JP5257428B2 - Method for setting proper temperature of solid-state laser device - Google Patents

Description

The present invention relates to a method for setting an appropriate temperature of a solid-state laser device. More specifically, the present invention relates to a solid-state laser device capable of reducing drive current and increasing a margin for temperature fluctuation while minimizing the influence of optical noise. It relates to an appropriate temperature setting method.

Conventionally, during temperature tuning, the optical noise (high-frequency component) of the output laser beam is measured while changing the temperature of the semiconductor laser, solid-state laser crystal, and nonlinear optical element, and the temperature at which the optical noise is minimized is stored as the optimum temperature. In use, a solid-state laser device is known that performs temperature adjustment so as to maintain the stored optimum temperature (see, for example, Patent Document 1).
JP2003-158318A ([0008])

In the conventional solid-state laser device, the temperature at which the optical noise is minimized is set as the optimum temperature.
However, if the optical noise is less than the allowable value, there is no need to be concerned with the temperature at which the optical noise is minimized. Rather, there is a problem that the drive current increases or the margin for temperature fluctuations (actual temperature fluctuates above and below the temperature control set temperature) becomes small for the temperature at which optical noise is minimized. . Here, the margin for temperature fluctuation refers to a temperature range in which optical noise can fluctuate from the temperature adjustment set temperature without exceeding an allowable value.
SUMMARY OF THE INVENTION An object of the present invention is to provide a solid-state laser device that can reduce the drive current and increase the margin for temperature fluctuation while minimizing the influence of optical noise.

The present invention includes a semiconductor laser that generates excitation laser light, a semiconductor laser drive circuit that supplies a drive current to the semiconductor laser, a reflection surface that is excited by the excitation laser light and is formed on an incident surface of the excitation laser light. In addition, a solid-state laser crystal having a predetermined thickness, an output-side mirror having a reflecting surface that forms an optical resonator with the reflecting surface, and an excitation laser beam that is inserted into the optical resonator and is incident thereon. A nonlinear optical element that generates a wave, an output adjustment circuit that controls the semiconductor laser drive circuit so that output laser light output from the output-side mirror has a predetermined output, the solid-state laser crystal, and the optical resonator, In the solid-state laser device comprising temperature control means for controlling so that at least one temperature of the nonlinear optical element becomes an appropriate temperature, the control temperature of the temperature control means While varying, by monitoring the optical noise components and the drive current of the output laser beam, the control temperature of the optical noise components the drive current becomes minimum in the range of the predetermined tolerance, it is set to a proper temperature When the optical noise component exceeding the allowable value is detected during the temperature control, the intermediate temperature between the minimum temperature and the maximum temperature in the range where the optical noise component is equal to or less than a predetermined allowable value, Provided is a method for setting an appropriate temperature of a solid-state laser device, which is characterized by setting a new appropriate temperature .

In the above solid-state laser device, the temperature is adjusted so that the drive current corresponding to the temperature region where the optical noise component of the output laser light is less than the allowable value is operated, so that the influence of the optical noise is minimized. However, the drive current can be reduced. In addition, when an optical noise component exceeding the allowable value is detected , the temperature is adjusted so as to operate at an intermediate temperature between the lowest temperature and the highest temperature in the temperature region where the optical noise component of the output laser light is less than the allowable value. Therefore, it is possible to increase the margin for temperature fluctuation while minimizing the influence of optical noise.

According to the solid-state laser device of the present invention, the temperature is controlled so that the drive current corresponding to the temperature region in which the optical noise component of the output laser beam is less than the allowable value is operated at the minimum temperature. The drive current can be reduced while minimizing. In addition, the temperature is controlled to operate at a temperature between the lowest temperature and the highest temperature in the temperature range where the optical noise component of the output laser light is below the allowable value, so temperature fluctuations are minimized while minimizing the effects of optical noise. The margin for can be increased.

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.

FIG. 1 is an explanatory diagram illustrating a solid-state laser device 100 according to the first embodiment.
The solid-state laser device 100 includes a laser oscillation unit 10 housed in a laser oscillation unit housing 4, a control unit 20 housed in a control unit housing 6, and a cable connecting the laser oscillation unit 10 and the control unit 20. It consists of eight.

The laser oscillation unit 10 includes a semiconductor laser 11 that generates excitation laser light (wavelength λa), a condensing lens system 12 that condenses the excitation laser light, a reflection surface on the incident surface of the excitation laser light that has a predetermined thickness. And a solid-state laser crystal 13 that generates a fundamental wave light (wavelength λb) when excited by excitation laser light, and a nonlinear optical element 14 that generates second harmonic light (wavelength λc = λb / 2) when the fundamental wave light is incident. And an output-side mirror 15 having a reflection surface that forms an optical resonator with the reflection surface of the solid-state laser crystal 13, and a part of the output laser light that is output from the output-side mirror 15 to the outside while remaining. A beam splitter 16 that branches the light, a photodiode 17 that receives the branched light and converts it into an electrical signal, and a high-pass filter that extracts optical noise (high-frequency component) N from the output P of the photodiode 17. 18, a temperature control unit 1 having a Peltier element and a temperature sensor for adjusting the temperature of the semiconductor laser 11, and a temperature control unit having a Peltier element and a temperature sensor for adjusting the temperature of the optical resonator. 2, a temperature adjustment unit 3 having a Peltier element and a temperature sensor for adjusting the temperature of the nonlinear optical element 14, and a connector 5.

The control unit 20 includes a semiconductor laser drive circuit 21 that outputs a drive current Iop for driving the semiconductor laser 11, a semiconductor laser temperature control circuit 24 that controls the temperature of the semiconductor laser 11 via the temperature control unit 1, and a temperature A resonator temperature control circuit 25 that controls the temperature of the resonator via the adjustment unit 2, a nonlinear optical element temperature control circuit 26 that controls the temperature of the nonlinear optical element 14 via the temperature adjustment unit 3, and the output of the photodiode 17 The semiconductor laser drive circuit 21 is controlled so that P becomes a predetermined output, and a control circuit 28 for controlling each temperature control circuit 24, 25, 26 and the connector 7 are provided.

The cable 8 couples the connector 5 of the laser oscillation unit 10 and the connector 7 of the control unit 20.

FIG. 2 is a flowchart showing the temperature scanning process. This process is executed by giving a temperature scanning instruction to the control circuit 28.
During this process, the semiconductor laser drive circuit 21 is controlled so that the output P of the photodiode 17 becomes a predetermined output. Further, the temperature of the semiconductor laser 11 is adjusted.

In step S1, the temperature T1 of the optical resonator is set to a start temperature T1s (for example, 30 ° C.).

In step S2, the temperature T2 of the nonlinear optical element 14 is set to a start temperature T2s (for example, 30 ° C.).

In step S3, the drive current Iop and the optical noise N are measured.

In step S4, the temperature T2 of the nonlinear optical element 14 is increased by ΔT2 (for example, 1 ° C.).
In step S5, if the temperature T2 is equal to or lower than the end temperature T2e (for example, 60 ° C.), the process returns to step S3, and if not, the process proceeds to step S6.

In step S6, the temperature T1 of the optical resonator is increased by ΔT1 (for example, 1 ° C.).
In step S7, if temperature T1 is below end temperature T1e (for example, 60 degreeC), it will return to step S2, and if that is not right, a process will be complete | finished.

When steps S1 to S7 in FIG. 2 are completed, the characteristic data of the drive current Iop and the characteristic data of the optical noise N with respect to the temperature in a state where the output laser beam is maintained at a predetermined output, for example, as shown in FIG. 3 and FIG. can get. Although there are two types of temperatures, T1 and T2, in FIG. 3 and subsequent figures, one type is used for the sake of simplicity.

FIG. 4 is a flowchart showing the temperature region search process. This process is executed after the temperature scanning process of FIG.

In step S11, as shown in FIG. 5, the temperature Tc is set to the start temperature “Ts + α”. Ts is the minimum temperature of the characteristic data. α is a temperature amplitude that fluctuates above and below the temperature control set temperature, and is 3 ° C., for example.

In step S12, the optical noise N characteristic data is examined to determine whether or not the optical noise N in the range of ± α centered on Tc is equal to or smaller than the allowable value Nth. If Nth is exceeded even at one place, the process proceeds to step S14. For example, in FIG. 5, since Tc = Ts + α and the optical noise N in the range of ± α (the range indicated by parentheses) around Tc is equal to or less than the allowable value Nth, the process proceeds to step S13. In FIG. 6, Tc = t1, and the optical noise N in the range of ± α (the range indicated by parentheses) around Tc is equal to or less than the allowable value Nth, so the process proceeds to step S13. On the other hand, in FIG. 7, Tc = t2, and there is a portion where the optical noise N in the range of ± α (range indicated by parentheses) around Tc is not less than the allowable value Nth, so the process proceeds to step S14.

In step S13, the temperature region is updated with the current Tc. That is,
(1) If no temperature region has been created so far, a temperature region # 1 of the current Tc is created. For example, in FIG. 5, the temperature region # 1 of Tc = Ts + α is created.
(2) Even if the temperature region has been created so far, if it is closed, a temperature region corresponding to the current Tc is newly created. A new number is assigned to this temperature region. For example, in FIG. 8, a temperature region # 2 of Tc = t3 is created.
(3) If there is an unclosed temperature region, the maximum value of the temperature region is changed to the current Tc. For example, in FIG. 6, Tc = t1 is set as the maximum value in the temperature region # 1.
Then, the process proceeds to step S15.

In step S14,
(1) If there is no unclosed temperature range, the process proceeds to step S15. For example, in FIG. 11, since no temperature region is created until Tc = t4, the process directly proceeds to step S15.
(2) If there is an unclosed temperature region, the temperature region is closed and the process proceeds to step S15. For example, in FIG. 7, the temperature region # 1 is closed, and the process proceeds to step S15.

In step S15, Tc is increased by ΔTc (for example, 1 ° C.).
In step S16, if Tc is equal to or lower than the end temperature “Te−α”, the process returns to step S12, and if not, the process ends. Te is the maximum temperature of the characteristic data. For example, it returns to step S12 until it becomes FIG. 9, and a process is complete | finished when FIG. 9 is complete | finished.

When the temperature region search process in FIG. 4 is completed, for example, temperature region # 1 (minimum value Ts + α, maximum value t1) and temperature region # 2 (minimum value t3, maximum value Te−α) as shown in FIG. 10 are obtained. It is done. Further, a temperature region # 1 (minimum value t4, maximum value t5) as shown in FIG. 11 is obtained.
The created temperature region is stored, and the drive current Iop corresponding to the temperature region is also stored.

FIG. 12 is a flowchart showing the temperature control process. This process is based on the premise that the temperature region search process in FIG. 4 has been completed, and is executed while the solid-state laser device 100 is in operation.

In step S21, temperature control is performed by setting the temperature that gives the minimum drive current Iop corresponding to the stored temperature range as the temperature adjustment set temperature. For example, in the case of temperature region # 1 and temperature region # 2 as shown in FIG. 10, the temperature t1 is set as the temperature adjustment set temperature. Further, in the temperature region # 1 as shown in FIG. 11, the temperature t4 is set as the temperature adjustment set temperature.

In step S22, the optical noise N is measured.
In step S23, if the measured optical noise N is less than or equal to the allowable value Nth, the process returns to step S22, and if not, the process proceeds to step S24.
In step S24, temperature control is performed by setting the temperature between the lowest value and the highest value in the current temperature range as the temperature adjustment set temperature. For example, if the optical noise N measured when the temperature t1 shown in FIG. 10 is the temperature adjustment set temperature exceeds the allowable value Nth, the temperature “(Ts + α + t1) / 2” is set as the new temperature adjustment set temperature, and temperature control is performed. To do. If the optical noise N measured when the temperature t4 shown in FIG. 11 is the temperature adjustment set temperature exceeds the allowable value Nth, the temperature “(t4 + t5) / 2” is set as the new temperature adjustment set temperature, and the temperature control is performed. To do.

According to the solid-state laser device 100 of the first embodiment, the temperature is adjusted so that the drive current corresponding to the temperature region in which the optical noise N is equal to or less than the allowable value Nth is operated at the minimum temperature. The drive current can be reduced while minimizing. Further, when the optical noise N exceeds the allowable value Nth when operating at a temperature at which the drive current corresponding to the temperature region where the optical noise N is the allowable value Nth or less is minimum, the optical noise N becomes the allowable value Nth or less. Since the temperature adjustment set temperature is changed so as to operate at a temperature intermediate between the lowest value and the highest value in the temperature region, it is possible to quickly shift to an operation point that is not affected by the optical noise N. At this shifted operating point, the margin for temperature fluctuation is large, so that the operation can be continued stably.

The solid-state laser device of the present invention can be used in the bioengineering field and the measurement field.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration explanatory diagram illustrating a solid-state laser apparatus according to a first embodiment. FIG. 3 is a flowchart illustrating a temperature scanning process according to the first embodiment. It is an illustration figure of characteristic data. It is a flowchart which shows the temperature area search process which concerns on Example 1. FIG. It is an illustration figure of characteristic data and search start temperature. It is an illustration figure of characteristic data and searching temperature. It is another example figure of characteristic data and temperature in search. It is another example figure of characteristic data and searching temperature. It is an illustration figure of characteristic data and search end temperature. It is an illustration figure of characteristic data and a temperature range. It is another example figure of characteristic data and a temperature range. FIG. 3 is a flowchart illustrating a temperature control process according to the first embodiment.

1, 2, 3
Temperature control unit 11
Semiconductor laser 12
Condensing lens system 13
Solid state laser crystal 14
Nonlinear optical element 15
Output side mirror 18
High pass filter 25
Resonator temperature control circuit 26
Nonlinear optical element temperature control circuit 28
Control unit 100
Solid state laser equipment

Claims (1)

A semiconductor laser that generates excitation laser light, a semiconductor laser drive circuit that supplies a drive current to the semiconductor laser, a excitation surface that is excited by the excitation laser light, has a reflection surface formed on an incident surface of the excitation laser light, and has a predetermined thickness A solid-state laser crystal having an output side mirror having a reflection surface that forms an optical resonator with the reflection surface, and the excitation laser beam inserted into the optical resonator generates a harmonic. A non-linear optical element, an output adjusting circuit for controlling the semiconductor laser driving circuit so that an output laser beam outputted from the output side mirror becomes a predetermined output, the solid-state laser crystal, the optical resonator, and the non-linear optical element A solid-state laser device comprising temperature control means for controlling so that at least one of the temperatures becomes an appropriate temperature.
While controlling the control temperature of the temperature control means, the optical noise component and the driving current of the output laser beam are monitored, and the control is performed such that the driving current is minimized when the optical noise component is within a predetermined allowable value or less. When the temperature is set to an appropriate temperature and temperature control is performed, and an optical noise component exceeding the allowable value is detected during the temperature control, the optical noise component is set to a minimum temperature within a predetermined allowable value range or less. A method for setting an appropriate temperature of a solid-state laser device, wherein an intermediate temperature between the maximum temperatures is set to a new appropriate temperature .

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