JP2009071231A - Laser oscillation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser oscillation apparatus which can be manufactured at low cost and with a simpler constitution than conventional ones. <P>SOLUTION: By having the laser oscillation apparatus 2A equipped with a loop optical path portion 8 comprising an optical fiber 22, an outgoing optical system 24 and an incident optical system 26 which are provided at both the ends of the optical fiber 22, and a total reflection mirror 16 for making a pumping light outgo from one end 22a of the optical fiber 22 and the pumping light incident to the other end 22b of the optical fiber 22, the pumping light is irradiated repeatedly on a laser medium portion 20 and a laser beam is output from the laser medium portion 20. As a result, the laser oscillation apparatus 2A is made compact and its manufacturing cost is reduced, without using complex optical systems. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser oscillation device.

Conventionally, in the case of performing solid-state laser oscillation, the laser medium shape is mostly a rod or a slab. However, in recent years, so-called thin disk lasers in which the medium shape is a thin disk are being used. (For example, refer to Patent Document 1).
A disk laser uses a beam output from a light source such as a semiconductor laser as excitation light, and irradiates a disk installed as a laser medium with the excitation light a plurality of times. The excitation light incident on the disk is reflected on the back surface of the disk, and is irradiated to the same position of the disk with the same beam diameter by the prism pair and the parabolic mirror. In this way, the excitation light is sequentially irradiated 16 times on the disk, so that 90% or more of the energy is absorbed by the disk, thereby enabling highly efficient laser oscillation.

Japanese translation of PCT publication No. 2002-524839

However, in the technology as described above, an optical system composed of prisms and mirrors for re-irradiating the light irradiated on the disk to the same position of the disk in the same shape and multiple times becomes very complicated. There was a problem that the manufacturing was difficult including cost and optical axis adjustment.
The present invention has been made based on such a technical problem, and an object thereof is to provide a laser oscillation device that can be manufactured with a simpler configuration and at a lower cost.

For this purpose, the laser oscillation device of the present invention is a laser that emits an excitation light source that outputs excitation light for exciting a laser medium that oscillates laser light, and excitation light output from the excitation light source. A laser medium section that oscillates light and a loop optical path section that forms an optical path for circulating the excitation light so that the excitation light output from the excitation light source is repeatedly irradiated onto the laser medium section a plurality of times. The loop optical path section includes an optical fiber into which the excitation light is introduced, an optical system and a reflection member that couple the excitation light emitted from one end of the optical fiber to the other end of the optical fiber, and the laser medium section includes a loop It is arranged on the optical path of the excitation light in the optical path part.
The excitation light output from the excitation light source is introduced into the optical fiber at an arbitrary position of the fiber length and emitted from one end surface. The excitation light output from the output end face is coupled to the other end face of the same fiber via the reflecting member and the condensing or imaging optical system. As a result, a loop optical path portion is formed, and the excitation light repeatedly circulates in the reflecting member, the optical system, and the optical fiber. Since the laser medium part is disposed on the optical path of the excitation light in the loop optical path part, the excitation light is repeatedly irradiated, and thereby the laser light is oscillated.

  Here, in the loop optical path portion, a multimode fiber in which a light guide fiber for guiding the excitation light to the fiber is fused, an optical fiber having a core portion in which the light guide fiber is fused in the clad and having a different refractive index, and a fiber laser Any one of these can be used.

  A reflection member can be laminated on the laser medium portion. This reflection member can be coated as a total reflection film on one surface of the laser medium portion. Thus, it is used as a resonator rear mirror of the disk laser together with the role of forming this loop optical path.

  It is preferable to provide an imaging optical system that forms an image of the fiber exit end face at an arbitrary magnification through the laser medium section with the fiber exit end face as an object. In the above optical fiber having a multi-mode fiber and a core part, the former has a coupling optical system installed at an arbitrary magnification from the exit end face to the entrance end face so that there is no energy loss. It is preferable to adjust the magnification so that the image of the image is coupled within the incident-side core area.

  According to the present invention, the excitation light is repeatedly irradiated to the laser medium portion by circulating through the loop optical path portion configured using an optical fiber. As a result, laser light can be oscillated from the laser medium section, and the device can be made more compact and the optical system can be made simpler than a method using a rod-shaped laser medium or a conventional disk laser method. Thus, the device can be manufactured at low cost.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
[First embodiment]
FIG. 1 is a diagram for explaining the configuration of a laser oscillation device 2A in the present embodiment.
As shown in FIG. 1, the laser oscillation device 2 </ b> A includes an excitation light source 4 that outputs laser excitation light, a laser oscillation unit 6 that oscillates a laser, and a loop optical path unit 8.

The excitation light source 4 includes a laser diode 10, and the laser diode 10 outputs laser light having a predetermined wavelength as excitation light. As the laser diode 10, for example, an InGaAs semiconductor laser can be used. Of course, the laser diode 10 of the present invention is not limited to this.
The excitation light source 4 includes a plurality of laser diodes 10. This is to increase the output value of the laser light oscillated by the excitation light source 4. However, if a single laser diode 10 can obtain a large output, it is needless to say that a plurality of laser diodes 10 need not be provided, and several laser diodes 10 are fused at a plurality of locations. It doesn't matter.

Excitation light output from each laser diode 10 is input to a light guiding optical fiber 12 using quartz glass.
The optical fiber 12 for light guide is optically connected to the loop optical path unit 8 via the multiplexing coupler 14A. Here, the light guide optical fibers 12 connected to the laser diodes 10 are fused to each other inside the multiplexing coupler 14A.

The laser oscillation unit 6 includes a laser resonator including an output mirror 28, a total reflection mirror (reflection member) 16, a heat sink 18, and a laser medium unit 20.
The total reflection mirror 16 is applied to the back surface of the laser medium unit 20 as a coating film that totally reflects the excitation light and the output beam.
The heat sink 18 is provided on the back surface side of the total reflection mirror 16 and suppresses thermal loads such as a thermal lens effect of the laser medium unit 20 due to heat caused by excitation light irradiation. As the heat sink 18, a Peltier element or the like can be used.
For example, Yb: YAG can be used as the laser crystal constituting the laser medium unit 20. An AR (anti-reflective) coating film 21 for the wavelengths of the excitation light and the output light is formed on the surface of the laser medium portion 20.

The loop optical path unit 8 includes a multimode optical fiber 22 using quartz glass, an output optical system 24 provided near one end 22a of the optical fiber 22, and an incident optical system provided near the other end 22b of the optical fiber 22. 26 and the total reflection mirror 16.
The emission optical system 24 is an optical system that irradiates a predetermined position on the total reflection mirror 16 of the laser oscillation unit 6 with an arbitrary area with excitation light emitted from one end 22a of the optical fiber 22, and includes a plurality of lenses and the like. It is configured by combining optical elements.
The excitation light reflected on the total reflection mirror 16 of the laser oscillation unit 6 from the one end 22a of the optical fiber 22 through the emission optical system 24 is input to the incident optical system 26. The incident optical system 26 incidentally couples the input excitation light to the other end 22b of the optical fiber 22 at an arbitrary magnification.

  In this manner, the loop optical path unit 8 circulates the excitation light reflected by the total reflection mirror 16 by the optical fiber 22, the emission optical system 24, and the incident optical system 26, and irradiates the same position of the total reflection mirror 16 again. As a result, the excitation light circulates in the loop optical path portion 8, so that the laser medium portion 20 disposed on the excitation light optical path is irradiated with the excitation light a plurality of times. By repeating the incidence on the laser medium unit 20, the photon energy of the excitation light is sequentially absorbed and disappears. The laser medium unit 20 is excited by the energy obtained from the excitation photons, and as a result, a laser beam is output from the laser resonator.

  It is necessary to arrange the optical fiber 22 so that the laser beam propagating out of the resonator from the output mirror 28 does not interfere with the optical fiber 22 in the loop optical path section 8.

  According to the laser oscillation device 2 </ b> A as described above, the excitation light is repeatedly irradiated to the laser medium unit 20 through the loop optical path unit 8. Thereby, in the conventional disk laser, the number of times of irradiation to the laser medium unit 20 is limited, but in the present invention, the laser medium unit 20 is excited until the photon energy is absorbed and disappeared by the laser medium unit 20. In addition, it is not necessary to use a complicated optical system as in the conventional method, so that a simpler configuration can be obtained and the apparatus can be manufactured at low cost. In particular, the loop optical path portion 8 is composed of the optical fiber 22, the exit optical system 24, the entrance optical system 26, and the total reflection mirror 16 provided at both ends thereof, so that a member manufactured using existing technology is used. This is particularly effective in terms of cost reduction.

  By the way, in the above, although it was set as the structure which irradiates excitation light to the same position of the laser medium part 20 in multiple times by the loop optical path part 8, it is not restricted to this. For example, the irradiation position in the laser medium unit 20 may be changed every time the laser beam unit 20 is irradiated with the excitation light in the loop optical path unit 8. However, for this, it is necessary to provide a plurality of sets of the optical fiber 22, the output optical system 24, and the incident optical system 26, which leads to complication of the apparatus. Nevertheless, the advantage of not having to use a complicated optical system can be enjoyed as compared with a conventional disk laser.

[Second Embodiment]
FIG. 2 is a diagram for explaining the configuration of the laser oscillation device 2B in the present embodiment. The difference between this embodiment and the first embodiment is that the fiber used for the loop optical path portion 8 is changed from the multimode optical fiber 22 to the optical fiber 32 having a core portion whose refractive index is larger than that of the cladding portion. In the following description, the same reference numerals are assigned to configurations common to the first embodiment, and the description thereof may be omitted.

  In the multiplexing coupler 14B, the light guide optical fiber 12 is fused to the clad portion of the optical fiber 32. In the process of first circulating around the cladding portion and the core portion, the excitation light is emitted from the emission end 32a to the space and then passes through the emission optical system 24 to excite the laser medium portion 20. The remaining excitation light that has not been absorbed by irradiation is propagated toward the incident optical system 26 by the total reflection mirror 16 as in the first embodiment, and then coupled to the core portion of the incident end face 32b.

  Therefore, after the nth cycle, the remaining pump light that has not been absorbed in the (n−1) th cycle propagating through the core portion and the pump light newly injected from the laser diode 10 circulate.

  At this time, the exit optical system 24 and the entrance optical system 26 constitute an optical system that projects and projects the clad diameter to be equal to or smaller than the core diameter.

  According to such a configuration, the excitation light that has not been absorbed in the (n−1) th round circulates only in the core portion, and therefore does not interfere with the multiplexing coupler 14B. Therefore, even if a factor causing loss in beam propagation occurs in the fused portion of the multiplexing coupler 14B, the excitation light is not lost because it propagates through the core portion. The performance required for the multiplexing coupler 14B is only to inject the excitation light output from the laser diode 10 into the cladding portion of the optical fiber 32 without loss.

[Third embodiment]
FIG. 3 is a diagram for explaining the configuration of the laser oscillation device 2C in the present embodiment. The difference between this embodiment and the first embodiment is that the fiber used for the loop optical path unit 8 is changed from the multimode optical fiber 22 to the fiber laser 42. In the following description, the same reference numerals are assigned to configurations common to the first embodiment, and the description thereof may be omitted.

First, in order to obtain a fiber laser beam, it is necessary to inject excitation light into a core portion that is a laser medium of the fiber laser 42. As in the first and second embodiments, it is possible to fuse the light guide fiber 12 to the cladding and inject the excitation light, but here, as another example, the following method will be described.
For example, if semiconductor laser light emitted from a fiber end surface not indicated in the drawing is used as the excitation light, the area of the emission end is imaged and projected into the cladding of the fiber laser 42 by the imaging optical system 43. So that

  At this time, a beam combiner 44 is arranged in the middle of the optical path to the cladding of the semiconductor laser so that a fiber laser beam described later can propagate along substantially the same optical axis. The beam combiner 44 is formed with a coating that totally reflects the wavelength of the semiconductor laser and totally transmits the wavelength of the fiber laser beam.

  The fiber laser excitation light propagating in the cladding of the fiber laser 42 is absorbed by the core portion depending on the propagation distance. As a result, the core, which is a laser medium, is excited and transition light is emitted.

  In the case of a general fiber laser, by providing a laser resonator such as a fiber Bragg grating (hereinafter referred to as FBG) on both end faces of the fiber, a laser beam having a uniform phase is output from one end face of the fiber and used for processing applications and the like. However, in the method of using the fiber laser 42 in the present invention, the laser beam generated in the core portion is used without being taken out from a predetermined optical path.

  That is, the laser beam once emitted from the core portion of the fiber laser 42 is used by the incident optical system 26, the emission optical system 24, the laser medium portion 20 of the laser oscillation portion 6 that is a disk laser, the total reflection mirror 16, and the beam combiner 44. Then, it is inserted again into the core portion of the fiber laser 42 to form a loop optical path for use. This is very similar to the case where the resonator mirror of a general laser oscillator is a total reflection mirror in both the front and rear. Originally, such a laser oscillator has little industrial utility value. By providing an absorption loss due to the laser medium portion 20 of the disk laser in the middle of the optical path, it is equivalent to using the laser beam extracted outside the laser resonator. Here, the semiconductor laser that is the excitation light of the fiber laser 42 may be output so as to compensate for the loss.

  The laser beam reflected without being absorbed by the laser medium section 20 of the laser oscillation section 6 after being incident once is injected again into the core section of the fiber laser 42, whereby light by stimulated emission, which is the basic principle of laser oscillation. Contributes to amplification. Further, because of the laser oscillation with such a loop configuration, special processing to the core portion like FBG is not required.

Using the laser beam from the fiber laser 42 as the excitation light of the disk laser has the following effects.
First, since the excellent directivity and convergence that are the essence of the laser beam can be used, the laser medium section 20 of the laser oscillation section 6 can be excited with a high laser power density. Therefore, the oscillation efficiency can be improved, and the peripheral devices such as the power supply can be downsized. As a result, the device can be inexpensive.
If a polarization-maintaining fiber is used as the fiber, the fiber laser beam becomes linearly polarized light, and if a laser medium of a disk laser whose absorptivity depends on the polarization direction is used, further improvement in oscillation efficiency can be expected.

In the above embodiment, specific examples of the excitation light, the laser medium, and the like have been illustrated. Needless to say, any wavelength or laser medium of the excitation light may be used.
The use of the oscillated laser is not limited at all, and can be used for various purposes.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

It is a figure which shows the structure of the laser oscillation apparatus of the multimode fiber system in this Embodiment. It is a figure which shows the structure of the laser oscillation apparatus of the optical fiber system which has a core part from which refractive index differs in this Embodiment. It is a figure which shows the structure of the laser oscillation apparatus of the fiber laser system in this Embodiment.

Explanation of symbols

  2A, 2B, 2C ... laser oscillation device, 4 ... excitation light source, 6 ... laser oscillation part, 8 ... loop optical path part, 10 ... laser diode, 12 ... optical fiber for light guide, 16 ... total reflection mirror (reflection member), 20 ... Laser medium part, 22 ... Optical fiber, 24 ... Emission optical system, 26 ... Incoming optical system, 28 ... Output mirror, 32 ... Optical fiber

Claims (4)

An excitation light source that outputs excitation light for exciting a laser medium that oscillates laser light;
A laser medium unit that oscillates the laser beam by being irradiated with the excitation light output from the excitation light source;
A loop optical path portion that forms an optical path for circulating the excitation light so that the excitation light output from the excitation light source is repeatedly irradiated to the laser medium portion a plurality of times,
The loop optical path unit includes an optical fiber into which the excitation light is introduced, an optical system that couples the excitation light emitted from one end of the optical fiber to the other end of the optical fiber, and a reflection member.
The laser oscillation device, wherein the laser medium section is disposed on an optical path of the excitation light in the loop optical path section.   The laser oscillation device according to claim 1, wherein the loop optical path unit includes any one of a multimode fiber, an optical fiber having a core part with different refractive index, and a fiber laser.   The laser oscillation apparatus according to claim 1, wherein the reflection member is stacked on the laser medium portion.   2. The laser oscillation device according to claim 1, further comprising: an imaging optical system that forms an image of the fiber exit end face on the fiber entrance end face with an arbitrary magnification through the laser medium section. .

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