JP2010251448A - Solid-state pulsed laser apparatus for output of third harmonic waves - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize the peak intensity of a pulse output. <P>SOLUTION: A peak intensity A of a pulse output detected by a photodiode is measured, and a difference B-A between the peak intensity A and a reference peak intensity B that is preliminarily set is determined (step D1). Then, a driving current correcting amount C=k(B-A) is determined (step D2). Next, a value obtained by adding the driving current correcting amount C to the last driving current I<SB>t-1</SB>is set as a new driving current I<SB>t</SB>. At the next pulse output, the new driving current I<SB>t</SB>is supplied to a semiconductor laser (step D3). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a solid-state pulse laser device that outputs a third harmonic, and more particularly to a solid-state pulse laser device that can stabilize the peak intensity of the third harmonic pulse output.

  In the conventional solid-state pulse laser device that outputs the third harmonic, the driving current of the semiconductor laser is controlled so that the average intensity of the pulse output is constant. Further, the temperature control is performed so that the temperature of the semiconductor laser, the solid laser medium, or the like becomes a preset temperature.

On the other hand, a technique is known in which the peak intensity of a pulse output is detected and the high-frequency power supplied to the Q switch is feedback-controlled based on the detected peak intensity to stabilize the peak intensity (for example, see Patent Document 1). A solid-state monitor that constantly monitors the drive current of the semiconductor laser, and if the change in the drive current exceeds a predetermined value, the temperature is tuned again while continuing to use, and the bottom temperature at which the minimum drive current is achieved is reset. A laser device is known (for example, refer to Patent Document 2).
Japanese Patent No. 3445390 ([0041]) JP 2007-234759 A ([0022])

In the conventional solid-state pulse laser device that outputs the third harmonic, the average intensity of the pulse output is constant, but there is a problem that variation in peak intensity cannot be suppressed. In addition, there is a problem that it cannot cope with fluctuations in temperature characteristics of a semiconductor laser or a solid-state laser medium due to changes with time.
On the other hand, the conventional technique described in Patent Document 1 has a problem in that the configuration becomes complicated because of the control of high-frequency power.

  The prior art described in Patent Document 2 can be applied to a solid-state pulse laser device that outputs a third harmonic.

  Accordingly, an object of the present invention is to provide a solid-state pulse laser device capable of stabilizing the peak intensity of the third harmonic pulse output and a solid-state pulse laser device in which the conventional technique described in Patent Document 2 is applied to the solid-state pulse laser device. There is to do.

In a first aspect, the present invention relates to a semiconductor laser that generates laser light, a semiconductor laser driving circuit that supplies a driving current to the semiconductor laser, and a solid-state laser medium that is excited by the laser light output from the semiconductor laser. A second harmonic generating crystal and a third harmonic crystal for outputting a third harmonic of a fundamental wave oscillated by the optical resonator installed in an optical resonator including the solid-state laser medium, Temperature control means for controlling the temperature of at least one of the semiconductor laser, the solid-state laser medium, the second harmonic generation crystal, and the third harmonic crystal; the fundamental wave, the second harmonic wave, or the first harmonic wave; A monitoring optical output detector that detects a part of any pulse output of the third harmonic, and a peak intensity of the pulse output detected by the monitoring optical output detector to detect the semiconductor laser drive. To provide a solid-state pulsed laser apparatus for outputting the third harmonic, characterized by comprising a peak intensity stabilizing means for stabilizing the peak intensity of the feedback control of the circuit pulse output.
In the solid-state pulse laser device that outputs the third harmonic according to the first aspect, the peak intensity of the pulse output can be stabilized because the peak intensity of the pulse output is detected and the semiconductor laser driving circuit is feedback controlled. . Further, since the driving current of the semiconductor laser is controlled, the configuration is simplified.

In a second aspect, the present invention provides a solid-state pulse laser device that outputs a third harmonic according to the first aspect, and constantly monitors a change in the drive current of the semiconductor laser, and the amount of change exceeds a predetermined value. Temperature control means for controlling the temperature of the semiconductor laser, temperature control means for controlling the temperature of the solid laser medium, temperature control means for controlling the temperature of the second harmonic generation crystal, and the third harmonic. And driving at least one of temperature control means for controlling the temperature of the crystal for crystal and sweeping the temperature in a predetermined temperature range to measure the driving current of the semiconductor laser to obtain a minimum bottom current value, and to calculate the bottom current value A solid-state pulse laser device for outputting a third harmonic is provided, comprising target value setting means for setting a target value of the temperature control means.
The “always monitoring” includes a case where monitoring is temporarily interrupted in order to perform other necessary processing.
In the solid-state pulse laser device that outputs the third harmonic according to the second aspect, the driving current of the semiconductor laser is constantly monitored, and if the change in the driving current exceeds a predetermined value, the temperature is maintained while being used continuously. Re-tune and reset the bottom temperature to the minimum drive current. For this reason, it is possible to cope with fluctuations in temperature characteristics of a semiconductor laser, a solid-state laser medium, and the like due to changes over time, and the minimum driving current can always be maintained.

  According to the solid-state pulse laser device that outputs the third harmonic of the present invention, the peak intensity of the pulse output can be stabilized. In addition, the driving current of the semiconductor laser can always be kept at a minimum.

  Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited thereby.

Example 1
FIG. 1 is an explanatory diagram illustrating a solid-state pulse laser device 100 that outputs a third harmonic according to the first embodiment.
The solid-state pulse laser device 100 that outputs the third harmonic includes a semiconductor laser 1 that generates excitation laser light, a temperature control unit 2 that includes a Peltier element and a temperature sensor, and controls the temperature of the semiconductor laser 1. A condensing lens system 3 that condenses the excitation laser beam, a solid laser medium 4 that has a reflection surface formed on the incident surface of the excitation laser beam and is excited by the excitation laser beam to generate a fundamental wave, and functions as a Q switch An acoustooptic device 5 that transmits a fundamental wave and reflects a second harmonic and a third harmonic, a THG device 7 that generates a third harmonic from the fundamental and the second harmonic, and a fundamental An SHG element 8 that generates a second harmonic from the wave, a mirror 9 that forms an optical resonator 15 between the solid-state laser medium 4, a temperature adjustment unit 10 that adjusts the temperature of the THG element 7, and SHG Element 8 A temperature control unit 11 for adjusting, a beam splitter 12 that transmits the second harmonic and reflects the third harmonic, and a beam splitter 13 that reflects a part of the third harmonic and transmits the other part. A photodiode 14 for receiving a part of the third harmonic, a temperature control unit 16 for controlling the temperature of the solid-state laser medium 4, and a semiconductor laser temperature control for controlling the temperature of the semiconductor laser 1 by the temperature control unit 2. A circuit 21, a solid-state laser medium temperature control circuit 22 for controlling the temperature of the solid-state laser medium 4 by the temperature control unit 16, a THG element temperature control circuit 23 for controlling the temperature of the THG element 7 by the temperature control unit 10, and a temperature control A THG element temperature control circuit 24 for controlling the temperature of the SHG element 7 by the unit 11 and a semiconductor laser driving circuit for outputting a driving current I for driving the semiconductor laser 1 5, and a control circuit 26 for controlling the respective temperature control circuits 21, 22, 23, 24 controls the semiconductor laser driving circuit 25 based on the output of the photodiode 14.

FIG. 2 is a flowchart illustrating the drive current control process according to the first embodiment. This process is executed for each pulse output.
In step D1, the peak intensity A of the pulse output detected by the photodiode 14 is measured, and the difference B−A from the preset reference peak intensity B is obtained.
In step D2, a drive current correction amount C = k (B−A) is obtained. Here, k is a proportionality coefficient.
In step D3, a value obtained by adding the drive current correction amount C to the drive current It-1 one time before is set as a new drive current It, which is supplied to the semiconductor laser 1 at the next pulse output time. Then, the process returns to step D1.

FIG. 3 is a flowchart illustrating the target temperature update process according to the first embodiment. This process is executed at regular time intervals.
In step R1, the drive current I of the semiconductor laser 1 is measured and stored as a reference current value.

In step R2, the drive current I is measured, and the difference from the reference current value is obtained.
In step R3, if the difference is smaller than a predetermined value (for example, 100 mA), the process returns to step R2, and if not smaller, the process proceeds to step R4.

  In step R4, the bottom temperature detection process shown in FIG. 4 is executed. Then, the process returns to step R1.

FIG. 4 is a flowchart illustrating the bottom temperature detection process according to the first embodiment. This process is executed at power-on. Note that it may be executed at regular intervals or when a user gives an instruction.
In step S1, the temporary minimum value Ib = Is is initialized.

  In step S2, if the change width of one step when stepwise changing the temperature T1 of the semiconductor laser 1 is ΔT1, the temperature T1 = T1−ΔT1 that is lower than the current temperature T1 by ΔT1 is set to the temperature of the semiconductor laser 1. Let T1.

  In step S3, it is checked whether the drive current I at the lowered temperature T1 is smaller than the temporary minimum value Ib. If smaller, the process proceeds to step S4, and if not smaller, the process proceeds to step S5.

  In step S4, the current temperature T1 is set as a temporary minimum current temperature Tb1. Further, the current drive current I is set to a new temporary minimum value Ib. Then, the process returns to step S2.

  In step S5, the temperature T1 = T1 + ΔT1 which is higher than the current temperature T1 by ΔT1 is set as the temperature T1 of the semiconductor laser 1.

  In step S6, it is checked whether the drive current I at the raised temperature T1 is smaller than the temporary minimum value Ib. If smaller, the process proceeds to step S7, and if not smaller, the process proceeds to step S8.

  In step S7, the current temperature T1 is set as a temporary minimum current temperature Tb1. Further, the current drive current I is set to a new temporary minimum value Ib. Then, the process returns to step S5.

  In step S8, steps S2 to S7 are also performed for the temperature T2 of the solid-state laser medium 4, the temperature T3 of the THG element 7, and the temperature T4 of the SHG element 8 to obtain temperatures T2b, T3b, and T4b that give the minimum drive current I.

  In step S9, the temperatures T2b, T3b, and T4b giving the minimum drive current I are set as new target temperatures T1, T2, T3, and T4, the semiconductor laser temperature control circuit 21, the solid laser medium temperature control circuit 22, and the THG element temperature control circuit. 23, to the SHG element temperature control circuit 24. Then, the process ends.

  According to the solid-state pulse laser device 100 that outputs the third harmonic of the first embodiment, the peak intensity of the pulse output can be stabilized. In addition, the drive current I of the semiconductor laser 1 can always be kept at a minimum.

-Example 2-
In step D1 of FIG. 2, instead of the peak intensity A, an average peak intensity obtained by averaging the peak intensities of a plurality of previous (for example, five) pulse outputs may be used.
In this case, the influence of an instantaneous abnormal value can be suppressed.

-Example 3-
In FIG. 4, the semiconductor laser temperature T1, the fixed laser medium temperature T2, the THG element temperature T3, and the SHG element temperature T4 are swept, but at least one of them may be swept.

  The solid-state pulse laser device that outputs the third harmonic of the present invention can be used in the bioengineering field and the measurement field.

1 is a configuration explanatory diagram illustrating a solid-state pulse laser device that outputs a third harmonic according to Example 1. FIG. FIG. 3 is a flowchart illustrating a drive current control process according to the first embodiment. It is a flowchart which shows the target temperature update process which concerns on Example 1. FIG. It is a flowchart which shows the bottom temperature detection process which concerns on Example 1. FIG.

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2, 10, 11, 16 Temperature control unit 3 Condensing lens system 4 Solid-state laser medium 5 Acousto-optic element 6, 12, 13 Beam splitter 7 THG element 8 SHG element 9 Mirror 14 Photo diode 15 Optical resonator 21 Semiconductor laser Temperature control circuit 22 Solid laser medium temperature control circuit 23 THG element temperature control circuit 24 SHG element temperature control circuit 25 Semiconductor laser drive circuit 26 Control circuit 100 Solid pulse laser device for outputting third harmonic

Claims (2)

A semiconductor laser that generates laser light, a semiconductor laser drive circuit that supplies a drive current to the semiconductor laser, a solid-state laser medium that is excited by laser light output from the semiconductor laser, and an optical resonance that includes the solid-state laser medium A second harmonic generating crystal and a third harmonic crystal for outputting a third harmonic of a fundamental wave oscillated by the optical resonator installed in a resonator, the semiconductor laser, the solid-state laser medium, and the Temperature control means for controlling the temperature of at least one of the second harmonic generation crystal and the third harmonic crystal, and the pulse output of either the fundamental wave, the second harmonic, or the third harmonic. A light output detector for monitoring for detecting a part of the output, and a peak intensity of the pulse output detected by the light output detector for monitoring is detected to feedback control the semiconductor laser driving circuit. Solid pulsed laser apparatus for outputting the third harmonic, characterized by comprising a peak intensity stabilizing means for stabilizing the peak intensity of the pulse output. 2. A solid-state pulse laser device for outputting third harmonics according to claim 1, wherein a change in the driving current of the semiconductor laser is constantly monitored, and the temperature of the semiconductor laser is controlled when the change exceeds a predetermined value. Temperature control means for controlling the temperature of the solid state laser medium, temperature control means for controlling the temperature of the second harmonic generation crystal, and temperature control means for controlling the temperature of the third harmonic crystal A minimum current value is obtained by measuring the drive current of the semiconductor laser while driving at least one of the laser diodes and sweeping the temperature in a predetermined temperature range, and setting the bottom current value as a target value of the temperature control means A solid-state pulse laser device for outputting a third harmonic, comprising a value setting means.

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