JP2007053160A - Laser resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an internal wavelength conversion laser resonator in which both protection of an optical component against damage and high efficiency operation of the resonator are satisfied. <P>SOLUTION: The laser resonator 10 generating laser light of first wavelength by exciting a laser medium 12 comprises a wavelength conversion element 14 arranged on the optical path of the laser resonator 10 and converting laser light of first wavelength into laser light of second wavelength different from the first wavelength, and an element 15 arranged on the optical path of the laser resonator and controlling loss of laser light of first wavelength. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an internal wavelength conversion type laser resonator having a damage preventing function.

  Conventionally, in a laser resonator composed of a laser medium such as Nd: YAG and a predetermined mirror, laser light having a predetermined wavelength generated by the laser medium is wavelength-converted using a wavelength conversion element such as an SHG crystal, and this wavelength is converted. There is provided an internal conversion type laser resonator that outputs converted light.

  In an internal wavelength conversion type laser, wavelength converted light from a wavelength conversion element placed inside a laser resonator is extracted as an output. As a result, the intensity of the internal laser beam can be increased, and the remaining laser beam that has not been wavelength-converted can be reused, so that it is possible to operate with higher efficiency than an external wavelength conversion laser.

  FIG. 1 is a diagram showing an outline of a conventional internal conversion laser resonator.

  This laser resonator 100 is a laser resonator composed of a terminal mirror 101 made of a total reflection mirror, a laser medium 102 such as Nd: YAG, and an output mirror 103 made of a wavelength selective mirror, on the optical axis of the laser resonator. A wavelength conversion element 104 such as an SHG crystal is provided.

The laser light having a predetermined wavelength generated by the laser resonator is converted in wavelength by the wavelength conversion element 104 and output through the output mirror 103.
Japanese Patent Laid-Open No. 5-206560 JP 2002-344051 A

  However, in the internal wavelength conversion type laser resonator, the loss of the laser beam in the laser resonator is minimized in order to confine the laser beam inside the laser resonator and ensure a highly efficient operation. For this reason, there is a concern that the optical intensity inside the laser resonator may be excessively increased and damage to the optical component in a state where the wavelength conversion efficiency of the wavelength conversion element is low, such as when initial conditions are set or when the resonator is started up. In order to avoid this, if the loss is intentionally given so as to reduce the intensity of the laser beam inside the laser resonator, there is a problem that the operating efficiency of the laser resonator is lowered.

  The present invention is proposed in view of the above-described circumstances, and ensures the laser resonator operation efficiency, and the laser intensity even when the conversion efficiency of the wavelength conversion element is low, such as when initial conditions are set up or during startup. An object of the present invention is to provide a laser resonator capable of controlling the above.

  In order to solve the above-described problems, a laser resonator according to the present invention is a laser resonator that excites a laser medium to generate a laser beam having a first wavelength, and is installed on an optical path of the laser resonator. A wavelength conversion element that converts laser light of one wavelength into laser light of a second wavelength different from the first wavelength, and a loss that is installed on the optical path of the laser resonator and controls the loss of the laser light of the first wavelength And a control element.

  The laser resonator includes a termination mirror, a laser medium, and an output mirror arranged on the same optical axis, and a laser beam having a first wavelength is amplified by the laser medium that repeatedly reflects between the termination mirror and the output mirror. It is preferable that the laser light of the first wavelength is converted to the second wavelength by the wavelength conversion element and output through the output mirror.

  The laser resonator includes a first terminal mirror, an output mirror, a second terminal mirror, and a laser medium, a first optical path connecting the first terminal mirror and the output mirror, and the second terminal mirror. And the second optical path connecting the output mirror and amplifying the light that repeatedly reflects the output mirror as a folding mirror of the first and second optical paths by the laser medium disposed on the second optical path A first wavelength laser beam, wherein the wavelength conversion element is disposed on the first optical path, and the loss control element is disposed on the second optical path between the laser medium and the output mirror. It is preferable that the laser light of the first wavelength is converted to the second wavelength by the wavelength conversion element and output through the output mirror.

  The loss control element is disposed between the output mirror and the laser medium on the second optical path, and a polarization selection element that turns back laser light in a predetermined polarization direction in the output mirror direction and the laser medium direction, and the second It is preferable to have a polarization control element capable of controlling the polarization direction of the laser light disposed between the output mirror on the optical path and the polarization selection element.

  The loss control element is disposed between the output mirror on the second optical path and the laser medium, and includes a pair of polarization control elements having parallel reflecting surfaces that fold back laser light in a predetermined polarization direction, and the second It is preferable to include a polarization control element capable of controlling the polarization direction of the laser light disposed between the pair of polarization control elements on the optical path.

  The polarization selection element is preferably a polarization beam splitter.

  The polarization control element is preferably a wave plate.

  It is preferable that a Q switch is provided between the second terminal mirror medium on the second optical path and the loss control element.

  In the present invention, the problem is solved by adjusting the laser intensity inside the laser resonator using a loss control element with variable loss. That is, when the efficiency of the wavelength conversion element is low, the loss due to the loss control element is increased. When the efficiency of the wavelength conversion element is high, the loss due to the loss control element is reduced. By changing, both damage prevention of the optical component and high-efficiency operation of the resonator are achieved.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a diagram showing a minimum configuration of a laser resonator according to the present invention.

  The laser resonator 10 is a laser resonator composed of a terminal mirror 11 made of a total reflection mirror, a laser medium 12 such as Nd: YAG, Nd: YLF, and an output mirror 13 made of a wavelength selective mirror. A wavelength conversion element 14 such as an LBO or BBO crystal placed on the optical axis, and a loss control element 15 placed on the optical axis.

  The laser resonator including the end mirror 11, the laser medium 12, and the output mirror 13 is excited by an excitation source such as a krypton lamp (not shown) that reflects and reciprocates between the end mirror 11 and the output mirror 13. The laser medium 12 amplifies and oscillates the laser to generate laser light having the first wavelength.

  The first wavelength laser light generated by the laser resonator is converted into a second wavelength by the wavelength conversion element 14, and the second wavelength light is output to the outside via the output mirror 13.

  Here, the loss of the laser beam in the laser resonator is designed to take an optimum value so that the output is maximized with respect to the laser beam of the second wavelength that is finally output. It is designed to be minimum for one wavelength of laser light.

  On the other hand, at the time of adjustment for setting initial conditions, at the time of starting up the laser oscillator, the conversion efficiency of the wavelength conversion element is low, so that the conversion from the first wavelength to the second wavelength is not sufficiently performed, and the laser resonator In the laser, the first wavelength laser beam is the main component. However, since the loss of the laser resonator with respect to the first wavelength is low as described above, the intensity of the first wavelength laser beam in the laser resonator is excessive. There is a fear.

  The loss control element 24 has a low conversion efficiency of the wavelength conversion element, such as at the time of initial adjustment or startup, and the laser light having the first wavelength in the laser resonator during a period until the laser light having the second wavelength is stably obtained. The intensity of the laser beam is controlled to be within a predetermined range by increasing the loss with respect to.

  By providing such a loss control element 15, the laser resonator 10 can control the intensity of the laser light inside the laser oscillator even when initial conditions are set or started up. Therefore, even in such a case, it is possible to prevent the optical component from being damaged.

  FIG. 3 is a diagram showing a first embodiment of a laser resonator according to the present invention.

  The laser resonator 20 includes a first terminal mirror 21 by a total reflection mirror, an output mirror 23 by wavelength selection, and a wavelength conversion element 22 disposed on a first optical path L21 connecting the first terminal mirror 21 and the output mirror 23. And have.

  The laser resonator 20 is disposed between the laser medium 26 and the laser medium 26 and the output mirror 23 on the second optical path L22 connecting the second terminal mirror 27 and the output mirror 23 and the second terminal mirror 27. A Q switch 25 and a loss control element 24 disposed between the Q switch 25 and the output mirror 23 are included.

  The output mirror 23 is disposed at an angle of approximately 45 degrees with respect to the optical axes of the first and second optical paths L21 and L22, emits laser light to the outside along the optical axis L21, and is configured to be in a first state. It also serves as a folding mirror that mutually switches the directions of the laser light along the optical path L21 and the laser light along the second optical path L22. The output mirror 23 has high reflectivity for the first wavelength laser beam generated by the laser medium 26 and high transmittance for the second laser beam obtained by converting the wavelength of the first laser beam by the wavelength conversion element 22. have.

  The loss control element 24 includes a polarization beam splitter (hereinafter referred to as PBS) 24b disposed between the Q switch 25 and the output mirror 23, and a quarter wavelength plate 24a disposed between the PBS 24b and the output mirror 23. Have.

  In the loss control element 24, the PBS 24b and the quarter wavelength plate 24a constitute a loss control element that controls the loss of laser light as a polarization selection element and a polarization control element, respectively.

  That is, the quarter wavelength plate 24a controls the polarization direction of the transmitted laser light by rotating around the optical axis of the second optical path L22. The PBS 24b reflects the s-polarized light of the laser light supplied from the quarter-wave plate 24a and bends it to the second optical path L22 in the direction of the Q switch 25, the laser medium 26, and the second terminal mirror 27, but the p-polarized light Transmit outside the optical path.

  Next, the operation of the laser resonator 20 according to the first embodiment having the above-described configuration will be described.

  The first optical path L21 between the first terminal mirror 21 and the output mirror 23 and the second optical path L22 between the output mirror 23 and the second terminal mirror 27 are placed on the laser medium 26 on a series of optical paths folded back by the output mirror 23. In the laser resonator provided, the light that repeatedly reflects this optical path is amplified by the laser medium 26 excited by an excitation source such as a krypton lamp (not shown) to generate laser light having the first wavelength.

  In the present embodiment, a Q switch 25 is provided in the second optical path L22, and the laser oscillation is stopped by sufficiently increasing the loss inside the Q switch 25 until the energy accumulated in the laser medium 26 becomes sufficiently large. The Q switch 25 is controlled so as to start the laser oscillation without the internal loss of the Q switch 25 after reaching a sufficient excitation intensity.

  When the Q switch 25 is turned on, the laser light transmitted through the Q switch 25 is converted from the first wavelength to the second wavelength by the wavelength conversion element 22 on the first optical path L21. The laser light having the second wavelength passes through the output mirror 23 and is output outside the laser resonator.

  The laser resonator 20 of the present embodiment intermittently generates laser light by switching with the Q switch 25. However, it is also possible to continuously output the laser beam by not providing the Q switch 25 and causing the laser resonator to continuously oscillate (CW) the laser beam.

  In the present embodiment, the loss control element 24 has a low conversion efficiency of the wavelength conversion element, such as at the time of initial adjustment or start-up, and in the laser resonator during a period until the laser light of the second wavelength is stably obtained. By increasing the loss with respect to the laser light of the first wavelength, the intensity of the laser light is controlled within a predetermined range.

  For this reason, the loss control element 24 controls the rotation angle of the quarter wavelength plate 24a around the second optical path L22 to control the ratio of s-polarized light and p-polarized light with respect to the reflecting surface of the PBS 24b. That is, when increasing the loss of laser light, the proportion of p-polarized light that passes through the reflecting surface of the PBS 24 and is emitted out of the optical path is increased. On the other hand, when reducing the loss of laser light, the proportion of s-polarized light reflected by the reflection surface of the PBS 24 and turned back to the second optical path L22 toward the Q switch 25, the laser medium 26, and the second terminal mirror 27 increases. Like that.

  As described above, by appropriately controlling the loss of the laser beam, the intensity of the laser beam is controlled so as not to become too large even at the time of initial condition setting or startup. Therefore, it is possible to prevent the optical component from being damaged by the intensity of the laser light becoming too large.

  On the other hand, when the laser oscillation at the first wavelength is stable and the wavelength conversion efficiency of the wavelength conversion element 22 is improved after a certain period of time has elapsed since the initial condition was set or started, the loss in the loss control element 24 is reduced. Is controlled to be minimal. As a result, a highly efficient operation of the laser resonator 20 can be ensured.

  Specifically, the above-described loss control of the laser beam can be set in the loss control element 24 so that a predetermined loss occurs in the laser beam until a predetermined time elapses from the initial condition or the startup time. Further, the state of the laser beam in the laser resonator can be monitored by an appropriate detection means, and the laser beam can be set to have a predetermined loss over a period until the laser beam is stabilized at the first wavelength.

  FIG. 4 is a diagram showing a second embodiment of a laser resonator according to the present invention.

  The laser resonator 30 includes a first terminal mirror 31 by a total reflection mirror, an output mirror 33 by wavelength selection, and a wavelength conversion element 32 disposed on a first optical path L31 connecting the first terminal mirror 31 and the output mirror 33. And have.

  The laser resonator 30 is disposed between the laser medium 37 and the laser medium 37 and the output mirror 23 on the second optical path L32 connecting the second terminal mirror 38, the output mirror 33, and the second terminal mirror 38. It has a Q switch 36, a loss control element 35 disposed between the Q switch 36 and the output mirror 33, and a bending mirror 34 disposed between the loss control element 35 and the output mirror 33.

  The output mirror 33 is disposed at an angle of approximately 45 degrees with respect to the optical axes of the first and second optical paths L31 and L32, and emits laser light to the outside along the optical axis L31. It also serves as a folding mirror that mutually switches the directions of the laser light along the optical path L31 and the laser light along the second optical path L32. The output mirror 33 has a high reflectivity for the first wavelength laser beam generated by the laser medium 37 and a high transmittance for the second laser beam obtained by converting the wavelength of the first laser beam by the wavelength conversion element 32. have.

  The loss control element 35 includes a pair of first and second PBSs 35a and 35c having reflecting surfaces parallel to each other between the bending mirror 34 and the Q switch on the second optical path L32, and 1 / between these first and second PBSs. And a two-wave plate 35b. Among these, the first and second PBSs 35a and 35c constitute a polarization selection element, and the half-wave plate 35b constitutes a polarization control element.

  The first PBS 35a bends the second optical path L32 at the reflecting surface between the direction of the mirror 34 and the direction of the half-wave plate 35b and the second PBS 35c. Here, the first PBS 35a reflects the s-polarized light of the laser light supplied from the half-wave plate 35b and bends it in the direction of the folding mirror 34, but transmits the P-polarized light out of the optical path. The half-wave plate 35b controls the polarization direction of the transmitted laser light by rotating around the optical axis of the second optical path L22. The third PBS 35c has its reflection surface bent the second optical path L32 between the first PBS 35a and the half-wave plate 35b direction and the second PBS 35bc direction. The second PBS 35c reflects the s-polarized light of the laser light supplied from the half-wave plate 35b and bends it to the second optical path L32 in the direction of the Q switch 36, the laser medium 37, and the second terminal mirror 38. Is transmitted outside the optical path.

  Next, the operation of the laser resonator 30 according to the second embodiment having the above-described configuration will be described.

  The first optical path L31 between the first terminal mirror 31 and the output mirror 33 and the second optical path L32 between the output mirror 33 and the second terminal mirror 38 are arranged on the series of optical paths folded back by the output mirror 33. In the laser resonator provided, the light that repeatedly reflects this optical path is amplified by a laser medium 37 excited by an excitation source such as a krypton lamp (not shown) to generate laser light having a first wavelength.

  In the present embodiment, a Q switch 36 is provided in the second optical path L32, and the laser light is reciprocated between the second terminal mirror 38 and the Q switch 36 until the intensity of the laser light amplified by the laser medium 37 becomes sufficiently large. The Q switch 36 is controlled so as to transmit the Q switch 36 after reaching a sufficient strength.

  When the Q switch 36 is turned on, the laser light transmitted through the Q switch 36 is converted from the first wavelength to the second wavelength by the wavelength conversion element 32 on the first optical path L31. The laser light having the second wavelength passes through the output mirror 33 and is output outside the laser resonator.

  The laser resonator 30 of the present embodiment intermittently generates laser light by switching by the Q switch 36. However, it is also possible to continuously output the laser light by not providing the Q switch 36 and continuously oscillating the laser light with the laser resonator.

  In the present embodiment, the loss control element 35 stabilizes the operation of the laser resonator when the laser beam supplied from the laser resonator deviates from a predetermined first wavelength, such as when initial conditions are set or started up. During the period until the laser beam having the first wavelength is obtained, the intensity of the laser beam is controlled within a predetermined range by increasing the loss of the laser beam in the laser resonator.

  For this reason, the loss control element 35 controls the rotation angle of the half-wave plate 35b around the second optical path L32 to control the ratio of s-polarized light and p-polarized light with respect to the reflecting surfaces of the first and second PBSs 35a and 35c. . That is, when increasing the loss of laser light, the ratio of p-polarized light that passes through the reflecting surfaces of the first and second PBSs 35a and 35c and is emitted out of the optical path is increased. On the other hand, in order to reduce the loss of the laser light, the s-polarized light is reflected from the reflection surfaces of the first and second PBSs 35a and 35c from the half-wave plate 35b and is returned to the second optical path L32 to the loss control element 35. To increase the percentage of

  As described above, by appropriately controlling the loss of the laser beam, the intensity of the laser beam is controlled so as not to become too large even at the time of initial condition setting or startup. Therefore, it is possible to prevent the optical component from being damaged by the intensity of the laser light becoming too large.

  On the other hand, in a state where the laser beam is stabilized at a predetermined first wavelength after a certain time has elapsed since initial condition setting or startup, the loss in the loss control element 35 is improved in the state where the wavelength conversion efficiency of the wavelength conversion element 32 is improved. Is controlled to be minimal. Thereby, highly efficient operation in the laser resonator 30 can be ensured.

  Specifically, the above-described loss control of the laser beam can be set in the loss control element 35 so that a predetermined loss occurs in the laser beam until a predetermined time elapses from the initial condition or the startup time. Further, the state of the laser beam in the laser resonator can be monitored by an appropriate detection means, and the laser beam can be set to have a predetermined loss over a period until the laser beam is stabilized at the first wavelength.

  In addition, as the polarization control element in the loss control elements 24 and 35 in the above-described embodiment, a Pockels cell, a dielectric multilayer film having a twist angle, instead of the quarter wavelength plate 24a or the half wavelength plate 35b, It is also possible to use a Fresnel element or a Faraday rotator. Instead of the polarization control element, it is also possible to use an ND filter or an acousto-optic element as the loss control element.

  In the above-described embodiment, the Q switches 25 and 36 are disposed between the laser media 26 and 37 and the output mirrors 23 and 33 in the second optical paths L22 and L32. However, the present invention is not limited to this. The Q switches 25 and 36 can be disposed between the laser media 26 and 37 and the second terminal mirrors 27 and 38.

It is a figure which shows the structure of the conventional laser resonator. It is a figure which shows the minimum structure of a laser resonator. It is a figure which shows 1st Embodiment of a laser resonator. It is a figure which shows 2nd Embodiment of a laser resonator.

Explanation of symbols

11 Termination mirror 12 Laser medium 13 Output mirror 14 Wavelength conversion element 15 Loss control element

Claims (8)

In a laser resonator that excites a laser medium to generate laser light having a first wavelength,
A wavelength conversion element that is installed on the optical path of the laser resonator and converts the laser light of the first wavelength into laser light of a second wavelength different from the first wavelength;
A loss control element that is installed on the optical path of the laser resonator and controls the loss of the laser light of the first wavelength;
A laser resonator comprising:   The laser resonator includes a termination mirror, a laser medium, and an output mirror arranged on the same optical axis, and a laser beam having a first wavelength is amplified by the laser medium that repeatedly reflects between the termination mirror and the output mirror. 2. The laser resonator according to claim 1, wherein the laser light having the first wavelength is converted into a second wavelength by the wavelength conversion element and output through the output mirror. The laser resonator includes a first terminal mirror, an output mirror, a second terminal mirror, and a laser medium, a first optical path connecting the first terminal mirror and the output mirror, and the second terminal mirror. And a second optical path connecting the output mirror and the laser disposed on the second optical path for light that repeatedly reflects a series of optical paths in which the output mirror is a folding mirror of the first and second optical paths Amplifying with a medium to generate laser light of the first wavelength,
The wavelength conversion element is disposed on the first optical path, the loss control element is disposed on the second optical path and between the laser medium and the output mirror, and the laser light of the first wavelength is the wavelength conversion The laser resonator according to claim 1, wherein the laser resonator is converted into a second wavelength by an element and output through the output mirror.   The loss control element is disposed between the output mirror and the laser medium on the second optical path, and a polarization selection element that turns back laser light in a predetermined polarization direction in the output mirror direction and the laser medium direction, and the second 4. The laser resonator according to claim 3, further comprising a polarization control element capable of controlling a polarization direction of the laser light disposed between the output mirror on the optical path and the polarization selection element.   The loss control element is disposed between the output mirror on the second optical path and the laser medium, and includes a pair of polarization control elements having parallel reflecting surfaces that fold back laser light in a predetermined polarization direction, and the second 4. The laser resonator according to claim 3, further comprising a polarization control element capable of controlling a polarization direction of the laser light disposed between the pair of polarization control elements on the optical path.   6. The laser resonator according to claim 4, wherein the polarization selection element is a polarization beam splitter.   The laser resonator according to claim 4, wherein the polarization control element is a wave plate.   6. The laser resonator according to claim 4, further comprising a Q switch between the second terminal mirror and the loss control element on the second optical path.

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