JP2005019428A - Laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a laser in which output power of laser light is regulated without varying the characteristics of output laser light and the plane of polarization can be varied continuously. <P>SOLUTION: Laser rods 13 and 14, a pair of mirrors 10 and 11, and an output variable means A are enclosed in a container T. The output variable means A is provided with a half wavelength plate and a polarizer. A laser light pumped in the laser rods 13 and 14 is reflected between a pair of mirrors 10 and 11 of a resonator R and amplified. The laser light from the resonator R is received by the half wavelength plate and the plane of polarization is rotated. The laser light passed through the half wavelength plate is received by the polarizer and a direct light, i.e. a first polarized light, is separated from a branch light, i.e. a second polarized light. Intensity of the second polarized light is detected by a photodetection means and rotation of the half wavelength plate is controlled such that the intensity of the first polarized light becomes constant based on the output from a photodetector. The first polarized light is outputted to the outside from an output window W provided in the container T. When the half wavelength plate and the polarizer are rotated in a specified relation, the plane of polarization of the output laser light can be varied continuously. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser apparatus, and more particularly to a laser apparatus that can stably output a high-power laser beam suitable for a processing machine, an exposure apparatus, etc. for a long period of time.
[0002]
[Prior art]
Conventionally, a solid-state laser device that emits light of a short wavelength with a combination of a solid-state laser medium and a nonlinear optical crystal is used as a fine processing device or an illumination device for exposure. This type of solid-state laser device is required to have accurate output control in addition to extremely small fluctuations in the output of the laser in order to perform processing on the workpiece in a stable state with a small size and high output. ing. A semiconductor laser light source used as an excitation light source for exciting a solid-state laser medium has been increased in output. At the same time, a solid-state laser device has been researched and developed for higher output and higher efficiency. In addition, there is a demand for higher output and higher efficiency as well as downsizing of the laser device, and it is desired to be able to adjust the output of the laser light safely and even when the laser device is in use. Several examples of conventional laser devices are given below.
[0003]
Patent Document 1 discloses a solid-state laser device in which a resonator is miniaturized by using a prism. As shown in FIG. 6, the solid-state laser device disclosed in Patent Document 1 includes a solid-state laser medium and a polarizer on a first optical axis between a reflecting mirror and a trapezoidal prism. A Pockels cell and a quarter-wave plate are provided on the second optical axis between the reflecting mirror and the trapezoidal prism. In this solid-state laser device, light that has passed through the solid-state laser medium from the polarizer side is equivalently transmitted through the half-wave plate in the reflecting mirror. That is, it passes through the quarter-wave plate, is reflected by the half mirror, and passes through the quarter-wave plate again. Then, in the resonator between the reflecting mirrors, the light stimulated and emitted in the solid-state laser medium excited by the excitation means reciprocates in the resonator on the optical axis folded back by the trapezoidal prism. Laser oscillation.
[0004]
Patent Document 2 discloses an exposure illumination device that can accurately control the amount of light during exposure without using a mechanical shutter. As shown in FIG. 7, the light source of the exposure illumination device generates ultraviolet light in a predetermined polarization state. A polarization state of light from the light source is changed by a half-wave plate which is a polarization control means. The light intensity control means is a polarizer that changes the intensity of light from the polarization control means in accordance with the polarization state. A part of the light from the light intensity control means is reflected by the beam splitter. The amount of reflected light from the beam splitter is detected by a photodetector. The polarization control means is controlled so that the amount of light detected by the photodetector is constant.
[0005]
Patent Document 3 discloses a solid-state laser device that can stably control the intensity even when high-power laser oscillation light is output. As shown in FIG. 8, on the first optical axis between the polarizer and the first reflecting mirror (left in the figure), the first optical having a solid-state laser medium and a first quarter-wave plate. There is a system. The reflecting surface of the first reflecting mirror is perpendicular to the first optical axis. There is a second optical system having a Pockels cell and a second quarter-wave plate on the second optical axis between the polarizer and the second reflecting mirror (lower right in the figure). The reflecting surface of the second reflecting mirror is perpendicular to the second optical axis. The polarizer transmits the first polarization component of the light incident along the first optical axis. The second polarization component orthogonal to the first polarization is reflected in the direction of the second optical axis. A solid-state laser medium is optically excited with an excitation light source to generate an inversion distribution. The rotation driving unit rotates the first quarter-wave plate with the first optical axis as the central axis. A part of the laser oscillation light transmitted through the polarizer is branched by a beam splitter. A light detector detects the intensity of the branched light. Based on the detected light intensity, the rotation drive unit is controlled by the control circuit. By adjusting the rotation angle of the first quarter-wave plate, the intensity of the laser oscillation light output from the solid-state laser device can be adjusted.
[0006]
[Patent Document 1]
JP-A-56-76587
[Patent Document 2]
JP-A-9-199394
[Patent Document 3]
Japanese Patent Laid-Open No. 11-97782
[0007]
[Problems to be solved by the invention]
However, in the solid-state laser device disclosed in Patent Document 1, the intensity of laser oscillation light can be adjusted to some extent by controlling the excitation means, but it is difficult to stably control the intensity of laser oscillation light. There is a problem that.
[0008]
In addition, the solid-state laser device disclosed in Patent Document 3 needs to include a second optical system having a first optical system and a quarter-wave plate, which causes a problem that the optical system becomes complicated. In addition, adjusting the laser output in the resonator also changes the laser output absorbed in the laser medium in the resonator, so the thermal gradient inside the laser medium changes and the optical path in the resonator changes. There is also a problem that the beam shape and properties of the laser light output outside the resonator change. On the other hand, if the user of the laser apparatus has an output adjusting means disposed outside the container, alignment with the laser optical axis output from the container is required, and dust countermeasures and safety measures are required. is there.
[0009]
In the device disclosed in Patent Document 2, consideration is given to adjusting or keeping the laser output constant, but due to long-term use, excitation light source deterioration, vibration, nonlinear optical crystal deterioration, etc. No consideration has been given to countermeasures for the case where the laser power itself required for processing the workpiece falls below the required specified value. That is, in the LD (laser diode) pumped solid-state laser device, the laser output decreases with time because the optical axis of the resonator is shifted due to the lifetime of the pumping light source LD and the vibration of the LD-pumped solid-state laser device. In order to stably control the laser output for a long time, a method of increasing the LD current as the laser output decreases is a known technique. However, even if this technique is used, the time for keeping the LD at a constant output is about Since it is as short as 5000 hours, the life of the LD-pumped solid-state laser device affected by this is as short as possible, and further long-term stability of the laser output is required.
[0010]
LD-pumped solid-state laser devices for industrial use are often used with the laser output maintained at a certain set value. However, when laser output stability control is performed by increasing the LD current, the laser output of the LD depends on the life of the LD. When the laser power drops significantly, the laser output cannot satisfy the set value output. In such a state, the LD-pumped solid-state laser device must be stopped to repair the LD-pumped solid-state laser device. In addition, since it takes time for a repair person to come, the work process is greatly delayed. Therefore, it is required to provide a function for generating an alarm one step before the set value of the laser output is not satisfied, and to contact the LD pump laser device manufacturer in advance for quick repair. However, in the above-described stable output control, it is very difficult to predict or measure the time during which the laser output of the LD can be controlled to be constant. Therefore, it is impossible to issue an alarm one step before the laser output set value is not satisfied. there were. The same can be said for the deterioration of the nonlinear optical crystal as well as the LD.
[0011]
When the optical axis of the laser beam of the LD-pumped solid-state laser device is bent by a total reflection mirror, for example, when the total reflection mirror is arranged at an angle of ... with respect to the optical axis and the laser beam is bent in the direction ... Therefore, in order to bend the optical axis with a high output, it is necessary to adjust the angle of the polarization plane. As shown in FIG. 9 (a), the total reflection mirror is arranged at an angle with respect to the optical axis, and the reflectance when the optical axis of the laser beam is bent with the total reflection mirror is determined by the laser. Depending on the polarization plane (P wave, S wave) of light, the reflectance changes as shown in FIG. In order to adjust the angle of the polarization plane, there is a known technique of inserting a half-wave plate into the optical axis of the laser beam. .
[0012]
On the other hand, in an LD-pumped solid-state laser device for research use, characteristics of a nonlinear crystal or a polarizer that greatly depends on the polarization plane may be measured by continuously changing the polarization plane while keeping the output constant. As a known technique, there is a method in which a half-wave plate is inserted into the exit of an LD-pumped solid-state laser and rotated around the optical axis. When changing the laser output, the LD current is adjusted, so that the shape and properties of the beam may change. If the output is changed, the laser output cannot be stably maintained for a long time due to the influence of the life of the LD. There is a problem that the polarization plane cannot be continuously changed while the laser output is freely changed and the output is kept constant for a long time.
[0013]
The present invention solves the above-mentioned conventional problems, and even in the case of outputting high-power laser oscillation light, it is possible to safely and easily perform laser over a long period without changing the beam shape and properties of the laser light. An object of the present invention is to take out the output in a stable state and to continuously change the polarization plane of the laser while maintaining the output of the laser for a long time.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, a laser device having a resonator that reflects and amplifies laser light excited in a laser medium arranged between a pair of mirrors between the pair of mirrors, A half-wave plate that rotates the plane of polarization by receiving laser light from the resonator, a first polarization that is straight light and a second polarization that is branch light that receives the laser light transmitted through the half-wave plate. Based on the output of the light detector, the light detection means for detecting the intensity of the laser output from the polarizer, and the output of the photodetector so that the intensity of the laser output from the polarizer becomes a predetermined value. A drive control means for driving and controlling the / 2 wavelength plate, a container for housing the laser medium, a pair of mirrors, a half wavelength plate and a polarizer, and a container for outputting the first polarized light to the outside. And an output window. With such a configuration, optical components can be reduced, alignment of the optical components is facilitated, and laser output can be stabilized.
[0015]
In addition, an informing means for notifying that the intensity of the first polarized light is close to the intensity of the laser beam from the resonator based on the output of the photodetector is provided. With this configuration, the repair timing can be appropriately determined, and the operation efficiency is improved.
[0016]
Furthermore, a drive control unit is provided that adjusts the polarization plane without changing the beam shape and properties of the first polarization by rotating the half-wave plate and the polarizer. With this configuration, it is possible to continuously change the angle of the polarization plane while keeping the laser output constant for a long time without providing a special optical element.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.
[0018]
(First embodiment)
In the first embodiment of the present invention, laser light from a laser resonator is separated into straight light and branched light by a polarizer, and is provided immediately after the laser resonator according to the intensity detection value of the branched light. This is a solid-state laser device that rotates the two-wave plate to make the intensity of the straight light constant.
[0019]
FIG. 1 is a configuration diagram of a solid-state laser device according to a first embodiment of the present invention. In FIG. 1, mirrors 10 and 11 are a pair of reflecting mirrors. The laser rods 13 and 14 are laser media that generate a fundamental wave of 1064 nm. The fundamental wave may be another wavelength. The excitation modules 15 and 16 are units that excite light. The laser diodes 17 and 18 are devices that excite a laser medium with laser light. The beam splitter 19 is an optical element that transmits the harmonic laser beam and reflects the fundamental laser beam. The Q switch 20 is a switch that controls laser oscillation. The nonlinear optical crystals 21 and 22 are optical elements that generate harmonic laser light from fundamental laser light. The harmonic generation module 23 is a unit that generates harmonic laser light. The output variable means A is means for adjusting the intensity of the laser light. The optical axis L1 is the optical axis of the fundamental laser beam. The resonator R is a resonator that oscillates laser light. The container T is a container that houses a component that generates laser light. The 1st arm T1 is an arm part which accommodates an excitation part among containers. The 2nd arm T2 is an arm part which accommodates a harmonic generation part among containers. 3rd arm T3 is an arm part which accommodates an output adjustment means among containers. The output window W is a window for leading laser light from the container to the outside.
[0020]
This solid-state laser device includes an excitation module 15 including laser rods 13 and 14 which are laser media that generate a fundamental wave of 1064 nm on an optical axis L1 between a pair of mirrors 10 and 11 forming a resonator R. 16 are arranged in series. The laser rods 13 and 14 are, for example, Nd: YVO ₄ It is. These excitation modules 15 and 16 include laser diodes 17 and 18 on the side surfaces of the respective laser rods in order to excite the laser rods 13 and 14. In this example, two excitation modules are arranged in series, but may be three. A Q switch 20 is disposed between the mirror 10 and the excitation module 15.
[0021]
Between the excitation module 16 and the reflection mirror 11, a beam splitter 19 and a harmonic generation module 23 composed of nonlinear optical crystals 21 and 22 that generate the third harmonic are provided. In this example, LBO type II that generates the third harmonic is used. When generating the second harmonic, LBO type I is used. Other nonlinear optical crystals, KTP, KDP, LNO, BBO, CLBO may be used. Optical components such as the mirrors 10 and 11, the excitation modules 16 and 17, the beam splitter 19, and the harmonic generation module 23 are accommodated in a T-shaped container T. The container T further accommodates an output variable means A that adjusts the power of the harmonic laser beam separated from the beam splitter 19.
[0022]
Excitation modules 15 and 16 and a Q switch 20 are accommodated in a portion of the T-shaped first arm T1 with the beam splitter 19 as a boundary. The harmonic generation module 23 is accommodated in the portion of the T-shaped second arm T2. The output variable means A is accommodated in the T-shaped third arm T3. The container T is filled with an inert gas such as nitrogen so that the laser oscillates stably. As shown in FIG. 1, the output variable means A is disposed between the beam splitter 19 and an output window W provided on the T-shaped third arm T3.
[0023]
FIG. 2 is a schematic diagram of output varying means used in the solid-state laser device according to the first embodiment of the present invention. In FIG. 2, a half-wave plate 30 is a means for rotating the polarization plane of the output laser light from the resonator R. The polarizer 31 is means for separating a horizontal polarization component and a vertical polarization component. The motor 32 is means for rotating the half-wave plate 30. The motor 33 is means for rotating the polarizer 31. The photodetector 36 is means for detecting the intensity (power) of the laser beam branched by the polarizer 31. The drive control device 38 is a device that controls the motors 32 and 33. The logic circuit 40 is a circuit that performs a logical operation on the output signal of the photodetector 36 and outputs a predetermined signal corresponding to the output from the polarizer 31. The drive circuit 42 is a circuit that drives the motors 32 and 33 according to the calculation result of the logic circuit 40. The drive controller 38 includes a logic circuit 40 and a drive circuit 42 and is coupled to the photodetector 36. The switch 44 is a switching unit for driving the motor 33 from the outside. A switch 44 provided between the drive circuit 42 and the motor 33 of the polarizer 31 is for allowing the motor 33 to be driven independently from the outside of the container T as needed. The alarm unit 45 is a unit that issues an alarm according to the calculation result of the logic circuit 40. The output variable means A includes a half-wave plate 30, a polarizer 31, a motor 32, a motor 33, a photodetector 36, and a drive control device 38. The half-wave plate 30 and the polarizer 31 is on the laser optical axis L2.
[0024]
FIG. 3 is a graph (a) showing the laser output relative value (power) of the horizontal polarization of the laser when the half-wave plate is tilted by the angle θ in the solid-state laser device according to the first embodiment of the present invention. And (b) is a graph showing the output characteristics (amplitude) of the laser when the half-wave plate is tilted by an angle θ. FIG. 4 is a graph showing the time relationship between the laser output relative value of the solid-state laser device, the rotation angle of the half-wave plate, and time.
[0025]
The operation of the solid-state laser device according to the first embodiment of the present invention configured as described above will be described. First, an outline of functions of the solid-state laser device will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the laser light is repeatedly reflected between the first mirror 10 and the second mirror 11 to resonate at the fundamental frequency. The fundamental laser beam is converted into the third harmonic by the harmonic generation module 23. Only the converted third harmonic is taken out of the container T by the beam splitter 19 via the output variable means A.
[0026]
As shown in FIG. 2, the laser light (optical axis is L2) transmitted through the half-wave plate 30 built in the output variable means A is incident on the polarizer 31. The polarizer 31 corresponds to light having a wavelength of 355 nm, which is the third harmonic. The polarizer 31 is held on the optical axis L2 of the laser beam that has passed through the half-wave plate 30 at an angle that maximizes the transmission intensity of horizontally polarized light. The polarizer 31 functions as a light intensity control unit in cooperation with the half-wave plate 30. The intensity of the laser beam that passes through the polarizer 31 changes according to the angle of the polarization plane of the laser beam that has passed through the half-wave plate 30 (optical axis is L2). Laser light whose optical intensity is changed by passing through the polarizer 31 (the optical axis is L3) is emitted from the output window of the container T and irradiated to the workpiece, and is used for various processing. .
[0027]
Next, a method for adjusting the intensity of the output laser beam will be described with reference to FIGS. An example in which light from a light source is horizontally polarized will be described, but the same applies to vertically polarized light. The light from the light source may be linearly polarized light at a specific angle. In this example, it is assumed that the laser light output from the resonator R is horizontally polarized light. The rotation angle of the polarizer 31 is adjusted so that the horizontally polarized light that is the first polarized light is transmitted and the vertically polarized light that is the second polarized light is branched. The polarizer 31 holds the horizontally polarized light so that it is transmitted and the vertically polarized light is branched. When the half-wave plate 30 is rotated, the polarization plane of the laser light incident on the polarizer 31 is rotated. When the polarization plane of the laser beam from the resonator R (optical axis is L2) is rotated by the half-wave plate 30 and the output of the laser beam (optical axis is L3) becomes maximum, 1/2 of that time The angle θ of the wave plate 30 is set to 0 °. When polarized light from the half-wave plate 30 is passed through the polarizer 31, the horizontally polarized light component is transmitted. The vertically polarized component is branched by the polarizer 31 toward the photodetector 36.
[0028]
In this laser apparatus, the rotation angle of the half-wave plate 30 is taken as the angle, and the intensity output from the resonator R is F. _in And Intensity F of laser light transmitted through the polarizer 31 (optical axis is L2) _out Is
F _out = F _in cos ² (2θ)
It becomes. That is, in this laser apparatus, as shown in FIGS. 3A and 3B, the intensity F of the output light is F. _out Varies depending on the rotation angle θ of the half-wave plate 30. When a signal is given from the drive control device 38 to the motor 32 and the half-wave plate 30 is rotated by an angle θ, the laser light transmitted through the half-wave plate 30 (optical axis is L2) is the angle of the polarization plane. Becomes 2θ linearly polarized light. Intensity F of laser light (optical axis is L3) output through the polarizer 31 _out Changes continuously corresponding to the rotation angle θ of the half-wave plate 30. In this way, the intensity of the laser light (optical axis L3) emitted from the polarizer 31 can be continuously changed. Examples of the polarizer include a Glan laser prism, a Glan tailor prism, a Glan Thompson prism, and a polarization beam splitter.
[0029]
Third, a method for maintaining the intensity of the output laser beam at a predetermined value will be described with reference to FIG. The intensity of the laser beam on the optical axis L2 is F _in And F is the maximum intensity of the laser beam on the optical axis L2. _max And The intensity of the laser beam on the optical axis L3 is F _out And F _max The relative value with reference to is a laser output relative value. Intensity F of laser light (optical axis is L3) _out Is always the maximum output F of the laser beam (optical axis is L2) _max On the other hand, the logic of the logic circuit 40 is set so as to maintain a predetermined ratio (for example, 80%). The predetermined ratio may be such that the laser output relative value is within the range of 0.3 to 0.95. A value close to 1.0 is not practical because it becomes immediately uncontrollable. As shown in FIG. 4, in the initial use of the laser apparatus, the resonator R has the maximum output and the laser output relative value is 1. When a certain time elapses, the laser output relative value of the laser light of the resonator R decreases due to the temporal change of the laser medium and the excitation light source. For example, F _out Is set to 0.8, the rotation angle of the half-wave plate 30 is about 13.5 ° in the initial use of the laser device. In a state where the laser output relative value of the resonator R is 0.9, the rotation angle of the half-wave plate 30 is about 10 °.
[0030]
Specifically, the vertical polarization component branched from the polarizer 31 is detected by the photodetector 36, and the motor is generated by a signal output from the drive circuit 42 of the drive control device 38 according to the detection output from the photodetector 36. 32 is driven to rotate the half-wave plate 30. The polarization plane of the laser light (optical axis is L2) from the resonator R rotates according to the rotation angle. Even if the intensity of the laser beam from the resonator R decreases with time, the rotation angle θ of the half-wave plate 30 is reduced in accordance with the decrease in the intensity of the laser beam from the resonator R, so that the laser beam ( The optical axis can keep the intensity of L3) constant. For example, the rotation angle θ of the half-wave plate 30 and the vertical polarization intensity F detected by the photodetector 36. _v And
F _in = F _v (1 / sin ² (2θ))
And the intensity F of the laser beam of the resonator R _in Ask for. F _in To F _out Is F _max The rotation angle θ ′ of the half-wave plate 30 that is × 0.8 is
F _out = F _in cos ² (2θ ′) = F _max × 0.8
Find and solve. If the rotation angle of the half-wave plate 30 is θ ′, the intensity of the laser beam (optical axis is L3) can be kept constant. Since the light branched by the polarizer 31 originally provided in the laser device is detected by the photodetector 36, it is not necessary to provide a separate beam splitter on the optical axis L2 of the laser light for the photodetector 36. . This simplifies the alignment of the optical components, prevents the output from being reduced, and reduces the cost.
[0031]
F _in When the relative value of the laser output becomes 0.85, for example, the logic circuit 40 notifies the alarm means 45 to issue a warning to inform the user that the laser device needs to be repaired. In a state where the solid-state laser device stably controls the laser output, the relative value of the laser output can be known from the rotation angle θ around the optical axis of the half-wave plate 30. Maximum output value of initial laser light source (F _max ) To present laser output (F _in ). Output value of laser beam from resonator R (F _in )
F _in = (F _out ) X (1 / cos ² (2θ))
Calculate from Current laser power (F _in ) Is the set value (F _out ), An alarm can be issued when it becomes difficult to control the output stably. For example, an alarm is issued when the relative output value of the resonator R approaches 0.8 and it becomes difficult to stably control the output. It can be effectively used for early repair of the laser device.
[0032]
Fourth, a method for rotating the polarization plane of the laser light will be described. When the half-wave plate 30 is rotated around the optical axis by an angle θ, the polarization plane of the laser light emitted from the half-wave plate 30 is rotated by an angle 2θ. When the polarizer 31 is rotated around the optical axis by the angle θ, the polarization plane of the emitted laser light is rotated by the angle θ. The ratio of the rotational angular velocity of the motor 33 that rotates the polarizer 31 and the rotational angular velocity of the motor 32 that rotates the half-wave plate 30 is set to 2: 1, and they are rotated simultaneously. When the half-wave plate 30 is rotated by the angle θ by the rotation of the motor 32, the polarization plane of the laser light between the half-wave plate 30 and the polarizer 31 is rotated by the angle 2θ. When the polarizer 31 is rotated by the angle 2θ by the rotation of the motor 33, the polarization plane of the emitted laser light is rotated by the angle 2θ. In this way, since the laser output does not change during the rotation of the polarization plane, the rotation angle speed ratio of the polarizer 31 and the half-wave plate 30 is set to 2: 1, and the polarization plane is rotated simultaneously. By doing so, the laser output can be kept constant for a long time. In this way, the angle of the polarization plane can be continuously changed while keeping the laser output constant. At this time, the contact of the switch 44 is connected to the a contact side. In order to adjust the alignment of the half-wave plate 30 and the polarizer 31, the switch 44 is connected to the contact b side, and the motor 33 of the polarizer 31 may be rotated independently from the outside.
[0033]
As described above, in the first embodiment of the present invention, the solid-state laser device separates the laser light from the laser resonator into straight light and branched light with a polarizer, and according to the intensity detection value of the branched light, Rotating the half-wave plate provided immediately after the laser resonator to make the intensity of the straight light constant, so that the optical parts can be reduced, the optical parts can be easily aligned, and the laser output is stable. Can be
[0034]
(Second Embodiment)
In the second embodiment of the present invention, output laser light from a polarizer is branched by a beam splitter, the branched light is guided to a photodetector to detect the intensity, and a half-wave plate is driven. This is a solid-state laser device that controls the intensity of output laser light to be constant.
[0035]
FIG. 5 is a schematic diagram of the output variable means A used in the solid-state laser device according to the second embodiment of the present invention. In FIG. 5, a beam splitter 50 is an optical element that branches a part of laser light. The damper 52 is a means for absorbing the light branched from the polarizer 31. The output variable means A includes a half-wave plate 30, a polarizer 31, a motor 32, a motor 33, a photodetector 36, a drive control device 38, a logic circuit 40, and a motor drive circuit 42. The switch 44 is provided. Alarm means 45 is connected to the logic circuit 40. The half-wave plate 30 and the polarizer 31 are on the laser output optical axis L2. The motor 32 drives the half-wave plate 30 to rotate. The motor 33 rotates the polarizer 31. The drive controller 38 is coupled to the photodetector 36. The logic circuit 40 is built in the drive control means. Although not shown, a switch 44 is provided between the drive circuit 42 and the motor 33 to drive and control the motor 33 from the outside of the container T as necessary, as in the first embodiment. Yes. The drive control device 38 includes a logic circuit 40 that receives the output of the photodetector 36 and a drive circuit 42 for the motors 32 and 33. Parts that are the same as in the first embodiment are indicated with the same reference numerals. 2 differs from the first embodiment shown in FIG. 2 in that a beam splitter 50 is disposed on the optical axis L3 of the laser light that is the output of the polarizer 31, and the light branched from the beam splitter 50 is converted into light. This is a point led to the detector 36.
[0036]
The operation of the solid-state laser device according to the second embodiment of the present invention configured as described above will be described. Since the method of rotating the half-wave plate 30 and adjusting the intensity of the output laser light is the same as that in the first embodiment, description thereof is omitted.
[0037]
A method for maintaining the intensity of the output laser beam at a predetermined value will be described. A beam splitter 50 arranged on the optical axis L3 branches a part (for example, 1%) of the laser light that is the output of the polarizer 31. The intensity of the branched laser beam is detected by the photodetector 36. Intensity F of laser light (optical axis is L3) _out Is the maximum output F of the laser beam (optical axis is L2). _max On the other hand, the logic of the logic circuit 40 is set so as to always maintain a predetermined ratio (for example, 80%). The half-wave plate 30 is rotated by driving the motor 32 by a signal output from the drive circuit 42 of the drive control device 38 so that the detection output from the photodetector 36 is constant. The polarization plane of the laser light (optical axis is L2) from the resonator R rotates according to the rotation angle. Even if the intensity of the laser beam from the resonator R decreases with time, the rotation angle の of the half-wave plate 30 is reduced in accordance with the decrease in the intensity of the laser beam from the resonator R, so that the laser beam ( The optical axis can keep the intensity of L3) constant. Since this control is simple feedback control, the logic of the logic circuit 40 is simpler than that of the first embodiment.
[0038]
With the laser output being stably controlled, the laser output from the resonator R can be obtained from the rotation angle θ around the optical axis of the half-wave plate 30. The laser output from the resonator R decreases from the maximum output value of the initial laser light source due to a change with time. Laser output from resonator R (F _in )
F _in = F _out × (1 / cos ² (2θ))
Calculated by F _out Is 0.8 × F _max It is. Laser output from resonator R (F _in ) Is F _out When there is no room and it becomes difficult to control the output stably, an alarm is issued. For example, F _out When the set value of 0.8 is 0.8 relative to the laser output relative value, F _in When the output relative value becomes 0.85, an alarm is issued. This is effective for early repair of the laser device.
[0039]
A method for rotating the polarization plane of the laser light will be described. When the half-wave plate 30 is rotated around the optical axis by an angle θ, the polarization plane of the emitted laser light is rotated by an angle 2θ. By the motor 32 and the motor 33, the polarizer 31 and the half-wave plate 30 are simultaneously rotated at a rotation angular velocity ratio of 2: 1. The angle of the polarization plane can be continuously changed while keeping the laser output constant for a long time. Since this point is the same as that of the first embodiment, detailed description thereof is omitted.
[0040]
As described above, in the second embodiment of the present invention, the solid-state laser device detects the intensity by branching the output laser light from the polarizer with the beam splitter and guiding the branched light to the photodetector. Since the half-wave plate is driven and the intensity of the output laser beam is controlled to be constant, the optical parts can be reduced, the optical parts can be easily aligned, and the laser output can be stabilized.
[0041]
【The invention's effect】
As apparent from the above description, in the present invention, a laser device having a resonator that reflects and amplifies laser light excited in a laser medium disposed between a pair of mirrors between the pair of mirrors, A half-wave plate that rotates the plane of polarization by receiving laser light from the resonator, a first polarization that is straight light and a second polarization that is branch light that receives the laser light transmitted through the half-wave plate. , A light detection means for detecting the intensity of the second polarized light, a drive control means for driving and controlling the half-wave plate based on the output of the light detector, a laser medium, a pair of mirrors, 1 / 2 Wave plate and polarizer are hermetically housed and an output window provided in the container for outputting the first polarized light to the outside. Alignment can be facilitated and laser output can be stabilized.
[0042]
Further, drive control means for driving and controlling the half-wave plate based on the output of the photodetector so that the intensity of the first polarization becomes a predetermined value, and the intensity of the first polarization based on the output of the photodetector. Since the notifying means for notifying that the intensity of the laser beam from the resonator is close is provided, it is possible to appropriately determine the repair timing and to improve the operation efficiency.
[0043]
In addition, since the drive control means for adjusting the polarization plane without changing the beam shape and properties of the first polarized light by rotating the half-wave plate and the polarizer, a long time without providing a special optical element is provided. The angle of the polarization plane can be continuously changed while keeping the laser output constant.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a solid-state laser device according to a first embodiment of the present invention;
FIG. 2 is a schematic diagram of output variable means used in the solid-state laser device according to the first embodiment of the present invention;
FIG. 3 is a graph showing a horizontal polarization laser output relative value of a laser when the half-wave plate is tilted by an angle θ in the solid-state laser device according to the first embodiment of the present invention; A graph showing the output characteristics of the laser when tilted by an angle θ,
FIG. 4 is a graph showing a laser output relative value of the solid-state laser device according to the first embodiment of the present invention, a rotation angle of a half-wave plate, and a time relationship;
FIG. 5 is a schematic diagram of output varying means of a solid-state laser device in a second embodiment of the present invention;
FIG. 6 is a conceptual diagram showing a configuration of a first example of a conventional solid-state laser device;
FIG. 7 is a conceptual diagram showing a configuration of a second example of a conventional solid-state laser device;
FIG. 8 is a conceptual diagram showing the configuration of a third example of a conventional solid-state laser device;
FIG. 9 is a graph showing the reflectivity of the beam splitter, S wave, and P wave of the laser device.
[Explanation of symbols]
10,11 mirror
13,14 Laser rod
15,16 Excitation module
17, 18 Laser diode
19 Beam splitter
20 Q switch
21, 22 Nonlinear optical crystal
23 Nonlinear optical module
30 1/2 wave plate
31 Polarizer
32, 33 motor
36 photodetectors
38 Drive control device
40 logic circuits
42 Drive circuit
44 switch
45 Alarm means
50 Beam splitter
52 Damper

Claims (7)

In a laser device having a resonator that reflects and amplifies laser light excited in a laser medium disposed between a pair of mirrors between the pair of mirrors, a polarization plane that receives the laser light from the resonator A polarizer that outputs laser light that has passed through the half-wave plate and outputs first polarized light that is straight light and second polarized light that is branched light, and this polarizer And a light detecting means for detecting the intensity of the laser output from the light source, and driving control of the half-wave plate based on the output of the photodetector so that the intensity of the laser output from the polarizer becomes a predetermined value. A drive control means, a container containing the laser medium, the pair of mirrors, the half-wave plate, and the polarizer, and an output provided in the container for outputting the first polarized light to the outside And a window Over laser device. In a laser device having a resonator that reflects and amplifies laser light excited in a laser medium disposed between a pair of mirrors between the pair of mirrors, a polarization plane that receives the laser light from the resonator A polarizer that outputs a first polarized light that is a straight-ahead light and a second polarized light that is a branched light upon receiving a laser beam transmitted through the half-wave plate; A beam splitter for branching a part of the polarized light; a light detecting means for detecting the intensity of the laser beam branched by the beam splitter; and the light detection so that the intensity of the laser output from the polarizer becomes a predetermined value. A drive control means for driving and controlling the half-wave plate based on the output of the detector, a container for housing the laser medium, the pair of mirrors, the half-wave plate, the polarizer, and the beam splitter; , Serial laser device characterized by comprising an output window provided in the container in order to externally output the first polarization. 3. The laser according to claim 1, further comprising an informing unit that informs that the intensity of the first polarized light is close to the intensity of the laser beam from the resonator based on an output of the photodetector. apparatus. The drive control unit includes a logic circuit that outputs a warning signal to the notification unit when a laser output from the resonator decreases and approaches a laser output from the output window. Item 4. The laser device according to any one of Items 1 to 3. The laser device according to claim 1, wherein the predetermined value is 0.3 to 0.95 of a maximum value of a laser output from the resonator. The drive control means is provided with means for adjusting the plane of polarization without changing the beam shape and properties of the first polarized light by rotating the polarizer according to the rotation of the half-wave plate. The laser device according to claim 1. The laser device according to claim 6, wherein the rotational angular velocity of the polarizer is twice the rotational angular velocity of the half-wave plate.

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