Laser device

Abstract

This laser device comprises: a laser resonator (100) having a laser medium (30) that absorbs excitation light (11) and emits oscillation light (101); an optical length adjustment unit (40) that adjusts the optical length of the laser resonator (100); and a control unit (60) that transmits to the optical length adjustment unit (40) a control signal (61) synchronized with the oscillation timings of the oscillation light emitted from the laser resonator (100).

Description

laser device

[0001] The present disclosure relates to laser devices.

[0002] A microchip laser disclosed in Non-Patent Document 1 is a pulse laser that is compact and capable of outputting high peak power. This microchip laser eliminates unnecessary components and spaces from the resonator by using techniques such as coating the laser crystal directly. Therefore, the microchip laser can output short pulses by shortening the optical length of the laser resonator, and as a result, can obtain laser pulses with high peak power.

[0003] To obtain short pulses, it is important to shorten the optical length of the laser resonator. Laser resonators have a parameter called the resonator lifetime, which is the length of time that light remains in the resonator when the light supply is stopped. For this reason, in principle, a laser resonator cannot output a laser pulse shorter than the resonator lifetime. In this case, mode-locked lasers are excluded.

[0004] Resonator life τ ｃ is the time τ required for light to travel around the laser cavity once, assuming a Fabry-Perot type laser cavity. ｒ and the reflectances R1 and R2 of the two mirrors that make up the laser resonator, it can be expressed by the following equation (1). It is assumed that the loss of the optical elements in the laser resonator is negligibly small. As the optical length of the laser resonator increases, the time τ ｒ becomes longer, and the resonator lifetime τ ｃ In other words, to obtain a short pulse, the resonator lifetime τ ｃ It is important to shorten the optical length of the laser cavity. ｃ =-τ ｒ / ln(R1・R2)...(1)

[0005] Pulse lasers generally use an element called a Q switch. This Q switch is an element that can change the Q value, which indicates the strength of confinement in the laser resonator. If the Q value of the laser resonator is low, it becomes difficult for the laser resonator to oscillate, and energy accumulates in the laser medium. After sufficient energy has accumulated in the laser medium, the Q value of the laser resonator can be increased to satisfy the laser oscillation conditions, and the energy stored in the laser medium is released all at once. This allows pulse lasers to emit pulsed laser light.

[0006] In microchip lasers, an element called a passive Q-switch is often used to shorten the optical length of the laser resonator. A passive Q-switch is an element with saturable absorption characteristics, such as a saturable absorption mirror made of Cr:YAG crystal or a semiconductor. Saturable absorption characteristics are the property of an element's absorption of photons decreasing when it absorbs photons. In laser resonators incorporating a passive Q-switch with saturable absorption characteristics, the absorption rate of the passive Q-switch decreases significantly when the spontaneous emission light emitted by the energy stored in the laser medium reaches a certain intensity. This allows the microchip laser to satisfy the laser oscillation conditions and emit pulsed laser light.

[0007] Microchip lasers using passive Q-switches have the problem that it is difficult to oscillate pulses at the desired timing because the pulse energy is determined by the design. This is because the conditions under which a passive Q-switch operates are determined by physical properties. For example, when the excitation light is intensified, the pulse energy increases in a typical Q-switch. In contrast, in a passive Q-switched laser, the pulse energy remains unchanged, but the repetition frequency increases. For this reason, Patent Document 1 discloses a method of monitoring a portion of the output pulse, adjusting the excitation light intensity, and controlling the timing.

[0008] H. Sakai et al., “>1 MW peak power single-mode high-brightness passively Q-switched Nd3+: YAG microchip laser,” Opt. Express 16, 19891-19899 (2008).

[0009] Patent Publication No. 2012-142523

[0010] The passively Q-switched laser device disclosed in Patent Document 1 is designed to generate repetitive pulses, and is unable to oscillate pulses at precisely the desired timing. Furthermore, the passively Q-switched laser device disclosed in Patent Document 1 is also unable to control the pulse energy.

[0011] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a laser device that can oscillate laser pulses at any timing and can independently control pulse energy and pulse oscillation timing.

[0012] The laser device according to the present disclosure includes a laser resonator having a laser medium that absorbs excitation light and emits oscillation light, an optical length adjustment unit that adjusts the optical length of the laser resonator, and a control unit that transmits a control signal to the optical length adjustment unit that is synchronized with the oscillation timing of the oscillation light emitted from the laser resonator.

[0013] According to the present disclosure, laser pulses can be emitted at any timing, and pulse energy and pulse emission timing can be controlled independently.

[0014] 6A and 6B are schematic diagrams showing the configuration of a laser device according to embodiment 1. FIG. 6B is a schematic diagram showing another configuration of a laser device according to embodiment 1. FIG. 6C is a diagram showing the relationship between the round-trip optical length of a laser resonator and the standing wave wavelength interval. FIG. 6D is a diagram showing the relationship between the round-trip optical length of a laser resonator and the oscillation wavelength. FIG. 6E is a schematic diagram showing the configuration of a laser device according to embodiment 2. FIG. 6A and FIG. 6B are diagrams showing the change over time in the optical length of a laser resonator.

[0015] In order to explain the present disclosure in more detail, embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0016] First Embodiment A laser device according to a first embodiment will be described with reference to FIGS.

[0017] 1 is a schematic configuration diagram of a laser device according to embodiment 1. As shown in FIG. 1, the laser device according to embodiment 1 includes an excitation light source 10, a control unit 60, and a laser resonator 100.

[0018] The pumping light source 10 emits pumping light 11 toward the laser resonator 100. The laser resonator 100 converts the energy of the emitted pumping light 11 into oscillation light 101, and emits the converted oscillation light 101.

[0019] The laser resonator 100 has a first mirror 20, a laser medium 30, an optical length adjusting unit 40, and a second mirror 50. The first mirror 20 is disposed on the incident side of the excitation light 11. The second mirror 50 is disposed on the emission side of the oscillation light 101. The first mirror 20, the laser medium 30, and the second mirror 50 are provided on the optical path of the laser resonator 100.

[0020] The laser medium 30 and the optical length adjustment unit 40 are provided between the first mirror 20 and the second mirror 50. The laser medium 30 is disposed on the first mirror 20 side, and the optical length adjustment unit 40 is disposed on the second mirror 50 side. Note that, as long as the laser medium 30 and the optical length adjustment unit 40 are disposed between the first mirror 20 and the second mirror 50, their installation positions can be adjusted as appropriate. The optical length adjustment unit 40 adjusts the optical length between the first mirror 20 and the second mirror 50.

[0021] The control unit 60 controls the optical length adjustment unit 40 by transmitting a control signal 61 to the optical length adjustment unit 40 in synchronization with the period or oscillation timing of the laser pulse in the oscillating light 101 emitted from the laser resonator 100.

[0022] The pumping light 11 is light of a wavelength that is absorbed by the laser medium 30. If the absorption spectrum of the laser medium 30 is narrow, the temperature of the pumping light source 10 may be adjusted to stabilize the wavelength of the pumping light 11. The pumping light 11 may be continuous light or pulsed light. In the case of pulsed light, a control signal 61 from a control unit 60 may be sent to the pumping light source 10 to control the pulse oscillation timing. Furthermore, the pumping light 11 may be emitted directly from the pumping light source 10 to the first mirror 20, or may pass through an optical fiber or the like, or may be transmitted through an optical element such as a lens.

[0023] The first mirror 20 is disposed between the pump light source 10 and the laser medium 30. The first mirror 20 has high reflectivity for the oscillation wavelength and anti-reflection for the pump wavelength. The first mirror 20 is formed, for example, of a dielectric multilayer film. The first mirror 20 may be coated on the surface of the laser medium 30 or attached to a separate glass substrate (not shown). The first mirror 20 has high transmittance for the pump light 11 and high reflectance for the oscillation light 101. Note that, in practice, it is difficult to achieve 100% transmittance or 100% reflectance in the first mirror 20. However, a first mirror 20 designed to have as high a transmittance or reflectance as possible is referred to as having a high transmittance or high reflectance. In practice, this refers to a transmittance or reflectance of 99% or higher.

[0024] The laser medium 30 is capable of absorbing the pumping light 11 and emitting or amplifying light of the wavelength of the oscillation light 101. The laser medium 30 is, for example, Nd ３＋ Ion-doped Yttrium Aluminum Garnet (YAG) or YVO ４ Fluorapatite (FAP) crystal or ceramic, Yb ３＋ Similar crystals or ceramics doped with ions, Er ３＋ Similar crystals or ceramics, glasses, etc. doped with ions may be used.

[0025] The second mirror 50 is provided on the opposite side of the first mirror 20 with respect to the laser medium 30 and the optical length adjusting unit 40. The second mirror 50 has a partial reflection function with a predetermined reflectance for the oscillation wavelength. The second mirror 50 is formed, for example, of a dielectric multilayer film. The second mirror 50 may be coated on the surface of the laser medium 30 or attached to a separate glass substrate (not shown). The second mirror 50 has partial reflectance for the oscillation light 101. If the absorption rate of the laser medium 30 for the pumping light 11 is insufficient, it is desirable that the second mirror 50 have a high reflectance and increase the absorption rate by making the pumping light 11 go back and forth. Furthermore, if the absorption rate of the laser medium 30 for the pumping light 11 is sufficient, the second mirror 50 may have any reflectance for the pumping light 11.

[0026] When the absorption rate of the laser medium 30 is insufficient even when the highly reflective second mirror 50 is used for the pumping light 11 and the pumping light 11 is made to go back and forth through the laser medium 30, the laser device according to the first embodiment resonates the pumping light 11 and makes the pumping light 11 go back and forth through the laser medium 30 multiple times. Therefore, the laser device according to the first embodiment can increase the absorption of the pumping light 11 in the laser medium 30. In this case, when the pumping light 11 emitted from the pumping light source 10 is partially reflected by the second mirror 50 and travels toward the pumping light source 10, the second mirror 50 is arranged perpendicular to the optical axis of the pumping light 11 so that the optical axis does not shift. Therefore, the pumping light 11 that is not absorbed by the laser medium 30 returns to the pumping light source 10.

[0027] The pumping light 11 is reflected by the end face of the pumping light source 10 or recombines inside the pumping light source 10 and is emitted again toward the laser medium 30. Therefore, in the laser device according to the first embodiment, the pumping light 11 can be sufficiently absorbed by the laser medium 30 by passing the pumping light 11 through the laser medium 30 multiple times. When the reflected light of the pumping light 11 recombines inside the pumping light source 10, this is called intracavity pumping, and it is possible to pump the laser medium 30 with high efficiency even if the absorption rate of the laser medium 30 is low. In the laser device according to the first embodiment, a thin laser medium 30 is used, so intracavity pumping is effective.

[0028] The laser resonator 100 includes a laser medium 30 between a first mirror 20 and a second mirror 50. The optical length adjustment unit 40 adjusts the optical length of the laser resonator 100, i.e., the optical length between the first mirror 20 and the second mirror 50. The optical length is the time it takes for light to travel multiplied by the speed of light in a vacuum, and is calculated by multiplying the actual length by the refractive index of light.

[0029] Therefore, the optical length adjusting unit 40 may be one that can adjust the actual length or may be a mechanism that can change the refractive index. Examples of the optical length adjusting unit 40 include an electro-optical element (EO element), a magneto-optical element (MO element), a temperature control element, a piezoelectric element, and a MEMS.

[0030] When an optical length adjusting unit 40 that adjusts the optical length of the laser resonator 100 using a refractive index, like an electro-optical element, is used, the optical length adjusting unit 40 is disposed inside the laser resonator 100, as shown in FIG. 1 .

[0031] 2 is a schematic diagram showing another configuration of the laser device according to the first embodiment. When an optical length adjustment unit 40 that adjusts the length of the laser resonator 100 using a physical length, such as a piezoelectric element, is used and the optical length adjustment unit 40 is opaque to the oscillation light 101, the optical length adjustment unit 40 is arranged outside the laser resonator 100, as shown in FIG. 2. When the optical length adjustment unit 40 utilizes thermal expansion due to temperature or the temperature dependency of the refractive index, the optical length adjustment unit 40 is a heater or Peltier element and is arranged outside the laser resonator 100. In this case, the optical length adjustment unit 40 controls the length of the laser resonator 100 by adjusting the temperature of the laser medium 30.

[0032] As shown in FIG. 2, when the optical length adjusting unit 40 is a piezoelectric element, the second mirror 50 or its holder extends to the outside of the laser resonator 100, and the optical length adjusting unit 40 is provided on the extended portion.

[0033] Here, the laser resonator 100 has a standing wave condition based on the optical length, and light other than the wavelength λ that satisfies this condition cannot be efficiently accumulated. ｃIf m is an arbitrary integer, the wavelength λ that satisfies the standing wave condition is ｍ can be expressed by the following formula (2). Note that the wavelength refers to the wavelength in a vacuum. ｃ = mλ ｍ ... (2)

[0034] As is clear from equation (2), the wavelength λ that satisfies the standing wave condition ｍ The distance between the laser resonator 100 and the optical length L ｃ The smaller the frequency, the wider the interval. This interval is called the Free Spectral Range (FSR), and is a constant interval in the frequency domain. This frequency interval ν ＦＳＲ can be expressed by the following equation (3): Note that there is a relationship between wavelength λ and frequency ν, λ=c / ν. ＦＳＲ = c / 2L ｃ ...(3)

[0035] On the other hand, among the laser media 30, for example, Nd ３＋ Y ion-doped ３ AI ５ O １２ Nd:YAG is known for its narrow stimulated emission spectrum width. According to Non-Patent Document 2, the peak width at 1064 nm used in Nd:YAG is 1.1 nm. The laser medium 30 may be an Nd:YAG crystal or any laser medium with a narrow stimulated emission spectrum width. For example, according to Non-Patent Document 2, Nd:YVO ４ Nd:YVO has a peak width of 1.1 nm, similar to Nd:YAG. Nd:FAP has a peak width of 0.6 nm. ４ Nd:FAP and Nd:FAP have birefringence and can provide linearly polarized laser output, so they are suitable for situations where linearly polarized output is desired.

[0036] T. Taira, “RE3+-Ion-Doped YAG Ceramic Lasers,” IEEE J. Sel. Top. Quant. Electron. 13, 798 (2007).

[0037] 3 is a diagram showing the relationship between the round-trip optical length of the laser resonator 100 and the standing wave wavelength interval. This FIG. 3 shows the wavelength λ that satisfies the standing wave condition around a wavelength of 1064 nm from equation (2). ｍ 3 shows the relationship between the distance between the laser resonator 100 and the round-trip optical length. The horizontal axis of FIG. 3 shows the round-trip optical length of the laser resonator 100, and the vertical axis of FIG. 3 shows the standing wave wavelength interval. As shown in FIG. 3, when the round-trip length of the laser resonator 100 is 1 mm or less, the wavelength λ 1 that satisfies the standing wave condition becomes ｍ It can be seen that the spacing between the two is 1.1 nm or less.

[0038] 4 is a diagram showing the relationship between the round-trip optical length and the oscillation wavelength of the laser resonator 100. This figure shows the relationship between the amount of change when the round-trip optical length is changed by about 1 mm and the wavelength λ that satisfies the standing wave condition. ｍ The horizontal axis of Fig. 4 indicates the round-trip optical length of the laser resonator 100, and the vertical axis of Fig. 4 indicates the oscillation wavelength. According to Non-Patent Document 2, the peak width of the stimulated emission cross section of Nd:YAG at a wavelength of about 1064 nm is 1064.2 nm, so when the optical length of the resonator is 1.00035 mm, the standing wave condition and the peak width of the stimulated emission cross section exactly match. On the other hand, when the optical length of the resonator is 0.9998 mm, the wavelength λ ｍ Since the standing wave condition is satisfied at 1064.75 nm or 1063.62 nm, the wavelength λ that satisfies the standing wave condition is ｍ However, this wavelength is separated from the peak wavelength of the stimulated emission cross section by 0.55 nm, which is half of 1.1 nm. This results in a significant decrease in gain compared to when the optical length of the resonator is 1.00035 mm.

[0039] In the laser device according to the first embodiment, the round-trip optical length of the laser resonator 100 is set to about 1 mm, and a slight change in the optical length of 0.55 μm (1.00035 mm - 0.9998 mm = 0.00055 mm) can significantly change the gain. Therefore, the laser device according to the first embodiment can oscillate a laser pulse at any timing. That is, when the optical length of the laser resonator 100 is 0.9998 mm, the wavelength λ that satisfies the standing wave condition is ｍSince the gain of the light is small, it is possible to store sufficient energy in the Nd:YAG crystal. After storing sufficient energy, the optical length adjusting unit 40 adjusts the optical length of the laser resonator 100 to 1.00035 mm, thereby achieving the wavelength λ 1 that satisfies the standing wave condition. ｍ The gain of the light increases, and a laser pulse is generated.

[0040] The timing at which this laser pulse is oscillated can be arbitrarily set by a control signal 61 sent from the control unit 60 to the optical length adjustment unit 40. The laser device according to the first embodiment can be considered a gain-switched laser because the gain is changed by the control unit 60 provided outside the laser resonator 100 to oscillate the laser in pulses. Therefore, the laser device according to the first embodiment can also adjust the pulse energy by the intensity of the excitation light 11, although to a certain extent, and can control the pulse energy and the laser pulse oscillation timing independently. Therefore, the control signal 61 sent from the control unit 60 is a signal that fluctuates in accordance with the laser pulse oscillation timing of the oscillating light 101.

[0041] The optical length of the laser resonator 100 is not limited to 1 mm round trip, but is set to a wavelength λ 1 that satisfies the standing wave condition, which can be calculated using equation (2). ｍ and the peak width of the stimulated emission cross section of the laser medium 30 used. That is, if the peak width of the laser medium 30 is narrow, the optical length of the laser resonator 100 may be long, but if the peak width of the laser medium 30 is wide, the optical length of the laser resonator 100 needs to be short. Here, the wavelength λ that satisfies the standing wave condition is more important than the peak width of the stimulated emission cross section of the laser medium 30. ｍ The optical length of the laser resonator 100 is set so that the gap between the peaks is wide. For example, according to Non-Patent Document 2, the peak width of Nd:FAP is 0.6 nm, and in this case, an optical length of 1.9 mm or less satisfies this condition.

[0042] Generally, the laser medium 30 has a plurality of peak wavelengths in the stimulated emission cross section. The wavelength at which the laser oscillates is determined by the relationship between the gain and the reflectance of the first mirror 20 and the second mirror 50.

[0043] Furthermore, the FSR has a constant interval in the frequency domain, but when converted to wavelength, it has a different wavelength interval at the center wavelength. ｍ The "interval" refers to a wavelength interval in the vicinity of the wavelength of the oscillating light 101.

[0044] As described above, the laser device according to the first embodiment can oscillate a laser pulse at any timing by controlling the optical length of the laser resonator 100. Furthermore, the laser device according to the first embodiment can greatly change the gain within the laser resonator 100, so that it can store energy in the laser medium 30 in a low-gain state and oscillate a laser pulse by transitioning from the low-gain state to a high-gain state. Furthermore, the laser device according to the first embodiment can adjust the pulse energy to some extent by the intensity of the excitation light 11, so that it can control the pulse energy and the laser pulse oscillation timing independently.

[0045] Second Embodiment A laser device according to a second embodiment will be described with reference to Figures 5 and 6. Note that components having the same functions as those described in the first embodiment above will be given the same reference numerals, and descriptions thereof will be omitted.

[0046] 5 is a schematic diagram showing the configuration of a laser device according to embodiment 2. The laser device according to embodiment 2 includes a laser resonator 200 instead of the laser resonator 100 of the laser device according to embodiment 1. The laser device according to embodiment 2 also includes a measuring device 70 and an optical length correction unit 80 in addition to the laser device according to embodiment 1.

[0047] As shown in FIG. 5, the laser device according to the second embodiment includes an excitation light source 10, an optical length adjusting unit 40, a control unit 60, a measuring device 70, and a laser resonator 200.

[0048] Laser resonator 200 emits oscillation light 201. Laser resonator 200 includes a first mirror 20, a laser medium 30, a second mirror 50, and an optical length correction unit 80. Laser medium 30 is disposed on the first mirror 20 side. Optical length correction unit 80 is in contact with laser medium 30. This optical length correction unit 80 is controlled by inputting a control signal 62 from control unit 60. In this case, if optical length adjustment unit 40 is a piezoelectric element, second mirror 50 or its holder extends to the outside of laser resonator 200, and optical length adjustment unit 40 is provided on this extended portion.

[0049] The measuring instrument 70 measures the oscillation timing of the laser pulse emitted from the laser resonator 100. The measuring instrument 70 also transmits the measurement result to the control unit 60 as a measurement signal 71. The measuring instrument 70 measures the laser pulse oscillation timing of the oscillating light 201, for example, from scattered light of the oscillating light 201. Note that the measuring instrument 70 may measure the laser pulse oscillation timing by extracting a portion of the oscillating light 201 using a mirror with a reflectance of several percent.

[0050] The control unit 60 controls the optical length adjustment unit 40 and the optical length correction unit 80 according to the measurement results of the measuring device 70 .

[0051] The optical length correction unit 80, like the optical length adjustment unit 40, is an EO element, MO element, temperature control element, piezoelectric element, MEMS, etc., and adjusts the optical length of the laser resonator 200 by changing the physical length or the refractive index of light.

[0052] However, while the optical length adjustment unit 40 varies the optical length in accordance with the laser pulse oscillation timing of the oscillating light 201, the optical length correction unit 80 corrects the optical length on a longer time scale. Therefore, a mechanism with a relatively slow response speed, such as a temperature control element, is acceptable. For this reason, in the laser device according to the second embodiment, the optical length correction unit 80 is assumed to be a Peltier element, which is a temperature control element.

[0053] In the laser device according to the second embodiment, for example, the gain is controlled by a change in optical length of 0.5 nm for an optical length of approximately 1 mm. Therefore, it is conceivable that the operating point may change due to ambient temperature or aging. If the operating point changes, the timing at which the laser pulse oscillates will deviate from the expected timing. Therefore, in the laser device according to the second embodiment, the control unit 60 compares the measurement signal 71 from the measuring device 70 with the expected laser pulse timing signal, and the control unit 60 transmits a control signal 62 to the optical length correction unit 80, indicating that the deviation in the laser pulse oscillation timing should be corrected.

[0054] FIG. 6 is a diagram showing the change in the optical length of the laser resonator 200 over time. The vertical axis of FIG. 6 represents the optical length of the laser resonator 200. The horizontal axis of FIG. 6 represents the passage of time. For example, as shown in FIG. 6A, when the optical length of the laser resonator 200 is controlled to oscillate a laser pulse, if the optical length becomes longer than originally designed due to changes in the ambient temperature or aging, the laser pulse is oscillated at the timing shown in FIG. 6B. The arrow in FIG. 6B indicates the direction in which the laser pulse oscillation timing is shifted.

[0055] When the optical length of the laser resonator 200 is increased, the laser pulse is oscillated at an earlier timing than expected. When the optical length of the laser resonator 200 is decreased, the laser pulse is oscillated at a later timing than expected. The laser device according to the second embodiment detects such a deviation and uses the optical length correction unit 80 to control the laser resonator 200 so that the optical length is decreased. The laser device according to the second embodiment can also detect, using the same logic, a case where the optical length of the laser resonator 200 is decreased compared to the initial design, and uses the optical length correction unit 80 to control the laser resonator 200 so that the optical length is decreased.

[0056] The laser device according to the second embodiment includes the optical length adjustment unit 40 and the optical length correction unit 80 as separate units, but the optical length adjustment unit 40 may also have the function of the optical length correction unit 80. In this case, the laser device according to the second embodiment compares the signal from the measuring device 70 with an assumed laser pulse timing signal in the control unit 60, corrects the operating point, and adjusts only the control signal 61.

[0057] As described above, the laser device according to the second embodiment can oscillate laser pulses at any timing by controlling the optical length of the laser resonator 200 .

[0058] It should be noted that within the scope of the present disclosure, the embodiments may be freely combined, or any component in each embodiment may be modified, or any component in each embodiment may be omitted.

[0059] The laser device according to the present disclosure can oscillate a laser pulse at any timing by transmitting a control signal synchronized with the oscillation timing of the oscillating light emitted from the laser resonator to the optical length adjustment unit, and is suitable for use in laser devices that can independently control the pulse energy and pulse oscillation timing.

[0060] 10 Pumping light source, 11 Pumping light, 20 First mirror, 30 Laser medium, 40 Optical length adjusting unit, 50 Second mirror, 60 Control unit, 61, 62 Control signal, 70 Measuring instrument, 71 Measurement signal, 80 Optical length correcting unit, 100, 200 Laser resonator, 101, 201 Oscillation light.

Claims

1. A laser device comprising: a laser resonator having a laser medium that absorbs pumping light and emits oscillating light; an optical length adjustment unit that adjusts the optical length of the laser resonator; and a control unit that sends a control signal to the optical length adjustment unit that is synchronized with the oscillation timing of the oscillating light emitted from the laser resonator.

2. The laser device according to claim 1, further comprising a measuring device that measures the oscillation timing of the oscillating light emitted from the laser resonator, and the control unit controls the optical length adjustment unit according to the measurement results of the measuring device.

3. The laser device according to claim 2, further comprising an optical length correction unit that corrects deviations of the optical length of the laser resonator from the design, and wherein the control unit controls the optical length correction unit in accordance with the measurement results of the measuring device.

4. The laser device according to claim 2, wherein the optical length adjusting section is provided outside the laser resonator.

5. A laser device according to any one of claims 1 to 4, characterized in that the optical length of the laser resonator is such that the interval between wavelengths that satisfy the standing wave condition based on said optical length is wider than the width of the stimulated emission cross-section area of ​​the laser medium.

6. A laser device according to any one of claims 1 to 5, characterized in that the laser resonator has a first mirror provided on one end side of the laser medium and totally reflecting the oscillating light, and a second mirror provided on the other end side of the laser medium and partially reflecting the oscillating light, and the excitation light absorbed in the laser medium is partially reflected by the second mirror and recombined with an excitation light source that radiates the excitation light, thereby performing intra-resonator excitation.

7. The laser medium is Nd ３＋ Ion-doped YAG or Nd ３＋ Ion-doped YVO ４ 7. The laser device according to claim 1, wherein the optical length of the laser resonator is 1 mm or less in a round trip.

8. The laser medium is Nd ３＋ 7. The laser device according to claim 1, wherein the laser is fluorapatite doped with ions, and the optical length of the laser resonator is 1.9 mm or less in a round trip.

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