JP2011081075A - Wavelength conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength conversion device which makes it possible to use an oscillator over a long term even in a situation that a place where the wavelength conversion device is installed is a place where disassembly adjustment work or replacement work can not be performed such as an aircraft. <P>SOLUTION: The wavelength conversion device includes: a pair of mirrors 5 and 6 constituting a resonator which reflects a laser beam having predetermined wavelength; a nonlinear optical crystal 4 provided in the resonator constituted of the pair of mirrors 5 and 6, and converting the laser beam having oscillation wavelength made incident from an incident surface and emitting the laser beam having conversion wavelength from an emitting surface; and an optical path shift mechanism 12 shifting the optical path of the laser beam made incident from one mirror 5 on the incident surface of the nonlinear optical crystal 4 from an optical axis of the laser beam, and emitting the transmitted light emitted from the emitting surface to the other mirror 6. If a damaged portion is caused on the incident surface of the nonlinear optical crystal 4, the optical path shift mechanism 12 makes the laser beam incident on a position kept away from the damaged portion on the incident surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wavelength converter.

  2. Description of the Related Art An optical parametric oscillator (OPO: optical parametric oscillator) that generates laser light having a wavelength converted by a nonlinear optical effect is known as a laser light wavelength converter.

  FIG. 4 is a configuration diagram of a conventional wavelength converter. The wavelength converter 50 is an optical parametric oscillator that receives the excitation light 56, performs wavelength conversion, and emits an OPO output light 57. The wavelength conversion device 50 includes a wavelength conversion crystal 51, a total reflection mirror 52 and an output mirror 53 that constitute a resonator with the wavelength conversion crystal 51 interposed therebetween, a pumping laser oscillator 54, and a condensing lens for condensing light. 55.

  The total reflection mirror 52 is a mirror that maximizes the amount of transmission with respect to the excitation light 56 and maximizes the amount of reflection with respect to the OPO light 57 generated by oscillation in the resonator. The output mirror 53 is a partial reflection mirror having a reflectance of, for example, 80%, and transmits several tens of percent, for example, 20% of laser light generated by oscillation in the resonator.

  The excitation light 56 is collected from the total reflection mirror 52 side by the condenser lens 55 and is incident on the wavelength conversion crystal 51. In order to maintain optical parametric oscillation, the pump light 56 requires high peak power and average output. The intensity of the laser beam at the resonator is greater than the intensity of the output laser beam.

  The intensity of the excitation light 56 suddenly increases for some reason, or the light intensity distribution on the irradiation surface of the wavelength conversion crystal 51 fluctuates, and the light intensity locally increases on the irradiation surface. Of the incident surface and the exit surface of the wavelength conversion crystal 51, the incident surface on the input side of the excitation light 56 is damaged, and the wavelength conversion device 50 cannot perform wavelength conversion.

  In this case, the wavelength conversion crystal 51 is rearranged so that the laser beam is irradiated at a position avoiding the damaged portion, or the wavelength conversion crystal 51 itself is replaced. After disassembling the wavelength conversion device 50, replacing the wavelength conversion crystal 51 with a normal crystal, and assembling components, it is necessary to adjust the wavelength conversion device 50.

  Conventionally known as a countermeasure against deterioration of the optical element is a laser device provided with a moving means for moving the irradiation position of the input laser light to the optical element to a portion not deteriorated by the irradiation of the input laser light (for example, Patent Documents). 1).

JP 2004-228222 A

  However, in the above-described prior art, when a wavelength conversion device is installed in a place where maintenance cannot be performed, the wavelength conversion device cannot be disassembled and adjusted. For example, once the wavelength conversion device 50 is installed in an aircraft, it is extremely difficult or practical to remove the wavelength conversion device 50 and readjust the position of the wavelength conversion crystal 51 in terms of schedule, procedure, and cost. Can not do.

  Therefore, in view of the above problems, the present invention makes it possible to use the oscillator for a long period of time even in a situation where the wavelength conversion device is installed in a place where it cannot be disassembled and replaced, such as an aircraft. An object of the present invention is to provide a wavelength conversion device that performs the above-described operation.

  In order to solve such a problem, according to one aspect of the present invention, a pair of mirrors that constitute a resonator that reflects laser light of a predetermined wavelength, and the pair of mirrors provided in the resonator and incident thereon A nonlinear optical crystal that converts laser light having an oscillation wavelength incident from a surface and emits laser light having a converted wavelength from an emission surface, and an optical path of laser light incident from one mirror on the incident surface of the nonlinear optical crystal An optical path shift mechanism that shifts from the optical axis of the laser light and emits the transmitted light emitted from the exit surface to the other mirror, and this optical path shift mechanism is damaged on the entrance surface of the nonlinear optical crystal. When a site is generated, a wavelength conversion device is provided in which the laser beam is incident on a position where the damaged site is avoided on the incident surface.

  According to the present invention, the oscillator can be used for a long period of time without any work such as disassembly adjustment and replacement.

It is a block diagram of the wavelength converter which concerns on one Embodiment of this invention. It is a figure for demonstrating the optical path of the wavelength converter of FIG. 1 after an optical path shifted. It is a block diagram of the wavelength converter which concerns on the modification of one Embodiment of this invention. It is a block diagram of the conventional wavelength converter.

  Hereinafter, a wavelength converter according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. In the drawings, the same portions are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a configuration diagram of a wavelength converter according to an embodiment of the present invention. In the same figure, each side surface of the two flat plate members 7 and 10 is shown. The wavelength conversion device 1 is an optical parametric oscillator that emits laser light having a wavelength of 4 μm by converting the wavelength of laser light having a wavelength of 2 μm, for example.

  The wavelength conversion device 1 includes a condenser lens 3 that condenses the input laser light 2, a wavelength conversion crystal 4 (nonlinear optical crystal) having a function of converting the wavelength of laser light having a wavelength of 2 μm into laser light having a wavelength of 4 μm, and The total reflection mirror 5 (one mirror) and the output mirror 6 (the other mirror), which are provided with the wavelength conversion crystal 4 in between and form a pair to form a resonator, the total reflection mirror 5 and the wavelength conversion Between the first parallel flat plate 7 (first flat optical element) provided between the crystals 4 so as to cross the optical axis of the light beam from the condenser lens 3, and between the output mirror 6 and the wavelength conversion crystal 4. And a second parallel flat plate 8 (second flat optical element) provided so as to cross the optical axis. The parallel plates 7 and 8 are both light-transmitting optical elements, and the material is, for example, glass.

  Further, the wavelength conversion device 1 includes a pair of hollow rotary stages 9 and 10 that rotatably support the parallel flat plates 7 and 8 around the axis of the parallel plates 7 and 8 intersecting the optical axis. A stage driving device 11 (driving means) for rotating the rotating stages 9 and 10 to a desired rotational position and then stopping the rotating stages 9 and 10 is provided. The parallel plates 7 and 8, the rotary stages 9 and 10, and the stage driving device 11 constitute an optical path shift mechanism 12.

The condenser lens 3 forms a light beam of laser light having a wavelength of 2 μm. The wavelength conversion crystal 4 is a nonlinear optical crystal formed of ZGP (ZnGeP ₂ ) or the like. The wavelength conversion crystal 4 has a rectangular parallelepiped shape. In the wavelength conversion crystal 4, one of the six surfaces is an incident surface on which a light beam is incident, and the other surface opposite to the one surface is an emission surface that emits laser light having a converted wavelength transmitted through the crystal. It is incorporated.

  The total reflection mirror 5 is a mirror that maximizes the amount of transmission with respect to excitation light and maximizes the amount of reflection with respect to OPO light generated by oscillation inside the resonator. That is, the total reflection mirror 5 totally transmits a laser beam having a wavelength of 2 μm and totally reflects a laser beam having a wavelength of 4 μm. The output mirror 6 is a partial reflection mirror having a reflectance of, for example, 80%, and transmits, for example, 20% of laser light having a wavelength of 4 μm generated by oscillation inside the resonator.

  The pair of parallel flat plates 7 and 8 are light-transmitting optical elements that are arranged to face each other with the wavelength conversion crystal 4 in between and processed into a flat plate shape. Two opposing surfaces having a large area among the six surfaces of the parallel plate 7 are used as a laser light incident surface and a laser light emission surface, respectively. The incident surface and the exit surface are formed in parallel with each other, and the entrance surface and the exit surface are coated to prevent reflection of light having an oscillation wavelength.

  The parallel plate 7 receives the laser beam from the total reflection mirror 5 at a light receiving angle inclined with respect to the plane orthogonal to the optical axis, and the laser beam incident from the incident surface to the incident surface of the wavelength conversion crystal 4. And an exit surface that exits vertically. The parallel plate 8 receives laser light emitted from the output surface of the wavelength conversion crystal 4 through the wavelength conversion crystal 4 from the parallel plate 7 at a light reception angle symmetric with respect to the light reception angle of the parallel plate 7 and the optical axis orthogonal plane. And a light emitting surface for emitting the laser light incident from the light incident surface perpendicularly to the surface of the output mirror 6. These parallel flat plates 7 and 8 are paired to emit laser light from the total reflection mirror 5 to the incident surface of the wavelength conversion crystal 4 in a direction inclined with respect to the optical axis, and from the emission surface of the wavelength conversion crystal 4. Are emitted to the output mirror 6 in parallel with the optical axis.

  The rotary stages 9 and 10 are members that hold the pair of parallel flat plates 7 and 8 in an inclined state with respect to the optical axis orthogonal plane. The surfaces of the rotary stages 9 and 10 are orthogonal to the optical axis of the laser light transmitted and output from the total reflection mirror 5. The rotational axes of the rotary stages 9 and 10 are made approximately coaxial with the optical axis in advance or are slightly shifted from the optical axis. These rotary stages 9 and 10 are annular frame members or cylindrical members, and each has a hollow portion through which laser light passes.

  The stage driving device 11 includes a stepping motor, a DC motor or an actuator (not shown), a power transmission member, a memory that stores a driver program that gives a signal of a rotation direction and a rotation amount to the motor and the actuator, and a processor that executes the driver program. And have. The rotary stages 9 and 10 are provided with a driving force for rotating around the optical axis from a shaft such as a motor via a power transmission member. While this driving force is not applied to the rotary stages 9, 10, the rotation is stopped.

  Further, the rotary stage 9 is provided with a tilt mechanism (not shown) for setting the tilt angle of the incident surface of the parallel plate 7 to a desired angle. As an example, the tilt mechanism has one end fixed to the peripheral edge of the rotary stage 9 and the other end positioned on the center side of the rotary stage 9 so that the outer side (total reflection mirror 5 side) and the inner side (wavelength conversion crystal 4 side). ) A plate-shaped pedestal, a spring that urges a restoring force toward the inside with respect to the other end of the pedestal, and a rotating stage with the other end against the spring restoring force. The screw screwed on 9 and the nail | claw-shaped latching tool which fixes the parallel plate 7 to a base are provided. By adjusting the screwing degree of the screw, the inclination of the pedestal is changed, and the tilt angle of the parallel plate 7 with respect to the optical axis is adjusted. The rotary stage 10 is also provided with a tilting mechanism having substantially the same configuration as that of the parallel plate 7 for setting the tilt angle of the incident surface of the parallel plate 8.

  An operation device can be connected to the stage driving device 11 via a communication interface or the like. An application program is mounted on this apparatus, and a rotation direction and a rotation amount are commanded to the application program via a person, so that the rotation stages 9 and 10 are rotated from the outside of the wavelength conversion apparatus 1. The angle can be adjusted. In the stage driving device 11, when a damaged part is generated on the incident surface of the wavelength conversion crystal 4, the rotation stage 9, 10 is rotated to shift the optical path of the laser light, and the position where the damaged part is avoided on the incident surface. A laser beam is incident on the laser beam.

  The wavelength conversion device 1 having the above-described configuration is mounted on, for example, an aircraft and performs wavelength conversion operation. When laser light having a wavelength of 2 μm is incident on the wavelength conversion device 1 from the outside through the condenser lens 3, the total reflection mirror 5 and the output mirror 6 are used as the resonator mirrors to enter a resonance state. Two signal wave lights and auxiliary wave lights having different wavelengths are generated by the second-order nonlinear optical effect of the wavelength conversion crystal 4. One or both of these lights are reflected by the output mirror 6, return on the optical axis, resonate with the total reflection mirror 5, resonate, and are amplified.

  When the incident surface is irradiated with the light beam by the condenser lens 3, the power power density at the spot position on the surface increases. If it continues to be used, scratches such as piercing with a needle occur at the spot irradiated position. The detection of the flaw is performed by providing, for example, an intensity detection means for detecting the light intensity on the output side of the wavelength conversion device 1. When the detection control means for monitoring the intensity detection information of the intensity detection means detects that the detection intensity of the laser beam has fallen below a predetermined threshold value, the rotary stage is rotated by a predetermined angle in any one direction with respect to the stage driving device 11. Command 9 and 10 to turn. Alternatively, after a certain time has elapsed, a command to turn the rotary stages 9 and 10 is output.

  FIG. 2 is a view for explaining an optical path in the wavelength conversion device 1 after the parallel plates 7 and 8 are rotated. In the figure, elements having the same reference numerals as those described above represent the same elements.

  The two parallel plates 7 and 8 installed on both ends of the wavelength conversion crystal 4 are both rotated by, for example, about 180 degrees. The stage driving device 11 stops the rotations after rotating the rotary stages 9 and 10 in the same direction. At the positions of the parallel plates 7 and 8 after the rotation, the laser light emitted from the total reflection mirror 5 is refracted by the light receiving surface of the parallel plate 7, and the refracted light passing through the parallel plate 7 is reflected on the parallel plate 7. The light is refracted and emitted at the other boundary surface, and the emitted light is incident perpendicular to the incident surface of the wavelength conversion crystal 4. The transmitted light passes through the wavelength conversion crystal 4 and enters the parallel plate 8 from the exit surface. The parallel plate 8 receives the light incident from the wavelength conversion crystal 4 in a state where the light receiving surface is inclined with respect to the optical axis orthogonal surface orthogonal to the optical axis of the laser light from the total reflection mirror 5. The refracted light refracted at the light receiving surface is again refracted at the other boundary surface of the parallel plate 8 and emitted. In this way, the stage driving device 11 shifts the optical path.

  As an example, the wavelength converter 1 is incorporated in an aircraft analyzer. In this analyzer, the outgoing light is guided into a vacuum vessel in which a sample gas is sealed, and an interaction between molecules is caused. When the mass spectrometer analyzes the ions generated by the interaction, a gas substance having a characteristic of absorbing a spectrum having a wavelength of about 4 μm can be specified, or the concentration of a specific gas can be analyzed.

  After the wavelength conversion device 1 is once installed in an aircraft analyzer, it cannot be disassembled and assembled after changing the spot position of the laser beam in terms of the aircraft schedule. It takes time to restore the operation of the optical parametric oscillator by performing the adjustment work. According to the wavelength conversion device 1 according to the present embodiment, the rotation amount of the optical path shift mechanism 12 can be specified from an equipment operation panel or the like in the aircraft while being mounted on the aircraft, and the wavelength conversion crystal 4 can be continuously used. It becomes possible.

  In addition, a plurality of types of gases contained in the sample gas can be specified by oscillating and outputting multi-wavelength laser light including a plurality of wavelengths in different wavelength bands as peaks. In this case, by providing a plurality of stages of the wavelength conversion device 1, a multi-wavelength laser beam having a plurality of different wavelength peaks is output, and the resultant substance obtained as a result of the interaction between molecules is sample-analyzed in the same manner as described above. It can be used for analysis.

  As described above, in the wavelength conversion device 1 according to the present embodiment, when the wavelength conversion crystal 4 is damaged for some reason, the optical path shift mechanism 12 shifts the optical path, and the damaged portion on the incident surface of the wavelength conversion crystal 4. Since the laser beam is incident at a position where the wavelength converter 1 is avoided, the damaged portion is avoided and the wavelength conversion device 1 can be used continuously. Even if the OPO crystal is damaged for some reason, the plate element can be rotated by external control. Therefore, the incident position of the wavelength conversion crystal 4 can be changed, and the damaged portion can be avoided. Accordingly, the laser oscillator can be used for a long period even in a situation where the wavelength converter 1 is installed at a place where it cannot be disassembled and replaced, such as an aircraft.

  A specific method for shifting the position of the damaged part is provided by external control to avoid the scratched part on the entrance surface.

(Modification)
In the above embodiment, the incident positions of the excitation light are changed using the parallel plates 7 and 8 installed at both ends of the wavelength conversion crystal 4, but instead, the wavelength conversion crystal 4 is orthogonal to each other in the X direction and the Y direction. You may comprise a wavelength converter so that it may install in the XY stage which can move to a direction linearly. In this case, the wavelength conversion apparatus installs an XY stage so that the XY plane is orthogonal to the optical axis, and this XY stage moves the wavelength conversion crystal 4.

  FIG. 3 is a configuration diagram of a wavelength converter according to a modification of the embodiment of the present invention. The above-mentioned symbols represent the same elements. The optical path shift mechanism 14 includes a linear motion stage 13 capable of reciprocating in the vertical direction on a vertical plane including the optical axis, and a stage driving device 11 that moves the linear motion stage 13 by a desired distance and then stops it. ing. The linear motion stage 13 includes, as an example, a track (not shown) extending in the vertical direction and a rolling or sliding member guided so as to be able to advance and retreat on the track, and is driven by a motor or an actuator constituting the stage driving device. It moves up and down by force and stops while no driving force is applied.

  When laser light is incident on the wavelength conversion device 1A having such a configuration from the outside via the condenser lens 3, resonance occurs with the total reflection mirror 5 and the output mirror 6 as resonator mirrors. As a result of continuing to irradiate the incident surface of the wavelength conversion crystal 4 with the light beam from the condensing lens 3, scratches such as those struck with a needle occur at the spot irradiated position. When a flaw is detected or a certain time has elapsed, distance information is commanded to the stage driving device 11 as in the example of the above embodiment.

  As shown in FIG. 3, the stage driving device 11 stops the movement by moving the linear motion stage 13 upward, for example, by a commanded distance. At this position, the laser beam emitted from the total reflection mirror 5 is directly incident on the incident surface of the wavelength conversion crystal 4. Through this wavelength conversion crystal 4, transmitted light enters the output mirror 6 from the exit surface, is reflected, and returns to the total reflection mirror 5. Thereafter, the reflection is repeated and a laser beam having a desired wavelength is amplified and output. In this way, the stage driving device 11 shifts the wavelength conversion crystal 4 and then shifts the optical path to cause mirror resonance. The optical axis of the irradiation optical system and the optical axis of the imaging optical system are relatively shifted.

  According to the wavelength converter according to this modification, the optical path can be shifted even if the parallel plates 7 and 8 are fixed and the wavelength conversion crystal 4 is moved.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In the above embodiment, for example, a light-transmitting prism lens may be used as the pair of flat optical elements. The wavelength of 4 μm is an example, and laser light having a different wavelength can be wavelength-converted, and can be used for laser welding by outputting laser light having a specific wavelength with high intensity.

  In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1,1A ... Wavelength conversion apparatus, 2 ... Laser beam, 3 ... Condensing lens, 4 ... Wavelength conversion crystal (nonlinear optical crystal), 5 ... Total reflection mirror (one mirror), 6 ... Output mirror (the other mirror) , 7, 8... Parallel plate (flat optical element), 9, 10... Rotating stage, 11... Stage driving device (driving means), 12, 14.

Claims (4)

A pair of mirrors constituting a resonator that reflects laser light of a predetermined wavelength;
A nonlinear optical crystal that is provided in the resonator of the pair of mirrors, converts laser light having an oscillation wavelength incident from an incident surface, and emits laser light having a converted wavelength from an emission surface;
An optical path shift mechanism that shifts the optical path of the laser light incident on the incident surface of the nonlinear optical crystal from one mirror from the optical axis of the laser light and emits the transmitted light emitted from the exit surface to the other mirror And comprising
This optical path shift mechanism is characterized in that, when a damaged part is generated on the incident surface of the nonlinear optical crystal, the laser beam is incident on a position avoiding the damaged part on the incident surface. The optical path shift mechanism is
The non-linear optical crystals are arranged opposite to each other, the laser beam from the one mirror is emitted in a direction inclined with respect to the incident surface in the direction of the optical axis, and the emitted light from the emission surface is parallel to the optical axis. A pair of optically transparent plate-like optical elements that are emitted to the other mirror,
A pair of rotary stages that hold the pair of flat optical elements in a state inclined with respect to the optical axis orthogonal plane, and that can adjust the rotation angle;
Drive means for rotationally driving these rotary stages,
2. The wavelength conversion apparatus according to claim 1, wherein the drive unit rotates the pair of rotary stages after a predetermined angle and then stops and shifts the optical path. The pair of flat optical elements includes:
A surface provided on one rotary stage for receiving laser light from the one mirror at a light receiving angle inclined with respect to the plane orthogonal to the optical axis, and the laser light incident from this surface being incident on the nonlinear optical crystal A first light-transmitting flat plate having a surface emitting perpendicular to the surface;
Laser light emitted from the exit surface of the nonlinear optical crystal from the first light-transmitting flat plate provided on the other rotation stage and passing through the nonlinear optical crystal with respect to the light receiving angle and the optical axis orthogonal plane A second light-transmitting light flat plate having a surface that receives light at a symmetric light receiving angle and a surface that emits laser light incident from the surface perpendicular to the surface of the other mirror. The wavelength conversion device according to claim 2. The optical path shift mechanism is
A linear motion stage capable of reciprocating in a direction orthogonal to the optical axis on a plane orthogonal to both the plane including the optical axis of the laser beam incident from the one mirror and the optical axis orthogonal plane;
Driving means for driving the linear motion stage to be displaced,
2. The wavelength conversion apparatus according to claim 1, wherein the driving unit moves the linear motion stage by a given distance, stops the linear movement stage, and shifts the optical path.

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