Laser device

Abstract

To reduce power consumption of a semiconductor laser element while appropriately controlling the temperature of the semiconductor laser element in a laser device including the semiconductor laser element.SOLUTION: The laser device 1 includes a semiconductor laser element 20 that emits a first laser beam L1, a temperature adjustment unit 51 that heats or cools the semiconductor laser element 20, and a control unit 80 that controls the temperature adjustment unit 51 based on a target temperature that is a control target of a temperature at an installation point of the semiconductor laser element 20, in which the control unit 80 supplies a voltage pulse to the temperature adjustment unit 51 and controls a voltage value of the voltage pulse based on at least one of an environmental temperature, a target temperature, a heat generation amount of the semiconductor laser element 20, and a duty ratio of the voltage pulse.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to laser devices. [Background technology]

[0002] Laser devices equipped with laser elements such as semiconductor laser elements are known. For example, in laser devices equipped with 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. In this way, the solid-state laser device described in Patent Document 1 attempts to suppress the total current consumption of the semiconductor laser element and the Peltier element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5070820 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a demand for further reduction in power consumption in laser devices.

[0005] An object of the present disclosure is to reduce power consumption in a laser device including a semiconductor laser element while appropriately controlling the temperature of the semiconductor laser element. [Means for solving the problem]

[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 temperature adjustment unit that heats or cools the semiconductor laser element, and a control unit that controls the 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, and the control unit supplies a voltage pulse to the temperature adjustment unit and controls a voltage value of the voltage pulse based on at least one of an ambient temperature, the target temperature, the heat generation amount of the semiconductor laser element, and a duty ratio of the voltage pulse. [Effects of the Invention]

[0007] According to the present disclosure, in a laser device including a semiconductor laser element, it is possible to reduce the power consumption of the semiconductor laser element while appropriately controlling the temperature of the semiconductor laser element. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the overall configuration of a laser device according to a first embodiment. [Figure 2] 4 is a flowchart showing a control method for the laser device according to the first embodiment. [Figure 3] 5 is a flowchart showing duty ratio control steps in the control method for the laser device according to the first embodiment. [Figure 4] 5 is a flowchart showing voltage value control steps in the control method for the laser device according to the first embodiment. [Figure 5] 5 is a diagram illustrating an example of the operation of the laser device according to the first embodiment. FIG. [Figure 6] FIG. 10 is a schematic diagram showing the overall configuration of a laser device according to a second embodiment. [Figure 7] 10 is a flowchart showing a control method for a laser device according to a second embodiment. [Figure 8] 10 is a flowchart showing voltage value control steps in a control method for a laser device according to a second embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of the operation of the laser device according to the second embodiment. [Figure 10] FIG. 10 is a schematic diagram showing the overall configuration of a laser device according to a third embodiment. [Figure 11] 10 is a graph showing the relationship between the ambient temperature, the voltage applied to the temperature adjusting unit, and the current flowing through the temperature adjusting unit. [Figure 12] 10 is a graph showing the relationship between the ambient temperature, the voltage applied to the temperature adjustment unit by the control unit according to the third embodiment, and the current flowing through the temperature adjustment unit. [Figure 13] 10 is a flowchart showing a control method for a laser device according to a third embodiment. [Figure 14] 11 is a flowchart showing voltage value control steps in a control method for a laser device according to a third embodiment. [Figure 15] 10 is a graph showing the relationship between the ambient temperature in a laser device according to a comparative example, the voltage applied to a temperature adjusting unit, the current flowing through the temperature adjusting unit, and the duty ratio of a voltage pulse. [Figure 16] 10 is a graph showing the relationship between the ambient temperature and the power consumption of the temperature adjusting unit according to a comparative example. [Figure 17] 10 is a graph showing the relationship between the environmental temperature in the laser device according to the third embodiment, the voltage applied to the temperature adjusting unit, the current flowing in the temperature adjusting unit, and the duty ratio of the voltage pulse. [Figure 18] 11 is a graph showing the relationship between the environmental temperature and the power consumption in the temperature adjusting unit according to the third embodiment. [Figure 19] 10 is a diagram illustrating a first example of the operation of the laser device according to the third embodiment. FIG. [Figure 20] FIG. 10 is a diagram illustrating a second example of the operation of the laser device according to the third embodiment. [Figure 21] FIG. 10 is a diagram illustrating a third example of operation of the laser device according to the third embodiment. [Figure 22] FIG. 10 is a diagram illustrating a fourth example of the operation of the laser device according to the third embodiment. [Figure 23] 11 is a flowchart showing voltage value control steps according to a modified example of the control method for the laser device of the third embodiment. [Figure 24]FIG. 10 is a schematic diagram showing the overall configuration of a laser device according to a fourth embodiment. [Figure 25] 1 is a first schematic graph showing the relationship between the amount of current supplied to a semiconductor laser element and the output optical power; [Figure 26] 10 is a schematic graph showing the relationship between the power supply time of a semiconductor laser element, the power supplied to the semiconductor laser element, the output optical power of the semiconductor laser element, and the amount of heat generated by the semiconductor laser element. [Figure 27] 10 is a flowchart showing a control method for a laser device according to a fourth embodiment. [Figure 28] 10 is a graph showing the relationship between the deterioration rate of a semiconductor laser element in a laser device of Comparative Example 1 and the power consumption in a temperature adjustment unit. [Figure 29] 10 is a graph showing the relationship between the deterioration rate of a semiconductor laser element in a laser device of Comparative Example 1, and the total power consumption of the laser device and the power consumption of the semiconductor laser element. [Figure 30] 10 is a graph showing the relationship between the deterioration rate of a semiconductor laser element in a laser device according to the fourth embodiment and the power consumption in a temperature adjustment unit. [Figure 31] 10 is a graph showing the relationship between the deterioration rate of a semiconductor laser element in a laser device according to the fourth embodiment and the total power consumption of the laser device and the power consumption of the semiconductor laser element. [Figure 32] 1 is a first graph showing the relationship between the wavelength of the primary laser light of the semiconductor laser element and the absorptance of the laser crystal. [Figure 33] 10 is a second graph showing the relationship between the wavelength of the primary laser light of the semiconductor laser element and the absorptance of the laser crystal. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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.

[0010] 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.

[0011] 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 mean a range that is substantially equivalent, for example, including a difference of about a few percent.

[0012] (Embodiment 1) A laser device and a control method thereof according to a first embodiment will be described.

[0013] [1-1. Overall configuration of the laser device] The overall configuration of a laser device 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 device 1 according to this embodiment.

[0014] 1, the laser device 1 includes a semiconductor laser element 20, a 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, a laser temperature sensor 81, and an environmental temperature sensor 83.

[0015] 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 the absorption band, which is the absorption wavelength band of the laser crystal 30. Here, the installation point of the semiconductor laser element 20 means the point at which the semiconductor laser element 20 is heated or cooled by the 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. The temperature of the installation point of the semiconductor laser element 20 corresponds to the temperature of the semiconductor laser element 20. The temperature of the installation point of the semiconductor laser element 20 is also referred to as the laser temperature.

[0016] 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.

[0017] 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 junction-down. 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.

[0018] 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.

[0019] 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.

[0020] 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 L2 is, for example, 400 nm or more and 800 nm or less. In this embodiment, the laser crystal 30 is doped with Pr 3+ :YLiF4, and the peak wavelength of second laser light L2 is 640 nm. In the present embodiment, laser crystal 30 is held by first holder 11.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The temperature adjustment unit 51 heats or cools the semiconductor laser element 20. The temperature adjustment unit 51 has a first surface 51a and a second surface 51b. The 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 this embodiment, the 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 temperature adjustment unit 51 receives 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.

[0025] 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. The heat sink 18 is made of, for example, Cu.

[0026] The laser temperature sensor 81 is a sensor that detects the temperature of the first holder 11. The laser temperature sensor 81 is thermally connected to the first holder 11. The laser temperature sensor 81 outputs a signal corresponding to the temperature of the first holder 11 to the control unit 80. As the laser temperature sensor 81, for example, a thermocouple, a resistance temperature detector, or the like can be used.

[0027] The environmental temperature sensor 83 is a sensor that detects the temperature of the environment in which the laser device 1 is placed. In this embodiment, the environmental temperature sensor 83 detects the temperature of the heat sink 18. The environmental temperature sensor 83 is thermally connected to the heat sink 18. The environmental temperature sensor 83 outputs a signal corresponding to the temperature of the heat sink 18 to the control unit 80. The environmental temperature sensor 83 can be, for example, a thermocouple, a resistance temperature detector, or the like.

[0028] 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 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 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 or processor that constitutes the control unit 80 executes a computer program (software) stored in the memory that constitutes the control unit 80.

[0029] The control unit 80 supplies a voltage pulse to the temperature adjustment unit 51 and controls the voltage value of the voltage pulse based on at least one of the ambient temperature of the semiconductor laser element 20, the target temperature, the amount of heat generated by the semiconductor laser element 20, and the duty ratio of the voltage pulse. In this embodiment, the control unit 80 controls the voltage value of the voltage pulse based on the ambient temperature Th, the target temperature Tc, and the amount of heat generated by the semiconductor laser element 20. The duty ratio of the voltage pulse supplied by the control unit 80 to the temperature adjustment unit 51 is not less than 0 and not more than 1. In this specification, a configuration in which a voltage pulse with a duty ratio of 1 is applied, that is, a configuration in which a voltage is applied continuously, is also included as an example of a configuration in which a voltage pulse is applied.

[0030] 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 in an ACC (Automatic Current Control) manner.

[0031] 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 laser temperature sensor 81. Here, the temperature of the first holder 11 corresponding to the output signal of the laser 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 laser 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.

[0032] [1-2. Laser device control method] A control method for the laser device 1 according to this embodiment will be described with reference to Fig. 2 to Fig. 4. Fig. 2 is a flowchart showing the control method for the laser device 1 according to this embodiment. Fig. 3 and Fig. 4 are flowcharts showing a duty ratio control step and a voltage value control step, respectively, in the control method for the laser device 1 according to this embodiment.

[0033] The control method for the laser device 1 according to this embodiment is executed by the control unit 80 of the laser device 1. As shown in Fig. 2, first, initial settings are performed in the control unit 80 (initial setting step S10). Specifically, initial values ​​for a target temperature Tc and a voltage value Vi of a voltage pulse to be applied to the temperature adjustment unit 51 are set. The target temperature Tc and the voltage value Vi may be set by the control unit 80, or may be set based on an input to the laser device 1 by a user or the like.

[0034] Subsequently, the control unit 80 starts the operation of the laser device 1 (operation start step S20). Specifically, the control unit 80 starts applying power to the semiconductor laser element 20.

[0035] Next, the control unit 80 controls the duty ratio of the voltage pulse applied to the temperature adjustment unit 51 (duty ratio control step S30), and also controls the voltage value Vi of the voltage pulse (voltage value control step S40). In this embodiment, the control unit 80 executes the duty ratio control step S30 and the voltage value control step S40 in parallel. Note that the manner in which the control unit 80 executes the duty ratio control step S30 and the voltage value control step S40 is not limited to this. For example, the control unit 80 may execute the duty ratio control step S30 and the voltage value control step S40 alternately. The details of each of the duty ratio control step S30 and the voltage value control step S40 will be described later.

[0036] 2, after the duty ratio control step S30 or the voltage value control step S40 is completed, the control unit 80 determines whether or not to terminate the operation of the laser device 1 (operation termination determination step S50). For example, the control unit 80 determines whether or not to terminate the operation of the laser device 1 based on whether or not a signal to terminate the operation of the laser device 1 has been received. The signal to terminate the operation may be input by a user or may be input from a timer, for example.

[0037] In the operation end determination step S50, if the control unit 80 determines that the operation of the laser device 1 should be ended (Yes in the operation end determination step S50), the control unit 80 ends the control of the laser device 1. In the operation end determination step S50, if the control unit 80 determines that the operation of the laser device 1 should not be ended (No in the operation end determination step S50), the control unit 80 executes the duty ratio control step S30 (and the voltage value control step S40) again.

[0038] In the duty ratio control step S30 shown in Figures 2 and 3, the control unit 80 controls the duty ratio of the voltage pulse applied to the temperature adjustment unit 51 so that the temperature Ts(t) of the installation point of the semiconductor laser element 20 approaches the target temperature Tc.

[0039] 3, in the duty ratio control step S30, first, the control unit 80 acquires the temperature Ts(t) of the installation point of the semiconductor laser element 20 (laser temperature acquisition step S31). Here, the temperature Ts(t) is expressed as a function of time t. In this embodiment, the control unit 80 acquires the temperature Ts(t) of the installation point of the semiconductor laser element 20 based on the output signal of the laser temperature sensor 81.

[0040] Next, the control unit 80 calculates the temperature difference ΔT(t) between the temperature Ts(t) and the target temperature Tc (temperature difference calculation step S32).

[0041] Next, the control unit 80 calculates a control input amount of the duty ratio of the voltage pulse to be applied to the temperature adjustment unit 51 (control input amount calculation step S33). In this embodiment, the control unit 80 calculates the control input amount based on PID (Proportional-Integral-Differential) control. The control input amount u(t) is expressed by the following equation using a proportional gain Kp, an integral gain Ki, and a differential gain Kd.

[0042]

number

[0043] Next, the control unit 80 calculates an updated duty ratio Ds' of the voltage pulse to be applied to the temperature adjustment unit 51 based on the control input amount u(t) (duty ratio calculation step S34). For example, the control input amount u(t) may be used as the updated duty ratio Ds'.

[0044] Subsequently, the control unit 80 stores the updated duty ratio Ds' as the duty ratio Ds (duty ratio storage step S35). That is, the control unit 80 updates the pre-update duty ratio Ds to the updated duty ratio Ds'.

[0045] Subsequently, the control unit 80 applies a voltage pulse with a duty ratio Ds' to the temperature adjustment unit 51 (voltage pulse application step S36).

[0046] After the above steps are completed, the control unit 80 ends the duty ratio control step S30 and executes the operation end determination step S50 described above.

[0047] 2 and 4, the control unit 80 controls the voltage value of the voltage pulse to be applied to the temperature adjustment unit 51 based on at least one of the environmental temperature Th, the target temperature Tc, the heat generation amount Q of the semiconductor laser element 20, and the duty ratio of the voltage pulse. In this embodiment, the control unit 80 controls the voltage value of the voltage pulse based on the environmental temperature Th, the target temperature Tc, and the heat generation amount Q of the semiconductor laser element 20. In this embodiment, the control unit 80 controls the voltage value of the voltage pulse to be applied to the temperature adjustment unit 51 so as to reduce the power supplied to the temperature adjustment unit 51. When performing predetermined cooling or heating in the temperature adjustment unit 51, the power supplied to the temperature adjustment unit 51 can be reduced by reducing the absolute value of the voltage value of the voltage pulse to be applied.

[0048] 4, in the voltage value control step S40, first, the control unit 80 acquires the power to be supplied to the semiconductor laser element 20 (supply power acquisition step S41). For example, the control unit 80 acquires the values ​​of the voltage and current to be supplied to the semiconductor laser element 20, and acquires the supply power based on these values.

[0049] Next, the control unit 80 acquires the heat generation amount Q of the semiconductor laser element 20 (heat generation amount acquisition step S42). For example, the control unit 80 may acquire the heat generation amount Q based on a database that indicates the relationship between the power supplied to the semiconductor laser element 20 and the heat generation amount Q. Note that the method of acquiring the heat generation amount Q is not limited to this. For example, in the supplied power acquisition step S41, the control unit 80 may acquire the output optical power of the semiconductor laser element 20 in addition to the supplied power, and acquire the value obtained by subtracting the output optical power from the supplied power as the heat generation amount Q. The output optical power may be acquired, for example, by reflecting a part of the first laser light L1 emitted by the semiconductor laser element 20 by a partial reflection mirror or the like and detecting it with a photodiode or the like, and acquiring the output optical power based on the power of the detected laser light.

[0050] Next, the control unit 80 acquires the environmental temperature Th (environmental temperature acquisition step S43). In the present embodiment, the control unit 80 acquires the temperature of the heat sink 18 as the environmental temperature Th based on the output signal of the environmental temperature sensor 83.

[0051] Next, the control unit 80 acquires the target temperature Tc (target temperature acquisition step S44). In this embodiment, the control unit 80 acquires the target temperature Tc set in the initial setting step S10.

[0052] Next, control unit 80 calculates an optimum voltage value Vx of the voltage pulse to be applied to temperature adjustment unit 51 (optimum voltage value calculation step S45). Here, the optimum voltage value Vx is the voltage value when the voltage value of the voltage pulse to be applied to temperature adjustment unit 51 is minimum when controlling so that the temperature Ts(t) at the installation point becomes the target temperature Tc. As the voltage value of the voltage pulse decreases, the duty ratio of the voltage pulse increases, so the optimum voltage value Vx is the voltage value when the duty ratio of the voltage pulse is maximum, that is, when the duty ratio is 1. In this embodiment, the optimum voltage value Vx is expressed by the following equation using the Seebeck coefficient α of the Peltier element used as temperature adjustment unit 51, the thermal resistance R of the Peltier element, and the Boltzmann constant K.

[0053]

number

[0054] Next, the control unit 80 updates the voltage value of the voltage pulse to be applied to the temperature adjustment unit 51 (voltage value update step S46). The control unit 80 updates the absolute value of the voltage pulse so that it becomes equal to or greater than the absolute value of the optimal voltage value Vx. That is, the control unit 80 controls the absolute value of the voltage pulse to a value equal to or greater than the absolute value of the optimal voltage value Vx. In other words, when the optimal voltage value Vx is positive, the control unit 80 controls the voltage pulse to a value equal to or greater than the optimal voltage value Vx, and when the optimal voltage value Vx is negative, the control unit 80 controls the voltage pulse to a value equal to or less than the optimal voltage value Vx. The control unit 80 may also control the absolute value of the voltage pulse to a value equal to or less than 1.2 times the absolute value of the optimal voltage value Vx. In this embodiment, the control unit 80 controls the voltage pulse to a value equal to or less than 1.1 times the optimal voltage value Vx. When the voltage pulse is equal to the optimal voltage value Vx, the voltage value may be insufficient, making it impossible to properly adjust the temperature. In this embodiment, the occurrence of such a problem can be prevented by making the absolute value of the voltage value of the voltage pulse greater than the absolute value of the optimum voltage value Vx.

[0055] After the above steps are completed, the control unit 80 ends the voltage value control step S40 and executes the operation end determination step S50 described above.

[0056] According to the control method for the laser device 1 according to the present embodiment, the duty ratio of the voltage pulse applied to the temperature adjustment unit 51 is controlled based on the temperature Ts(t) and the target temperature Tc, thereby making it possible to appropriately control the temperature of the semiconductor laser element 20. Furthermore, by controlling the voltage value of the voltage pulse applied to the temperature adjustment unit 51, it is possible to reduce the power supplied to the temperature adjustment unit 51. Therefore, the power consumption of the laser device 1 can be reduced.

[0057] [1-3. Example of operation] An example of operation of the laser device 1 according to this embodiment will be described with reference to FIG. 5. FIG. 5 is a diagram showing an example of operation of the laser device 1 according to this embodiment. Graph (a) of FIG. 5 is a graph showing the relationship between the ambient temperature Th and time. Graph (b) of FIG. 5 is a graph showing the relationship between the amount of heat Q of the semiconductor laser element 20 and time. Graph (c) of FIG. 5 is a graph showing the relationship between the laser temperature Ts(t) and time. Graph (d) of FIG. 5 is a graph showing the relationship between the applied voltage applied to the temperature adjustment unit 51 and time. Graph (e) of FIG. 5 is a graph showing the relationship between the current flowing through the temperature adjustment unit 51 and time.

[0058] In the operation example shown in Fig. 5, the ambient temperature is constant at 25°C, as shown in graph (a) of Fig. 5. The operation of the laser device 1 starts at time t1 in Fig. 5. That is, at time t1 in Fig. 5, the supply of power to the semiconductor laser element 20 starts, and the heat generation amount of the semiconductor laser element 20 is constant at 5 W, as shown in graph (b) of Fig. 5.

[0059] At time t1 in FIG. 5, as the operation of the laser device 1 begins, application of a voltage pulse to the temperature adjustment unit 51 begins, as shown in graph (d) in FIG. 5. In the example of operation shown in FIG. 5, during the period from time t1 to time t2, during which the laser temperature Ts(t) approaches the target temperature Tc (=40°C), the control unit 80 performs only duty ratio control and does not perform voltage value control. During the period from time t1 to time t2, the control unit 80 applies a voltage pulse to the temperature adjustment unit 51 to perform cooling. As a result, part of the heat generated by the semiconductor laser element 20 is offset by the cooling. Accordingly, the laser temperature Ts(t) gradually rises and approaches the target temperature Tc.

[0060] A current flows due to the voltage value Von applied to the temperature adjustment unit 51 and the temperature difference between the first surface 51a and the second surface 51b. When a voltage pulse of voltage value Von is applied to the temperature adjustment unit 51, the current Ion flowing through the temperature adjustment unit 51 is expressed by the following equation.

[0061]

number

[0062] As shown in equation (3), in graph (e) of FIG. 5, in the period from time t1 to time t2, as the difference between laser temperature Ts(t) and ambient temperature Th increases, current Ion gradually decreases.

[0063] On the other hand, when no voltage pulse is applied to the temperature adjustment unit 51, the current Ioff flowing through the temperature adjustment unit 51 is expressed by the following equation.

[0064]

number

[0065] As shown in equation (4), in graph (e) of FIG. 5, in the period from time t1 to time t2, as the difference between laser temperature Ts(t) and ambient temperature Th increases, current Ioff gradually increases.

[0066] After time t2 shown in Fig. 5, the control unit 80 performs duty ratio control and voltage value control in parallel. Therefore, after time t2, the control unit 80 controls the voltage value Von of the voltage pulse applied to the temperature adjustment unit 51. In the operation example shown in Fig. 5, the control unit 80 reduces the voltage value of the voltage pulse after time t2. The voltage value is 1.1 times the above-mentioned optimum voltage value Vx.

[0067] As the voltage value of the voltage pulse is reduced, the amount of heat absorbed by the temperature adjustment unit 51 decreases, and therefore the duty ratio of the voltage pulse is increased by the duty ratio control by the control unit 80, as shown in graph (d) of Fig. 5. As a result, from time t3 onwards, the laser temperature Ts(t) is maintained at the target temperature Tc while the control unit 80 maintains the voltage value and duty ratio of the voltage pulse constant.

[0068] After time t2 when the laser temperature Ts(t) becomes substantially constant, the currents Ion and Ioff flowing through the temperature adjustment unit 51 are maintained substantially constant.

[0069] In this way, in the laser device 1 according to this embodiment, the power consumption of the laser device 1 can be reduced by appropriately controlling the laser temperature Ts(t) while reducing the voltage value of the voltage pulse applied to the temperature adjustment unit 51.

[0070] (Embodiment 2) A laser device 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 the method of controlling the voltage value, but is the same in other configurations. The laser device according to this embodiment will be described below, focusing on the differences from the laser device 1 according to embodiment 1.

[0071] [2-1. Overall configuration of the laser device] The overall configuration of the laser device according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a schematic diagram showing the overall configuration of a laser device 101 according to this embodiment.

[0072] 6, laser device 101 includes semiconductor laser element 20, temperature adjustment unit 51, and control unit 180. In this embodiment, laser device 101 further includes laser crystal 30, selective transmission mirror 31, first holder 11, output mirror 16, heat sink 18, and laser temperature sensor 81.

[0073] Similar to the control unit 80 according to the first embodiment, the control unit 180 according to the present embodiment controls the duty ratio of the voltage pulse applied to the temperature adjustment unit 51. The control unit 180 according to the present embodiment controls the voltage value of the voltage pulse based on the duty ratio of the voltage pulse applied to the temperature adjustment unit 51. Specifically, when the duty ratio of the voltage pulse is less than a first duty ratio, the control unit 180 reduces the absolute value of the voltage value of the voltage pulse. This increases the duty ratio. Furthermore, when the duty ratio of the voltage pulse is greater than a second duty ratio, the control unit 180 increases the absolute value of the voltage value of the voltage pulse. This reduces the duty ratio. Here, the second duty ratio is greater than the first duty ratio. The control unit 180 may feedback-control the absolute value of the voltage value of the voltage pulse so that the duty ratio of the voltage pulse is equal to or greater than the first duty ratio and equal to or less than the second duty ratio.

[0074] For example, the first duty ratio may be 0.90 or more (i.e., 90% or more), or 0.95 or more (i.e., 95% or more). In this way, by setting the first duty ratio to a sufficiently large value, the absolute value of the voltage value of the voltage pulse can be reduced. Therefore, similar to the laser device 1 according to the first embodiment, in the laser device 101 according to this embodiment, the power consumption of the laser device 101 can be reduced by appropriately controlling the laser temperature Ts(t) and reducing the absolute value of the voltage value of the voltage pulse applied to the temperature adjustment unit 51.

[0075] For example, the second duty ratio may be 0.99 or less (i.e., 99% or less), 0.98 or less (i.e., 98% or less), 0.97 or less (i.e., 97% or less), or 0.96 or less (i.e., 96% or less).

[0076] [2-2. Laser device control method] A control method for laser apparatus 101 according to this embodiment will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a flowchart showing the control method for laser apparatus 101 according to this embodiment. Fig. 8 is a flowchart showing voltage value control steps in the control method for laser apparatus 101 according to this embodiment.

[0077] The control method for laser device 101 according to this embodiment is executed by control unit 180 of laser device 101. As shown in Fig. 7, the control method for laser device 101 according to this embodiment differs from the control method for laser device 1 according to embodiment 1 in voltage value control step S140, but is the same in the other steps.

[0078] In voltage value control step S140 shown in FIGS. 7 and 8, control unit 180 controls the absolute value of the voltage value of the voltage pulse applied to temperature adjustment unit 51 based on the duty ratio of the voltage pulse applied to temperature adjustment unit 51.

[0079] As shown in FIG. 8, in the voltage value control step S140, first, the control unit 180 acquires the duty ratio of the voltage pulse applied to the temperature adjustment unit 51 (duty ratio acquisition step S141).

[0080] Next, the control unit 180 compares the acquired duty ratio with the first duty ratio and determines whether the duty ratio is equal to or greater than the first duty ratio (first comparison step S142). In this embodiment, the first duty ratio is 95%.

[0081] In the first comparison step S142, if the duty ratio is less than the first duty ratio (No in the first comparison step S142), the control unit 180 reduces the absolute value of the voltage value of the voltage pulse by ΔV (voltage value reduction step S143), and returns to the duty ratio acquisition step S141, where ΔV is the manipulated variable in the feedback control.

[0082] In the first comparison step S142, if the duty ratio is equal to or greater than the first duty ratio (Yes in the first comparison step S142), the control unit 180 compares the duty ratio with the second duty ratio and determines whether the duty ratio is equal to or less than the second duty ratio (second comparison step S144). In this embodiment, the second duty ratio is 97%.

[0083] In the second comparing step S144, if the duty ratio is greater than the second duty ratio (No in the second comparing step S144), the control unit 180 increases the absolute value of the voltage value of the voltage pulse by ΔV (voltage value increasing step S145) and returns to the duty ratio obtaining step S141.

[0084] In the second comparing step S144, if the duty ratio is equal to or less than the second duty ratio (Yes in the second comparing step S144), the control unit 180 ends the voltage value control step S140.

[0085] As described above, in this embodiment, the control unit 180 feedback controls the absolute value of the voltage value of the voltage pulse so that the duty ratio of the voltage pulse is equal to or greater than the first duty ratio and less than the second duty ratio.

[0086] As a result, for example, by setting the first duty ratio to a sufficiently large value, the absolute value of the voltage value of the voltage pulse can be reduced. Therefore, similar to the control method for laser apparatus 1 according to embodiment 1, the control method for laser apparatus 101 according to this embodiment also reduces the absolute value of the voltage value of the voltage pulse applied to temperature adjustment unit 51 while appropriately controlling laser temperature Ts(t), thereby reducing the power consumption of laser apparatus 101.

[0087] [2-3. Example of operation] An example of operation of the laser device 101 according to this embodiment will be described with reference to FIG. 9. FIG. 9 is a diagram showing an example of operation of the laser device 101 according to this embodiment. Graph (a) of FIG. 9 is a graph showing the relationship between the ambient temperature Th and time. Graph (b) of FIG. 9 is a graph showing the relationship between the amount of heat Q of the semiconductor laser element 20 and time. Graph (c) of FIG. 9 is a graph showing the relationship between the laser temperature Ts(t) and time. Graph (d) of FIG. 9 is a graph showing the relationship between the applied voltage applied to the temperature adjustment unit 51 and time. Graph (e) of FIG. 9 is a graph showing the relationship between the current flowing through the temperature adjustment unit 51 and time.

[0088] In the operation example shown in Fig. 9, the ambient temperature Th is constant at 25°C, as shown in graph (a) of Fig. 9. At time t1 in Fig. 9, the operation of the laser device 101 starts. That is, at time t1 in Fig. 9, the supply of power to the semiconductor laser element 20 starts, and the heat generation amount of the semiconductor laser element 20 is constant at 5 W, as shown in graph (b) of Fig. 9.

[0089] At time t1 in FIG. 9 , the laser device 101 starts operating, and as shown in graph (d) in FIG. 9 , application of voltage pulses to the temperature adjustment unit 51 begins. In the example of operation shown in FIG. 9 , during the period from time t1 to time t2, during which the laser temperature Ts(t) approaches the target temperature Tc (=40° C.), the control unit 180 according to this embodiment performs only duty ratio control and does not perform voltage value control, similar to the control unit 80 according to the first embodiment. During the period from time t1 to time t2, the control unit 180 applies voltage pulses to the temperature adjustment unit 51 to perform cooling. This offsets some of the heat generated by the semiconductor laser element 20. Accordingly, the laser temperature Ts(t) gradually rises and approaches the target temperature Tc.

[0090] The voltage shown in graph (d) of Figure 9 and the current shown in graph (e) of Figure 9 during the period from time t1 to time t2 are the same as the voltage shown in graph (d) of Figure 5 and the current shown in graph (e) of Figure 5, respectively.

[0091] After time t2 shown in Fig. 9, the control unit 180 performs duty ratio control and voltage value control in parallel. Therefore, after time t2, the control unit 180 controls the voltage value Von of the voltage pulse applied to the temperature adjustment unit 51. In the operation example shown in Fig. 9, the control unit 180 reduces the voltage value of the voltage pulse by ΔV after time t2. The current Ion flowing through the temperature adjustment unit 51 gradually decreases as the voltage value of the voltage pulse decreases.

[0092] As the voltage value of the voltage pulse is reduced, the amount of heat absorbed by temperature adjustment unit 51 decreases, and therefore the duty ratio of the voltage pulse is increased by duty ratio control by control unit 180, as shown in graph (d) of Fig. 5. As a result, from time t3 onwards, laser temperature Ts(t) is maintained at target temperature Tc in a state where control unit 180 maintains the voltage value and duty ratio of the voltage pulse to be equal to or greater than the first duty ratio and equal to or less than the second duty ratio.

[0093] After time t2 when the laser temperature Ts(t) becomes substantially constant, the current Ioff flowing through the temperature adjustment unit 51 is maintained substantially constant. After time t3, the current Ion flowing through the temperature adjustment unit 51 is maintained substantially constant.

[0094] In this way, in the laser device 101 according to this embodiment, the power consumption of the laser device 101 can be reduced by appropriately controlling the laser temperature Ts(t) while reducing the voltage value of the voltage pulse applied to the temperature adjustment unit 51.

[0095] (Embodiment 3) A laser device according to embodiment 3 will be described. The laser device according to this embodiment differs from the laser device 1 according to embodiment 1 in the method of controlling the voltage value, but is the same in other configurations. The laser device according to this embodiment will be described below, focusing on the differences from the laser device 1 according to embodiment 1.

[0096] [3-1. Overall configuration of the laser device] The overall configuration of the laser device according to this embodiment will be described with reference to Fig. 10. Fig. 10 is a schematic diagram showing the overall configuration of a laser device 201 according to this embodiment.

[0097] 10 , the laser device 201 includes a semiconductor laser element 20, a 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 laser temperature sensor 81, and an environmental temperature sensor 83.

[0098] The control unit 280 according to this embodiment controls the voltage value of the voltage pulse to be equal to or greater than a reference voltage value Vs, which is greater than 0, when the temperature adjustment unit 51 cools the semiconductor laser element 20. When the temperature adjustment unit 51 heats the semiconductor laser element 20, the minimum absolute value of the voltage value of the voltage pulse may be equal to the reference voltage value.

[0099] The effect of the control unit 280 according to this embodiment will be described with reference to Figs. 11 and 12. Fig. 11 is a graph showing the relationship between the ambient temperature Th, the voltage applied to the temperature adjustment unit 51, and the current flowing through the temperature adjustment unit 51. Fig. 12 is a graph showing the relationship between the ambient temperature Th, the voltage applied to the temperature adjustment unit 51 by the control unit 280 according to this embodiment, and the current flowing through the temperature adjustment unit 51. The vertical axis on the left side of Figs. 11 and 12 represents the current, and the vertical axis on the right side represents the voltage. Furthermore, each of the graphs shown in Figs. 11 and 12 shows a case where the target temperature Tc is 40°C and the heat generation amount of the semiconductor laser element 20 is 5W.

[0100] As shown in FIG. 11, there is a range of environmental temperatures Th where the voltage value is positive and the current value is negative (i.e., a range where the environmental temperature Th includes 25°C). In this range, the direction of applied voltage and the direction of current flow are reversed. With a normal power supply, the direction of applied voltage and the direction of current flow cannot be reversed in this way.

[0101] Therefore, in this embodiment, as shown in environmental temperature ranges A and B in Fig. 12, when the temperature adjustment unit 51 cools the semiconductor laser device 20, the control unit 280 controls the voltage value of the voltage pulse to be equal to or greater than a reference voltage value Vs that is greater than 0. Specifically, in the range in which the current value shown in Fig. 12 is positive, the control unit 280 controls the voltage value of the voltage pulse to be equal to or greater than the reference voltage value Vs. In environmental temperature range B shown in Fig. 12, the control unit 280 sets the voltage value of the voltage pulse to the reference voltage value Vs. This makes it possible to prevent the direction of the voltage applied to the temperature adjustment unit 51 from being reversed from the direction of the current flow.

[0102] Furthermore, in this embodiment, the minimum absolute value of the voltage value of the voltage pulse when the temperature adjustment unit 51 heats the semiconductor laser device 20 may be equal to the reference voltage value Vs. That is, in the environmental temperature range C in FIG. 12 where the current value is negative, the absolute value of the voltage value of the voltage pulse when the current value is approximately 0 may be equal to the reference voltage value Vs. As a result, for example, when the environmental temperature Th fluctuates between the environmental temperature ranges B and C, the voltage pulse can be continuously applied smoothly by reversing only the direction of the voltage without changing the absolute value of the voltage value of the voltage pulse.

[0103] [3-2. Laser device control method] The control method for laser apparatus 201 according to this embodiment will be described with reference to Fig. 12, 13, and 14. Fig. 13 is a flowchart showing the control method for laser apparatus 201 according to this embodiment. Fig. 14 is a flowchart showing voltage value control steps in the control method for laser apparatus 201 according to this embodiment.

[0104] The control method for laser device 201 according to this embodiment is executed by control unit 280 of laser device 201. As shown in Fig. 13, the control method for laser device 201 according to this embodiment differs from the control method for laser device 1 according to embodiment 1 in voltage value control step S240, but is the same in the other steps.

[0105] In the voltage value control step S240 shown in Figures 13 and 14, the control unit 280 controls the voltage value of the voltage pulse based on the ambient temperature Th, the target temperature Tc, and the heat generation amount Q of the semiconductor laser element 20, similar to the voltage value control step S40 in embodiment 1.

[0106] As shown in FIG. 14, in the voltage value control step S240, the steps from the supply power acquisition step S41 to the optimum voltage value calculation step S45 are the same as the steps according to the first embodiment.

[0107] In this embodiment, after the optimum voltage value calculation step S45, the direction of the current flowing through the temperature adjustment unit 51 is determined (current direction determination step S247).

[0108] If the control unit 280 determines that the current direction is negative, that is, that the semiconductor laser element 20 is being heated by the temperature adjustment unit 51 (Yes in current direction determination step S247), the control unit 280 determines that the environmental temperature Th is within the environmental temperature range C shown in Fig. 12, and proceeds to voltage value update step S46. In voltage value update step S46, similar to voltage value update step S46 in the first embodiment, the control unit 280 updates the voltage value of the voltage pulse to be applied to the temperature adjustment unit 51.

[0109] If the control unit 280 determines that the current direction is not negative (No in current direction determination step S247), the control unit 280 determines that the environmental temperature Th is within the environmental temperature range A or the environmental temperature range B shown in FIG. 12, and determines whether the optimum voltage value Vx is equal to or greater than the reference voltage value Vs (optimum voltage value determination step S248).

[0110] In the optimum voltage value determination step S248, if the control unit 280 determines that the optimum voltage value Vx is equal to or greater than the reference voltage value Vs (Yes in the optimum voltage value determination step S248), the control unit 280 determines that the environmental temperature Th is within the environmental temperature range A shown in FIG. 12, and proceeds to the voltage value update step S46.

[0111] In the optimum voltage value determination step S248, if the control unit 280 determines that the optimum voltage value Vx is less than the reference voltage value Vs (No in the optimum voltage value determination step S248), the control unit 280 determines that the environmental temperature Th is within the environmental temperature range B shown in FIG. 12, and updates the voltage value of the voltage pulse to the reference voltage value Vs (updating to reference voltage value step S249).

[0112] As described above, when the temperature adjustment unit 51 cools the semiconductor laser element 20 (that is, when the direction of the current flowing through the temperature adjustment unit 51 is the same as the direction of the applied voltage), the control unit 280 controls the voltage value of the voltage pulse to be equal to or greater than the reference voltage value Vs, which is greater than 0. This makes it possible to prevent the direction of the voltage applied to the temperature adjustment unit 51 and the direction of the current flow from being reversed.

[0113] Furthermore, in this embodiment, when the temperature adjustment unit 51 heats the semiconductor laser element 20 (i.e., when the direction of the current flowing through the temperature adjustment unit 51 is negative), the minimum absolute value of the voltage value of the voltage pulse may be equal to the reference voltage value Vs. As a result, for example, when the environmental temperature Th fluctuates between the environmental temperature range B and the environmental temperature range C, the voltage pulse can be continuously applied smoothly by reversing only the direction of the voltage without changing the absolute value of the voltage value of the voltage pulse.

[0114] [3-3. Effects] The effects of laser device 201 according to this embodiment will be described in comparison with a comparative example using Fig. 15 to Fig. 18. Fig. 15 and Fig. 17 are graphs showing the relationship between the ambient temperature Th and the voltage applied to temperature adjustment unit 51, the current flowing through temperature adjustment unit 51, and the duty ratio of the voltage pulse in each laser device according to the comparative example and this embodiment, respectively. Fig. 16 and Fig. 18 are graphs showing the relationship between the ambient temperature Th and the power consumption in temperature adjustment unit 51 in the comparative example and this embodiment, respectively.

[0115] The laser device of the comparative example differs from the laser device 201 according to the present embodiment in that the absolute value of the voltage value of the voltage pulse applied to the temperature adjustment unit 51 is constant. As shown in FIG. 15, in the laser device of the comparative example, the absolute value of the voltage applied to the temperature adjustment unit 51 is 5V. In the laser device of the comparative example, when the direction of the current flowing through the temperature adjustment unit 51 is negative, the voltage value of the voltage pulse applied to the temperature adjustment unit 51 is −5V. In such a laser device of the comparative example, as shown in FIG. 15, the absolute value of the voltage value of the voltage pulse is 5V regardless of the ambient temperature Th. Therefore, the duty ratio of the voltage pulse changes depending on the ambient temperature Th. In addition, the current flowing through the temperature adjustment unit 51 is relatively large.

[0116] 17, by controlling the voltage value of the voltage pulse in accordance with the environmental temperature Th, it is possible to maintain the duty ratio of the voltage pulse at approximately 1 except for the range in which the environmental temperature Th is equal to or higher than approximately 25° C. and equal to or lower than approximately 42° C. Also, in this embodiment, by maintaining the voltage value at a minimum, it is possible to minimize the current flowing through the temperature adjustment unit 51.

[0117] Therefore, as shown in FIGS. 16 and 18, the laser device 201 according to this embodiment can reduce power consumption more than the laser device of the comparative example.

[0118] [3-4. Example of operation 1] Operation example 1 according to this embodiment will be described with reference to FIG. 19. FIG. 19 is a diagram showing operation example 1 of laser device 201 according to this embodiment. Graph (a) of FIG. 19 is a graph showing the relationship between ambient temperature Th and time. Graph (b) of FIG. 19 is a graph showing the relationship between heat generation amount Q of semiconductor laser element 20 and time. Graph (c) of FIG. 19 is a graph showing the relationship between laser temperature Ts(t) and time. Graph (d) of FIG. 19 is a graph showing the relationship between applied voltage applied to temperature adjustment unit 51 and time.

[0119] In the operation example shown in FIG. 19, as shown in graph (a) of FIG. 19, the environmental temperature Th is 55° C. until time t1, and decreases from 55° C. to 25° C. at a constant rate from time t1 to time t4. After time t4, the environmental temperature Th is 25° C. At time t2, the environmental temperature Th is 42° C., and at time t3, the environmental temperature Th is 40° C., which is equal to the target temperature Tc.

[0120] The laser device 201 is constantly operating during the time shown in Fig. 19. As shown in graph (b) of Fig. 19, the heat generation amount of the semiconductor laser element 20 is constant at 5 W. Furthermore, the control unit 280 applies an appropriate voltage pulse to the temperature adjustment unit 51, so that the laser temperature Ts(t) is maintained at the target temperature Tc (=40°C), as shown in graph (c) of Fig. 19.

[0121] As shown in graph (d) of FIG. 19, up to time t1, the voltage value of the voltage pulse is constant and the duty ratio is 1. After time t1, as the environmental temperature Th decreases, the optimum voltage value Vx decreases, and so the voltage value of the voltage pulse decreases. At time t2, the optimum voltage value Vx becomes equal to the reference voltage value Vs. After time t2, the optimum voltage value Vx becomes less than the reference voltage value Vs, and so the voltage value of the voltage pulse is maintained at the reference voltage value Vs.

[0122] As described above, in the laser device 201 according to the present embodiment, the voltage value of the voltage pulse is set to the reference voltage value Vs when the environmental temperature Th is equal to or higher than 25° C. and lower than 42° C. This makes it possible to prevent the direction of the voltage applied to the temperature adjustment unit 51 and the direction of the current flowing through the temperature adjustment unit 51 from being reversed.

[0123] [3-5. Example of operation 2] Operation example 2 according to this embodiment will be described with reference to FIG. 20. FIG. 20 is a diagram showing operation example 2 of laser device 201 according to this embodiment. Graph (a) of FIG. 20 is a graph showing the relationship between ambient temperature Th and time. Graph (b) of FIG. 20 is a graph showing the relationship between heat generation amount Q of semiconductor laser element 20 and time. Graph (c) of FIG. 20 is a graph showing the relationship between laser temperature Ts(t) and time. Graph (d) of FIG. 20 is a graph showing the relationship between applied voltage applied to temperature adjustment unit 51 and time.

[0124] In the operation example shown in Fig. 20, as shown in graph (a) of Fig. 20, the environmental temperature Th is 25°C until time t1, and rises from 25°C to 55°C at a constant rate from time t1 to time t3. After time t3, the environmental temperature Th is 55°C. At time t2, the environmental temperature Th is 42°C.

[0125] The laser device 201 is constantly operating during the time shown in Fig. 20. As shown in graph (b) of Fig. 20, the heat generation amount of the semiconductor laser element 20 is constant at 5 W. Furthermore, the control unit 280 applies an appropriate voltage pulse to the temperature adjustment unit 51, so that the laser temperature Ts(t) is maintained at the target temperature Tc (=40°C), as shown in graph (c) of Fig. 20.

[0126] 20, the optimum voltage value Vx is less than the reference voltage value Vs until time t2, so the voltage value of the voltage pulse is maintained at the reference voltage value Vs. After time t2, as the ambient temperature Th rises, the optimum voltage value Vx becomes equal to or greater than the reference voltage value Vs, so the voltage value of the voltage pulse increases and the duty ratio becomes 1. After time t3, the ambient temperature Th is maintained at 55°C, so the voltage value of the voltage pulse is also maintained constant.

[0127] As described above, in the laser device 201 according to the present embodiment, the voltage value of the voltage pulse is set to the reference voltage value Vs when the environmental temperature Th is equal to or higher than 25° C. and lower than 42° C. This makes it possible to prevent the direction of the voltage applied to the temperature adjustment unit 51 and the direction of the current flowing through the temperature adjustment unit 51 from being reversed.

[0128] [3-6. Example of operation 3] Operation example 3 according to this embodiment will be described with reference to FIG. 21. FIG. 21 is a diagram showing operation example 3 of laser device 201 according to this embodiment. Graph (a) in FIG. 21 is a graph showing the relationship between ambient temperature Th and time. Graph (b) in FIG. 21 is a graph showing the relationship between heat generation amount Q of semiconductor laser element 20 and time. Graph (c) in FIG. 21 is a graph showing the relationship between laser temperature Ts(t) and time. Graph (d) in FIG. 21 is a graph showing the relationship between applied voltage applied to temperature adjustment unit 51 and time.

[0129] In the operation example shown in Fig. 21, as shown in graph (a) of Fig. 21, the environmental temperature Th is 0°C until time t1, and rises from 0°C to 15°C at a constant rate from time t1 to time t2. After time t2, the environmental temperature Th is 15°C.

[0130] The laser device 201 is constantly operating during the time shown in Fig. 21. As shown in graph (b) of Fig. 21, the heat generation amount of the semiconductor laser element 20 is constant at 5 W. Furthermore, the control unit 280 applies an appropriate voltage pulse to the temperature adjustment unit 51, so that the laser temperature Ts(t) is maintained at the target temperature Tc (=40°C), as shown in graph (c) of Fig. 21.

[0131] As shown in graph (d) of Fig. 21, the current is always flowing in the negative direction during the time shown in Fig. 21, so the voltage value of the voltage pulse is continuously updated based on the optimum voltage value Vx in the control unit 280. As a result, the duty ratio of the voltage pulse is maintained at 1.

[0132] As described above, in the laser device 201 according to the present embodiment, the voltage value of the voltage pulse is continuously updated based on the optimum voltage value Vx when the environmental temperature Th is equal to or higher than 0° C. and equal to or lower than 15° C. Therefore, the absolute value of the voltage value of the voltage pulse can be reduced, and the power supplied to the temperature adjustment unit 51 can be reduced.

[0133] Similarly, when the environmental temperature Th changes from 15° C. to 0° C., the voltage value of the voltage pulse continues to be updated based on the optimum voltage value Vx, as in Operation Example 3. Therefore, the absolute value of the voltage value of the voltage pulse can be reduced, and the power supplied to the temperature adjustment unit 51 can be reduced.

[0134] [3-7. Example 4] Operation example 4 according to this embodiment will be described with reference to FIG. 22. FIG. 22 is a diagram showing operation example 4 of the laser device 201 according to this embodiment. Graph (a) of FIG. 22 is a graph showing the relationship between the ambient temperature Th and time. Graph (b) of FIG. 22 is a graph showing the relationship between the heat generation amount Q of the semiconductor laser element 20 and time. Graph (c) of FIG. 22 is a graph showing the relationship between the laser temperature Ts(t) and time. Graph (d) of FIG. 22 is a graph showing the relationship between the applied voltage applied to the temperature adjustment unit 51 and time.

[0135] In the operation example shown in Fig. 22, as shown in graph (a) of Fig. 22, the environmental temperature Th is 55°C until time t1, and rises from 55°C to 5°C at a constant rate from time t1 to time t4. After time t4, the environmental temperature Th is 5°C. At time t2, the environmental temperature Th is 42°C, and at time t3, the environmental temperature Th is 20°C.

[0136] The laser device 201 is constantly operating during the time shown in Fig. 22. As shown in graph (b) of Fig. 22, the heat generation amount of the semiconductor laser element 20 is constant at 5 W. Furthermore, the control unit 280 applies an appropriate voltage pulse to the temperature adjustment unit 51, so that the laser temperature Ts(t) is maintained at the target temperature Tc (=40°C), as shown in graph (c) of Fig. 22.

[0137] As shown in graph (d) of FIG. 22, until time t2, the optimum voltage value Vx is equal to or greater than the reference voltage value Vs, so the voltage value of the voltage pulse is maintained at the reference voltage value Vs. After time t2, as the ambient temperature Th decreases, the optimum voltage value Vx becomes less than the reference voltage value Vs, so the voltage value of the voltage pulse is maintained at the reference voltage value Vs, and the duty ratio becomes less than 1. After time t3, the ambient temperature Th becomes less than 20°C, the current direction becomes negative, and the voltage value of the voltage pulse is updated based on the optimum voltage value Vx. At this time, the voltage value of the voltage pulse is switched from the reference voltage value Vs to -Vs. In this way, the absolute values ​​of the voltage values ​​of the voltage pulse are switched to the same value, allowing for smooth voltage value switching.

[0138] After time t3, the voltage value of the voltage pulse is updated based on the optimum voltage value Vx, so the duty ratio of the voltage pulse becomes 1. After time t4, the environmental temperature Th becomes constant, so the voltage value of the voltage pulse also becomes constant.

[0139] As described above, in laser device 201 according to the present embodiment, when the environmental temperature Th is equal to or higher than 5° C. and equal to or lower than 55° C., the voltage value of the voltage pulse is maintained at the reference voltage value when the environmental temperature Th is in the range of equal to or higher than 20° C. and lower than 42° C. This makes it possible to prevent the direction of the voltage applied to temperature adjustment unit 51 and the direction of the current flowing through temperature adjustment unit 51 from being reversed.

[0140] Furthermore, in this embodiment, since the minimum absolute value of the voltage value of the voltage pulse when the temperature adjustment unit 51 heats the semiconductor laser element 20 is equal to the reference voltage value Vs, when the environmental temperature Th changes from 20° C. or higher to below 20° C., the voltage pulse can be continued to be applied smoothly by reversing only the direction of the voltage without changing the absolute value of the voltage value of the voltage pulse. Similarly, when the environmental temperature Th changes from below 20° C. to 20° C. or higher, the voltage pulse can be continued to be applied smoothly by reversing only the direction of the voltage without changing the absolute value of the voltage value of the voltage pulse.

[0141] [3-8. Modifications] A modification of the voltage value control step S240 according to this embodiment will be described with reference to Fig. 23. Fig. 23 is a flowchart showing the voltage value control step S240a according to a modification of the control method for the laser device 201 according to this embodiment.

[0142] In the voltage value control step S240a according to this modification, the voltage value of the voltage pulse is controlled based on the duty ratio of the voltage pulse.

[0143] As shown in FIG. 23, in the voltage value control step S240a, the steps up to the first comparison step S142 are controlled in the same manner as in the voltage value control step S140 according to the second embodiment.

[0144] In the first comparison step S142, if the duty ratio is equal to or greater than the first duty ratio (Yes in the first comparison step S142), the control unit 280 compares the duty ratio with the second duty ratio and determines whether the duty ratio is equal to or less than the second duty ratio (second comparison step S144). In the present embodiment, the second duty ratio is 97%.

[0145] In the second comparing step S144, if the duty ratio is greater than the second duty ratio (No in the second comparing step S144), the control unit 280 increases the absolute value of the voltage value of the voltage pulse by ΔV (voltage value increasing step S145) and returns to the duty ratio obtaining step S141.

[0146] In the second comparing step S144, if the duty ratio is equal to or less than the second duty ratio (Yes in the second comparing step S144), the control unit 280 ends the voltage value control step S240a.

[0147] In the first comparison step S142, if the duty ratio is less than the first duty ratio (No in the first comparison step S142), the direction of the current flowing through the temperature adjustment unit 51 is determined (current direction determination step S247).

[0148] If the control unit 280 determines that the current direction is negative, that is, that the semiconductor laser element 20 is being heated by the temperature adjustment unit 51 (Yes in the current direction determination step S247), the control unit 280 reduces the absolute value of the voltage value of the voltage pulse by ΔV (voltage value reduction step S143) and returns to the duty ratio acquisition step S141.

[0149] If the control unit 280 determines that the current direction is not negative (No in current direction determination step S247), the control unit 280 determines that the environmental temperature Th is within the environmental temperature range A or the environmental temperature range B shown in FIG. 12, and determines whether the voltage value of the voltage pulse is equal to or greater than the reference voltage value Vs (voltage value determination step S248a).

[0150] In voltage value determination step S248a, if control unit 280 determines that the voltage value is equal to or greater than reference voltage value Vs (Yes in voltage value determination step S248a), control unit 280 proceeds to voltage value reduction step S143.

[0151] In the voltage value determination step S248a, if the control unit 280 determines that the voltage value is less than the reference voltage value Vs (No in the voltage value determination step S248a), the control unit 280 updates the voltage value to the reference voltage value Vs (updating to the reference voltage value step S249), and returns to the duty ratio acquisition step S141.

[0152] The voltage value control step S240a according to the above-described modified example also achieves the same effects as the voltage value control step S240.

[0153] (Fourth embodiment) A laser device according to embodiment 4 will be described. The laser device according to this embodiment is characterized by a method for setting a target temperature for the semiconductor laser element 20 in an initial state. The laser device and its control method according to this embodiment will be described below, focusing on the differences from the laser device 1 and its control method according to embodiment 1.

[0154] [4-1. Overall configuration of the laser device] The overall configuration of the laser device according to this embodiment will be described with reference to Fig. 24. Fig. 24 is a schematic diagram showing the overall configuration of a laser device 301 according to this embodiment.

[0155] 24, the laser device 301 includes a semiconductor laser element 20, a temperature adjustment unit 51, and a control unit 380. In this 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, and a laser temperature sensor 81.

[0156] Changes in the characteristics of the semiconductor laser element 20 over time of power supply will be described with reference to Figs. 25 and 26. Fig. 25 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. 25 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. 26 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 heat generation amount of the semiconductor laser element 20. Fig. 26 shows a graph for the case where the power supplied to the semiconductor laser element 20 is constant.

[0157] As shown in FIGS. 25 and 26, the semiconductor laser element 20 deteriorates over time, and the output optical power decreases even if 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 and the stripe width of the light-emitting region is 10 μm or more and 100 μm or less. In this specification, 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 is referred to as the deterioration rate (see FIG. 25).

[0158] 26, 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, and Joule heat increases. 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.

[0159] In this specification, the state of the semiconductor laser element 20 at the start of energization in the laser apparatus 301 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.

[0160] 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.

[0161] In this embodiment, the control unit 380 detects the temperature of the installation point of the semiconductor laser element 20 based on the output signal of the laser temperature sensor 81. Here, the temperature of the first holder 11 corresponding to the output signal of the laser 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 laser 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.

[0162] As described above, the control unit 380 controls the 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 the temperature to which the temperature adjustment unit 51 needs to heat the semiconductor laser element 20. In this embodiment, the control unit 380 sets the target temperature so that the temperature adjustment unit 51 heats the semiconductor laser element 20 in the initial state. In this embodiment, the control unit 380 maintains the target temperature constant throughout the entire life 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 380 reduces the power consumption required for the 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 380 sets the target temperature so that the sum of the energy consumed by the semiconductor laser element 20 and the energy consumed by the temperature adjustment unit 51 during the life of the semiconductor laser element 20 is minimized.

[0163] [4-2. Laser device control method] A method for controlling the laser device 301 according to this embodiment will be described with reference to Fig. 27. Fig. 27 is a flowchart showing the method for controlling the laser device 301 according to this embodiment.

[0164] 27, first, a target temperature is set in the control unit 380 (target temperature setting step S310). The target temperature may be set by the control unit 380 or may be set based on an input to the laser device 301 by a user or the like. 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 temperature adjustment unit 51. In this embodiment, the control unit 380 maintains the target temperature constant throughout the entire life of the semiconductor laser element 20.

[0165] Next, the control unit 380 controls the amount of current supplied to the semiconductor laser element 20 (current control step S320). The amount of current supplied to the semiconductor laser element 20 may be determined in advance, or may be determined based on an input to the laser apparatus 301 by a user, for example. In this embodiment, the control unit 380 maintains the amount of current supplied to the semiconductor laser element 20 constant.

[0166] Subsequently, the control unit 380 uses the 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 S330). Specifically, the control unit 380 detects the temperature of the installation point of the semiconductor laser element 20 based on a signal from the laser temperature sensor 81, and feedback-controls the temperature adjustment unit 51 so that the temperature of the installation point of the semiconductor laser element 20 approaches the target temperature.

[0167] Subsequently, the process returns to the current control step S320, and the current control step S320 and the first temperature control step S330 are repeated. As described above, the amount of heat generated increases as the semiconductor laser element 20 deteriorates. Therefore, in the first temperature control step S330, the control unit 380 reduces the power consumption required for heating by the temperature adjustment unit 51 as the deterioration of the semiconductor laser element 20 progresses.

[0168] As described above, the control unit 380 controls the laser device 301.

[0169] [4-3. Effects, etc.] The effects of the laser device 301 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 1. The laser device of Comparative Example 1 is a laser device whose configuration is identical to that of the laser device 301 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 temperature adjustment unit 51 is substantially zero (that is, heating and cooling are almost unnecessary).

[0170] 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 this embodiment will be described with reference to FIGS. 28 to 31. FIG. 28 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 temperature adjustment unit 51. FIG. 29 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. 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 power consumption in the temperature adjustment unit 51. FIG. 31 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 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 this embodiment is ALL As shown in the following equation (5), the power consumption W of the semiconductor laser element 20 LD and the power consumption W of the temperature adjustment unit 51 P1 It means harmony with.

[0171] W ALL =W LD +W P1 (5)

[0172] 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 regarded as the temperature of the first holder 11.

[0173] 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 temperature adjustment unit 51 are substantially unnecessary. In this case, heat generated from the semiconductor laser element 20 can be dissipated only by heat transport caused by the temperature difference between the first surface 51a and the second surface 51b of the 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 temperature adjustment unit 51 is substantially zero as shown in FIG. 28, and the total power consumption is equal to the power consumption of the semiconductor laser element 20 as shown in FIG. 29. 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.

[0174] 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 temperature adjustment unit 51 increases as shown in Fig. 28. Therefore, as shown in Fig. 29, 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%.

[0175] 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 (5) ALL is expressed by the following equation (6).

[0176]

number

[0177] In contrast, in the laser apparatus 301 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 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 temperature adjustment unit 51 is not 0, as shown in Fig. 30. Furthermore, as shown in Fig. 31, the total power consumption is larger than the power consumption of the semiconductor laser element 20.

[0178] 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 380 reduces the power consumption required for heating by the temperature adjustment unit 51 as the deterioration of the semiconductor laser element 20 progresses. Therefore, as shown in FIG. 30 , 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 temperature adjustment unit 51 decreases. As a result, as shown in FIG. 31 , the total power consumption of the laser device 301 also decreases as the semiconductor laser element 20 deteriorates. In the laser device 301 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 temperature adjustment unit 51, and the power consumption of the 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 51a and the second surface 51b of the temperature adjustment unit 51, and therefore the control unit 380 causes the 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 the temperature adjustment unit 51 to cool the semiconductor laser element 20 increases.

[0179] In the laser device 301 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%.

[0180] The total energy consumption over the lifetime of the laser device 301 according to this embodiment is 211 MJ. As described above, the total energy consumption over the lifetime of the laser device 301 according to this embodiment can be reduced by 15 MJ compared to the laser device of Comparative Example 1.

[0181] As described above, the laser device 301 according to the present embodiment includes the semiconductor laser element 20 that emits the first laser light L1, the temperature adjustment unit 51 that heats or cools the semiconductor laser element 20, and the control unit 380 that controls the amount of current supplied to the semiconductor laser element 20 and controls the 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 temperature adjustment unit 51.

[0182] This allows the temperature adjustment unit 51 to suppress temperature fluctuations at the installation point of the semiconductor laser element 20. Furthermore, as the 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 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 380 to reduce the power consumption required for heating by the temperature adjustment unit 51 as the deterioration of the semiconductor laser element 20 progresses. In other words, the control unit 380 controls the 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 20 and the installation point, thereby suppressing changes in the temperature of the active layer. This allows the long-term temperature fluctuation of the laser device 301 to be suppressed, while also suppressing the total energy consumption of the laser device 301 over its lifetime.

[0183] In this embodiment, the control unit 380 may cause the 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.

[0184] In this way, the 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 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 temperature adjustment unit 51. Therefore, it is possible to reduce the total energy consumption of the laser device 301 over its lifetime.

[0185] In this embodiment, the control unit 380 may maintain the amount of current supplied to the semiconductor laser device 20 constant.

[0186] This allows the power consumption in the semiconductor laser device 20 to be kept constant.

[0187] In this embodiment, the control unit 380 may maintain the target temperature constant throughout the entire life of the semiconductor laser device 20.

[0188] This makes it possible to suppress fluctuations in the wavelength of the first laser light L1 emitted by the semiconductor laser device 20.

[0189] In this embodiment, the control unit 380 calculates the sum of the energy consumed by the semiconductor laser element 20 and the energy consumed by the temperature adjustment unit 51 (i.e., the total consumed energy P ALL The target temperature may be set so that the temperature is minimized.

[0190] This allows the total energy consumption in the laser device 301 to be minimized.

[0191] The control method for laser apparatus 301 according to this embodiment includes a current control step S320 for controlling the amount of current supplied to semiconductor laser element 20, and a first temperature control step S330 for using temperature adjustment unit 51 to control the temperature of the installation point of semiconductor laser element 20 based on a target temperature for semiconductor laser element 20. The target temperature for semiconductor laser element 20 in the initial state is a temperature to which semiconductor laser element 20 needs to be heated by temperature adjustment unit 51.

[0192] This provides the same effects as those of the laser device 301 according to the present embodiment described above.

[0193] Furthermore, in the first temperature control step S330 according to this embodiment, the power consumption required for heating by the temperature adjustment unit 51 is reduced as the deterioration of the semiconductor laser device 20 progresses.

[0194] This makes it possible to suppress long-term temperature fluctuations in the laser device 301, while also suppressing the total energy consumption of the laser device 301 over its lifespan.

[0195] In the current control step S320 of this embodiment, the amount of current supplied to the semiconductor laser device 20 may be kept constant.

[0196] This allows the power consumption in the semiconductor laser device 20 to be kept constant.

[0197] [4-4. Other Examples of Wavelength Configuration of 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.

[0198] In the laser device 301 according to this 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 j is 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 (7).

[0199] T j =R th Q LD +T c (7)

[0200] As shown in equation (7), the thermal resistance R th and target temperature T c When is constant, the temperature of the active layer T j is the heat generation amount Q of the semiconductor laser element 20 LD increases with increasing

[0201] This temperature rise in the active layer causes the wavelength of the first laser light L1 to shift to a longer wavelength. This wavelength shift of the first laser light L1 will be explained using FIG. 32. FIG. 32 is a first graph showing the relationship between the wavelength of the first laser light L1 of the semiconductor laser device 20 and the absorptance of the laser crystal 30. The horizontal axis of FIG. 32 represents the wavelength, and the vertical axis represents the absorptance of the laser crystal 30.

[0202] 32, even if the wavelength of the first laser light L1 emitted by semiconductor laser element 20 in an initial state is equal to the absorption peak wavelength (λp) of laser crystal 30, the wavelength of the first laser light L1 will shift to wavelength λpc in Fig. 32 after the lifetime has elapsed as semiconductor laser element 20 deteriorates. Accordingly, the absorptance in laser crystal 30 will decrease from absorptance Ra0 at the absorption peak wavelength to absorptance Rac at wavelength λpc.

[0203] Therefore, the characteristics of semiconductor laser element 20 may be selected so that the wavelength of first laser light L1 emitted by semiconductor laser element 20 in an initial state is shorter than the absorption peak wavelength of laser crystal 30. Such a configuration example will be described with reference to FIG. 33. FIG. 33 is a second graph showing the relationship between the wavelength of first laser light L1 from semiconductor laser element 20 and the absorptance of laser crystal 30. The horizontal axis of FIG. 33 represents wavelength, and the vertical axis represents the absorptance of laser crystal 30.

[0204] As shown in FIG. 33 , by setting the wavelength of the first laser beam L1 emitted by the semiconductor laser element 20 in an 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 beam L1 changes from a wavelength shorter than the absorption peak wavelength of the laser crystal 30 (λ1 in FIG. 33 ) to a wavelength longer than the absorption peak wavelength (λ2 in FIG. 33 ). For example, in the example shown in FIG. 33 , the absorptance (Ra1) of the first laser beam 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 beam 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. 33 is significantly greater than the minimum absorptance value Rac shown in FIG. 32 . Therefore, according to this configuration example, it is possible to increase the wavelength conversion efficiency in the laser crystal 30.

[0205] (Other embodiments) While the laser device and the control method thereof according to the present disclosure have been described above based on the embodiments and modifications thereof, the present disclosure is not limited to these embodiments and modifications. As long as they do not deviate from the gist of the present disclosure, various modifications that a person skilled in the art could conceive of to the embodiments and other forms constructed by combining some of the components of the embodiments and modifications are also included within the scope of the present disclosure.

[0206] For example, although the laser devices according to the first to fourth embodiments and their modifications include laser crystal 30 and output mirror 16, laser crystal 30 and output mirror 16 may not be included.

[0207] Furthermore, in each of the above embodiments, the semiconductor laser element 20 is driven by ACC, but it may be driven by APC (Automatic Power Control).

[0208] Furthermore, the above-described embodiments can be modified, replaced, added, omitted, and the like in various ways within the scope of the claims or their equivalents.

[0209] For example, the control unit 380 and the control method thereof according to the fourth embodiment may be applied to each of the laser devices according to the first to third embodiments. [Industrial Applicability]

[0210] The laser device according to the present disclosure can be used as a laser light source capable of suppressing power consumption for various purposes such as illumination and processing. [Explanation of symbols]

[0211] 1, 101, 201, 301 Laser device 11 First Holder 16 Output Mirror 18 Heatsink 20 Semiconductor laser element 30 Laser Crystal 30a Incidence plane 31 Selectively transparent mirror 51 Temperature adjustment section 51a Front page 51b Second side 80, 180, 280, 380 control section 81 Laser temperature sensor 83 Environmental temperature sensor L1 First laser beam L2 Second laser beam

Claims

1. a semiconductor laser element that emits a first laser beam; a temperature adjusting unit that heats or cools the semiconductor laser element; a control unit that controls the temperature adjustment unit based on a target temperature that is a control target for the temperature at the installation point of the semiconductor laser element, The control unit supplies a voltage pulse to the temperature adjustment unit and controls a voltage value of the voltage pulse based on at least one of an environmental temperature, the target temperature, the heat generation amount of the semiconductor laser element, and a duty ratio of the voltage pulse. Laser device.

2. The control unit controls a voltage value of the voltage pulse based on the environmental temperature, the target temperature, and the amount of heat generated by the semiconductor laser element.

2. The laser device according to claim 1.

3. The control unit controls the voltage value of the voltage pulse based on the duty ratio of the voltage pulse.

2. The laser device according to claim 1.

4. The control unit reduces an absolute value of a voltage value of the voltage pulse when a duty ratio of the voltage pulse is less than a first duty ratio.

4. The laser device according to claim 3.

5. The control unit increases an absolute value of a voltage value of the voltage pulse when the duty ratio of the voltage pulse is greater than a second large duty ratio.

5. The laser device according to claim 4.

6. The control unit feedback controls an absolute value of a voltage value of the voltage pulse so that the duty ratio of the voltage pulse is equal to or greater than the first duty ratio and less than the second duty ratio.

6. The laser device according to claim 5.

7. The control unit controls the voltage value of the voltage pulse to be equal to or greater than a reference voltage value greater than 0 when the temperature adjustment unit cools the semiconductor laser element. The laser device according to any one of claims 1 to 6.

8. The minimum absolute value of the voltage value of the voltage pulse when the temperature adjustment unit heats the semiconductor laser element is equal to the reference voltage value.

8. The laser device according to claim 7.

9. the temperature adjustment unit is a Peltier element, the control unit controls the absolute value of the voltage value of the voltage pulse to a value equal to or greater than an absolute value of an optimal voltage value determined based on the environmental temperature, the target temperature, and the heat generation amount of the semiconductor laser element; When the optimum voltage value is represented by Vx, the environmental temperature is represented by Th, the target temperature is represented by Tc, the heat generation amount is represented by Q, the Seebeck coefficient of the Peltier element is represented by α, the thermal resistance of the Peltier element is represented by R, and the Boltzmann constant is represented by K, the optimum voltage value is [Equation 1] is expressed as 2. The laser device according to claim 1.

10. The control unit controls the absolute value of the voltage value of the voltage pulse to a value equal to or less than 1.2 of the absolute value of the optimum voltage value.

10. The laser device according to claim 9.

11. The target temperature for the semiconductor laser element in the initial state is the temperature to which the semiconductor laser element needs to be heated by the temperature adjustment unit. The laser device according to any one of claims 1 to 10.

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