuit 9c, and a signal inversion amplification circuit 9d.
[0012]
FIG. 2 shows a circuit example of the phase shift circuit 9c.
The phase shift circuit 9c advances the phase by, for example, 90 degrees near the relaxation oscillation frequency fk. In practice, the amount of phase shift is determined so that the delay of the entire system (delay of an electric circuit, a transmission cable, or the like) is also canceled.
On the other hand, as shown in FIG. 4, in the phase transfer function of the nonlinear optical element 4 and the microchip laser crystal 3, the phase near the relaxation oscillation frequency fk at which optical noise occurs is delayed by 90 °.
Then, in the phase transfer function obtained by combining the nonlinear optical element 4 and the microchip laser crystal 3 with the phase shift circuit 9c, the delay phase shift near the relaxation oscillation frequency fk becomes 0 °, and the optical noise is fed back by the high-speed APC circuit 9. It can be suppressed by control.
[0013]
-2nd Embodiment-
FIG. 3 is a configuration diagram illustrating a solid-state laser device 200 according to the second embodiment. The solid-state laser device 200 has the same configuration except that the microchip laser crystal 3 is omitted from the solid-state laser device 100 according to the first embodiment.
[0014]
In the solid-state laser device 200, the same effects as those of the solid-state laser device 100 according to the first embodiment are obtained. That is, optical noise can be suppressed by feedback control by the high-speed APC circuit 9.
[0015]
【The invention's effect】
According to the solid-state laser device of the present invention, the phase control circuit for advancing the phase near the relaxation oscillation frequency of the solid-state laser device is provided in the output control circuit, so the phase transfer characteristic of the nonlinear optical element or the nonlinear optical element and the microchip laser crystal When the phase transfer characteristic is added to the above, the lag phase becomes 0 ° in the vicinity of the relaxation oscillation frequency, and optical noise can be suppressed by feedback control by the output control circuit.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating a solid-state laser device according to a first embodiment.
FIG. 2 is a circuit diagram illustrating a circuit example of a phase shift circuit.
FIG. 3 is a configuration diagram illustrating a solid-state laser device according to a second embodiment.
FIG. 4 is a characteristic diagram showing an actual measurement example of gain transfer characteristics and phase transfer characteristics of a nonlinear optical element and a microchip laser crystal in an example of a conventional solid-state laser device.
FIG. 5 is a waveform chart showing an actual measurement example of an optical noise waveform in an example of a conventional solid-state laser device.
[Explanation of symbols]
Reference Signs List 1 semiconductor laser 3 microchip laser crystal 4 nonlinear optical element 8 low-speed APC circuit 9c phase-shift circuit 9 high-speed APC circuit 100, 200 solid-state laser device

Claims (2)

A semiconductor laser that generates laser light, a crystal that is excited by the laser light from the semiconductor laser, a microchip laser crystal that forms an optical resonator with a coating applied to a crystal end face, and a microchip laser crystal. A non-linear optical element that receives laser light and emits harmonics, a monitoring light detection unit that detects the intensity of light emitted from the non-linear optical element, and the semiconductor device so that the intensity of the light becomes a predetermined value. In a solid-state laser device comprising an output control circuit for driving a laser,
A solid-state laser device, wherein a phase shift circuit for advancing a phase near a relaxation oscillation frequency of the solid-state laser device is provided in the output control circuit. A semiconductor laser that generates laser light, a non-linear optical element into which laser light from the semiconductor laser is incident and emits harmonics, and a monitoring light detection unit that detects the intensity of light emitted from the non-linear optical element, A solid-state laser device comprising: an output control circuit that drives the semiconductor laser such that the light intensity becomes a predetermined value.
A solid-state laser device, wherein a phase shift circuit for advancing a phase near a relaxation oscillation frequency of the solid-state laser device is provided in the output control circuit.

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