Laser device and method for controlling laser device

Abstract

This laser device (1) comprises: a semiconductor laser element (20) that emits first laser light (L1); a first temperature adjustment unit (51) that heats or cools the semiconductor laser element (20); and a control unit (80) that controls the amount of current supplied to the semiconductor laser element (20) and controls the first temperature adjustment unit (51) on the basis of a target temperature that is a control target for the temperature at an installation point of the semiconductor laser element (20). The target temperature for the semiconductor laser element (20) in an initial state is the temperature that requires heating of the semiconductor laser element (20) by means of the first temperature adjustment unit (51).

Description

Laser device and method for controlling laser device

[0001] The present disclosure relates to a laser device and a method for controlling a laser device.

[0002] Laser devices including laser elements such as semiconductor laser elements are known. For example, in laser devices including a laser crystal (i.e., a solid-state laser crystal) excited by laser light from the semiconductor laser element, the temperature of the semiconductor laser element is controlled by a Peltier element or the like to stabilize the wavelength and power of the laser light from the semiconductor laser element. For example, in the solid-state laser device described in Patent Document 1, the current consumption of the Peltier element is limited within a predetermined range. This attempts to suppress the total current consumption of the semiconductor laser element and the Peltier element.

[0003] Patent No. 5070820

[0004] However, the solid-state laser device described in Patent Document 1 cannot suppress a long-term temperature rise of the semiconductor laser element due to deterioration of the semiconductor laser element, which leads to a decrease in the output efficiency of the laser light from the semiconductor laser element and an increase in total power consumption.

[0005] The present disclosure aims to suppress the total energy consumption of a laser device including a semiconductor laser element over the lifetime of the semiconductor laser element while suppressing long-term changes in the installation temperature of the semiconductor laser element.

[0006] In order to achieve the above object, a laser device according to one aspect of the present disclosure includes a semiconductor laser element that emits a first laser beam, a first temperature adjustment unit that heats or cools the semiconductor laser element, and a control unit that controls the amount of current supplied to the semiconductor laser element and controls the first temperature adjustment unit based on a target temperature that is a control target for the temperature of the installation point of the semiconductor laser element, wherein the target temperature for the semiconductor laser element in an initial state is a temperature to which the semiconductor laser element needs to be heated by the first temperature adjustment unit.

[0007] In order to achieve the above object, in a control method for a laser device according to one aspect of the present disclosure, the laser device includes a semiconductor laser element that emits a first laser beam and a first temperature adjustment unit that heats or cools the semiconductor laser element, and the control method for the laser device includes a current control step that controls an amount of current supplied to the semiconductor laser element, and a first temperature control step that uses the first temperature adjustment unit to control a temperature of an installation point of the semiconductor laser element based on a target temperature for the semiconductor laser element, and the target temperature for the semiconductor laser element in an initial state is a temperature to which the semiconductor laser element needs to be heated by the first temperature adjustment unit.

[0008] According to the present disclosure, in a laser device including a semiconductor laser element, it is possible to suppress long-term changes in the installation temperature of the semiconductor laser element while suppressing the total energy consumption of the semiconductor laser element over its lifetime.

[0009] 1 is a schematic diagram showing the overall configuration of a laser device according to a first embodiment; FIG. 2 is a schematic first graph showing the relationship between the amount of current supplied to a semiconductor laser element and output optical power; FIG. 3 is a schematic graph showing the relationship between the power supplied to the semiconductor laser element, the output optical power of the semiconductor laser element, and the heat generation amount of the semiconductor laser element; FIG. 4 is a flowchart showing a control method of the laser device according to the first embodiment; FIG. 5 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device of Comparative Example 1 and power consumption in a first temperature adjustment unit; FIG. 6 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device of Comparative Example 1 and the total power consumption of the laser device and the power consumption of the semiconductor laser element; FIG. 7 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the first embodiment and power consumption in a first temperature adjustment unit; FIG. 8 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the first embodiment and the total power consumption of the laser device and the power consumption of the semiconductor laser element; 1 is a schematic diagram showing the overall configuration of a laser device according to a second embodiment; FIG. 2 is a second schematic graph showing the relationship between the amount of current supplied to the semiconductor laser element and the output optical power; FIG. 3 is a flowchart showing a method for controlling the laser device according to the second embodiment; FIG. 4 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device of Comparative Example 2 and the power consumption in the first temperature adjustment unit and the semiconductor laser element; FIG. 5 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device of Comparative Example 2 and the total power consumption of the laser device; FIG. 6 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the second embodiment and the power consumption in the first temperature adjustment unit and the semiconductor laser element; FIG. 7 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the second embodiment and the total power consumption of the laser device; FIG. 8 is a schematic diagram showing the overall configuration of a laser device according to a third embodiment; and FIG. 9 is a flowchart showing a method for controlling the laser device according to the third embodiment.10 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device of Comparative Example 3 and the power consumption in the first temperature adjustment unit and the semiconductor laser element. FIG. 11 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device of Comparative Example 3 and the total power consumption of the laser device. FIG. 12 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the third embodiment and the power consumption in the first temperature adjustment unit and the semiconductor laser element. FIG. 13 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the third embodiment and the total power consumption of the laser device. FIG. 14 is a schematic diagram showing the overall configuration of a laser device according to a modification of the third embodiment. FIG. 15 is a schematic diagram showing the overall configuration of a laser device according to a fourth embodiment. FIG. 16 is a graph showing an example of the wavelength range of the semiconductor laser element. FIG. 17 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the fourth embodiment and the wavelength of the first laser light. FIG. 18 is a flowchart showing a control method of the laser device according to the fourth embodiment. FIG. 19 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the fourth embodiment and the power consumption in the first temperature adjustment unit and the semiconductor laser element. FIG. 19 is a graph showing the relationship between the deterioration rate of the semiconductor laser element in the laser device according to the fourth embodiment and the total power consumption of the laser device. Fig. 1 is a schematic diagram showing the overall configuration of a laser device according to a modification of embodiment 4. Fig. 2 is a schematic diagram showing the overall configuration of a laser device according to embodiment 5. Fig. 3 is a flowchart showing a control method for the laser device according to embodiment 5. Fig. 4 is a schematic diagram showing the overall configuration of a laser device according to a modification of embodiment 5. Fig. 5 is a schematic diagram showing the overall configuration of a laser device according to embodiment 6. Fig. 6 is a schematic diagram showing the overall configuration of a laser device according to a modification of embodiment 6.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, arrangement and connection of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0011] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0012] Furthermore, in this specification, terms indicating relationships between elements, such as "equal," and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0013] First Embodiment A laser device and a control method thereof according to a first embodiment will be described.

[0014] [1-1. Overall Configuration of Laser Apparatus] The overall configuration of a laser apparatus according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the overall configuration of a laser apparatus 1 according to this embodiment.

[0015] 1 , the laser device 1 includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 80. In this embodiment, the laser device 1 further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, and a first temperature sensor 81.

[0016] The semiconductor laser element 20 is an element that emits the first laser light L1. In this embodiment, when the temperature of the installation point of the semiconductor laser element 20 is at a target temperature that is a control target, the wavelength of the first laser light L1 is included in an absorption band that is an absorption wavelength band of the laser crystal 30. Here, the installation point of the semiconductor laser element 20 means a point at which the semiconductor laser element 20 is heated or cooled by the first temperature adjustment unit 51. For example, the installation point of the semiconductor laser element 20 may be the temperature of a package or case that houses the semiconductor laser element 20.

[0017] For example, the wavelength of the first laser light L1 is the absorption peak wavelength of the laser crystal 30. The configuration of the semiconductor laser element 20 is not particularly limited. The peak wavelength of the first laser light L1 is, for example, 350 nm or more and 500 nm or less. The semiconductor laser element 20 may be, for example, a nitride semiconductor laser element. The semiconductor laser element 20 may include an AlInGaN-based nitride semiconductor. This allows the semiconductor laser element 20 to efficiently emit light with a wavelength of 350 nm or more and 500 nm or less. It is known that AlInGaN-based nitride semiconductor laser elements are prone to deterioration over time when the laser is operated, resulting in a decrease in output optical power.

[0018] In this embodiment, the semiconductor laser element 20 emits first laser light L1 having a peak wavelength of 444 nm. The semiconductor laser element 20 may be a transverse multimode laser. The stripe width of the light-emitting region of the semiconductor laser element 20 may be 10 μm or more and 100 μm or less. The stripe width of the light-emitting region of the semiconductor laser element 20 may be 25 μm or more and 60 μm or less. The semiconductor laser element 20 may be mounted in a junction-down manner. This reduces the temperature of the active layer (junction temperature), making it difficult for the output optical power of the semiconductor laser element 20 to decrease over time when the laser is driven, thereby suppressing a decrease in the output optical power of the laser device 1.

[0019] The semiconductor laser element 20 may be housed in, for example, a container. In the example shown in Fig. 1, the semiconductor laser element 20 is housed in a CAN package and held by the first holder 11. A current is supplied to the semiconductor laser element 20 from the control unit 80.

[0020] Changes in the characteristics of the semiconductor laser element 20 over time of power supply will be described with reference to Figs. 2 and 3. Fig. 2 is a first schematic graph showing the relationship between the amount of current supplied to the semiconductor laser element 20 and the output optical power. Fig. 2 shows the relationship for the semiconductor laser element 20 in an initial state and the relationship for the semiconductor laser element 20 after deterioration. Fig. 3 is a schematic graph showing the relationship between the power supply time of the semiconductor laser element 20, the power supplied to the semiconductor laser element 20, the output optical power of the semiconductor laser element 20, and the amount of heat generated by the semiconductor laser element 20. Fig. 3 shows a graph for the case where the power supplied to the semiconductor laser element 20 is constant.

[0021] 2 and 3 , the semiconductor laser element 20 deteriorates over time, and the output optical power decreases even when the supplied current (or power) is constant. This is likely to occur in AlInGaN-based nitride semiconductor laser elements. It can also occur when the semiconductor laser element 20 is a transverse multimode laser with a stripe width of the light-emitting region of 10 μm or more and 100 μm or less. In this specification, the deterioration rate is defined as the ratio (PLd / PLi) of the output optical power PLd when a current i0 is supplied to the semiconductor laser element 20 to the output optical power PLi when a current i0 is supplied to the semiconductor laser element 20 in an initial state (see FIG. 2 ).

[0022] 3, as the semiconductor laser element 20 deteriorates, the output optical power decreases and the amount of heat generated increases. For example, as the semiconductor laser element 20 deteriorates, the element resistance (electrical resistance of the semiconductor laser element 20) increases, which increases Joule heat. Therefore, even if the current (or power) supplied to the semiconductor laser element 20 is constant, the amount of heat generated increases as the semiconductor laser element 20 deteriorates.

[0023] In this specification, the state of the semiconductor laser element 20 at the start of energization in the laser apparatus 1 is referred to as the initial state. Also, the period during which the semiconductor laser element 20 can be used while maintaining predetermined output characteristics is referred to as the lifetime. The lifetime may be, for example, a predetermined energization time, or may be the energization time from the start of energization until a predetermined degradation rate is reached.

[0024] The laser crystal 30 is a solid-state laser crystal that is excited by the first laser light L1. The laser crystal 30 is excited by the first laser light L1 and is placed in a resonator to emit a second laser light L2 having a wavelength different from that of the first laser light L1. The absorption band, which is the absorption wavelength range of the laser crystal 30, includes the wavelength of the first laser light L1. The laser crystal 30 is placed on the optical axis of the first laser light L1 between the semiconductor laser element 20 and the output mirror 16. In this embodiment, a selective transmission mirror 31 is placed on an incident surface 30a of the laser crystal 30, on which the first laser light L1 is incident.

[0025] The laser crystal 30 is a crystal doped with at least one of, for example, Pr, Tb, and Dy. The peak wavelength of the second laser light is, for example, 400 nm or more and 800 nm or less. In this embodiment, the laser crystal 30 is doped with Pr ３＋ : YLiF ４ In this embodiment, laser crystal 30 is held by first holder 11.

[0026] The selective transmission mirror 31 is disposed on the optical axis of the first laser light L1 and is a mirror that transmits at least a portion of the first laser light L1 and reflects at least a portion of the second laser light L2. In this embodiment, the selective transmission mirror 31 is a dielectric multilayer film formed on the incident surface 30a of the laser crystal 30. The transmittance of the selective transmission mirror 31 at the peak wavelength of the first laser light L1 is, for example, 95% or more. The reflectance of the selective transmission mirror 31 at the peak wavelength of the second laser light L2 is, for example, 95% or more.

[0027] The output mirror 16 is disposed on the optical axis of the second laser light L2, and reflects a portion of the second laser light L2 and transmits the other portion. The second laser light L2 that transmits through the output mirror 16 is the output light of the laser device 1. In this embodiment, the output mirror 16 is a concave mirror. The output mirror 16 and the selective transmission mirror 31 form a resonator in which the second laser light L2 resonates.

[0028] The first holder 11 is a member that holds the semiconductor laser element 20. The first holder 11 is thermally connected to the semiconductor laser element 20. The first holder 11 is made of a material with high thermal conductivity. The first holder 11 is made of, for example, Cu. In this embodiment, the first holder 11 holds not only the semiconductor laser element 20 but also the laser crystal 30 and the output mirror 16.

[0029] The first temperature adjustment unit 51 heats or cools the semiconductor laser element 20. The first temperature adjustment unit 51 has a first surface 51a and a second surface 51b. The first temperature adjustment unit 51 is controlled by the control unit 80 to adjust the temperature difference between the first surface 51a and the second surface 51b. In the present embodiment, the first temperature adjustment unit 51 is a Peltier element. The first surface 51a and the second surface 51b correspond to one and the other electrodes of the Peltier element. The first temperature adjustment unit 51 is supplied with a voltage and a current from the control unit 80, and adjusts the temperature difference between the first surface 51a and the second surface 51b in accordance with the supplied voltage and current. The first surface 51a is thermally connected to the first holder 11 and heats or cools the semiconductor laser element 20 via the first holder 11. The second surface 51b is thermally connected to the heat sink 18.

[0030] The heat sink 18 is a member that dissipates heat generated by the semiconductor laser element 20. The heat sink 18 is made of a material with high thermal conductivity. For example, the heat sink 18 is made of Cu.

[0031] The first temperature sensor 81 is a sensor that detects the temperature of the first holder 11. The first temperature sensor 81 is thermally connected to the first holder 11. The first temperature sensor 81 outputs a signal corresponding to the temperature of the first holder 11 to the control unit 80. As the first temperature sensor 81, for example, a thermocouple, a resistance temperature detector, or the like can be used.

[0032] The control unit 80 is a processing unit that controls the amount of current supplied to the semiconductor laser element 20 and also controls the first temperature adjustment unit 51 based on a target temperature that is a control target for the temperature at the installation point of the semiconductor laser element 20. The control unit 80 includes hardware for realizing the control function and a power supply that supplies power to the semiconductor laser element 20 and the first temperature adjustment unit 51. As the hardware for realizing the control function of the control unit 80, for example, a microcomputer can be used, but a processor or a dedicated circuit may also be used. The control function of the control unit 80 is realized when the microcomputer, processor, etc. that constitutes the control unit 80 executes a computer program (software) stored in the memory, etc. that constitutes the control unit 80.

[0033] In this embodiment, the control unit 80 maintains a constant amount of current supplied to the semiconductor laser element 20. That is, the control unit 80 drives the semiconductor laser element 20 under automatic current control (ACC).

[0034] In this embodiment, the control unit 80 detects the temperature of the installation point of the semiconductor laser element 20 based on the output signal of the first temperature sensor 81. Here, the temperature of the first holder 11 corresponding to the output signal of the first temperature sensor 81 may be regarded as the temperature of the installation point of the semiconductor laser element 20, or the relationship between the output signal of the first temperature sensor 81 and the temperature of the installation point of the semiconductor laser element 20 may be obtained in advance, and the temperature of the installation point of the semiconductor laser element 20 may be detected based on this relationship.

[0035] As described above, the control unit 80 controls the first temperature adjustment unit 51 based on the target temperature for the semiconductor laser element 20. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the first temperature adjustment unit 51 needs to heat the semiconductor laser element. In this embodiment, the control unit 80 sets the target temperature in the initial state so that the first temperature adjustment unit 51 heats the semiconductor laser element 20. In this embodiment, the control unit 80 maintains the target temperature constant throughout the entire lifetime of the semiconductor laser element 20. As described above, the amount of heat generated by the semiconductor laser element 20 increases as the semiconductor laser element 20 deteriorates. Therefore, the control unit 80 reduces the power consumption required for the first temperature adjustment unit 51 to heat the semiconductor laser element 20 as the deterioration of the semiconductor laser element 20 progresses. In this embodiment, the control unit 80 sets the target temperature so that the sum of the energy consumed by the semiconductor laser element 20 and the energy consumed by the first temperature adjustment unit 51 during the lifetime of the semiconductor laser element 20 is minimized.

[0036] [1-2. Control Method of Laser Apparatus] A control method of the laser apparatus 1 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a flowchart showing the control method of the laser apparatus 1 according to this embodiment.

[0037] 4, first, a target temperature is set in the control unit 80 (target temperature setting step S10). The target temperature may be set by the control unit 80 or may be set based on an input to the laser apparatus 1 by a user or the like. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51. In this embodiment, the control unit 80 maintains the target temperature constant throughout the entire life of the semiconductor laser element 20.

[0038] Next, the control unit 80 controls the amount of current supplied to the semiconductor laser element 20 (current control step S20). The amount of current supplied to the semiconductor laser element 20 may be determined in advance, or may be determined based on, for example, an input to the laser apparatus 1 by a user. In this embodiment, the control unit 80 maintains the amount of current supplied to the semiconductor laser element 20 constant.

[0039] Subsequently, the control unit 80 uses the first temperature adjustment unit 51 to control the temperature of the installation point of the semiconductor laser element 20 based on the target temperature for the semiconductor laser element 20 (first temperature control step S30). Specifically, the control unit 80 detects the temperature of the installation point of the semiconductor laser element 20 based on a signal from the first temperature sensor 81, and feedback-controls the first temperature adjustment unit 51 so that the temperature of the installation point of the semiconductor laser element 20 approaches the target temperature.

[0040] Subsequently, the process returns to the current control step S20, and the current control step S20 and the first temperature control step S30 are repeated. As described above, the amount of heat generated increases with deterioration of the semiconductor laser element 20. Therefore, in the first temperature control step S30, the control unit 80 reduces the power consumption required for heating by the first temperature adjustment unit 51 as the deterioration of the semiconductor laser element 20 progresses.

[0041] As described above, the control unit 80 controls the laser device 1 .

[0042] [1-3. Effects, etc.] The effects of the laser device 1 according to this embodiment and the control method thereof will be explained in comparison with the laser device and control method thereof of Comparative Example 1. The laser device of Comparative Example 1 is a laser device whose configuration is identical to that of the laser device 1 according to this embodiment except for the target temperature. In the laser device and control method thereof of Comparative Example 1, the target temperature for the semiconductor laser element 20 in the initial state is set to a temperature at which the power consumption by the first temperature adjustment unit 51 is substantially zero (that is, heating and cooling are almost unnecessary).

[0043] The relationship between the deterioration rate of the semiconductor laser element 20 and power consumption in each laser device according to Comparative Example 1 and the present embodiment will be described with reference to FIGS. 5 to 8. FIG. 5 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device according to Comparative Example 1 and power consumption in the first temperature adjustment unit 51. FIG. 6 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device according to Comparative Example 1 and the total power consumption of the laser device and the power consumption of the semiconductor laser element 20. FIG. 7 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 1 according to the present embodiment and power consumption in the first temperature adjustment unit 51. FIG. 8 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 1 according to the present embodiment and the total power consumption of the laser device 1 and the power consumption of the semiconductor laser element 20. Note that each graph shows power consumption calculated by simulation. Note that the total power consumption W of each laser device according to Comparative Example 1 and the present embodiment is ＡＬＬ As shown in the following formula (1), the power consumption W of the semiconductor laser element 20 ＬＤ and the power consumption W of the first temperature adjustment unit 51 Ｐ１ It means harmony with.

[0044] W ＡＬＬ =W ＬＤ +W Ｐ１ (1)

[0045] In this simulation, the ambient temperature was set to 25° C., and the voltage and current supplied to the semiconductor laser element 20 were set to 4.5 V and 1.28 A, respectively. In this simulation and the simulations described below, the temperature of the heat sink 18 was assumed to be equal to the ambient temperature, and the temperature of the installation point of the semiconductor laser element 20 was considered to be the temperature of the first holder 11.

[0046] In the laser device of Comparative Example 1, the target temperature for the semiconductor laser element 20 in the initial state (i.e., 0% degradation rate) is set to 41.1°C, a temperature at which heating and cooling by the first temperature adjustment unit 51 are substantially unnecessary. In this case, heat generated from the semiconductor laser element 20 can be dissipated solely by heat transport caused by the temperature difference between the first surface 51a and the second surface 51b of the first temperature adjustment unit 51. Therefore, in the laser device of Comparative Example 1, when the semiconductor laser element 20 is in the initial state, the power consumption of the first temperature adjustment unit 51 is substantially zero, as shown in FIG. 5, and the total power consumption is equal to the power consumption of the semiconductor laser element 20, as shown in FIG. 6. Note that in Comparative Example 1 and the present embodiment, the amount of current supplied to the semiconductor laser element 20 is maintained constant, and therefore the power consumption of the semiconductor laser element 20 is constant.

[0047] However, as described above, the amount of heat generated by the semiconductor laser element 20 increases as the semiconductor laser element 20 deteriorates, and therefore, when the temperature at the installation point of the semiconductor laser element 20 is controlled to be constant, the power consumption required for cooling the semiconductor laser element 20 by the first temperature adjustment unit 51 increases as shown in Fig. 5. Therefore, as shown in Fig. 6, the total power consumption of the laser device also increases as the semiconductor laser element 20 deteriorates. In the laser device of Comparative Example 1, the total power consumption was 5.8 W when the deterioration rate of the semiconductor laser element 20 was 0%, but was 6.8 W when the deterioration rate of the semiconductor laser element 20 was 20%.

[0048] The period from the initial state of the semiconductor laser element 20 to the state where the degradation rate is 20% is defined as the lifespan, and if the lifespan is 10,000 hours, the total energy consumption during the lifespan of the laser device of Comparative Example 1 is 226 MJ. ＡＬＬ is the total power consumption W shown in equation (1) ＡＬＬ is expressed by the following equation (2).

[0049]

[0050] In contrast, in the laser apparatus 1 according to this embodiment, the target temperature for the semiconductor laser element 20 in the initial state is 42.1° C., which is the temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51. Therefore, in the laser apparatus 1 according to this embodiment, when the semiconductor laser element 20 is in the initial state, the power consumption of the first temperature adjustment unit 51 is not 0, as shown in FIG. 7. Furthermore, as shown in FIG. 8, the total power consumption is larger than the power consumption of the semiconductor laser element 20.

[0051] However, the amount of heat generated by the semiconductor laser element 20 increases as the semiconductor laser element 20 deteriorates. Therefore, when the temperature at the installation point of the semiconductor laser element 20 is controlled to be constant, the control unit 80 reduces the power consumption required for heating by the first temperature adjustment unit 51 as the deterioration of the semiconductor laser element 20 progresses. Therefore, as shown in FIG. 7 , as the deterioration rate of the semiconductor laser element 20 increases from 0% to approximately 17%, the power consumption required for heating the semiconductor laser element 20 by the first temperature adjustment unit 51 decreases. As a result, as shown in FIG. 8 , the total power consumption of the laser apparatus 1 also decreases as the semiconductor laser element 20 deteriorates. In the laser apparatus 1 according to this embodiment, when the deterioration rate of the semiconductor laser element 20 is approximately 17%, the heat generated by the semiconductor laser element 20 can be dissipated solely by heat transport caused by the temperature difference between the first surface 51 a and the second surface 51 b of the first temperature adjustment unit 51, and the power consumption of the first temperature adjustment unit 51 becomes zero. Furthermore, as deterioration of the semiconductor laser element 20 progresses, when the temperature at the installation point of the semiconductor laser element 20 is controlled to be constant, the heat generated from the semiconductor laser element 20 cannot be dissipated solely by heat transport caused by the temperature difference between the first surface 51 a and the second surface 51 b of the first temperature adjustment unit 51, and therefore the control unit 80 causes the first temperature adjustment unit 51 to cool the semiconductor laser element 20. Therefore, as the deterioration rate of the semiconductor laser element 20 increases from approximately 17% to 20%, the power consumption required for cooling the semiconductor laser element 20 by the first temperature adjustment unit 51 increases.

[0052] In the laser device 1 according to this embodiment, the total power consumption was 5.95 W when the deterioration rate of the semiconductor laser element 20 was 0%, and the total power consumption was 5.95 W when the deterioration rate of the semiconductor laser element 20 was 20%.

[0053] The total energy consumption over the lifetime of the laser device 1 according to this embodiment is 211 MJ. As described above, the total energy consumption over the lifetime of the laser device 1 according to this embodiment can be reduced by 15 MJ compared to the laser device of Comparative Example 1.

[0054] As described above, the laser device 1 according to the present embodiment includes the semiconductor laser element 20 that emits the first laser light L1, the first temperature adjustment unit 51 that heats or cools the semiconductor laser element 20, and the control unit 80 that controls the amount of current supplied to the semiconductor laser element 20 and controls the first temperature adjustment unit 51 based on the target temperature that is a control target for the temperature at the installation point of the semiconductor laser element 20. The target temperature for the semiconductor laser element 20 in the initial state is the temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51.

[0055] This allows the first temperature adjustment unit 51 to suppress temperature fluctuations at the installation point of the semiconductor laser element 20. Furthermore, as deterioration of the semiconductor laser element 20 progresses, the amount of heat generated by the semiconductor laser element 20 increases, thereby reducing the power consumption of the first temperature adjustment unit 51. In other words, the heat generated by the semiconductor laser element 20 can be utilized for heating to bring the temperature of the installation point of the semiconductor laser element 20 closer to the target temperature. This allows the control unit 80 to reduce the power consumption required for heating by the first temperature adjustment unit 51 as deterioration of the semiconductor laser element progresses. In other words, the control unit 80 controls the first temperature adjustment unit 51 to lower the temperature of the installation point by an amount corresponding to an increase in the temperature difference between the temperature of the active layer of the semiconductor laser element and the installation point, thereby suppressing changes in the temperature of the active layer. Therefore, it is possible to suppress long-term temperature fluctuations in the laser device 1 while also suppressing the total energy consumption of the laser device 1 over its lifetime.

[0056] In addition, in this embodiment, the control unit 80 may cause the first temperature adjustment unit 51 to cool the semiconductor laser element 20 when the deterioration of the semiconductor laser element 20 progresses at a predetermined deterioration rate.

[0057] In this way, the first temperature adjustment unit 51 heats the semiconductor laser element 20 until the deterioration rate of the semiconductor laser element 20 reaches a predetermined deterioration rate, and after the predetermined deterioration rate is reached, the first temperature adjustment unit 51 cools the semiconductor laser element 20. By performing such control, it is possible to reduce the power consumption required for heating and cooling by the first temperature adjustment unit 51. Therefore, it is possible to reduce the total energy consumption over the life of the laser device 1.

[0058] In this embodiment, the control unit 80 may maintain the amount of current supplied to the semiconductor laser element 20 constant.

[0059] This allows the power consumption in the semiconductor laser element 20 to be kept constant.

[0060] In this embodiment, the control unit 80 may maintain the target temperature constant throughout the entire life of the semiconductor laser device 20 .

[0061] This makes it possible to suppress fluctuations in the wavelength of the first laser light L1 emitted by the semiconductor laser element 20.

[0062] In the present embodiment, the control unit 80 calculates the sum of the energy consumed by the semiconductor laser element 20 and the energy consumed by the first temperature adjustment unit 51 (i.e., the total energy consumption P ＡＬＬ The target temperature may be set so that the temperature difference (T) is minimized.

[0063] This allows the total energy consumption in the laser device 1 to be minimized.

[0064] The control method for the laser device 1 according to this embodiment includes a current control step S20 of controlling the amount of current supplied to the semiconductor laser element 20, and a first temperature control step S30 of using the first temperature adjustment unit 51 to control the temperature of the installation point of the semiconductor laser element 20 based on a target temperature for the semiconductor laser element 20. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51.

[0065] This provides the same effects as those of the laser device 1 according to the present embodiment described above.

[0066] Furthermore, in the first temperature control step S30 according to this embodiment, the power consumption required for heating by the first temperature adjustment unit 51 is reduced as the deterioration of the semiconductor laser element 20 progresses.

[0067] This makes it possible to suppress long-term temperature fluctuations in the laser device 1 while also suppressing the total energy consumption of the laser device 1 over its lifetime.

[0068] In the current control step S20 of this embodiment, the amount of current supplied to the semiconductor laser element 20 may be kept constant.

[0069] This allows the power consumption in the semiconductor laser element 20 to be kept constant.

[0070] [1-4. Other Configuration Examples of the Wavelength of the First Laser Light] Although the configuration has been described in which the wavelength of the first laser light L1 emitted by the semiconductor laser element 20 matches the absorption peak wavelength of the laser crystal 30, the wavelength of the first laser light L1 is not limited to this. Other configuration examples of the wavelength of the first laser light L1 will be described below.

[0071] In the laser device 1 according to the present embodiment, the target temperature of the semiconductor laser element 20 is maintained constant, so that the change in the wavelength of the first laser light L1 emitted by the semiconductor laser element 20 is suppressed. However, when the amount of heat generated increases with deterioration of the semiconductor laser element 20, the temperature of the active layer of the semiconductor laser element 20 rises due to the thermal resistance of the semiconductor laser element 20 itself (including the package). The temperature T of the active layer ｊis the thermal resistance R of the semiconductor laser element 20 ｔｈ , the heat generation amount Q of the semiconductor laser element 20 ＬＤ , and target temperature T ｃ is expressed by the following equation (3).

[0072] T ｊ =R ｔｈ Q ＬＤ +T ｃ (3)

[0073] As shown in equation (3), the thermal resistance R ｔｈ and target temperature T ｃ When is constant, the temperature T ｊ is the heat generation amount Q of the semiconductor laser element 20 ＬＤ It increases with increasing

[0074] Due to this temperature rise in the active layer, the wavelength of the first laser light L1 shifts to the longer wavelength side. This wavelength shift of the first laser light L1 will be explained using Fig. 9. Fig. 9 is a first graph showing the relationship between the wavelength of the first laser light L1 of the semiconductor laser element 20 and the absorptance of the laser crystal 30. The horizontal axis of Fig. 9 represents the wavelength, and the vertical axis represents the absorptance of the laser crystal 30.

[0075] 9, even if the wavelength of the first laser light L1 emitted by the semiconductor laser element 20 in an initial state is equal to the absorption peak wavelength (λp) of the laser crystal 30, the wavelength of the first laser light L1 will shift to the wavelength λpc in Fig. 9 after the lifetime has elapsed as the semiconductor laser element 20 deteriorates. Accordingly, the absorptance in the laser crystal 30 will decrease from the absorptance Ra0 at the absorption peak wavelength to the absorptance Rac at the wavelength λpc.

[0076] Therefore, the characteristics of the semiconductor laser element 20 may be selected so that the wavelength of the first laser light L1 emitted by the semiconductor laser element 20 in an initial state is shorter than the absorption peak wavelength of the laser crystal 30. Such a configuration example will be described with reference to Fig. 10. Fig. 10 is a second graph showing the relationship between the wavelength of the first laser light L1 from the semiconductor laser element 20 and the absorptance of the laser crystal 30. The horizontal axis of Fig. 10 represents the wavelength, and the vertical axis represents the absorptance of the laser crystal 30.

[0077] As shown in FIG. 10 , by setting the wavelength of the first laser light L1 emitted by the semiconductor laser element 20 in the initial state shorter than the absorption peak wavelength of the laser crystal 30, it is possible to suppress a decrease in the absorptance in the laser crystal 30 over the lifetime of the semiconductor laser element 20. More specifically, over the lifetime of the semiconductor laser element 20, the wavelength of the first laser light L1 changes from a wavelength shorter than the absorption peak wavelength of the laser crystal (λ1 in FIG. 10 ) to a wavelength longer than the absorption peak wavelength (λ2 in FIG. 10 ). For example, in the example shown in FIG. 10 , the absorptance (Ra1) of the first laser light L1 in the laser crystal 30 in the initial state of the semiconductor laser element 20 is equal to the absorptance (Ra1) of the first laser light L1 in the laser crystal 30 at the end of the lifetime of the semiconductor laser element 20. The minimum absorptance value Ra1 in the example shown in FIG. 10 is significantly greater than the minimum absorptance value Rac shown in FIG. 9 . Therefore, this configuration example can improve the wavelength conversion efficiency in the laser crystal 30.

[0078] (Embodiment 2) A laser device and a control method thereof according to embodiment 2 will be described. The laser device according to this embodiment differs from the laser device 1 according to embodiment 1 in that the amount of current supplied to the semiconductor laser element 20 is controlled so that the power of the first laser light L1 output from the semiconductor laser element 20 is constant. The laser device and control method thereof according to this embodiment will be described below, focusing on the differences from the laser device 1 and control method thereof according to embodiment 1.

[0079] [2-1. Overall Configuration of Laser Apparatus] The overall configuration of the laser apparatus according to this embodiment will be described with reference to Fig. 11. Fig. 11 is a schematic diagram showing the overall configuration of a laser apparatus 101 according to this embodiment.

[0080] 11 , the laser device 101 includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 180. In this embodiment, the laser device 101 further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a first selective transmission mirror M1, and a first optical sensor D1.

[0081] The first selective transmitting mirror M1 according to this embodiment is a mirror that is arranged on the optical axis of the first laser light L1 and reflects at least a portion of the first laser light L1. The first selective transmitting mirror M1 may selectively transmit the wavelength of the second laser light L2. In this embodiment, the first selective transmitting mirror M1 is arranged on the optical axis of the first laser light L1 before it enters the laser crystal 30. In other words, the first selective transmitting mirror M1 is arranged on the optical axis of the first laser light L1 between the semiconductor laser element 20 and the laser crystal 30. The first laser light L1 that has entered the first selective transmitting mirror M1 is reflected by the first selective transmitting mirror M1 and enters the first optical sensor D1.

[0082] The first optical sensor D1 is a sensor that detects the power of the first laser beam L1. In the present embodiment, the first optical sensor D1 detects the power of the first laser beam L1 before it is incident on the laser crystal 30. The first optical sensor D1 outputs a signal corresponding to the power of the first laser beam L1 to the control unit 180. A photodiode, for example, can be used as the first optical sensor D1.

[0083] The control unit 180 is a processing unit that controls the amount of current supplied to the semiconductor laser element 20, and also controls the first temperature adjustment unit 51 based on a target temperature that is a control target for the temperature at the installation point of the semiconductor laser element 20. In the present embodiment, as in the first embodiment, the control unit 180 controls the first temperature adjustment unit 51 based on the target temperature for the semiconductor laser element 20. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the semiconductor laser element needs to be heated by the first temperature adjustment unit 51. The control unit 180 maintains the target temperature constant throughout the entire life of the semiconductor laser element 20.

[0084] In the present embodiment, the control unit 180 controls the amount of current supplied to the semiconductor laser element 20 so that the power of the first laser beam L1 is constant. That is, the control unit 180 performs APC (Automatic Power Control) driving of the semiconductor laser element 20. The control unit 180 detects the power of the first laser beam L1 based on a signal from the first optical sensor D1, and performs feedback control of the amount of current supplied to the semiconductor laser element 20 so that the power of the first laser beam L1 approaches a predetermined target power.

[0085] Changes in the amount of current supplied to the semiconductor laser element 20 in this embodiment over time will be described with reference to Fig. 12. Fig. 12 is a second schematic graph showing the relationship between the amount of current supplied to the semiconductor laser element 20 and the output optical power. Fig. 12 shows the relationship for the semiconductor laser element 20 in an initial state and the relationship for the semiconductor laser element 20 after degradation.

[0086] As described above, the semiconductor laser element 20 deteriorates over time, and the output optical power decreases even if the current (or power) supplied is constant. Therefore, in order to maintain the output optical power constant, the amount of current must be increased. As shown in FIG. 12 , in the initial state of the semiconductor laser element 20, when the amount of current supplied is i0, the output optical power is PLi. In this case, when the semiconductor laser element 20 is in a deteriorated state, in order to maintain the output optical power at PLi, the amount of current supplied to the semiconductor laser element 20 must be increased to i1.

[0087] [2-2. Control Method of Laser Apparatus] A control method of the laser apparatus 101 according to this embodiment will be described with reference to Fig. 13. Fig. 13 is a flowchart showing the control method of the laser apparatus 101 according to this embodiment.

[0088] 13 , first, a target temperature is set in the control unit 180 (target temperature setting step S10) in the same manner as in the first embodiment. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51. In this embodiment, the control unit 180 maintains the target temperature constant throughout the entire life of the semiconductor laser element 20.

[0089] Next, the control unit 180 controls the amount of current supplied to the semiconductor laser element 20 (current control step S120). In the present embodiment, the control unit 180 controls the amount of current supplied to the semiconductor laser element 20 so that the power of the first laser light L1 is constant. The control unit 180 detects the power of the first laser light L1 based on a signal from the first optical sensor D1, and performs feedback control on the amount of current supplied to the semiconductor laser element 20 so that the power of the first laser light L1 approaches a predetermined target power.

[0090] Next, similarly to the first embodiment, the control unit 180 uses the first temperature adjustment unit 51 to control the temperature of the installation point of the semiconductor laser element 20 based on the target temperature for the semiconductor laser element 20 (first temperature control step S30).

[0091] Subsequently, the process returns to the current control step S20, and the current control step S20 and the first temperature control step S30 are repeated. As described above, the amount of heat generated increases with the deterioration of the semiconductor laser element 20. Therefore, the control unit 180 reduces the power consumption required for heating by the first temperature adjustment unit 51 as the deterioration of the semiconductor laser element 20 progresses.

[0092] As described above, the control unit 180 controls the laser device 101 .

[0093] [2-3. Effects, etc.] The effects of the laser device 101 according to this embodiment and the control method thereof will be described in comparison with the laser device and control method thereof of Comparative Example 2. The laser device of Comparative Example 2 is a laser device whose configuration is identical to that of the laser device 101 according to this embodiment except for the target temperature. In the laser device and control method thereof of Comparative Example 2, the target temperature for the semiconductor laser element 20 in the initial state is set to a temperature at which the power consumption by the first temperature adjustment unit 51 is substantially zero.

[0094] The relationship between the deterioration rate of the semiconductor laser element 20 and power consumption in each laser device according to Comparative Example 2 and the present embodiment will be described with reference to FIGS. 14 to 17 . FIG. 14 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device according to Comparative Example 2 and the power consumption in the first temperature adjustment unit 51 and the semiconductor laser element 20. FIG. 15 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device according to Comparative Example 2 and the total power consumption of the laser device. FIG. 16 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 101 according to the present embodiment and the power consumption in the first temperature adjustment unit 51 and the semiconductor laser element 20. FIG. 17 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 101 according to the present embodiment and the total power consumption of the laser device 101. Note that each graph shows power consumption calculated by simulation.

[0095] In this simulation, the ambient temperature was set to 25° C., and the voltage and current supplied to the semiconductor laser element 20 in the initial state were set to 4.5 V and 1.28 A, respectively.

[0096] In the laser device of Comparative Example 2, the target temperature for the semiconductor laser element 20 in the initial state is set to 41.2°C, a temperature at which heating and cooling by the first temperature adjustment unit 51 are not required. Therefore, in the laser device of Comparative Example 2, when the semiconductor laser element 20 is in the initial state, the power consumption of the first temperature adjustment unit 51 is substantially zero, as shown in FIG. 14, and the total power consumption is equal to the power consumption of the semiconductor laser element 20, as shown in FIG. 15. Furthermore, in Comparative Example 2 and the present embodiment, the output optical power of the semiconductor laser element 20 is maintained constant. As described above, as the semiconductor laser element 20 deteriorates, the ratio of the output optical power to the power consumption decreases, and therefore, when the output optical power of the semiconductor laser element 20 is maintained constant, the power consumption of the semiconductor laser element 20 increases as the semiconductor laser element 20 deteriorates.

[0097] Furthermore, since the amount of heat generated by the semiconductor laser element 20 increases with deterioration, when the temperature at the installation point of the semiconductor laser element 20 is controlled to be constant, the power consumption required for cooling the semiconductor laser element 20 by the first temperature adjustment unit 51 increases as shown in Fig. 14. Therefore, as shown in Fig. 15, the total power consumption of the laser device increases with deterioration of the semiconductor laser element 20. In the laser device of Comparative Example 2, the total power consumption was 5.8 W when the deterioration rate of the semiconductor laser element 20 was 0%, but was 9.9 W when the deterioration rate of the semiconductor laser element 20 was 20%.

[0098] If the life span is defined as the period from the initial state of the semiconductor laser element 20 to the state where the degradation rate reaches 20%, the total energy consumption during the life span of the laser device of Comparative Example 2 was 281 MJ.

[0099] In contrast, in the laser apparatus 101 according to this embodiment, the target temperature for the semiconductor laser element 20 in the initial state is 44° C., which is the temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51. Therefore, in the laser apparatus 101 according to this embodiment, when the semiconductor laser element 20 is in the initial state, the power consumption of the first temperature adjustment unit 51 is not 0, as shown in Fig. 16. Furthermore, as shown in Fig. 17, the total power consumption is larger than the power consumption of the semiconductor laser element 20.

[0100] However, the amount of heat generated by the semiconductor laser element 20 increases as it deteriorates. Furthermore, in this embodiment, in order to maintain the output optical power of the semiconductor laser element 20 constant, the amount of current supplied increases as it deteriorates. Therefore, the amount of heat generated by the semiconductor laser element 20 further increases as it deteriorates. Therefore, when controlling the temperature of the installation point of the semiconductor laser element 20 to be constant, the control unit 180 reduces the power consumption required for heating by the first temperature adjustment unit 51 as the deterioration of the semiconductor laser element 20 progresses. Therefore, as shown in FIG. 16 , as the deterioration rate of the semiconductor laser element 20 increases from 0% to approximately 18%, the power consumption required for heating the semiconductor laser element 20 by the first temperature adjustment unit 51 decreases. Therefore, as shown in FIG. 17 , the increase in the total power consumption of the laser apparatus 101 due to deterioration of the semiconductor laser element 20 is smaller than the increase in the power consumption of the semiconductor laser element 20 due to deterioration. When the deterioration rate of the semiconductor laser element 20 is approximately 18%, the heat generated from the semiconductor laser element 20 can be dissipated solely by heat transport caused by the temperature difference between the first surface 51 a and the second surface 51 b of the first temperature adjustment unit 51, and the power consumption of the first temperature adjustment unit 51 becomes zero. As the deterioration of the semiconductor laser element 20 further progresses, when the temperature of the installation point of the semiconductor laser element 20 is controlled to be constant, the heat generated from the semiconductor laser element 20 cannot be dissipated solely by heat transport caused by the temperature difference between the first surface 51 a and the second surface 51 b of the first temperature adjustment unit 51, and therefore the control unit 180 causes the first temperature adjustment unit 51 to cool the semiconductor laser element 20. Therefore, as the deterioration rate of the semiconductor laser element 20 increases from approximately 18% to 20%, the power consumption required for cooling the semiconductor laser element 20 by the first temperature adjustment unit 51 increases.

[0101] In the laser device 101 according to this embodiment, the total power consumption was 6.4 W when the deterioration rate of the semiconductor laser element 20 was 0%, and the total power consumption was 6.9 W when the deterioration rate of the semiconductor laser element 20 was 20%.

[0102] The total energy consumption over the lifetime of the laser device 101 according to this embodiment is 233 MJ. As described above, the total energy consumption over the lifetime of the laser device 101 according to this embodiment can be reduced by 48 MJ compared to the laser device of Comparative Example 2.

[0103] As described above, the laser device 101 according to the present embodiment, like the laser device 1 according to the first embodiment, includes the semiconductor laser element 20 that emits the first laser light L1, the first temperature adjustment unit 51 that heats or cools the semiconductor laser element 20, and the control unit 180 that controls the amount of current supplied to the semiconductor laser element 20 and controls the first temperature adjustment unit 51 based on a target temperature that is a control target for the temperature at the installation point of the semiconductor laser element 20. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51.

[0104] As a result, similar to the laser device 1 according to the first embodiment, it is possible to suppress long-term temperature fluctuations in the laser device 101 while suppressing the total energy consumption of the laser device 101 over its lifetime.

[0105] Furthermore, in this embodiment, the control unit 180 controls the amount of current supplied to the semiconductor laser element 20 so that the power of the first laser light L1 is constant.

[0106] This allows the power of the first laser light L1 to be maintained constant even if the semiconductor laser element 20 deteriorates.

[0107] In addition, in this embodiment, the control unit 180 may set the target temperature so that the sum of the energy consumed in the semiconductor laser element 20 and the energy consumed in the first temperature adjustment unit 51 over the lifetime of the semiconductor laser element 20 is minimized.

[0108] This allows the total energy consumption in the laser device 101 to be minimized.

[0109] As in the first embodiment, the control method for the laser apparatus 101 according to this embodiment includes a current control step S120 for controlling the amount of current supplied to the semiconductor laser element 20, and a first temperature control step S30 for using the first temperature adjustment unit 51 to control the temperature of the installation point of the semiconductor laser element 20 based on a target temperature for the semiconductor laser element 20. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the first temperature adjustment unit 51 needs to heat the semiconductor laser element 20.

[0110] This makes it possible to suppress long-term temperature fluctuations in the laser device 101 while also suppressing the total energy consumption of the laser device 101 over its lifetime.

[0111] Furthermore, in the current control step S120 of the present embodiment, the amount of current supplied to the semiconductor laser element 20 is controlled so that the power of the first laser light L1 is constant.

[0112] This allows the power of the first laser light L1 to be maintained constant even when the semiconductor laser element 20 is deteriorated.

[0113] (Embodiment 3) A laser device and a control method thereof according to embodiment 3 will be described. The laser device according to this embodiment differs from laser device 101 according to embodiment 2 in that the temperature of the installation point of semiconductor laser element 20 is controlled so that the wavelength of first laser light L1 output from semiconductor laser element 20 is constant. The laser device and control method thereof according to this embodiment will be described below, focusing on the differences from laser device 101 and control method thereof according to embodiment 2.

[0114] [3-1. Overall Configuration of Laser Apparatus] The overall configuration of the laser apparatus according to this embodiment will be described with reference to Fig. 18. Fig. 18 is a schematic diagram showing the overall configuration of a laser apparatus 201 according to this embodiment.

[0115] 18 , the laser device 201 includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 280. In this embodiment, the laser device 201 further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a first selective transmission mirror M1, a first optical sensor D1, a second selective transmission mirror M2, a second optical sensor D2, a third selective transmission mirror M3, and a third optical sensor D3.

[0116] The second selective transmission mirror M2 is disposed on the optical axis of the first laser light L1, and is a mirror that reflects at least a portion of the first laser light L1 and selectively transmits the wavelength of the second laser light L2. In the present embodiment, the second selective transmission mirror M2 is disposed on the optical axis of the first laser light L1 that has passed through the output mirror 16. The first laser light L1 that has entered the second selective transmission mirror M2 is reflected by the second selective transmission mirror M2 and enters the second optical sensor D2.

[0117] The second optical sensor D2 is a sensor that detects the power of the first laser beam L1. In the present embodiment, the second optical sensor D2 detects the power of the first laser beam L1 that has passed through the output mirror 16. The second optical sensor D2 outputs a signal corresponding to the power of the first laser beam L1 to the control unit 280. A photodiode, for example, can be used as the second optical sensor D2.

[0118] The third selective transmission mirror M3 is a mirror that is disposed on the optical axis of the second laser light L2 and reflects at least a portion of the second laser light L2. In the present embodiment, the third selective transmission mirror M3 is disposed on the optical axis of the second laser light L2 emitted from the output mirror 16. A portion of the second laser light L2 that is incident on the third selective transmission mirror M3 is reflected by the third selective transmission mirror M3 and enters the third optical sensor D3.

[0119] The third optical sensor D3 is a sensor that detects the power of the second laser beam L2. In the present embodiment, the third optical sensor D3 detects the power of the second laser beam L2 emitted from the output mirror 16. The third optical sensor D3 outputs a signal corresponding to the power of the second laser beam L2 to the control unit 280. A photodiode, for example, can be used as the third optical sensor D3.

[0120] The control unit 280 is a processing unit that controls the amount of current supplied to the semiconductor laser element 20 and also controls the first temperature adjustment unit 51 based on a target temperature that is a control target for the temperature at the installation point of the semiconductor laser element 20.

[0121] The control unit 280 controls the amount of current supplied to the semiconductor laser element 20 so that the power of the second laser light L2 is constant. The control unit 280 detects the power of the second laser light L2 based on a signal from the third optical sensor D3, and performs feedback control on the amount of current supplied to the semiconductor laser element 20 so that the power of the second laser light L2 approaches a predetermined target power.

[0122] Also in this embodiment, similarly to the first embodiment, the control unit 280 controls the first temperature adjustment unit 51 based on the target temperature for the semiconductor laser element 20. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the first temperature adjustment unit 51 needs to heat the semiconductor laser element.

[0123] In this embodiment, the control unit 280 sets a target temperature and controls the first temperature adjustment unit 51 based on the target temperature so that the wavelength of the first laser light L1 is constant. That is, the control unit 280 controls the first temperature adjustment unit 51 so that the wavelength of the first laser light L1 is constant. The control unit 280 calculates the temperature T ｊ Specifically, the heat generation amount Q of the semiconductor laser element 20 shown in formula (3) is maintained constant. ＬＤ increases with the deterioration of the semiconductor laser device 20. Accordingly, the temperature T ｊ In order to suppress an increase in the target temperature T ｃ Reduces the amount of heat generated Q ＬＤ As the target temperature T ｃ In this way, the temperature T ｊBy keeping the power of the second laser beam L2 and the wavelength of the first laser beam L1 constant, the wavelength of the first laser beam L1 can be kept constant. Note that in the present embodiment, by keeping the power of the second laser beam L2 and the wavelength of the first laser beam L1 constant, the power of the first laser beam L1 is also kept constant.

[0124] In the present embodiment, the control unit 280 detects the wavelength of the first laser beam L1 based on the absorptance of the first laser beam L1 in the laser crystal 30 using the wavelength dependency of the absorptance in the laser crystal 30. Specifically, the control unit 280 detects the absorptance of the first laser beam L1 in the laser crystal 30 using the power of the first laser beam L1 before it enters the laser crystal 30, detected by the first optical sensor D1, and the power of the first laser beam L1 after it has passed through the laser crystal 30, detected by the second optical sensor D2. The control unit 280 sets (i.e., updates) the target temperature Tc as needed to maintain a constant absorptance of the first laser beam L1 in the laser crystal 30. For example, the control unit 280 may set the target temperature Tc so that a constant ratio is maintained between the power of the first laser beam L1 before it enters the laser crystal 30, detected by the first optical sensor D1, and the power of the first laser beam L1 after it has passed through the laser crystal 30, detected by the second optical sensor D2.

[0125] 3-2. Control Method of Laser Apparatus A control method of the laser apparatus 201 according to this embodiment will be described with reference to Fig. 19. Fig. 19 is a flowchart showing the control method of the laser apparatus 201 according to this embodiment.

[0126] 19 , first, a target temperature is set in the control unit 280 (target temperature setting step S10). The target temperature in the initial state may be set by the control unit 280 or may be set based on an input to the laser device 201 by a user or the like. The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51.

[0127] Next, control unit 280 controls the amount of current supplied to semiconductor laser element 20 (current control step S220). In the present embodiment, control unit 280 controls the amount of current supplied to semiconductor laser element 20 so that the power of second laser light L2 is constant. Control unit 280 detects the power of second laser light L2 based on a signal from third optical sensor D3, and feedback-controls the amount of current supplied to semiconductor laser element 20 so that the power of second laser light L2 approaches a predetermined target power.

[0128] Next, similarly to the first embodiment, the control unit 280 uses the first temperature adjustment unit 51 to control the temperature of the installation point of the semiconductor laser element 20 based on the target temperature for the semiconductor laser element 20 (first temperature control step S30).

[0129] Next, control unit 280 updates the target temperature (target temperature updating step S240). In this embodiment, control unit 280 updates (i.e., resets) the target temperature so that the wavelength of first laser beam L1 is constant. Based on signals from first optical sensor D1 and second optical sensor D2, control unit 280 sets the target temperature so that the absorptance of first laser beam L1 in laser crystal 30 is constant.

[0130] Subsequently, the process returns to the current control step S220, and the current control step S220, the first temperature control step S30, and the target temperature update step S240 are repeated.

[0131] As described above, the control unit 280 controls the laser device 201 .

[0132] [3-3. Effects, etc.] The effects of the laser apparatus 201 according to this embodiment and the control method thereof will be described in comparison with the laser apparatus and control method thereof of Comparative Example 3. The laser apparatus of Comparative Example 3 is a laser apparatus whose configuration is identical to that of the laser apparatus 101 according to this embodiment except for the target temperature. In the laser apparatus and control method thereof of Comparative Example 3, the target temperature for the semiconductor laser element 20 in the initial state is set to a temperature at which the power consumption by the first temperature adjustment unit 51 is substantially zero.

[0133] The relationship between the deterioration rate of the semiconductor laser element 20 and power consumption in each laser device according to Comparative Example 3 and the present embodiment will be described with reference to FIGS. 20 to 23 . FIG. 20 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device according to Comparative Example 3 and the power consumption in the first temperature adjustment unit 51 and the semiconductor laser element 20. FIG. 21 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device according to Comparative Example 3 and the total power consumption of the laser device. FIG. 22 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 201 according to the present embodiment and the power consumption in the first temperature adjustment unit 51 and the semiconductor laser element 20. FIG. 23 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 201 according to the present embodiment and the total power consumption of the laser device 201. Note that each graph shows power consumption calculated by simulation.

[0134] In this simulation, the ambient temperature was set to 25° C., and the voltage and current supplied to the semiconductor laser element 20 in the initial state were set to 4.5 V and 1.28 A, respectively.

[0135] In the laser device of Comparative Example 3, the target temperature for the semiconductor laser element 20 in the initial state is set to 41.2°C, a temperature at which heating and cooling by the first temperature adjustment unit 51 are not necessary. Therefore, in the laser device of Comparative Example 3, when the semiconductor laser element 20 is in the initial state, the power consumption of the first temperature adjustment unit 51 is substantially zero, as shown in FIG. 20 , and the total power consumption is equal to the power consumption of the semiconductor laser element 20, as shown in FIG. 21 . Furthermore, in Comparative Example 3, the power of the second laser light L2 is maintained constant. As described above, as the semiconductor laser element 20 deteriorates, the ratio of the output light power to the power consumption decreases, and therefore, when the power of the second laser light L2 is maintained constant, the power consumption of the semiconductor laser element 20 increases as the semiconductor laser element 20 deteriorates.

[0136] In Comparative Example 3, the first temperature adjusting unit 51 is controlled so that the wavelength of the first laser light L1 is constant. In this case, the heat generation amount Q of the semiconductor laser element 20 is ＬＤincreases with the deterioration of the semiconductor laser element 20, and the control unit 280 sets the target temperature T ｃ 20, the power consumption required for cooling the semiconductor laser element 20 by the first temperature adjustment unit 51 increases as the semiconductor laser element 20 deteriorates. Therefore, as shown in FIG. 21, the total power consumption of the laser device increases as the semiconductor laser element 20 deteriorates. In the laser device of Comparative Example 3, the total power consumption was 5.8 W when the deterioration rate of the semiconductor laser element 20 was 0%, but was 19 W when the deterioration rate of the semiconductor laser element 20 was 20%.

[0137] If the life span is defined as the period from the initial state of the semiconductor laser element 20 to the state where the degradation rate reaches 20%, the total energy consumption during the life span of the laser device of Comparative Example 3 was 448 MJ.

[0138] In contrast, in the laser apparatus 201 according to this embodiment, the target temperature for the semiconductor laser element 20 in the initial state is 53° C., which is the temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51. Therefore, in the laser apparatus 201 according to this embodiment, when the semiconductor laser element 20 is in the initial state, the power consumption of the first temperature adjustment unit 51 is not 0, as shown in Fig. 22. Furthermore, as shown in Fig. 23, the total power consumption is larger than the power consumption of the semiconductor laser element 20.

[0139] In addition, in the present embodiment, the power of the second laser beam L2 is maintained constant. As described above, the ratio of the output light power to the power consumption decreases as the semiconductor laser element 20 deteriorates, and therefore, when the power of the second laser beam L2 is maintained constant, the power consumption of the semiconductor laser element 20 increases as the semiconductor laser element 20 deteriorates.

[0140] In this embodiment, the first temperature adjusting unit 51 is controlled so that the wavelength of the first laser light L1 is constant. In this case, the heat generation amount Q of the semiconductor laser element 20 is ＬＤ increases with the deterioration of the semiconductor laser element 20, and the control unit 280 sets the target temperature T ｃ22 , the power consumption required for heating the semiconductor laser element 20 by the first temperature adjustment unit 51 decreases as the semiconductor laser element 20 deteriorates. In the example shown in FIG. 22 , the amount of decrease in power consumption by the first temperature adjustment unit 51 as the semiconductor laser element 20 deteriorates is greater than the amount of increase in power consumption by the semiconductor laser element 20, so as shown in FIG. 23 , the total power consumption of the laser device 201 decreases as the semiconductor laser element 20 deteriorates. In the laser device 201 according to this embodiment, the total power consumption was 8.3 W when the deterioration rate of the semiconductor laser element 20 was 0%, but was 6.6 W when the deterioration rate of the semiconductor laser element 20 was 20%.

[0141] The total energy consumption over the lifetime of the laser device 201 according to this embodiment is 268 MJ. As described above, the total energy consumption over the lifetime of the laser device 201 according to this embodiment can be reduced by 180 MJ compared to the laser device of Comparative Example 3.

[0142] As described above, the laser device 201 according to this embodiment also achieves the same effects as those of the second embodiment.

[0143] In the laser device 201 according to the present embodiment, the control unit 280 controls the first temperature adjustment unit 51 so that the wavelength of the first laser light L1 is constant.

[0144] This makes it possible to suppress a decrease in the absorptance of the first laser light L1 in the laser crystal 30, for example, when the first laser light L1 is used to excite the laser crystal 30. Therefore, wavelength conversion can be performed efficiently in the laser crystal 30.

[0145] Furthermore, in the laser device 201 according to this embodiment, the control unit 280 lowers the target temperature as the deterioration of the semiconductor laser element progresses.

[0146] This makes it possible to suppress the wavelength of the first laser light L1 from shifting to the longer wavelength side.

[0147] Furthermore, the control method for the laser device 201 according to this embodiment also achieves the same effects as the control method for the laser device 101 according to the second embodiment.

[0148] The control method for the laser device 201 according to the present embodiment also includes a target temperature updating step S240 for updating the target temperature. In the target temperature updating step S240, the target temperature is updated so that the wavelength of the first laser beam L1 is constant.

[0149] This makes it possible to suppress a change in the wavelength of the first laser light L1.

[0150] Furthermore, in the current control step S220 of the control method for the laser apparatus 201 according to the present embodiment, the amount of current supplied to the semiconductor laser element 20 is controlled so that the power of the second laser light L2 is constant.

[0151] This makes it possible to suppress changes in the power of the second laser light L2.

[0152] [3-4. Modifications] The configuration of the laser device according to this embodiment is not limited to the configuration example shown in Fig. 18. A laser device according to a modification of this embodiment will be described below with reference to Fig. 24, focusing on differences from laser device 201 according to this embodiment. Fig. 24 is a schematic diagram showing the overall configuration of laser device 201a according to a modification of this embodiment.

[0153] 24, the laser device 201a includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 280a. In this embodiment, the laser device 201a further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a third selective transmission mirror M3, and a third optical sensor D3.

[0154] The laser device 201a according to the modified example of this embodiment differs from the laser device 201 according to this embodiment in that it does not have a configuration for detecting the power of the first laser light L1 and in the control method in the control unit 280a.

[0155] The control unit 280a in this embodiment controls the first temperature adjustment unit 51 based on the amount of current supplied to the semiconductor laser element 20, the amount of current supplied to the first temperature adjustment unit 51 (or the power consumption of the first temperature adjustment unit 51), and the temperature of the installation point of the semiconductor laser element 20, so that the wavelength of the first laser light L1 is constant.

[0156] Specifically, the control unit 280a has a database showing the relationship between, for example, the amount of current supplied to the semiconductor laser element 20 in the initial state, the target temperature, and the amount of current supplied to the first temperature adjustment unit 51 required to achieve the target temperature. The control unit 280a can detect the amount of increase in the amount of heat generated due to deterioration of the semiconductor laser element 20 based on this information, the amount of current supplied to the semiconductor laser element 20, and the amount of change in the amount of current supplied to the first temperature adjustment unit 51 from the amount of current supplied in the initial state. The control unit 280a calculates the temperature T ｊ The target temperature T ｃ Set.

[0157] By including such a control unit 280a, the laser device 201a according to this modification can achieve the same effects as the laser device 201 according to the present embodiment.

[0158] (Embodiment 4) A laser device and a control method thereof according to embodiment 4 will be described. The laser device according to this embodiment differs from laser device 201 according to embodiment 3 in that the wavelength of first laser light L1 output from semiconductor laser element 20 is maintained within a predetermined wavelength range. The laser device and control method thereof according to this embodiment will be described below, focusing on the differences from laser device 201 and control method thereof according to embodiment 3.

[0159] [4-1. Overall Configuration of Laser Apparatus] The overall configuration of the laser apparatus according to this embodiment will be described with reference to Fig. 25. Fig. 25 is a schematic diagram showing the overall configuration of a laser apparatus 301 according to this embodiment.

[0160] 25 , the laser device 301 includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 380. In the present embodiment, the laser device 301 further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a third selective transmission mirror M3, and a third optical sensor D3.

[0161] The control unit 380 according to this embodiment sets a target temperature so that the wavelength of the first laser light L1 is maintained within a predetermined wavelength range. The control unit 380 controls the first temperature adjustment unit 51 based on the target temperature. The predetermined wavelength range will now be described with reference to FIG. 26 . FIG. 26 is a graph showing an example of the wavelength range of the semiconductor laser element 20. The horizontal axis of FIG. 26 represents the wavelength, and the vertical axis represents the absorptance of the laser crystal 30.

[0162] The predetermined wavelength range corresponds to, for example, the absorption band of the laser crystal 30. The absorption band is defined, for example, as a wavelength range in which the absorptance of the laser crystal 30 is 90% or more of the peak absorptance. If the absorptance Rar shown in FIG. 26 is 90% of the peak absorptance value Ra0, the predetermined wavelength range can be set to be greater than or equal to λr1 and less than or equal to λr2. The predetermined wavelength range and the absorptance range of the laser crystal 30 corresponding to the absorption band are not limited to the above-mentioned ranges. For example, the predetermined wavelength range may be a range in which the absorptance of the laser crystal 30 is 85% or more of the peak value Ra0, a range in which the absorptance is 95% or more of the peak value Ra0, or a range in which the absorptance is 99% or more of the peak value Ra0. In this embodiment, the absorption peak wavelength of the laser crystal 30 is 444 nm, and the predetermined wavelength range is 443.75 nm or more and 444.25 nm or less.

[0163] The control unit 380 has a database showing the relationship between, for example, the amount of current supplied to the semiconductor laser element 20, the deterioration rate, the temperature (target temperature), the wavelength of the first laser light L1 (or the absorption rate of the laser crystal 30), and the amount of current supplied to the first temperature adjustment unit 51. Such a database can be obtained by conducting an operation test of the semiconductor laser element 20 in advance. The control unit 380 sets the amount of current supplied to the semiconductor laser element 20 and the target temperature based on the database. An example of the relationship between the deterioration rate of the semiconductor laser element 20 controlled by the control unit 380 and the wavelength of the first laser light L1 will be described with reference to FIG. 27 . FIG. 27 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 according to the present embodiment and the wavelength of the first laser light L1. 27 , the control unit 380 appropriately sets the target temperature in accordance with parameters such as the amount of current supplied to the semiconductor laser element 20, so that the wavelength of the first laser light L1 shifts from 443.75 nm, which is the lower limit of the predetermined wavelength range, to 444.25 nm, which is the upper limit, as the deterioration rate increases from 0% to 20%. In this way, the control unit 380 sets the target temperature in accordance with the deterioration rate of the semiconductor laser element 20 so that the wavelength of the first laser light L1 fluctuates from the lower limit to the upper limit within the predetermined wavelength range over the life of the semiconductor laser element 20.

[0164] Furthermore, similar to the third embodiment, the control unit 380 detects the power of the second laser light L2 based on the signal from the third optical sensor D3, and performs feedback control on the amount of current supplied to the semiconductor laser element 20 so that the power of the second laser light L2 approaches a predetermined target power.

[0165] 4-2. Control Method of Laser Apparatus A control method of the laser apparatus 301 according to this embodiment will be described with reference to Fig. 28. Fig. 28 is a flowchart showing the control method of the laser apparatus 301 according to this embodiment.

[0166] 28 , first, a target temperature is set in the control unit 380 (target temperature setting step S10). The target temperature for the semiconductor laser element 20 in the initial state is a temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51.

[0167] Next, the control unit 380 controls the amount of current supplied to the semiconductor laser element 20 (current control step S220). In the present embodiment, the control unit 380 controls the amount of current supplied to the semiconductor laser element 20 so that the power of the second laser light L2 is constant. The control unit 280 detects the power of the second laser light L2 based on a signal from the third optical sensor D3, and performs feedback control on the amount of current supplied to the semiconductor laser element 20 so that the power of the second laser light L2 approaches a predetermined target power.

[0168] Next, similarly to the first embodiment, the control unit 380 uses the first temperature adjustment unit 51 to control the temperature of the installation point of the semiconductor laser element 20 based on the target temperature for the semiconductor laser element 20 (first temperature control step S30).

[0169] Next, the control unit 380 updates the target temperature (target temperature updating step S340). In the present embodiment, the control unit 380 updates the target temperature so that the wavelength of the first laser light L1 is maintained within a predetermined wavelength range. The control unit 380 updates the target temperature so that the wavelength of the first laser light L1 is maintained within the predetermined wavelength range, for example, by using a database indicating the relationship between the amount of current supplied to the semiconductor laser element 20, the deterioration rate, the temperature (target temperature), the wavelength of the first laser light L1, and the amount of current supplied to the first temperature adjustment unit 51, as described above.

[0170] Subsequently, the process returns to the current control step S220, and the current control step S220, the first temperature control step S30, and the target temperature update step S340 are repeated.

[0171] As described above, the control unit 380 controls the laser device 301 .

[0172] [4-3. Effects, etc.] The effects of the laser device 301 and its control method according to this embodiment will be described. First, the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 301 according to this embodiment and power consumption will be described using FIGS. 29 and 30. FIG. 29 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 301 according to this embodiment and the power consumption of the first temperature adjustment unit 51 and the semiconductor laser element 20. FIG. 30 is a graph showing the relationship between the deterioration rate of the semiconductor laser element 20 in the laser device 301 according to this embodiment and the total power consumption of the laser device 301. Note that each graph shows power consumption calculated by simulation.

[0173] In this simulation, the ambient temperature was set to 25° C., and the voltage and current supplied to the semiconductor laser element 20 in the initial state were set to 4.5 V and 1.28 A, respectively.

[0174] In the laser apparatus 301 according to this embodiment, the target temperature for the semiconductor laser element 20 in the initial state is 44.9° C., which is the temperature to which the semiconductor laser element 20 needs to be heated by the first temperature adjustment unit 51. Therefore, in the laser apparatus 301 according to this embodiment, when the semiconductor laser element 20 is in the initial state, the power consumption of the first temperature adjustment unit 51 is not 0, as shown in Fig. 29. Furthermore, as shown in Fig. 30, the total power consumption is larger than the power consumption of the semiconductor laser element 20.

[0175] In addition, in the present embodiment, the power of the second laser beam L2 is maintained constant. As described above, the ratio of the output light power to the power consumption decreases as the semiconductor laser element 20 deteriorates, and therefore, when the power of the second laser beam L2 is maintained constant, the power consumption of the semiconductor laser element 20 increases as the semiconductor laser element 20 deteriorates.

[0176] In this embodiment, the target temperature is set so that the wavelength of the first laser beam L1 is maintained within a predetermined wavelength range. In this simulation, the predetermined wavelength range is set to 443.75 nm or more and 444.25 nm or less, and semiconductor laser element 20 is used in which, in the initial state, the wavelength of first laser beam L1 when the temperature is set to 44.9° C. is approximately 443.75 nm, which is the shortest wavelength within the predetermined wavelength range.

[0177] In this case, the heat generation amount Q of the semiconductor laser element 20 ＬＤ increases as the semiconductor laser element 20 deteriorates, and the wavelength of the first laser light L1 shifts to the longer wavelength side. The control unit 380 sets the target temperature and the amount of current supplied to the semiconductor laser element 20 so as to satisfy the relationship shown in FIG. 27 . As a result, the laser device 301 according to this embodiment allows the wavelength of the first laser light L1 to shift to the longer wavelength side compared to the laser device 201 according to the third embodiment. In other words, the laser device 301 according to this embodiment allows a temperature rise in the active layer of the semiconductor laser element 20 compared to the laser device 201 according to the third embodiment. This makes it possible to suppress power consumption by the first temperature adjustment unit 51.

[0178] In the laser device 301 according to this embodiment, the total power consumption was 6.6 W when the deterioration rate of the semiconductor laser element 20 was 0%, and the total power consumption was 7.5 W when the deterioration rate of the semiconductor laser element 20 was 20%.

[0179] The total energy consumption over the lifetime of the laser device 301 according to this embodiment is 237 MJ. As described above, the total energy consumption over the lifetime of the laser device 301 according to this embodiment is reduced by 31 MJ compared to the laser device 201 according to the third embodiment.

[0180] As described above, the laser device 301 according to this embodiment can suppress the decrease in the absorption rate in the laser crystal 30, while suppressing energy consumption even more than the laser device 201 according to the third embodiment.

[0181] [4-4. Modifications] The configuration of the laser device according to this embodiment is not limited to the configuration example shown in Fig. 25. A laser device according to a modification of this embodiment will be described below with reference to Fig. 31, focusing on differences from laser device 401 according to embodiment 4. Fig. 31 is a schematic diagram showing the overall configuration of laser device 301a according to a modification of this embodiment.

[0182] 31 , the laser device 301a includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 380a. In this modification, the laser device 301a further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a first selective transmission mirror M1, a first optical sensor D1, a second selective transmission mirror M2, a second optical sensor D2, a third selective transmission mirror M3, and a third optical sensor D3.

[0183] The control unit 380a according to this modification sets the target temperature so that the wavelength of the first laser beam L1 is maintained within a predetermined wavelength range, and controls the first temperature adjustment unit 51 based on the target temperature.

[0184] The control unit 380a has a database showing the relationship between, for example, the amount of current supplied to the semiconductor laser element 20, the deterioration rate, the temperature (target temperature), the wavelength of the first laser light L1 (or the absorption rate of the laser crystal 30), and the amount of current supplied to the first temperature adjustment unit 51.

[0185] In this modification, the control unit 380a sets the target temperature based on the signals from the first optical sensor D1 and the second optical sensor D2 and the database so that the deterioration rate of the semiconductor laser element 20 and the wavelength of the first laser beam L1 (or the absorptance of the laser crystal 30) satisfy the relationship shown in Fig. 27. The control unit 380a has information indicating the relationship between the amount of change in the target temperature and the amount of change in the wavelength of the first laser beam L1 (or the absorptance of the laser crystal 30), and may set the target temperature based on this information.

[0186] The laser device 301a having such a configuration also provides the same effects as the laser device 301 according to the present embodiment.

[0187] (Embodiment 5) A laser device and a control method thereof according to embodiment 5 will be described. The laser device according to this embodiment differs from laser device 201 according to embodiment 3 mainly in that it includes a nonlinear optical crystal. The laser device and control method thereof according to this embodiment will be described below, focusing on the differences from laser device 201 according to embodiment 3 and the control method thereof.

[0188] [5-1. Overall Configuration of Laser Apparatus] The overall configuration of the laser apparatus according to this embodiment will be described with reference to Fig. 32. Fig. 32 is a schematic diagram showing the overall configuration of a laser apparatus 401 according to this embodiment.

[0189] 32 , the laser device 401 includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 480. In the present embodiment, the laser device 401 further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a nonlinear optical crystal 40, a second temperature adjustment unit 52, a second holder 12, a second temperature sensor 82, a first selective transmission mirror M1, a first optical sensor D1, a second selective transmission mirror M2, a second optical sensor D2, a fourth selective transmission mirror M4, and a fourth optical sensor D4.

[0190] The nonlinear optical crystal 40 is an optical crystal that converts the second laser light L2 into the third laser light L3. The nonlinear optical crystal 40 is disposed on the optical axis of the second laser light L2 between the laser crystal 30 and the output mirror 16. In this embodiment, the nonlinear optical crystal 40 emits the second harmonic of the second laser light L2. That is, the peak wavelength of the third laser light L3 is half the peak wavelength of the second laser light L2. The peak wavelength of the third laser light L3 is, for example, 400 nm or less. In this embodiment, the peak wavelength of the third laser light L3 is 320 nm.

[0191] The material of the nonlinear optical crystal 40 is not particularly limited as long as it is a crystal that can emit second harmonic waves. The nonlinear optical crystal 40 may be, for example, LBO (LiB ３ O ５ ), BBO (β-BaB ２ O４ ), or KTP (KTiOPO ４ ) The transmission wavelength range of LBO is 160 nm or more. In other words, LBO can be used when the wavelength of the second harmonic is 160 nm or more. The transmission wavelength range of BBO is 190 nm or more. The transmission wavelength range of KTP is 350 nm or more. In this embodiment, LBO is used as the nonlinear optical crystal 40. Note that the output mirror 16 according to this embodiment transmits the third laser light L3.

[0192] The fourth selective transmission mirror M4 is a mirror that is disposed on the optical axis of the third laser light L3 and reflects at least a portion of the third laser light L3. In the present embodiment, the fourth selective transmission mirror M4 is disposed on the optical axis of the third laser light L3 emitted from the output mirror 16. A portion of the third laser light L3 that has entered the fourth selective transmission mirror M4 is reflected by the fourth selective transmission mirror M4 and enters the fourth optical sensor D4.

[0193] The fourth optical sensor D4 is a sensor that detects the power of the third laser beam L3. In the present embodiment, the fourth optical sensor D4 detects the power of the third laser beam L3 emitted from the output mirror 16. The fourth optical sensor D4 outputs a signal corresponding to the power of the third laser beam L3 to the control unit 480. A photodiode, for example, can be used as the fourth optical sensor D4.

[0194] The second holder 12 is a member that holds the nonlinear optical crystal 40. The second holder 12 is thermally connected to the nonlinear optical crystal 40. The second holder 12 is made of a material with high thermal conductivity. The second holder 12 is made of, for example, Cu.

[0195] The second temperature adjustment unit 52 heats or cools the nonlinear optical crystal 40. The second temperature adjustment unit 52 has a first surface 52a and a second surface 52b. The second temperature adjustment unit 52 is controlled by the control unit 480 to adjust the temperature difference between the first surface 52a and the second surface 52b. In this embodiment, the second temperature adjustment unit 52 is a Peltier element. The first surface 52a and the second surface 52b correspond to one and the other electrodes of the Peltier element. The second temperature adjustment unit 52 is supplied with a voltage and a current from the control unit 480, and adjusts the temperature difference between the first surface 52a and the second surface 52b in accordance with the supplied voltage and current. The first surface 52a is thermally connected to the second holder 12 and heats or cools the nonlinear optical crystal 40 via the second holder 12. In this manner, the first surface 52a is thermally connected to the nonlinear optical crystal 40. The second surface 52b is thermally connected to the heat sink 18.

[0196] The second temperature sensor 82 is a sensor that detects the temperature of the second holder 12. The second temperature sensor 82 is thermally connected to the second holder 12. The second temperature sensor 82 outputs a signal corresponding to the temperature of the second holder 12 to the control unit 480. As the second temperature sensor 82, for example, a thermocouple, a resistance temperature detector, or the like can be used.

[0197] Similar to the control unit 280 according to the third embodiment, the control unit 480 sets a target temperature and controls the first temperature adjustment unit 51 based on the target temperature so that the wavelength of the first laser light L1 is constant. The control unit 480 also controls the amount of current supplied to the semiconductor laser element 20 so that the power of the third laser light L3 is constant. The control unit 480 detects the power of the third laser light L3 based on a signal from the fourth optical sensor D4, and feedback-controls the amount of current supplied to the semiconductor laser element 20 so that the power of the third laser light L3 approaches a predetermined target power.

[0198] The control unit 480 controls the second temperature adjustment unit based on the target crystal temperature, which is a control target for the temperature of the nonlinear optical crystal 40. This allows the temperature of the nonlinear optical crystal 40 to be maintained at a temperature that satisfies the phase matching condition. The control unit 480 detects the temperature of the nonlinear optical crystal 40 based on the output signal of the second temperature sensor 82. Here, the temperature of the second holder 12 corresponding to the output signal of the second temperature sensor 82 may be regarded as the temperature of the nonlinear optical crystal 40, or the relationship between the output signal of the second temperature sensor 82 and the temperature of the nonlinear optical crystal 40 may be obtained in advance, and the temperature of the nonlinear optical crystal 40 may be detected based on this relationship.

[0199] 5-2. Control Method of Laser Apparatus A control method of the laser apparatus 401 according to this embodiment will be described with reference to Fig. 33. Fig. 3 is a flowchart showing the control method of the laser apparatus 401 according to this embodiment.

[0200] As shown in FIG. 33, first, a target temperature is set in the control unit 480 (target temperature setting step S10).

[0201] Next, control unit 480 controls the amount of current supplied to semiconductor laser element 20 (current control step S420). In the present embodiment, control unit 480 controls the amount of current supplied to semiconductor laser element 20 so that the power of third laser light L3 is constant. Control unit 380 detects the power of third laser light L3 based on a signal from fourth optical sensor D4, and feedback-controls the amount of current supplied to semiconductor laser element 20 so that the power of third laser light L3 approaches a predetermined target power.

[0202] Subsequently, the control unit 480 controls the temperature of the installation point of the semiconductor laser element 20 based on the target temperature for the semiconductor laser element 20 using the first temperature adjustment unit 51 (first temperature control step S30).

[0203] Subsequently, the control unit 480 controls the temperature of the nonlinear optical crystal 40 using the second temperature adjusting unit 52 (second temperature control step S432).

[0204] Next, the control unit 480 updates the target temperature (target temperature updating step S240). In the present embodiment, the control unit 280 updates the target temperature so that the wavelength of the first laser light L1 is constant.

[0205] Subsequently, the process returns to the current control step S420, and the current control step S420, the first temperature control step S30, the second temperature control step S432, and the target temperature update step S240 are repeated.

[0206] As described above, the control unit 480 controls the laser device 401 .

[0207] [5-3. Effects, etc.] In the laser device 401 according to the present embodiment, similar to the laser device 201 according to the third embodiment, it is possible to suppress long-term temperature fluctuations in the laser device 401 and also suppress the total energy consumption of the laser device 401 over its lifetime.

[0208] In addition, the laser device 401 of this embodiment includes a nonlinear optical crystal 40 that converts the second laser light L2 into a third laser light L3, and a second temperature adjustment unit 52 having a first surface 52a and a second surface 52b and adjusting the temperature difference between the first surface 52a and the second surface 52b, and the first surface 52a is thermally connected to the nonlinear optical crystal 40.

[0209] By providing such second temperature adjustment unit 52, it becomes possible to control the temperature of nonlinear optical crystal 40 independently of semiconductor laser element 20. Therefore, the temperature of nonlinear optical crystal 40 can be maintained constant, and therefore the temperature of nonlinear optical crystal 40 can be maintained at a temperature that satisfies the phase matching condition.

[0210] The control method for laser device 401 according to this embodiment also includes a second temperature control step S 432 of controlling the temperature of nonlinear optical crystal 40 using second temperature adjustment unit 52 .

[0211] This allows the temperature of the nonlinear optical crystal 40 to be maintained constant, so that the temperature of the nonlinear optical crystal 40 can be maintained at a temperature that satisfies the phase matching condition.

[0212] [5-4. Modifications] The configuration of the laser device according to this embodiment is not limited to the configuration example shown in Fig. 32. A laser device according to a modification of this embodiment will be described below with reference to Fig. 34, focusing on differences from laser device 401 according to this embodiment. Fig. 34 is a schematic diagram showing the overall configuration of laser device 401a according to a modification of this embodiment.

[0213] As shown in FIG. 34, the laser device 401a further includes a semiconductor laser element 20, a first temperature adjustment unit 51, a control unit 480, a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a nonlinear optical crystal 40, a second temperature adjustment unit 52, a second temperature sensor 82, a first selective transmission mirror M1, a first optical sensor D1, a second selective transmission mirror M2, a second optical sensor D2, a fourth selective transmission mirror M4, and a fourth optical sensor D4.

[0214] 34 , the second temperature adjustment unit 52 according to this modification is disposed in the first holder 11. As a result, the second surface 52b of the second temperature adjustment unit 52 is heated or cooled by the first temperature adjustment unit 51.

[0215] In this modification, the laser device 401a may not include the second holder 12. The nonlinear optical crystal 40 may be directly disposed on the first surface 52a of the second temperature adjustment unit 52. In this case, the second temperature sensor 82 may be thermally connected to the first surface 52a.

[0216] The laser device 401a according to this modification also provides the same effects as those of the laser device 401 according to the present embodiment.

[0217] Furthermore, in the laser device 401a and its control method according to this modification, the control unit 480 may control the second temperature adjustment unit 52 to maintain the temperature of the first surface 52a at the target temperature of the semiconductor laser element 20. In other words, the target crystal temperature of the nonlinear optical crystal 40 may be equal to the target temperature of the semiconductor laser element 20. Because the nonlinear optical crystal 40 itself does not generate heat, the power consumption of the second temperature adjustment unit 52 is minimized when the temperature of the first surface 52a and the temperature of the second surface 52b of the second temperature adjustment unit 52 are equal. Therefore, by maintaining the temperature of the first surface 52a at the target temperature of the semiconductor laser element 20, the power consumption of the laser device 401a can be reduced.

[0218] (Embodiment 6) A laser device and a control method thereof according to embodiment 6 will be described. The laser device according to this embodiment differs from laser device 401 according to embodiment 5 mainly in that laser crystal 30 and nonlinear optical crystal 40 are thermally connected. The laser device and control method thereof according to this embodiment will be described below, focusing on the differences from laser device 401 and control method thereof according to embodiment 5.

[0219] [6-1. Overall Configuration of Laser Apparatus and Control Method] The overall configuration of a laser apparatus according to this embodiment and a control method thereof will be described with reference to Fig. 35. Fig. 35 is a schematic diagram showing the overall configuration of a laser apparatus 501 according to this embodiment.

[0220] 35 , a laser device 501 includes a semiconductor laser element 20, a first temperature adjustment unit 51, and a control unit 480. In the present embodiment, the laser device 401 further includes a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a nonlinear optical crystal 40, a second temperature adjustment unit 52, a second holder 12, a second temperature sensor 82, a first selective transmission mirror M1, a first optical sensor D1, a second selective transmission mirror M2, a second optical sensor D2, a fourth selective transmission mirror M4, and a fourth optical sensor D4.

[0221] In laser device 501 and its control method according to this embodiment, first surface 52a of second temperature adjustment unit 52 is thermally connected to laser crystal 30. Laser crystal 30 is thermally connected to first surface 52a of second temperature adjustment unit 52 via second holder 12, which is placed on first surface 52a of second temperature adjustment unit 52. Laser crystal 30 may also be placed directly on first surface 52a of second temperature adjustment unit 52.

[0222] As a result, when the laser device 501 is in operation, heat generated in the laser crystal 30 is conducted to the first surface 52a, thereby indirectly heating the nonlinear optical crystal 40 that is thermally connected to the first surface 52a.

[0223] Here, in the nonlinear optical crystal 40, the angle between the Poynting vectors of the ordinary light and the extraordinary light becomes smaller in a high-temperature environment. As a result, walk-off of the third laser light L3 as the second harmonic wave with respect to the second laser light L2 as the fundamental wave can be suppressed. In this way, setting the target crystal temperature of the nonlinear optical crystal 40 higher can suppress walk-off.

[0224] In this embodiment, since laser crystal 30 and nonlinear optical crystal 40 are thermally connected to first surface 52a, heat generated in laser crystal 30 can be utilized to maintain the temperature of nonlinear optical crystal 40 at a high temperature. Therefore, laser device 501 and its control method according to this embodiment can reduce the power consumption of second temperature adjustment unit 52 while suppressing walk-off in nonlinear optical crystal 40.

[0225] [6-2. Modifications] The configuration of the laser device according to this embodiment is not limited to the configuration example shown in Fig. 35. A laser device according to a modification of this embodiment will be described below with reference to Fig. 36, focusing on differences from laser device 501 according to this embodiment. Fig. 36 is a schematic diagram showing the overall configuration of laser device 501a according to a modification of this embodiment.

[0226] As shown in FIG. 36, the laser device 501a further includes a semiconductor laser element 20, a first temperature adjustment unit 51, a control unit 480, a laser crystal 30, a selective transmission mirror 31, a first holder 11, an output mirror 16, a heat sink 18, a first temperature sensor 81, a nonlinear optical crystal 40, a second temperature adjustment unit 52, a second temperature sensor 82, a first selective transmission mirror M1, a first optical sensor D1, a second selective transmission mirror M2, a second optical sensor D2, a fourth selective transmission mirror M4, and a fourth optical sensor D4.

[0227] 36 , the second temperature adjustment unit 52 according to this modification is disposed in the first holder 11. As a result, the second surface 52b of the second temperature adjustment unit 52 is heated or cooled by the first temperature adjustment unit 51.

[0228] In this modification, the laser device 501a does not need to include the second holder 12. The laser crystal 30 and the nonlinear optical crystal 40 may be directly disposed on the first surface 52a of the second temperature adjustment unit 52. In this case, the second temperature sensor 82 may be thermally connected to the first surface 52a.

[0229] The laser device 501a according to this modification also provides the same effects as those of the laser device 501 according to the present embodiment.

[0230] Furthermore, since the first surface 51a of the first temperature adjustment unit 51 is usually maintained at a temperature higher than the ambient temperature, this modification makes it possible to reduce the power consumption of the second temperature adjustment unit 52 while suppressing walk-off in the nonlinear optical crystal 40.

[0231] Furthermore, in the laser device 501a and the control method thereof according to this modification, the control unit 480 may control the second temperature adjustment unit 52 to maintain the temperature of the first surface 52a at the target temperature of the semiconductor laser element 20. In other words, the target crystal temperature of the nonlinear optical crystal 40 may be equal to the target temperature of the semiconductor laser element 20. This makes it possible to reduce the power consumption of the laser device 501a, similar to the modification of the fifth embodiment.

[0232] (Other Embodiments) While the solid-state laser device according to the present disclosure has been described above based on the embodiments and modifications thereof, the present disclosure is not limited to these embodiments and modifications thereof. As long as the modifications do not deviate from the gist of the present disclosure, various modifications conceivable by a person skilled in the art to the embodiments and other forms constructed by combining some of the components of the embodiments and modifications thereof are also included in the scope of the present disclosure.

[0233] For example, although the laser devices according to the first to fourth embodiments and their modifications include a laser crystal and an output mirror 16, the laser crystal and the output mirror 16 may not be included.

[0234] In addition, in the above-mentioned embodiments 5 and 6, the first optical sensor D1 and the second optical sensor D2 are used to maintain a constant wavelength, but these optical sensors may not be used by using a method similar to that of the modified embodiment 4.

[0235] Furthermore, the above-described embodiments can be modified, substituted, added, omitted, and the like in various ways within the scope of the claims or their equivalents.

[0236] For example, the amount of current supplied to the semiconductor laser device 20 according to the third to sixth embodiments may be constant, similar to the first embodiment.

[0237] Furthermore, in each of the laser devices according to the fifth and sixth embodiments, similarly to the fourth embodiment, the wavelength of the first laser light L1 may be maintained within a predetermined wavelength range.

[0238] The laser device according to the present disclosure can be used as a laser light source capable of reducing energy consumption for various purposes such as illumination and processing.

[0239] DESCRIPTION OF SYMBOLS 1, 101, 201, 201a, 301, 301a, 401, 401a, 501, 501a Laser device 11 First holder 12 Second holder 16 Output mirror 18 Heat sink 20 Semiconductor laser element 30 Laser crystal 30a Incident surface 31 Selective transmission mirror 40 Nonlinear optical crystal 51 First temperature adjustment unit 51a, 52a First surface 51b, 52b Second surface 52 Second temperature adjustment unit 80, 180, 280, 280a, 380, 380a, 480 Control unit 81 First temperature sensor 82 Second temperature sensor D1 First optical sensor D2 Second optical sensor D3 Third optical sensor D4 Fourth optical sensor L1 First laser beam L2 Second laser beam L3 Third laser beam M1 First selective transmission mirror M2 Second selective transmission mirror M3 Third selective transmission mirror M4 Fourth selective transmission mirror

Claims

1. A laser device comprising: a semiconductor laser element that emits a first laser beam; a first temperature adjustment unit that heats or cools the semiconductor laser element; and a control unit that controls the amount of current supplied to the semiconductor laser element and controls the first temperature adjustment unit based on a target temperature that is a control target for the temperature of an installation point of the semiconductor laser element, wherein the target temperature for the semiconductor laser element in an initial state is a temperature to which the semiconductor laser element needs to be heated by the first temperature adjustment unit.

2. The laser device according to claim 1, wherein the semiconductor laser element is a nitride semiconductor laser element.

3. The laser device according to claim 1 or 2, wherein the control unit causes the first temperature adjustment unit to reduce heating of the semiconductor laser element as deterioration of the semiconductor laser element progresses.

4. A laser device according to any one of claims 1 to 3, wherein the control unit causes the first temperature adjustment unit to cool the semiconductor laser element when deterioration of the semiconductor laser element progresses beyond a predetermined deterioration rate.

5. The laser device according to any one of claims 1 to 4, wherein the control unit maintains a constant amount of current supplied to the semiconductor laser element.

6. The laser device according to any one of claims 1 to 4, wherein the control unit controls the amount of current supplied to the semiconductor laser element so that the power of the first laser light is constant.

7. The laser device according to claim 5 or 6, wherein the control unit maintains the target temperature constant throughout the entire life of the semiconductor laser element.

8. The laser device according to claim 7, wherein the control unit sets the target temperature so that the sum of the energy consumed by the semiconductor laser element and the energy consumed by the first temperature adjustment unit over the lifetime of the semiconductor laser element is minimized.

9. The laser device according to any one of claims 1 to 4, wherein the control unit controls the first temperature adjustment unit so that the wavelength of the first laser light is constant.

10. The laser device according to claim 9, wherein the control unit lowers the target temperature as deterioration of the semiconductor laser element progresses.

11. The laser device according to any one of claims 1 to 4, wherein the control unit sets the target temperature so that the wavelength of the first laser light is maintained within a predetermined wavelength range.

12. A laser device according to any one of claims 1 to 8 and 11, comprising a laser crystal that is excited by the first laser light, wherein the wavelength of the first laser light changes from a wavelength shorter than the absorption peak wavelength of the laser crystal to a wavelength longer than the absorption peak wavelength during the lifetime of the semiconductor laser element.

13. The laser device according to claim 11, comprising a laser crystal that is excited by the first laser light, and the predetermined wavelength range corresponds to an absorption band of the laser crystal.

14. A laser device according to any one of claims 1 to 11, comprising: a laser crystal that is excited by the first laser light and emits a second laser light having a wavelength different from that of the first laser light; a nonlinear optical crystal that converts the second laser light into a third laser light; and a second temperature adjustment unit having a first surface and a second surface and adjusting a temperature difference between the first surface and the second surface, wherein the first surface is thermally connected to the nonlinear optical crystal.

15. The laser device according to claim 14, wherein the second surface is heated or cooled by the first temperature adjustment unit.

16. The laser device according to claim 15, wherein the control unit controls the second temperature adjustment unit to maintain the temperature of the first surface at the target temperature.

17. A laser device according to any one of claims 14 to 16, wherein the first surface is thermally connected to the laser crystal.

18. A method for controlling a laser device, the laser device comprising: a semiconductor laser element that emits a first laser beam; and a first temperature adjustment unit that heats or cools the semiconductor laser element; the method for controlling the laser device includes: a current control step that controls an amount of current supplied to the semiconductor laser element; and a first temperature control step that uses the first temperature adjustment unit to control a temperature of an installation point of the semiconductor laser element based on a target temperature for the semiconductor laser element, wherein the target temperature for the semiconductor laser element in an initial state is a temperature to which the semiconductor laser element needs to be heated by the first temperature adjustment unit.

19. The method for controlling a laser device according to claim 18, wherein in the first temperature control step, the power required for heating by the first temperature adjustment unit is reduced as deterioration of the semiconductor laser element progresses.

20. A method for controlling a laser device according to claim 18 or 19, wherein the laser device comprises: a laser crystal that is excited by the first laser light and emits a second laser light having a wavelength different from that of the first laser light; a nonlinear optical crystal that converts the second laser light into a third laser light; and a second temperature adjustment unit that has a first surface and a second surface and adjusts a temperature difference between the first surface and the second surface; and the method for controlling the laser device includes a second temperature control step of controlling the temperature of the nonlinear optical crystal using the second temperature adjustment unit, and the first surface is thermally connected to the nonlinear optical crystal.

21. The method for controlling a laser device according to claim 20, wherein the second surface is heated or cooled by the first temperature adjustment unit.

22. The method for controlling a laser device according to claim 21, wherein in the second temperature control step, the temperature of the first surface is maintained at the target temperature by controlling the second temperature adjustment unit.

23. A method for controlling a laser device according to any one of claims 20 to 22, wherein the first surface is thermally connected to the laser crystal.

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