JP7116567B2 - Irradiation position detector - Google Patents

Description

The present invention relates to an irradiation position detection device for detecting an irradiation position for linearly polarizing a laser beam emitted from a laser oscillation device.

Q-switch laser devices and CW (Continuous Wave) laser devices using isotropic laser media such as Nd:YAG and Cr:YAG crystals as laser oscillation devices used for spectroscopic measurement, shape measurement, nonlinear crystal excitation, etc. There is For example, a Q-switched laser device is composed of a light-emitting portion that emits a laser beam of a predetermined wavelength, and an optical resonator. a laser medium and a saturable absorber disposed between a first dielectric reflector and a second dielectric reflector.

In a Q-switched laser device, a laser medium is excited by excitation laser light emitted from a light emitting portion, and spontaneous emission light emitted from the laser medium is absorbed by a saturable absorber. As the spontaneous emission light is absorbed, the electron density of the excitation level of the saturable absorber gradually increases, and the saturable absorber becomes transparent when the electron density is saturated. When the saturable absorber becomes transparent, laser oscillation occurs and pulsed light is emitted.

When performing wavelength conversion or shape measurement of pulsed light, it is desirable that the emitted pulsed light has the same polarization direction. However, in the case of the Q-switched laser device described above, when the frequency of the excitation laser light is set to several kHz or more, the polarization characteristic is such that the pulsed light is alternately polarized in orthogonal directions and emitted. Similarly, in the case of a CW laser device, emitted laser beams are alternately polarized in orthogonal directions and continuously oscillated. Therefore, conventionally, the polarization direction of pulsed light has been controlled by providing a polarizing element in the optical resonator.

Conventionally, there is also a method in which stress is applied to the laser medium from the outside and the laser beams are polarized in the same direction (linearly polarized light) by birefringence caused by internal strain generated inside the laser medium. However, in the conventional case, it is necessary to repeatedly irradiate a predetermined position of the laser medium with a laser beam and confirm whether or not the laser beam excited by this irradiation is linearly polarized over the entire surface, which increases the work. It was complicated and time consuming.

JP 2016-63063 A

SUMMARY OF THE INVENTION The present invention provides an irradiation position detection device that can easily specify the irradiation position on a laser medium in which pulsed light is linearly polarized light in a short period of time.

The present invention comprises a light-emitting portion that emits a laser beam, a medium holding portion that holds a laser medium and can move the laser medium to adjust the incident position of the laser beam, and the laser beam that has passed through the laser medium. A polarizing optical member that separates S-polarized light and P-polarized light, a first light quantity detector that detects the output of the S-polarized laser beam, a second light quantity detector that detects the output of the P-polarized laser beam, and a controller. and the control unit drives the medium holding unit so that the end face of the laser medium is scanned with the laser beam, and the first light amount detector and the first light amount detector for the laser beam that has passed through the laser medium. 2. An irradiation position configured to calculate an extinction ratio based on the detection result of the light amount detector, and detect an irradiation position where the extinction ratio is equal to or greater than a preset value as an irradiation position for linearly polarizing the laser beam. It relates to a detection device.

Further, according to the present invention, the control unit converts the laser beam into linearly polarized light only at irradiation positions where the sum of the detected values of the first light quantity detector and the second light quantity detector exceeds a preset threshold value. The present invention relates to an irradiation position detection device configured to detect the irradiation position of the .

Further, the present invention further comprises a phase difference camera capable of acquiring a phase difference distribution image and a phase difference direction arrow on the end face of the laser medium, the laser medium has birefringence inside, and one side of the laser medium has birefringence. The present invention relates to an irradiation position detecting device configured to detect the irradiation position only when the phase difference direction arrow perpendicular to the phase difference direction arrow exists.

Further, the present invention relates to an irradiation position detecting device, wherein the control section drives the medium holding section so that the laser beam scans a portion of the end surface of the laser medium excluding a predetermined range from the center thereof. is.

Further, the present invention is directed to an irradiation position detection device, wherein the control unit is configured to end scanning of the end surface of the laser medium with the laser beam when a preset number of the irradiation positions are detected. It is related.

According to the present invention, a light emitting part that emits a laser beam, a medium holding part that holds a laser medium and can move the laser medium to adjust the incident position of the laser beam, and the laser beam transmitted through the laser medium. a polarizing optical member that separates a light beam into S-polarized light and P-polarized light; a first light detector that detects the output of the S-polarized laser beam; a second light detector that detects the output of the P-polarized laser beam; The controller drives the medium holding unit so that the end surface of the laser medium is scanned with the laser beam, and the first light quantity detector for the laser beam transmitted through the laser medium; An extinction ratio is calculated based on the detection result of the second light quantity detector, and an irradiation position where the extinction ratio is equal to or greater than a preset value is detected as an irradiation position for linearly polarizing the laser beam. Therefore, the number of times of actually irradiating the laser medium with the excitation laser beam and checking the polarization direction of the emitted laser beam can be reduced, and the work for linearly polarizing the laser beam can be easily performed. At the same time, it exerts an excellent effect that the working time can be shortened.

1 is a configuration diagram showing an example of a laser oscillation device; FIG. FIG. 4 is an explanatory diagram showing a state in which pulsed light is alternately polarized in orthogonal directions and emitted. 1 is a configuration diagram showing an irradiation position detection device according to a first embodiment of the present invention; FIG. It is a front view which shows the holder and laser medium of this irradiation position detection apparatus. FIG. 4 is a flow chart for explaining a process of detecting an irradiation position according to the first embodiment of the present invention; FIG. FIG. 10 is an explanatory diagram for explaining a first output image showing the scanning order of the laser medium end surface and the divided regions; FIG. 10 is an explanatory diagram showing a second output image; FIG. 4 is an explanatory diagram showing an extinction ratio image; FIG. 4 is a configuration diagram showing an irradiation position detection device according to a second embodiment of the present invention; (A) and (B) are explanatory diagrams showing an example of an end surface of a laser medium photographed by a phase-contrast camera.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, with reference to FIG. 1, an example of a laser oscillation device 1 using a laser medium whose irradiation position of a laser beam is determined according to an embodiment of the present invention will be described. The laser oscillation device 1 is, for example, a Q-switched laser oscillation device, and is composed of a light emitting section 2 and an optical resonance section 3 . The light emitting unit 2 is composed of a light emitting device (not shown) for emitting laser light such as a semiconductor laser, a condensing lens (not shown) and the like. It's becoming

A required cooling means such as a Peltier element 10 is provided on the lower surface of the light emitting section 2 . The Peltier element 10 cools the light-emitting portion 2, thereby suppressing temperature rise of the light-emitting portion 2 when the excitation laser beam 4 is emitted.

The optical resonator 3 has a laser medium 5 as a first optical crystal and a saturable absorber 6 as a second optical crystal, and the laser medium 5 and the saturable absorber 6 are optical It has an integrated structure by means of contacts, thermal diffusion bonding, and the like. The incident surface of the laser medium 5 is a first resonator mirror 7 and the exit surface of the saturable absorber 6 is a second resonator mirror 8 . Furthermore, the laser medium 5 and the saturable absorber 6 are integrally held by a holder 9 .

As the laser medium 5, an Nd:YAG/Cr:YAG crystal is used, for example. The laser medium 5 is excited by the excitation laser beam 4 having a wavelength of 808 nm, amplifies the incident excitation laser beam 4, and emits spontaneous emission light (photons) (not shown) having a wavelength of 1064 nm. there is

A Cr:YAG crystal, for example, is used as the saturable absorber 6 . The saturable absorber 6 has the property of absorbing the spontaneous emission light emitted from the laser medium 5 . Moreover, the saturable absorber 6 has a property that the transmittance increases as the spontaneous emission light is absorbed, and becomes transparent when the electron density increases and the saturable absorber 6 becomes saturated. By making the saturable absorber 6 transparent, the pulsed light 11 having a wavelength of 1064 nm is emitted from the saturable absorber 6 .

The first resonator mirror 7 is highly transparent to the excitation laser light 4 from the light emitting section 2 and highly reflective to the spontaneous emission light emitted from the laser medium 5 . Also, the pulsed light 11 is emitted from the second resonator mirror 8 .

When the excitation laser beam 4 is emitted from the light emitting unit 2 , the excitation laser beam 4 passes through the first resonator mirror 7 and enters the laser medium 5 . The laser medium 5 is excited by the excitation laser beam 4 , and part of the spontaneous emission light generated at that time enters the saturable absorber 6 . As the spontaneous emission light is absorbed, the electron density of the saturable absorber 6 increases and when saturated, the saturable absorber 6 becomes transparent, and the pulsed light 11 passes through the second resonator mirror 8. injected.

When the saturable absorber 6 is removed from the laser oscillation device 1, continuous wave (CW) laser light is emitted from the laser oscillation device 1. FIG.

FIG. 2 shows an example of the polarization direction of the pulsed light 11 emitted from the laser oscillation device 1. As shown in FIG.

Normally, the excitation laser beam 4 is applied to the central portion of the laser medium 5 . In this case, the pulsed light 11 emitted from the saturable absorber 6 alternately generates a P-polarized pulse 11a and an S-polarized pulse 11b, and the polarization direction of the pulsed light 11 is unstable. This is the same when CW laser light is oscillated, and P-polarized light and S-polarized light are continuously oscillated alternately.

In the present invention, the inventors have found that the polarization of the pulsed light 11 can be changed depending on the irradiation position of the excitation laser light 4 with respect to the laser medium 5, even if stress is not applied to the laser medium 5 from the outside. It has been found that the direction may be linearly polarized. Furthermore, the inventors have found that this phenomenon is caused by internal residual stress occurring in the laser medium 5 .

The laser medium 5 may be subject to processing strain due to cutting, or may be subject to processing strain due to the release of originally held strain during cutting. Processing strain becomes internal residual stress, and birefringence occurs inside the laser medium 5 . Therefore, in the first embodiment, the pulsed light 11 is linearly polarized by utilizing the birefringence caused by the processing distortion of the laser medium 5. FIG. It should be noted that the internal residual stress that causes birefringence is not generated uniformly in the laser medium 5, and the state of internal residual stress generation differs for each laser medium 5. FIG. The inventors have also found that the state of birefringence varies depending on the state of internal residual stress.

3 and 4, the irradiation position detection device 12 for detecting irradiation position candidates of the excitation laser light 4 in which the polarization direction of the pulsed light 11 is linearly polarized according to the first embodiment of the present invention will be described below. explain.

The irradiation position detection device 12 includes a light emitting unit 13, a medium holding unit 14, an optical path dividing member 15, a shutter 22, a camera 16, a polarizing optical member 17, a first light amount detector 18, and a second light amount. It has a detector 19 and a controller 21 . The laser oscillation device 1 is composed of the light emitting portion 13 and the medium holding portion 14 .

The medium holding portion 14 , the optical path dividing member 15 , the polarization optical member 17 , and the first light amount detector 18 are provided on the emission optical axis 23 of the light emitting portion 13 . Also, the camera 16 and the shutter 22 are provided on the reflected optical axis 24 of the optical path dividing member 15 . The second light amount detector 19 is provided on the reflected optical axis 25 of the polarization optical member 17 .

The light emitting unit 13 includes a light emitter 26, for example, a laser diode (LD) that emits a laser beam of a predetermined wavelength, and an optical fiber 27 that guides the laser beam emitted from the light emitter 26 to an arbitrary emission position. , and a projection lens 28 for condensing the laser beam 20 emitted from the optical fiber 27 . The light emitter 26 can adjust the output of the emitted laser beam.

The projection lens 28 is composed of a plurality of lenses, and the position of each lens is adjusted so that the laser beam 20 is incident on the laser medium 5 with a predetermined beam diameter.

The medium holding unit 14 includes a laser medium 5 arranged on the emission optical axis 23, for example, the laser medium 5 having a rectangular parallelepiped with a cross section of about 1 mm square, a holder 29 holding the laser medium 5, An XY stage 31 for moving the laser medium 5 vertically and horizontally with respect to the emission optical axis 23 is provided. The holder 29 is held on the XY stage 31 .

As shown in FIG. 4, the holder 29 has a holder body 29a on which the laser medium 5 is placed, and a holding piece 29b that can be attached to and detached from the holder body 29a via a fastener 30 such as a bolt. The laser medium 5 is held between the holder main body 29a and the holding piece 29b. In the sandwiched state, the holder 29 does not apply an external force to the laser medium 5. By holding the laser medium 5 with the holder 29, internal stress is prevented. A temperature detector 37 such as a thermocouple is provided on the holder main body 29a, and the in-plane temperature distribution of the laser medium 5 can be measured by the temperature detector 37. As shown in FIG.

The optical path dividing member 15 is, for example, a half mirror, and has an optical characteristic of reflecting a laser beam 20' out of the laser beam 20 transmitted through the laser medium 5 and transmitting a laser beam 20''. .

The camera 16 can photograph the end surface of the laser medium 5 . Based on the image of the end surface of the laser medium 5 photographed by the camera 16, the irradiation position of the laser beam 20 on the laser medium 5 can be confirmed.

Further, the shutter 22 can be inserted into and removed from the reflected optical axis 24 by a driving mechanism (not shown). When the shutter 22 is inserted on the reflecting optical axis 24, the laser beam 20' is blocked by the shutter 22 so that the laser beam 20' does not enter the camera 16. FIG. Incidentally, the optical path dividing member 15 may be made removable with respect to the emission optical axis 23 . In this case, since the incidence of the laser beam 20' to the camera 16 can be controlled by inserting or removing the optical path dividing member 15, the shutter 22 can be omitted.

The polarizing optical member 17 is, for example, a dichroic mirror, and has a polarization characteristic of transmitting the S-polarized laser beam and reflecting the P-polarized laser beam out of the laser beam 20'' transmitted through the optical path dividing member 15. is doing.

The first light quantity detector 18 receives the S-polarized laser beam 20'' transmitted through the polarization optical member 17, and the second light quantity detector 19 receives the P-polarized laser beam reflected by the polarization optical member 17. It receives the laser beam 20'' and detects the amount of received light (the amount of each polarized light).

The control unit 21 is an arithmetic device such as a PC, for example, and controls the light emission of the light emitter 26, the driving of the XY stage 31, and the insertion/removal of the shutter 22. FIG. Also, the control section 21 calculates the extinction ratio based on the detection values of the first light quantity detector 18 and the second light quantity detector 19 . Here, the extinction ratio is obtained by using the smaller detection value among the detection values of the first light quantity detector 18 and the second light quantity detector 19 as the numerator. Furthermore, the control unit 21 specifies an irradiation position where the pulsed light 11 becomes linearly polarized light or substantially linearly polarized light, based on the calculated extinction ratio.

The image acquired by the camera 16 is stored in the storage unit (not shown) of the control unit 21, and the incidence of the laser beam within the end face of the laser medium 5 is determined based on the image. position, detection values of the first light quantity detector 18 and the second light quantity detector 19 with respect to the incident position, an image created based on the detection values of the first light quantity detector 18 and the second light quantity detector 19, The calculated extinction ratio is stored.

Further, in the storage unit, a program for controlling the driving of the light emitter 26, the XY stage 31, the shutter 22, etc., and a program for scanning the end surface of the laser medium 5 with the laser beam 20 in a predetermined order are stored. a program for creating a first output image 34 to be described later; a program for creating a second output image 35 to be described later; A program for calculating the extinction ratio based on the extinction ratio, a program for creating an extinction ratio image 36 described later based on the extinction ratio, and a program for selecting the irradiation position where the pulsed light 11 is linearly polarized or substantially linearly polarized based on the extinction ratio and other programs are stored. The control unit 21 executes or develops programs stored in the storage unit, and executes various processes.

The light emitter 26 emits the laser beam 20 , and the laser beam 20 is incident on the end surface of the laser medium 5 at a predetermined position via the optical fiber 27 and the projection lens 28 . The beam diameter of the laser beam 20 incident on the laser medium 5 is the same as the beam diameter of the excitation laser beam 4 in the laser oscillation device 1, eg, 50 μm.

A laser beam that has passed through the laser medium 5 is incident on the optical path dividing member 15 . The optical path dividing member 15 reflects a portion 20' of the laser beam and transmits the remaining portion 20''.

The laser beam 20 ″ transmitted through the optical path dividing member 15 is incident on the polarizing optical member 17 . The polarizing optical member 17 transmits the S-polarized laser beam 20'', reflects the P-polarized laser beam 20'', and separates the S-polarized light and the P-polarized light. The S-polarized laser beam 20'' transmitted through the polarization optical member 17 is received by the first light quantity detector 18, and the P-polarized laser beam 20'' reflected by the polarization optical member 17 is detected by the second light quantity. Received by the detector 19 . The first light amount detector 18 and the second light amount detector 19 output detection values corresponding to the light amounts of S-polarized light and P-polarized light, and the output detection values are stored in the control unit 21 .

Next, the irradiation position detection method for the laser medium 5 using the irradiation position detection device 12 will be described with reference to the flow chart of FIG.

STEP: 01 First, the controller 21 causes the light emitter 26 to emit a laser beam at a predetermined frequency so that the output is low, and the laser beam 20 is incident on the laser medium 5 .

In this state, an image of the end surface of the laser medium 5 is acquired by the camera 16 and displayed on the display section (not shown) of the control section 21 . In the image, the irradiation position of the laser beam 20 with respect to the laser medium 5 is displayed as a light spot within the end surface of the laser medium 5 . The controller 21 recognizes the light spot as the current irradiation position on the laser medium 5 .

STEP: 02 When the current irradiation position is recognized, the control unit 21 stops driving the light emitter 26, drives a drive mechanism (not shown), and inserts the shutter 22 into the reflection optical axis 24. .

STEP: 03 Based on the recognized current irradiation position, the control unit 21 irradiates the laser beam at a predetermined irradiation start position, for example, the lower left corner in FIG. The XY stage 31 is driven so that

STEP: 04 When the XY stage 31 is moved to the irradiation start position, the control unit 21 drives the light emitter 26 again to emit the laser beam 20 of a predetermined wavelength so as to have a high output. The laser beam 20 transmitted through the laser medium 5 is incident on the polarizing optical member 17 via the optical path dividing member 15 . Also, the laser beam 20 ′ reflected by the optical path dividing member 15 is blocked by the shutter 22 so as not to enter the camera 16 .

The laser beam 20'' incident on the polarizing optical member 17 is separated by the polarizing optical member 17 into an S-polarized laser beam 20'' and a P-polarized laser beam 20''. 18 and the second light quantity detector 19, respectively. The respective polarized outputs detected by the first light intensity detector 18 and the second light intensity detector 19 are stored in a storage unit (not shown) of the control unit 21 in association with the irradiation position of the laser beam 20. be done.

STEP: 05 When the irradiation start position is irradiated with the laser beam 20, the control unit 21 moves the irradiation position of the laser beam 20 at a predetermined interval, for example, a pitch of 20 μm, in a predetermined direction, for example, clockwise along the outer shape. be changed. That is, the XY stage 31 is driven so that the laser beam 20 is scanned along one side of the laser medium 5 at a predetermined pitch.

When the laser beam makes a round along the outer shape of the laser medium 5, the XY stage 31 moves the irradiation position of the laser beam inward by a predetermined amount, for example, 20 μm, and rotates the laser beam clockwise at a pitch of 20 μm. . The scanning of the laser beam is repeated until the entire end surface of the laser medium 5 is scanned.

The laser beam 20 that has passed through the laser medium 5 is split into an S-polarized laser beam 20'' and a P-polarized laser beam 20'' by the polarization optical member 17, as in STEP 04. The light is received by the detector 18 and the second light intensity detector 19, respectively. The detection values detected by the first light quantity detector 18 and the second light quantity detector 19 are stored in the storage section of the control section 21 in association with the irradiation position of the laser beam 20 .

STEP: 06 When the scanning of the laser medium 5 by the laser beam 20 is completed, the control unit 21, based on the detection results of the first light quantity detector 18 and the second light quantity detector 19 for each irradiation position, A first output image 34 as shown in FIG. 6 is produced.

In the first embodiment, the end surface of the laser medium 5 is divided into four areas a to d by diagonal lines. b and region d. Further, with respect to the laser beam 20 irradiated to the regions a and c, the output of the P-polarized light is detected by the second light amount detector 19 . With respect to the laser beam 20 irradiated to the regions b and d, the S-polarized output is detected by the first light amount detector 18 .

The first output image 34 is color-coded for each irradiation position so that the higher the detection value of the first light quantity detector 18 or the second light quantity detector 19, the redder, and the lower the output, the bluer the output image ( shown in shading). In FIG. 6, the entire area b and area d and the outer periphery of area a and area c are blue, and the areas a and c have a distribution that changes to red toward the center. The created first output image 34 is stored in the storage section of the control section 21 and displayed on a display section (not shown).

As described above, in the first embodiment, the detection values of the second light quantity detector 19 are used for the regions a and c, and the detection values of the first light quantity detector 18 are used for the regions b and d. The first output image 34 is created. On the other hand, the detected value of the first light quantity detector 18 may be used for the regions a and c, and the detected value of the second light quantity detector 19 may be used for the regions b and d. It is desirable to use a low output value because detection can increase the resolution and detect the amount of received light with high precision.

STEP: 07 The control section 21 creates a second output image 35 based on the first output image 34 . FIG. 7 shows the second output image 35 in the first embodiment. The bar-like figure shown on the right side of FIG. 7 is a scale showing the relationship between the detection value of the first light quantity detector 18 or the second light quantity detector 19 and the change in hue (in the figure, gradation). In this scale, the upper end where the detected value is the maximum value is red, and the lower end where the detected value is the minimum value is blue. It shows a changed state.

In the second output image 35, the detection values of the second light quantity detector 19 in the regions a and c, and the detection values of the first light quantity detector 18 in the regions b and d are each a predetermined threshold value, For example, the irradiation position (38 in FIG. 7) where the power is greater than 10 mW is displayed in red. In the second output image 35, the detection values of the second light quantity detector 19 in the regions a and c and the detection values of the first light quantity detector 18 in the regions b and d are 10 mW or less. The irradiation positions (39 to 41, etc. in FIG. 7) are displayed in different colors so that the closer they are to 0 mW, the bluer they become. The created second output image 35 is stored in the storage section of the control section 21 and displayed on the display section.

STEP: 08 Next, the control section 21 calculates the extinction ratio for each irradiation position of the regions a to d. In regions a and c, the extinction ratio is the ratio of S-polarized light to the total amount of light (S/S+P), and in regions b and d, the extinction ratio is the ratio of P-polarized light to the total amount of light (P/ S+P). Here, the value of the S-polarized light in the regions a and c is obtained by subtracting the detected value of the P-polarized light from the light amount of the laser beam 20''. Also, the value of the P-polarized light in the regions b and d is obtained by subtracting the detected value of the S-polarized light from the light amount of the laser beam 20''.

STEP: 09 Based on the calculated extinction ratio, the control unit 21 selects all irradiation positions where the extinction ratio is a preset value, for example, 60:1 or more. Based on the detection results of the first light quantity detector 18 and the second light quantity detector 19, the control unit 21 determines that the sum of the output values of the first light quantity detector 18 and the second light quantity detector 19 is , selects all the irradiation positions where the threshold is set in advance, for example, 110 mW or more.

The control unit 21 creates an extinction ratio image 36 based on all irradiation positions where the extinction ratio is equal to or greater than the set value and the total output value is equal to or greater than the threshold. FIG. 8 shows the extinction ratio image 36 in the first embodiment. The bar-like figure shown on the right side of FIG. 8 is a scale showing the relationship between the extinction ratio and the change in hue (shading in the drawing). In this scale, the upper end, which is the minimum value of the extinction ratio, is red, and the lower end, which is the maximum value of the extinction ratio, is purple. It shows a changed state.

The extinction ratio image 36 has an extinction ratio of 60:1 or more, and the irradiation position (Fig. 8 39′ to 41′ etc.) are shown. Further, in the extinction ratio image 36, each irradiation position 39' to 41' is color-coded so that the hue changes from red to purple as the extinction ratio increases (displayed in shades in the drawing). ). The extinction ratio image 36 is stored in the storage unit and displayed on the display unit.

STEP: 10 Finally, the control unit 21 selects, among the irradiation positions 39' to 41' displayed in the extinction ratio image 36, a predetermined number of irradiation positions having a particularly high extinction ratio, for example, an extinction ratio of 120: The irradiation position (for example, the irradiation position 39') of 1 or more is detected as a candidate for the irradiation position of the excitation laser beam 4 for linearly polarizing the pulsed light 11, and the irradiation position detection process is terminated. do.

When the irradiation position candidate is determined, the laser medium 5 is incorporated into the laser oscillator 1, and the incident position is adjusted so that the excitation laser beam 4 is incident on the irradiation position candidate. The same process is repeated for each irradiation position candidate until the pulsed light 11 is linearly polarized, and the process for linearly polarizing the pulsed light 11 is completed.

When the irradiation positions are in the regions a and c, the pulsed light 11 is P-polarized linearly polarized light. Further, when the irradiation positions are present in the regions b and d, the pulsed light 11 becomes S-polarized linearly polarized light.

As described above, in the first embodiment, the end face of the laser medium 5 is scanned with the laser beam 20, and the extinction ratio of the S-polarized light and the P-polarized light of the laser beam 20 transmitted through the laser medium 5 is calculated. Then, candidates for irradiation positions of the excitation laser beam 4 are detected based on the extinction ratio.

Therefore, in the laser oscillation device 1, the number of times of actually irradiating the laser medium 5 with the excitation laser light 4 and confirming the polarization direction of the emitted pulse light 11 can be reduced. The operation for linearly polarizing the pulsed light 11 can be easily performed, and the operation time can be shortened.

Moreover, since a mechanism for applying stress to the laser medium 5 from the outside is not required, the construction of the apparatus can be simplified and the manufacturing cost can be reduced.

Further, irradiation positions where the sum of detected values of S-polarized light and P-polarized light is less than the threshold value are not displayed in the extinction ratio image 36 and are not selected as candidate irradiation positions. Therefore, when the sum of the detection values of the first light quantity detector 18 and the second light quantity detector 19 becomes smaller than the total light quantity of the laser beam 20 due to distortion of the laser medium 5 or the like, Calculation of an extinction ratio different from the actual extinction ratio is prevented, and it is possible to prevent selection of an irradiation position where the actual extinction ratio is less than the set value.

In the first embodiment, a single crystal Nd:YAG/Cr:YAG crystal is used as the laser medium 5, but a polycrystal such as ceramic may be used.

In the first embodiment, the laser beam 20 is scanned at a pitch of 20 .mu.m when scanning the end surface of the laser medium 5, but the scanning pitch is not limited to 20 .mu.m. For example, a pitch of 25 μm or a pitch of 40 μm may be used. Alternatively, a scanning pitch exceeding 50 μm, which is the beam diameter of the laser beam 20, may be set. By increasing the scanning pitch of the laser beam 20, the scanning time of the end surface of the laser medium 5 can be shortened. Needless to say, the beam diameter of the laser beam 20 is not limited to 50 μm, and may be 50 μm or more or less than 50 μm.

In the first embodiment, a predetermined number of irradiation positions with an extinction ratio of 120:1 or more are detected as irradiation position candidates, but the irradiation position with the largest extinction ratio may be specified as the irradiation position. . In this case, it is not necessary to make multiple attempts to determine whether or not the pulsed light 11 is linearly polarized, so the working time can be further shortened.

Further, in the first embodiment, the irradiation position of the excitation laser beam 4 is detected from among all the irradiation positions where the extinction ratio is equal to or higher than the set value and the total output value is equal to or higher than the threshold. On the other hand, the irradiation position of the excitation laser beam 4 may be detected from all the irradiation positions where the extinction ratio is equal to or higher than the set value.

Furthermore, in the first embodiment, the entire surface of the laser medium 5 is scanned with the laser beam 20, but the extinction ratio tends to increase mainly in the peripheral portion of the laser medium 5 and decrease in the central portion. be. Therefore, the central portion (predetermined range from the center) of the laser medium 5 may be set in advance as a non-scanning range and the scanning may be omitted. Alternatively, the scanning of the laser beam 20 may be terminated when a predetermined number of irradiation positions satisfying a preset condition are detected.

Next, with reference to FIG. 9, an irradiation position detection device 12 according to a second embodiment of the present invention will be described. In FIG. 9, the same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

In the second embodiment, a second optical path dividing member 42 is provided between the light projecting lens 28 and the medium holding section 14 . The second optical path dividing member 42 can be inserted into and removed from the emission optical axis 23 . A phase difference camera 44 is provided on the reflected optical axis 43 of the second optical path dividing member 42 .

The phase-difference camera 44 has a function of detecting, as a phase difference, a difference in transmission time due to birefringence when light is transmitted through the laser medium 5 . Further, the phase difference camera 44 has a function of detecting the direction of the phase difference as well as the phase difference. The phase difference and the direction of the phase difference detected by the phase difference camera 44 are the phase difference distribution image 32 of the incident end face of the laser medium 5 and the phase difference distribution image 32 as shown in FIGS. It is obtained as a phase difference direction arrow 33 .

Here, the inventors have found that when the laser beam 20 is applied to the position where the phase difference direction arrow 33 perpendicular to one side of the laser medium 5 exists, the pulsed beam 11 is linearly polarized or substantially linearly polarized. I found out that it is easy to become.

The phase difference distribution image 32 is displayed in blue where there is no strain due to internal residual stress (no phase difference), and is color-coded so that the hue changes from blue to red as the phase difference increases. . In FIGS. 10A and 10B, the central black portion is displayed in blue, and the outer black portion is displayed in red. Also, the phase difference direction arrow 33 is displayed in a state of being superimposed on the phase difference distribution image 32 . The acquired phase difference distribution image 32 and the phase difference direction arrow 33 are stored in the control unit 21 .

A case of detecting the irradiation position on the laser medium 5 using the irradiation position detection device 12 in the second embodiment will be described.

In the second embodiment, the control unit 21 first drives the phase difference camera 44 to photograph the end face of the laser medium 5 .

The phase difference camera 44 acquires the phase difference distribution image 32 based on the phase difference of the light transmitted through the laser medium 5, and acquires a large number of phase difference direction arrows 33 indicating the direction of the phase difference.

Based on the phase difference distribution image 32, the operator determines whether birefringence occurs inside the laser medium 5 or not. Also, based on the phase difference direction arrow 33, the operator determines whether or not there is the phase difference direction arrow 33 perpendicular to one side of the laser medium 5 having a rectangular cross section.

If birefringence does not occur inside the laser medium 5 and the phase difference direction arrow 33 perpendicular to one side of the laser medium 5 does not exist, the pulsed light 11 is linearly polarized or substantially Assuming that there is no irradiation position for linearly polarized light, the laser medium 5 held in the medium holding section 14 is replaced with a new laser medium 5 .

When birefringence occurs inside the laser medium 5 and the phase difference direction arrow 33 perpendicular to one side of the laser medium 5 exists, the pulsed light 11 is linearly polarized or substantially linearly polarized. Assuming that there is an irradiation position that becomes polarized light, detection processing of the irradiation position is executed. The irradiation position detection processing is the same as that of the first embodiment (STEP: 01 to STEP: 10 in FIG. 5), so the description is omitted. It should be noted that the second optical path dividing member 42 is removed from the exit optical axis 23 when performing the process of detecting the irradiation position.

As described above, in the second embodiment, based on the phase difference distribution image 32 acquired by the phase difference camera 44 and the phase difference direction arrow 33, the pulsed light 11 is linearly polarized in the laser medium 5. Alternatively, it is determined in advance whether or not there is an irradiation position where substantially linearly polarized light exists.

Therefore, it is possible to prevent the irradiation position detection processing from being performed on the laser medium 5 where there is no irradiation position where the pulsed light 11 becomes linearly polarized light or substantially linearly polarized light. As a result, it is possible to improve the yield of the laser medium 5 in the irradiation position detection process and improve the workability.

In the second embodiment, it is determined whether or not birefringence occurs inside the laser medium 5, and whether or not the phase difference direction arrow 33 perpendicular to one side of the laser medium 5 exists. Although the determination is made by the operator, the control unit 21 may be made to make the determination by image processing or the like. Since the control unit 21 makes judgments, all processing can be automated, and workability can be improved.

REFERENCE SIGNS LIST 1 laser oscillation device 4 excitation laser light 5 laser medium 11 pulsed light 12 irradiation position detection device 13 light emitting unit 14 medium holding unit 16 camera 17 polarization optical member 18 first light intensity detector 19 second light intensity detector 20 laser beam 21 control unit 23 exit optical axis 31 XY stage 32 phase difference distribution image 33 phase difference direction arrow 34 first output image 35 second output image 36 extinction ratio image 44 phase difference camera

Claims (5)

a light-emitting portion that emits a laser beam; a medium holding portion that holds a laser medium and moves the laser medium to adjust the incident position of the laser beam; A polarization optical member that separates into polarized light, a first light intensity detector that detects an output of an S-polarized laser beam, a second light intensity detector that detects an output of a P-polarized laser beam, and a controller, The control unit drives the medium holding unit so that the end surface of the laser medium is scanned with the laser beam, and the first light amount detector and the second light amount detector for the laser beam that has passed through the laser medium. An irradiation position detection device configured to calculate an extinction ratio based on the detection result of and detect an irradiation position where the extinction ratio is equal to or greater than a preset value as an irradiation position for linearly polarizing the laser beam. The control unit detects only the irradiation position where the sum of the detection values of the first light quantity detector and the second light quantity detector exceeds a preset threshold as the irradiation position for linearly polarizing the laser beam. 2. The irradiation position detecting device according to claim 1, which is configured to A phase difference camera capable of acquiring a phase difference distribution image and a phase difference direction arrow of an end surface of the laser medium is further provided, and the laser medium has birefringence inside and is perpendicular to one side of the laser medium. 3. The irradiation position detecting device according to claim 1, wherein said irradiation position is detected only when a phase difference direction arrow is present. 4. Any one of claims 1 to 3, wherein the controller is configured to drive the medium holder so that the laser beam scans a portion excluding a predetermined range from the center of the end surface of the laser medium. The irradiation position detection device according to the item. 4. Any one of claims 1 to 3, wherein the control unit is configured to end scanning of the end face of the laser medium with the laser beam when a preset number of the irradiation positions are detected. The irradiation position detection device according to item 1.

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