JP2000082859A - Solid-state laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state laser device which can stably emit a laser beam having a fixed wavelength for a long time. SOLUTION: A solid-state laser device is provided with a semiconductor laser 1 which emits an exciting laser beam, a light condensing optical system 2, a laser resonator 30, base parts 12 on which the supporting bodies 4, 6, 8, and 10 of the parts 3, 5, 7, and 9 constituting the resonator 30 are fixed, a temperature control element 13 which is fixed under the base parts 12 for making the temperatures of the parts 3, 5, 7, and 9 constant, and a heat sink 14 which supports the element 13 and, at the same time, is fixed to the bottom plate 16 of a laser device case 18. In the laser device, the laser resonator 30, base parts 12, temperature control element 13, and heat sink 14 are surrounded by an airtight cover 15 and the cover 15 is airtightly fixed to the bottom plate 16 of the case 18 so that the air pressure in the optical path of the resonator 30 for laser beam may become constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device that emits a laser beam having a stable wavelength without a change over time.
In particular, the present invention relates to a low-noise solid-state laser device that is not affected by fluctuations in atmospheric pressure.

[0002]

2. Description of the Related Art Solid-state lasers have a longer lifespan than other lasers such as gas lasers.
In addition to advantages such as low power consumption and maintenance-free, there are advantages that high-frequency noise can be reduced and the device can be miniaturized. For this reason, recently, many developments regarding photo-excitation type solid-state lasers have been advanced. In general, long-wavelength laser light in the red to infrared region is easy to oscillate, and thus practical use has preceded. However, short-wavelength laser light is difficult to oscillate. Under these circumstances, in order to obtain short-wavelength laser light such as green, blue, and violet, which is considered to be difficult to oscillate, an internal-resonance type laser having an optical wavelength conversion element made of a nonlinear optical material in a laser resonator is used. Two-harmonic solid-state lasers are entering the practical stage.

FIG. 2 shows a typical example of an internal resonance type second harmonic solid-state laser device. In this internal resonance type second harmonic solid-state laser device, a semiconductor laser 1 provided outside a laser resonator is used as an excitation light source for a solid-state laser crystal 5. First, the excitation light emitted from the semiconductor laser 1 is focused on the solid-state laser crystal 5 through the focusing optical system 2. As shown in FIG. 3, the condenser optical system 2 includes lenses 2a to 2d.
It consists of.

The laser light emitted from the solid-state laser crystal 5 is called a “fundamental wave”, and generates a second mirror and a resonance mirror 3 a coated on the concave curved surface of the concave lens 3 constituting the laser resonator 30. It reciprocates between a mirror 11 coated on the end face of the nonlinear optical crystal 9. Resonant mirror 3a and mirror 11
Has a characteristic of reflecting a fundamental wave. The nonlinear optical crystal 9 absorbs energy from the reciprocating fundamental wave, and emits a second harmonic determined by its optical nonlinear characteristics, dimensions, and the like. Since the second harmonic can pass through the mirror 11, it is obtained as a laser beam 17.

[0005] The wavelength of the laser beam 17 can be arbitrarily selected by a wavelength selecting element 7 such as an etalon or a birefringent filter. Accordingly, when a wavelength of 750 to 1000 nm is obtained as the fundamental wave, the wavelength is halved by the nonlinear optical crystal 9 for generating the second harmonic arranged in the laser resonator 30, and the wavelength becomes 375 to 1000 nm.
It becomes blue or green laser light of 500 nm.

[0006] The output level of the second harmonic laser light 17 is very sensitive to temperature. This is a laser resonator such as a solid-state laser crystal 5, a wavelength selection element 7, and a nonlinear optical crystal 9.
This is because the optical components constituting 30 have a very high temperature dependency. Accordingly, the temperature of each component constituting the laser resonator 30 is controlled by the temperature control element 13 such as a Peltier element to each of the component supports 4, 6, 8 supporting the optical components 3, 5, 7, 9 respectively. , 10 and each component support 4, 6,
It is controlled to be constant via the base part 12 supporting 8, 10, etc. The temperature control element 13 is provided with a heat radiating mechanism 14 such as a heat sink for radiating heat from the solid-state laser device to the outside.

As shown in FIG. 3, a separation filter that reflects a part of the second harmonic laser light behind the nonlinear optical crystal 9.
32 are arranged. The reflected second harmonic laser light is introduced into the photodiode 34, and the current of the feedback signal is supplied to the input side of the semiconductor laser 1 through the feedback circuit 36. Thus, the output of the output laser light 17 is kept constant.

[0008] The internal resonance type solid-state laser has a problem of noise, and it is very important to reduce the noise for application to high-performance equipment. In the internal resonance type second harmonic solid-state laser having the nonlinear optical crystal 9 in the laser resonator 30, many oscillation longitudinal modes can be generated in the laser resonator 30. Is desired. However, it is very difficult to form a single longitudinal mode. In addition, the change over time of the oscillation longitudinal mode depends on the fluorescence lifetime of the solid-state laser crystal 5,
This is also caused by surface loss of each optical component in the laser resonator 30, a change in loss due to nonlinear optical conversion, and the like. In the case of the multiple longitudinal mode, a mode competition phenomenon occurs in which the output intensity constantly changes as shown in FIG.

Due to the mode competition phenomenon, chaos changes in time and laser output occur, and are observed as high frequency noise.
The actual frequency of high-frequency noise is determined mainly by the time constant τ such as the excitation life of the solid-state laser crystal and the attenuation constant in the resonator.
Within the range of 100 ms. Assuming that the noise frequency is lower than the reciprocal of the time constant τ, the frequency range of the high-frequency noise is 10 kHz to 100 MHz, as typically shown in FIG. 4B, and a noise component can be obtained by performing output frequency analysis.

Several methods have been proposed for removing high-frequency noise due to such a mode competition phenomenon. For example, a wavelength selecting element 7 such as an etalon plate composed of parallel flat plates is added, and a laser resonator 30 is provided.
By setting the condition of the single longitudinal mode oscillation of the fundamental wave within the above, the mode competition phenomenon can be substantially prevented. As shown in FIG. 4C, in the case of single longitudinal mode oscillation, no mode competition phenomenon can occur, so that the output of the oscillating laser light does not include high-frequency noise (see FIG. 4D).

Further, even when the oscillation wavelength is in the multimode, the mode can be improved by designing the laser resonator 30 in consideration of the sum frequency conversion effect of the nonlinear optical crystal as disclosed in Japanese Patent Application Laid-Open No. 10-65254. The conflict phenomenon can be prevented, but the reason is not yet elucidated physically.

However, in practice, in order to keep the output constant and to maintain a low noise state, a solid-state laser resonator is required.
It is necessary to keep the oscillation mode within 30 constant.

The laser light generated from the laser resonator 30 is
Generally, it exists as a plurality of discontinuous wavelengths at specific intervals. This is because the mirrors 3a located at both ends of the laser resonator 30
And 11 always have a node of the laser light wave, which is apparent from the condition that the distance of an integral multiple of a half wavelength matches the effective optical path length of the laser resonator 30. The adjacent wavelength interval (longitudinal mode interval) Δλc is defined as the wavelength interval between adjacent laser beams of the multi-mode laser beam as shown in FIG. 4A, and is expressed by the following equation (1): Δλc = λ ² / 2Lc ・ ・ ・
(1) (where Lc is the effective optical path length of the laser resonator 30, and λ is the center wavelength in the oscillation wavelength region). For example, a typical solid-state laser, 860 nm
: LiSAF (Cr: LiSrAlF ₆ ) having an oscillation wavelength component of
When the system single crystal solid laser is arranged in the laser resonator 30 having a length of 30 mm, the longitudinal mode interval Δλc is about 0.01 nm.

In order to obtain a laser beam having a stable wavelength in a low-noise solid-state laser, the wavelength fluctuation should be within the range of the longitudinal mode interval, preferably within about 15% of the longitudinal mode interval Δλc, more preferably 10% of the longitudinal mode interval. Must be controlled within the range. Such a single-mode low-noise laser transmits only a predetermined wavelength by a wavelength selection element such as an etalon, and outputs laser light having a frequency exactly twice as high as that of light incident on the nonlinear optical crystal. Therefore, by appropriately selecting the incident laser light using the nonlinear optical crystal, a discontinuous variable wavelength laser light can be obtained.

Therefore, when the oscillation wavelength is shifted by about 15% or more of the longitudinal mode interval Δλc determined by the effective optical path length of the laser resonator 30, the single longitudinal mode state is broken. As a result, the output of the longitudinal mode is reduced, the adjacent longitudinal mode is amplified and the oscillation is enhanced, and a double or triple mode state is set. The low noise state is broken by such a mode competition phenomenon. On the other hand, in the multi-mode low-noise laser, the mechanism for preventing the mode competition phenomenon is closely related to the spatial hole burning effect and the sum frequency conversion effect of the solid-state laser crystal for each longitudinal mode, so wavelength control of the longitudinal mode is important. And the noise state may be broken by a change in the wavelength distribution of the longitudinal mode. Thus, the longitudinal mode spacing of low-noise solid-state lasers is at most within 15%, especially
Must be controlled within the range of 10%.

Conventionally, wavelength fluctuations have been suppressed by keeping the temperature of a base component supporting each element in the laser resonator 30 constant by a temperature control element such as a Peltier element. By maintaining a constant temperature, the thermal expansion of the base component is suppressed, the effective optical path length of the laser resonator 30 becomes constant, and the wavelength of the resulting laser light also becomes constant. The wavelength of the laser light becomes constant in the laser resonator 30 because the wavelength of the standing wave is an integer multiple of a half wavelength of the laser light in the laser resonator 30 having a fixed length. This is for satisfying the boundary condition of being equal to the optical path length. For example, as described in JP-A-7-306429, by controlling the temperature of the laser resonator 30 with a Peltier element, it is possible to prevent the distance between the elements from changing due to thermal expansion or thermal contraction. .

However, from a long running test,
It has been found that it is very difficult to maintain a low noise state for several hours or tens of hours by temperature control alone. Therefore, it is necessary not only to keep the temperature of the entire laser resonator 30 constant, but also to clarify and solve other causes that cause wavelength fluctuation and break the low noise state.

Conventionally, attempts have been made to suppress the fluctuation of the oscillation wavelength by controlling the temperature of the base component of the laser resonator 30 that has been operating for a long time, but a complete low noise state is maintained for a long time. I have not been able to.

Accordingly, it is an object of the present invention to provide a solid-state laser device capable of stably emitting laser light having a constant wavelength for a long time.

[0020]

Means for Solving the Problems As a result of earnest research on the cause of fluctuation of the oscillation wavelength of the solid-state laser, the present inventors have found that
It was found that the fluctuation of the atmospheric pressure is also a major factor that breaks the low noise state and greatly changes the oscillation wavelength. this is,
This is because a change in the atmospheric pressure causes a change in the density of a medium such as air in the optical path of the laser resonator, and a change in the refractive index directly related to the change in the oscillation wavelength. As a result, the inventors have found that a change in the refractive index of air that causes a change in the oscillation wavelength can be prevented by keeping the atmospheric pressure of the laser resonator constant, and completed the present invention.

That is, in the solid-state laser device of the present invention, a solid-state laser crystal is arranged between a pair of mirrors to form a laser resonator, and the solid-state laser crystal is excited by an excitation light source provided outside the laser resonator. An optically-pumped solid-state laser device for obtaining required laser light, characterized by comprising means for keeping the effective optical path length of the laser resonator substantially constant.

The means for keeping the effective optical path length of the laser resonator substantially constant is a component having at least the function of keeping the refractive index of the medium (air) in the effective optical path of the laser resonator constant. Is preferably an airtight cover fixed in an airtight manner to the bottom plate of the case of the solid-state laser device in order to keep the internal pressure constant. The hermetic cover is fixed to the bottom plate so as not to transmit mechanical deformation or stress to the laser resonator, and not to apply compressive or tensile stress to each part of the laser resonator and a base component supporting each part. Is preferred. Further, the pressure inside the airtight cover is preferably lower than the outside air pressure.

Preferably, the base component is fixed to the heat sink via temperature control means, and the heat sink does not directly contact the airtight cover.

Preferably, the laser resonator has a wavelength selecting element for enabling single longitudinal mode oscillation. As the wavelength selection element, a birefringent filter or an etalon element is often used.

The high-frequency noise of the laser light output from the solid-state laser device of the present invention is reduced. Further, the fluctuation width of the wavelength of the output laser light is the FSR of the laser resonator (= λ ² / 2L
_{CAVI ty,} however λ is the wavelength, L _cavity is a laser resonator length. ). Specifically, the fluctuation width of the output wavelength is preferably in the range of 0.001 nm. The fluctuation range of the output wavelength is within the range of 0.0015 nm.

An example of the solid-state laser device according to the present invention having such features is a semiconductor device in which a solid-state laser crystal is disposed between a pair of mirrors to form a laser resonator, and the solid-state laser crystal is provided outside the laser resonator. An internal resonance type solid-state laser device which is excited by a laser and has a wavelength conversion element comprising a wavelength selection element and a non-linear optical medium provided inside a laser resonator to obtain laser light of a required wavelength, comprising at least a laser resonator And the pressure inside the airtight cover is kept constant irrespective of the atmospheric pressure fluctuation, so that the effective optical path length of the laser resonator is kept substantially constant, and thus the output wavelength is kept substantially constant. It is characterized by the following.

A solid-state laser device according to a preferred embodiment of the present invention comprises: (a) a semiconductor laser that emits excitation light; (b) a pair of mirrors; a solid-state laser crystal that emits a fundamental wave by receiving the excitation light; A laser resonator having an element and a wavelength conversion element that emits a second harmonic laser beam in response to the fundamental wave, and (c) the semiconductor laser and the laser for condensing the excitation light onto the solid-state laser crystal. A condensing optical system arranged between the resonators, (d) a base component supporting all components in the laser resonator, (e) a temperature control means fixed to the bottom surface of the base component, (f) A heat sink fixed to the bottom surface of the temperature control means and supported on the bottom plate of the case of the solid-state laser device, and (g) the laser resonator, the base component, the temperature control means, and the heat sink. Surround A dense cover, which is fixed to the bottom plate of the solid-state laser device in an airtight manner, and thereby keeps the pressure therein substantially constant, thereby reducing the refractive index of air in the laser beam path of the laser resonator. It is characterized by having an airtight cover that keeps it substantially constant.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the structure of the solid-state laser device of the present invention in detail, the principle of the present invention will be described. The pressure P (hPa) of the air and the refractive index n thereof are approximated by the following formula (2) through the density of air molecules: n = A × P + 1 (2) (where A is the composition and temperature of the air) Which is approximately 2.713 × 10 ⁻⁷ at 15 ° C. and 1 atm.). When the refractive index of air existing in the laser beam path changes due to pressure fluctuations according to the equation (2), the effective optical path length of the laser resonator 30 becomes the following equation (3): D = n × L (3) Is represented by Here, L is the actual distance of the air in the laser beam path, that is, the distance excluding the dimensions of the optical components, and varies according to the following equation (4): ΔD = Δn × L (4)

For example, assuming that there are two solid media (i = 1, 2) and one gaseous medium (air) that forms a laser beam path in the laser resonator 30, a certain number of waves in the laser resonator 30 the number n is the following formula _{(5): n = 2n 1} L 1 / λ + 2n 2 L 2 / λ + 2n air L air / λ ··· (5) ( provided that, n ₁ and n ₂ are the refractive index of the solid medium And L ₁ and L ₂ are the distances of each solid medium, n _air is the refractive index of _air , and L _air is the distance of air in the laser beam path.)
Is represented by The new oscillation wavelength λ ₂ = λ ₁ + Δλ due to the refractive index fluctuation of Δn _air = | n _air2 −n _air1 |
(5) can be summarized as follows. λ ₂ = λ ₁ × (n ₁ L ₁ + n ₂ L ₂ + n _air2 L _air ) / (n ₁ L ₁ + n ₂ L ₂ + n _air1 L _air ) ・ ・ ・ (6)

As is apparent from the equation (6), the optical path length L _air of air in the laser optical path and the refractive index change Δn of air
_The greater the product of _air, the greater the change in oscillation wavelength. Therefore, if the product of the optical path length of air and the refractive index of air in the laser optical path is kept within a small range,
The change in oscillation wavelength is determined by the longitudinal mode interval Δ
Since it is sufficiently smaller than λc, the fluctuation of the output wavelength can be suppressed. As a typical example, the relationship between pressure and wavelength can be calculated from Equations (2) and (6) under the following conditions. Length of laser cavity (effective optical path length) Lc = 30 mm, length of first solid medium L ₁ = 5 mm, refractive index of first solid medium n ₁ = 1.40, length of second solid medium L ₂ = 5 mm, refractive index n ₂ of the second solid medium = 1.60, wavelength of fundamental wave = 860 nm, and temperature = 15 ° C.

FIG. 5 shows the results. The slope K of the straight line in the figure
Is 0.0001 nm / hPa. If the allowable range is within about 10% of the longitudinal mode interval (0.01 nm), the pressure change ΔP
Is obtained by dividing Δλ by the slope K as follows. ΔP = Δλ / K = (0.01 × 10%) / K = 10 (hPa) (7)

By providing a means for maintaining the pressure fluctuation of the air in the laser beam path within the range obtained by the equation (7), the wavelength of the output laser beam can be made substantially constant. However, the allowable range of the wavelength depends on the effective optical path length and the wavelength of the laser resonator 30 from the equation (1) .Therefore, considering the various factors affecting the wavelength of the laser light emitted from the solid-state laser, the wavelength The tolerance is preferably 0.0015
nm, more preferably 0.001 nm.

In order to keep the pressure in the laser beam path constant, the laser resonator 30 must be hermetically sealed in an airtight cover that separates the inside from the external pressure. In order to prevent the thermal expansion and contraction of the components so that the effective optical path length of the laser light is constant, it is necessary to keep the temperature of the components of the laser resonator 30 strictly constant. Furthermore, when an unexpected stress is applied to the base component from an external component, the base component is slightly deformed, so that the length of the laser light path and the position of the component are changed.
As a result, the oscillation wavelength changes. If there is a pressure difference between the inside and outside of the airtight cover 15, the airtight cover 15 may exert a stress on the base component 12 supporting the component due to a change in the external pressure.
In order to prevent such stress, the hermetic cover 15 is not deformed by pressure, and the components 3, 5,
It is important that the base parts 12 supporting the support members 7, 9, the supports 4, 6, 8, 10 and the supports 4 to 10 do not directly contact the bottom plate 16 and the airtight cover 15 of the device case 18.

FIG. 1 shows a solid-state laser device according to one embodiment of the present invention. This solid-state laser device includes a semiconductor laser 1 for emitting excitation laser light, a condensing optical system 2, a laser resonator
The first coated on the concave curved surface of the concave lens 3 constituting 30
, A solid-state laser crystal 5 that receives a pump laser beam and emits a fundamental wave, a wavelength selection element 7, a nonlinear optical crystal 9, and a second mirror 11 coated on the rear surface of the nonlinear optical crystal 9. Have. The fundamental wave emitted from the solid-state laser crystal 5 is transmitted to the first mirror 3a and the second
Reciprocates between the mirrors 11 and is amplified. The fundamental wave is wavelength-controlled by the wavelength selection element 7 and has a single laser light component,
That is, a single longitudinal mode laser beam is obtained. For example,
When the longitudinal mode laser light has a wavelength of 860 nm, the wavelength of the second harmonic laser light emitted from the nonlinear optical crystal 9 is
430 nm.

The semiconductor laser 1 that emits an excitation laser beam
It can be constituted by a red laser light diverging semiconductor laser having a center wavelength of 670 nm at 500 mW. The solid-state laser crystal 5 is, for example, Cr: LiSAF (Cr: LiSrAlF ₆ ) and has a Cr content of
It can be composed of 1.5% of a single crystal of 3 mm × 3 mm × 5 mm, and the nonlinear optical crystal 9 is, for example, 3 mm × 3 mm × 5 mm.
mm of LBO (LiB ₃ O ₅ ) single crystal.

As shown in FIG. 1, the components 3, 5, 7, 9 and the supports 4, 6, 8, 10 (the concave lens 3 on which the first mirror 3a is formed and the Support 4,
The Cr: LiSAF single crystal 5 and its support 6, the wavelength selection element 7 and its support 8, the LBO crystal 9 and its support 10) are fixed to a base component 12. Base component 12 and laser resonator 30
A temperature control element 13 such as a Perrier element for keeping the temperature of each component constant is fixed below the base component 12. Further, a heat sink 14 is fixed below the temperature control element 13,
The heat sink 14 is fixed to the bottom plate 16 of the laser device case 18.

The hermetic cover 15 surrounding the laser resonator 30, the base component 12, the temperature control element 13 and the heat sink 14
The laser resonator 30 is fixed to the bottom plate 16 of the laser device case 18 in an airtight manner so that the pressure of the air in the laser beam path is constant. Further, in order to improve the airtightness of the airtight cover 15 with the bottom plate 16 of the solid-state laser device case 18, it is preferable to provide a flange 15a at the bottom of the airtight cover 15 and fix the flange 15a to the bottom plate 16 via a sealing material 20. .

The hermetic cover 15 is provided with openings 15a and 15b at positions where the laser beam passes.
Transparent bodies 19a and 19b are adhered to the outside of 15b. The transparent bodies 19a and 19b are preferably made of a material having a high transparency and a low laser beam absorbing ability, such as a quartz glass or a transparent plastic plate. The adhesive is not particularly limited as long as it can maintain airtightness in the airtight cover 15 sufficiently. Also, instead of using an adhesive, a transparent body 19
a and 19b may be bolted around the opening of the airtight cover 15.

[0039]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 A laser device shown in FIG. 1 having an airtight cover 15 was installed in a pressure control chamber, and the pressure in the chamber was set to 1002 hPa.
The wavelength of the fundamental wave of the laser resonator 30 and the output of the second harmonic laser light were measured by alternately changing the width of the laser resonator 30 between 10 hPa and 992 hPa. FIG. 6 shows the measurement results. Even when the external pressure changed by 10 hPa, the wavelength of the fundamental wave changed only slightly to 0.001 nm or less. Also, the output of the second harmonic laser light hardly changed. From now on, the bottom plate of the laser device case 18
It was confirmed that the hermetic cover 15 fixed to 16 was effective in keeping the oscillation wavelength of the laser light constant.

COMPARATIVE EXAMPLE 1 As shown in FIG. 2, the same solid-state laser device as in Example 1 was installed in a pressure control chamber except that the airtight cover 15 was not fixed, and the pressure in the chamber was increased to 10 hPa between 998 hPa and 988 hPa.
The wavelength of the fundamental wave of the laser resonator 30 and the output of the second harmonic laser light were measured. FIG. 7 shows the measurement results. A change in the atmospheric pressure of 10 hPa caused a change in the wavelength of the fundamental wave of about 0.002 nm. Therefore, the output of the second harmonic laser light also fluctuates, and the wavelength fluctuation is within about 15% of the level obtained in accordance with the equation (1), that is, 0.0015 nm or less, especially 0.1 mm.
The objective of suppressing the thickness to 001 nm or less could not be achieved.

[0042]

As described in detail above, since the solid-state laser device of the present invention has an airtight cover for isolating the laser resonator from the outside air pressure, the output light is substantially output even when the outside air pressure fluctuates greatly. It is very stable with low noise without fluctuation. Therefore, the solid-state laser device of the present invention can be used without a large output fluctuation regardless of the weather or the place accompanied by the fluctuation of the atmospheric pressure.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a solid-state laser device according to one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a solid-state laser device without an airtight cover.

FIG. 3 is a schematic diagram showing a specific configuration example of the solid-state laser device of the present invention.

FIGS. 4A and 4B schematically show a mode competition phenomenon, in which FIG. 4A is a schematic view showing a state in which five competing output laser beams are present, and FIG. 4B is a laser output when a mode competition phenomenon occurs. (C) is a schematic diagram showing single longitudinal mode oscillation, and (d) is a graph showing output of oscillation laser light in the case of single longitudinal mode oscillation.

FIG. 5 is a graph showing a relationship between an external pressure and an output wavelength.

FIG. 6 is a graph showing how the wavelength of the fundamental wave and the output of the second harmonic laser light change with time when the external pressure changes with time in the experiment of Example 1.

FIG. 7 is a graph showing how the wavelength of the fundamental wave and the output of the second harmonic laser light change with time when the atmospheric pressure changes with time in the experiment of Comparative Example 1.

Continued on the front page (72) Inventor Taisei Matsumoto 450, Niibori Nitta, Kumagaya-shi, Saitama Prefecture (72) Inventor Satoshi Makio 202-10, Jorokuma, Kumagaya-shi, Saitama 202-72 (72) Inventor Hidenobu Ishida, Kumagaya-shi, Saitama Shinbori Nitta 450 Wajiang dormitory (72) Inventor Masazumi Sato 4-12-13, Toho-cho, Fukaya-shi, Saitama (72) Inventor Tetsuo Ando 80301, Colorado, U.S.A., Boulder, Zu In Lakes Road 4870 No. 12 Room (72 Inventor Bernard Masterson Boulder, 80303, Colorado, U.S.A., 945, 36th Avenue

Claims (16)

[Claims] 1. A laser resonator is formed by disposing a solid-state laser crystal between a pair of mirrors, and the solid-state laser crystal is excited by an excitation light source provided outside the laser resonator.
An optically-pumped solid-state laser device for obtaining a required laser beam, comprising: means for keeping an effective optical path length of the laser resonator substantially constant. 2. The solid-state laser device according to claim 1, wherein the means for keeping the effective optical path length of the laser resonator substantially constant is such that at least the refractive index of a medium in the effective optical path of the laser resonator is constant. A solid-state laser device, characterized in that the device is a member to be kept. 3. The solid-state laser device according to claim 1, wherein the means for keeping the effective optical path length of the laser resonator substantially constant is fixed to a bottom plate of a case of the solid-state laser device in an airtight manner. A solid-state laser device, wherein the pressure inside the airtight cover is constant. 4. A laser resonator is formed by disposing a solid-state laser crystal between a pair of mirrors, and the solid-state laser crystal is excited by a semiconductor laser provided outside the laser resonator. In a solid-state laser device of an internal resonance type in which a laser beam of a required wavelength is obtained by being incident on a wavelength conversion element formed of a non-linear optical medium disposed in a vessel, at least the laser resonator is surrounded by an airtight cover, and atmospheric pressure fluctuations around the laser resonator are changed. A solid-state laser device, wherein the pressure inside the airtight cover is kept constant irrespective of this, whereby the effective optical path length of the laser resonator is kept substantially constant, so that the output wavelength is kept substantially constant. . 5. The solid-state laser device according to claim 3, wherein the airtight cover is fixed to the bottom plate so as not to transmit mechanical deformation or stress to the laser resonator. Laser device. 6. The solid-state laser device according to claim 3, wherein the hermetic cover does not exert a compressive stress or a tensile stress on each component of the laser resonator and a base component supporting each component. A solid-state laser device characterized by the above-mentioned. 7. The solid-state laser device according to claim 6, wherein said base component is fixed to a heat sink via temperature control means, and said heat sink does not directly contact said airtight cover. 8. The solid-state laser device according to claim 2, wherein said medium is a gas. 9. The solid-state laser device according to claim 1, wherein said laser resonator has a wavelength selection element for enabling single longitudinal mode oscillation. . 10. The solid-state laser device according to claim 9, wherein the wavelength selection element includes a birefringent filter or an etalon element. 11. The solid-state laser device according to claim 1, wherein high-frequency noise included in output of a laser beam is reduced. 12. The solid-state laser device according to claim 3, wherein a pressure in the airtight cover is lower than an external pressure. 13. The solid-state laser device according to claim 4, wherein the variation range of the output wavelength is an FSR of the laser resonator (= λ ² / 2L _cavity , where λ is a wavelength, and L _{wherein the cavity} is the length of the laser _cavity .). 14. The solid-state laser device according to claim 1, wherein a fluctuation width of the output wavelength is 0.0015 nm.
A solid-state laser device, wherein 15. The solid-state laser device according to claim 14, wherein a fluctuation width of the output wavelength is within a range of 0.001 nm. 16. (a) a semiconductor laser emitting excitation light, (b)
A laser resonator including a pair of mirrors, a solid-state laser crystal that receives the excitation light and emits a fundamental wave, a wavelength selection element, and a wavelength conversion element that receives the fundamental wave and emits a second harmonic laser light, c) a focusing optical system arranged between the semiconductor laser and the laser resonator to focus the pumping light on the solid-state laser crystal, and (d) a base supporting all components in the laser resonator. Component, (e) temperature control means fixed to the bottom surface of the base component, (f) a heat sink fixed to the bottom surface of the temperature control means and supported by a bottom plate of a case of the solid-state laser device, and g) an airtight cover surrounding the laser resonator, the base component, the temperature control means, and the heat sink, the airtight cover being hermetically fixed to the bottom plate of the solid-state laser device, and of Solid-state laser apparatus characterized by having a substantially substantially airtight cover that maintains a constant refractive index of air in the laser beam path of the laser resonator by keeping constant the force.