JP2004273649A - End face excitation fine rod type laser gain module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an end face excitation fine rod type laser gain module which can perform a high excitation density and a high cooling efficiency necessary for a high output and a high efficiency of a semi-4 level laser. <P>SOLUTION: In order to perform the high excitation density and the high cooling efficiency necessary for the high output and the high efficient operation of the semi-4 level laser 1 in the end face excitation fine rod type laser gain module, the end face of a fine rod shape laser crystal is excited by an oblique incident multiple optical path. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laser device, and more particularly to an edge-pumped fine rod laser gain module.
[0002]
[Prior art]
Heretofore, there has been one of the end-pumped fine rod type laser gain modules disclosed below.
[0003]
FIG. 8 is a configuration diagram of a conventional laser gain module, and FIG. 9 is an enlarged schematic diagram of a portion A in FIG.
[0004]
In these figures, 101 is a laser crystal (Yb: YAG) device, 102 is a fine rod-shaped laser crystal (hereinafter simply referred to as a laser crystal), 103 is a heat sink, 104 is a gold film, 105 is a laser beam, and 111 is a laser beam. Reference numeral 1 denotes a laser diode (LD), 112 denotes an optical fiber, 113 denotes a lens, 114 denotes an excitation light obliquely incident on the laser beam 105 emission side of the laser crystal 102, 121 denotes a second laser diode (LD), 122 Is an optical fiber, 123 is a lens, and 124 is excitation light that is obliquely incident on the other side of the laser beam 105 of the laser crystal 102.
[0005]
As shown in these figures, in the conventional laser gain module, pumping lights 114 and 124 are made to be incident obliquely on both end faces of the laser crystal 102 and the propagation distance of the pumping lights 114 and 124 in the laser crystal 102 is reduced. The laser light is stretched and multiple-reflected on the inner surface of the laser crystal 102 to make the intensity distribution of the excitation lights 114 and 124 uniform.
[0006]
In order to reflect the excitation lights 114 and 124 on the inner surface of the laser crystal 102, a dielectric total reflection film, a high reflection film, a coating or film 104 of a metal having high reflectivity, such as gold or silver, is used. . At this time, by using the extremely long and thin laser crystal 102, the laser can be operated at high efficiency at room temperature.
[0007]
[Problems to be solved by the invention]
When the number of laser ions in a laser crystal is too small, a four-level laser, which is a general laser, has a low absorption efficiency of excitation light, and thus has a low conversion efficiency from excitation light to laser output light. However, unlike the four-level laser, the quasi-four-level laser has a non-zero distribution of the lower laser level, and the loss increases when the number of laser ions is large. Therefore, in the case of a quasi-four-level laser, it is necessary to optimize the number of laser ions in order to increase the efficiency.
[0008]
For the same reason, it is impossible to obtain an upper level distribution higher than the lower level distribution unless the pump power density is increased, so that high efficiency operation is difficult, and if the pump density is increased, the thermal lens effect increases, The temperature of the laser crystal increases. Furthermore, the efficiency lowers because the laser lower level distribution increases due to the rise in the temperature of the laser crystal. Therefore, it is necessary to increase the cooling efficiency for high-efficiency operation.
[0009]
The present invention has been made in view of the above circumstances, and provides an end-pumped fine rod-type laser gain module capable of achieving a high pumping density and a high cooling efficiency necessary for high-power and high-efficiency operation of a quasi-four-level laser. With the goal.
[0010]
[Means for Solving the Problems]
The present invention, in order to achieve the above object,
[1] End face of laser crystal with fine rod shape in order to achieve high pumping density and high cooling efficiency required for high output and high efficiency operation of quasi-four-level laser in edge-pumped fine rod type laser gain module Is excited in an oblique incidence multiple optical path.
[0011]
[2] In the edge-pumped fine rod-type laser gain module according to [1], continuous waves from a plurality of pumping light devices (5, 6) are provided on a first end face of the fine rod-shaped laser crystal (2). And simultaneously irradiating the excitation light (5C, 6C), and a folding mirror (4) is disposed on the second end face of the fine rod-shaped laser crystal (2).
[0012]
[3] In the end-pumped fine rod-type laser gain module according to [1], a continuous wave from one pumping light device (15) is provided on a first end face of the fine rod-shaped laser crystal (12). A certain excitation light is irradiated through a parabolic mirror (16) or a spherical mirror, and a folding mirror (14) is arranged on the second end face of the fine rod-shaped laser crystal (12). 14) The returned excitation light is greatly expanded by multiple reflection on the inner surface of the fine rod-shaped laser crystal (12), and is converted into a parallel beam by the parabolic mirror (16) or spherical mirror. The light beam is further turned back by the plane mirror (17) to form a multiple optical path.
[0013]
[4] In the end-pumped fine rod type laser gain module according to the above [3], a paraboloid is also provided on a second end face side of the fine rod-shaped laser crystal (22) instead of the folding mirror (14). By arranging a plane mirror (27) or a spherical mirror and a plane mirror (28, 29), the excitation light in the laser crystal (22) is increased by multiple reflections on both inner surfaces of the fine rod-shaped laser crystal (22). It is characterized in that it is spread and made into parallel rays by the parabolic mirrors (25, 27) or spherical mirrors, and the parallel rays are turned back by plane mirrors (26, 28, 29) to form a multiple optical path.
[0014]
[5] In the edge-pumped fine rod-type laser gain module according to the above [3], a second rod-shaped laser crystal (32) may be provided on the second end face side instead of the folding mirror (14). Means for irradiating the excitation light, which is a continuous wave from the excitation light device (37), through a parabolic mirror (38) or a spherical mirror and a plane mirror (39) is arranged to convert the excitation light in the laser crystal (32). The laser beam (32) having a fine rod shape is greatly expanded by multiple reflections on both inner surfaces, and is made parallel by the parabolic mirror (35, 38) or spherical mirror, and the parallel light is converted into a plane mirror (36, 38). 39) to form a multiple optical path.
[0015]
The present invention overcomes the problem of the quasi-four-level laser as follows.
[0016]
(1) A rod (or slab) type laser gain module having a long crystal length, a very thin crystal, and a low laser ion concentration.
[0017]
In order to increase the cooling efficiency of the laser crystal, the thickness of the crystal in the cooling direction is reduced, the cooling area is increased with respect to the crystal volume, and the laser ion concentration is reduced.
[0018]
(2) Oblique incidence multiple optical path excitation In order to excite a crystal having a long crystal length, a very thin crystal, and a low ion concentration with high density, excitation at both ends is performed. Furthermore, in order to efficiently absorb the excitation light without increasing the number of ions in the crystal,
(1) Oblique excitation is performed to increase the propagation distance of the excitation light.
[0019]
(2) Multi-path excitation is performed to increase the propagation distance of the excitation light.
[0020]
(3) Uniformity of excitation light intensity distribution by multiple reflection excitation In general, a high-power laser diode for solid-state laser excitation has a distorted intensity distribution of an output laser beam. Is distorted, so that the efficiency of the laser and the beam quality of the laser light are reduced. In order to solve this problem, after the excitation light is made incident on the crystal, it is multiple-reflected on the inner surface of the laser crystal to make the intensity distribution of the excitation light uniform.
[0021]
In the present invention, the return mirror (except for the return mirrors shown in FIGS. 1, 2 and 5) is a roof mirror (mirror for returning two reflected mirrors in the direction of incident light by adjusting two mirrors to 90 degrees). ) And corner cube mirrors (mirrors for returning the reflected light in the direction of the incident light by adjusting each of the three mirrors to 120 degrees) (the same applies to the following embodiments).
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
FIG. 1 is a configuration diagram of an edge-pumped fine rod laser gain module showing a first embodiment of the present invention.
[0024]
In this figure, 1 is a laser crystal (Yb: YAG) device, 2 is a fine rod (thin-rod) laser crystal (hereinafter simply referred to as a laser crystal), 3 is a heat sink, 4 is a folding mirror, and 5 is a first mirror. The first pumping light device 5 includes a first laser diode (LD) 5A, a lens 5B, and a first pumping light 5C. Reference numeral 6 denotes a second pumping light device. The second pumping light device 6 includes a second laser diode (LD) 6A, a lens 6B, and a second pumping light 6C. Reference numeral 7 denotes a laser beam.
[0025]
As described above, the first and second excitation lights 5C and 6C are obliquely incident on the first end face of the laser crystal 2, and are returned by the return mirror 4 disposed on the second end face on the side opposite to the incident side, thereby obtaining double light. Excitation in the path (double pass).
[0026]
With this configuration, the number of laser ions required to absorb the first and second excitation light beams 5C and 6C obliquely incident is reduced by half, so that the threshold value of laser oscillation is reduced by half. Also enables highly efficient operation.
[0027]
In this case, it is effective to use a rod (or slab) type laser gain module having a long crystal length, a very thin crystal, and a low laser ion concentration.
[0028]
In order to increase the cooling efficiency of the laser crystal, it is desirable to reduce the thickness of the crystal in the cooling direction, increase the cooling area with respect to the crystal volume, and reduce the laser ion concentration.
[0029]
In this embodiment, since the oblique excitation is performed, the propagation distance of the excitation light can be increased. Further, since the multi-path excitation is performed, the propagation distance of the excitation light can be further increased.
[0030]
FIG. 2 is a configuration diagram of an edge-pumped fine rod laser gain module showing a second embodiment of the present invention.
[0031]
In this embodiment, a crystal having a very small crystal thickness, a long crystal length, and a low ion concentration is subjected to oblique incidence multiple optical path excitation.
[0032]
In this figure, 11 is a laser crystal (Yb: YAG) device, 12 is a fine rod-shaped laser crystal, 13 is a heat sink, 14 is a folding mirror, 15 is an excitation light device, and this excitation light device 15 is a laser diode. (LD) 15A, lens 15B, and excitation light 15C. 16 is a parabolic mirror (or a spherical mirror), 17 is a plane mirror, and 18 is a laser beam.
[0033]
Therefore, the excitation light 15C is reflected by the parabolic mirror (or spherical mirror) 16, condensed and incident on the first end face of the laser crystal 12, and is turned over at the second end face opposite to the incident side. Turn around at 14. The returned excitation light 15C is greatly spread due to multiple reflections on the inner surface of the laser crystal 12, so that it is converted into a parallel light by the parabolic mirror 16 and the parallel light is turned back by the plane mirror 17 to obtain a multiple optical path (double light path). Path) can be formed. At this time, since the return light is largely spread, the return light to the laser diode 15A is small. Even if the number is too large to be ignored, there is no problem if an optical isolator or the like is used.
[0034]
As described above, according to this embodiment, a multiplex optical path of the excitation light 15C can be formed, so that the efficiency can be further improved.
[0035]
In addition, by performing the oblique excitation as described above, the excitation light can be efficiently absorbed without increasing the number of ions in the crystal, so that the propagation distance of the excitation light can be increased. Further, since the multi-path excitation is performed, the propagation distance of the excitation light can be increased. In addition, since the excitation light that is incident on the crystal and is reflected by the turning mirror and is returned is multiple-reflected on the inner surface of the crystal, the intensity distribution of the excitation light can be made uniform.
[0036]
FIG. 3 is a configuration diagram of an edge-pumped fine rod type laser gain module showing a third embodiment of the present invention.
[0037]
In this figure, 21 is a laser crystal (Yb: YAG) device, 22 is a fine rod-shaped laser crystal, 23 is a heat sink, 24 is an excitation light device, and this excitation light device 24 is a laser diode (LD) 24A, The lens 24B includes the excitation light 24C. 25 is a first parabolic mirror (or a spherical mirror), 26, 28, and 29 are plane mirrors, 27 is a second parabolic mirror (or a spherical mirror), and 30 is a laser beam.
[0038]
In this embodiment, the operation and effect of the second embodiment (FIG. 2) are obtained, and, unlike the second embodiment, the return mirror of the excitation light on the end face on the side opposite to the incident side of the laser crystal 22 is unnecessary. Therefore, the degree of freedom in designing a laser oscillator or an amplifier using this gain module is increased, and it can be used for various configurations.
[0039]
FIG. 4 is a configuration diagram of an edge-pumped fine rod laser gain module showing a fourth embodiment of the present invention.
[0040]
In this figure, 31 is a laser crystal (Yb: YAG) device, 32 is a fine rod-shaped laser crystal, 33 is a heat sink, 34 is a first excitation light device, and the first excitation light device 34 is a laser diode. (LD) 34A, lens 34B, and excitation light 34C. 35 is a first parabolic mirror (or may be a spherical mirror), 36 and 39 are plane mirrors, 37 is a second excitation light device, and the second excitation light device 37 is a laser diode 37A and a lens 37B. , And excitation light 37C. 38 is a second parabolic mirror (or may be a spherical mirror), and 40 is a laser beam.
[0041]
As described above, in the fourth embodiment, since the laser crystal 32 is configured to be excited from both end faces, the operation and effect of the third embodiment (FIG. 3) can be obtained, and the third embodiment can be further developed. .
[0042]
Further, the edge-pumped fine rod type laser gain module of the present invention may be configured such that a lens is incorporated in the optical path as shown in FIGS.
[0043]
FIG. 5 is a configuration diagram of an end-pumped fine rod type laser gain module in which a lens is incorporated in the middle of an optical path according to a fifth embodiment of the present invention.
[0044]
In this figure, 41 is a laser crystal (Yb: YAG) device, 42 is a fine rod-shaped laser crystal, 43 is a heat sink, 44 is a return mirror, 45 is an excitation light device, and this excitation light device 45 is a laser diode ( LD) 45A, lens 45B, and excitation light 45C. Reference numeral 46 denotes a lens, 47 denotes a mirror or a roof reflector, and 48 denotes a laser beam.
[0045]
FIG. 6 is a configuration diagram of an edge-pumped fine rod type laser gain module in which a lens is incorporated in the middle of an optical path according to a sixth embodiment of the present invention.
[0046]
In this figure, 51 is a laser crystal (Yb: YAG) device, 52 is a fine rod-shaped laser crystal, 53 is a heat sink, 54 is an excitation light device, and this excitation light device 54 is a laser diode (LD) 54A, a lens 54B and an excitation light 54C. Reference numerals 55 and 57 denote lenses, and reference numerals 56 and 58 denote mirrors or roof reflectors.
[0047]
FIG. 7 is a configuration diagram of an edge-pumped fine rod type laser gain module in which a lens is incorporated in the middle of an optical path according to a seventh embodiment of the present invention.
[0048]
In this drawing, 61 is a laser crystal (Yb: YAG) device, 62 is a fine rod-shaped laser crystal, 63 is a heat sink, 64 is a first excitation light device, and the first excitation light device 64 is a laser diode. (LD) 64A, lens 64B, and excitation light 64C. Reference numeral 65 denotes a lens, 66 denotes a mirror or a roof reflector, and 67 denotes a second excitation light device. The second excitation light device 67 includes a laser diode (LD) 67A, a lens 67B, and excitation light 67C. Reference numeral 68 denotes a lens, 69 denotes a mirror or a roof reflector, and 70 denotes a laser beam.
[0049]
Although these methods are mainly focused on the excitation of rod-type and slab-type laser crystals, they can also be used for excitation of disk-type lasers, and are very versatile. These methods can also be applied to the case of side excitation.
[0050]
In the conventional method, when the quasi-four-level laser is side-excited, the number of ions must be increased in order for the laser crystal to efficiently absorb the excitation light, and the oscillation threshold increases and the efficiency decreases. High-efficiency operation was difficult without excitation. However, by performing the multi-pass excitation according to the present invention, it is possible to dramatically reduce the number of ions required to absorb the excitation light and to lower the oscillation threshold, so that a gain module for a high-power laser exceeding 1 kW is used. It is also possible to increase efficiency.
[0051]
In the above-described embodiment of the present invention, the excitation light is condensed on the end face or the inner surface of the laser crystal, and is emitted from the laser crystal at a focal distance to collimate the excitation light emerging from the end face or the inner face of the laser crystal. Although an object mirror, a spherical mirror or a lens is provided, a parabolic mirror, a spherical mirror or a lens may be provided at a position twice the focal length instead.
[0052]
Further, the structure of the laser crystal can be applied to any rod type, slab type, and core-doped type crystal in which a crystal to which laser ions are added and a crystal to which laser ions are not added are combined. In general, when a core-doped crystal is used, the mode matching efficiency between the excitation light and the laser light is increased, but there is a problem that the absorption efficiency of the excitation light is deteriorated. By doing so, it is possible to compensate for a decrease in the absorption efficiency of the excitation light.
[0053]
According to the present invention, the performance and reliability of pulse lasers in the nanosecond to femtosecond range with a high average output are much higher than before, so that the price of lasers is reduced and industrial applications of high-power lasers are promoted. Is done. For this reason, new manufacturing technologies, such as laser processing and laser micromachining, will be industrialized and become seeds technologies that will support society in the future.
[0054]
It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.
[0055]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained.
[0056]
(1) Crystals with extremely thin crystals, long crystal lengths, and low ion concentrations can be excited at a high density by excitation of both end faces. Furthermore, in order to efficiently absorb the excitation light without increasing the number of ions in the crystal, oblique excitation is performed, so that the propagation distance of the excitation light can be increased. Further, since the multi-path excitation is performed, the propagation distance of the excitation light can be further increased.
[0057]
(2) The excitation light intensity distribution can be made uniform by multiple reflection excitation. That is, in general, a high-power laser diode for solid-state laser excitation has a distorted intensity distribution of an output laser beam, and when condensed and excited as it is, the intensity distribution of the excitation light is also distorted. Reduce beam quality. However, according to the present invention, after the excitation light is made incident on the crystal, the intensity distribution of the excitation light can be made uniform by multiple reflection on the inner surface of the crystal.
[0058]
(3) Compared with the prior art, a long crystal with a low concentration is used, so that the cooling efficiency is excellent and a decrease in gain due to a rise in temperature of the crystal is small. Since the absorption length of the excitation light can be made very long, the excitation efficiency is high. Further, since the gain length can be increased, the gain is high, and efficient operation is possible even if the loss inside the laser resonator and the amplifier is large.
[0059]
In addition, since the cross-sectional area is orders of magnitude larger than fiber lasers, it is possible to obtain high pulse energy exceeding 10 mJ and high peak output of 10 MW or more, and it is easy to achieve high average output and high energy of the pulse laser. Become.
[0060]
(4) Generally, in the case of a quasi-four-level laser, there is a distribution of laser lower levels, so that high-density pumping is required for high-efficiency operation. For this reason, it is necessary to reduce the cross-sectional area through which the laser beam passes inside the laser crystal, so that it is difficult to increase the energy per pulse. On the other hand, the use of the multi-pass excitation of the present invention can reduce the lower level loss of the laser. For this reason, even if the excitation density is reduced, high-efficiency operation is possible, the cross-sectional area through which the laser beam passes can be increased, and the energy per pulse can be increased.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an edge-pumped fine rod type laser gain module showing a first embodiment of the present invention.
FIG. 2 is a configuration diagram of an edge-pumped fine rod type laser gain module showing a second embodiment of the present invention.
FIG. 3 is a configuration diagram of an edge-pumped fine rod laser gain module showing a third embodiment of the present invention.
FIG. 4 is a configuration diagram of an edge-pumped fine rod laser gain module showing a fourth embodiment of the present invention.
FIG. 5 is a configuration diagram of an edge-pumped fine rod laser gain module in which a lens is incorporated in the middle of an optical path according to a fifth embodiment of the present invention.
FIG. 6 is a configuration diagram of an edge-pumped fine rod type laser gain module in which a lens is incorporated in the middle of an optical path according to a sixth embodiment of the present invention.
FIG. 7 is a configuration diagram of an end-pumped fine rod type laser gain module in which a lens is incorporated in the middle of an optical path according to a seventh embodiment of the present invention.
FIG. 8 is a configuration diagram of a conventional edge-pumped fine rod laser gain module.
FIG. 9 is an enlarged schematic diagram of a portion A in FIG. 5;
[Explanation of symbols]
1,11,21,31,41,51,61 Laser crystal (Yb: YAG) device 2,12,22,32,42,52,62 Fine rod-shaped laser crystal 3,13,23,33,43, 53, 63 Heat sinks 4, 14, 44 Folding mirrors 5, 34, 64 First excitation light device 5A First laser diode (LD)
5B, 6B, 15B, 24B, 34B, 37B, 45B, 46, 54B, 55, 57, 64B, 65, 67B, 68 Lens 5C First excitation light 6, 37, 67 Second excitation light device 6A Second Laser diode (LD)
6C Second excitation light 7, 18, 30, 40, 48, 59, 70 Laser beam 15, 24, 45, 54 Excitation light device 15A, 24A, 34A, 37A, 45A, 54A, 64A, 67A Laser diode (LD )
15C, 24C, 34C, 37C, 45C, 54C, 64C, 67C Excitation light 16 Parabolic mirror (or may be spherical mirror)
17 Plane mirror 25, 35 First parabolic mirror (or may be spherical mirror)
26, 28, 29, 36, 39 Plane mirror 27, 38 Second parabolic mirror (or may be spherical mirror)
47,56,58,66,69 Mirror or roof reflector

Claims (5)

In order to achieve the high pumping density and high cooling efficiency required for high-power and high-efficiency operation of the quasi-four-level laser, the end face of the fine rod-shaped laser crystal is configured to be excited by oblique incidence multiple optical paths. An end-pumped fine rod type laser gain module characterized by the following. 2. The end-pumped fine rod-type laser gain module according to claim 1, wherein the first end face of the fine rod-shaped laser crystal is simultaneously irradiated with excitation light that is a continuous wave from a plurality of excitation light devices, and the fine crystal is irradiated with the fine light. An end-face-pumped fine rod-type laser gain module, wherein a folding mirror is arranged on a second end face of a laser crystal having a simple rod shape. 2. The edge-pumped fine rod-type laser gain module according to claim 1, wherein the first end face of the fine rod-shaped laser crystal is provided with a parabolic mirror or a spherical mirror. And a return mirror is arranged on the second end face of the fine rod-shaped laser crystal, and the excitation light returned from the return mirror is applied to the inner surface of the fine rod-shaped laser crystal. Characterized in that the beam is greatly expanded by the multiple reflection, and is made into a parallel beam by the parabolic mirror or the spherical mirror, and the parallel beam is further turned back by a plane mirror to form a multiple optical path. 4. The edge-pumped fine rod-type laser gain module according to claim 3, wherein a parabolic mirror or a spherical mirror and a plane mirror are arranged on the second end face side of the fine rod-shaped laser crystal instead of the folding mirror. The excitation light in the laser crystal is greatly expanded by multiple reflections on both inner surfaces of the fine rod-shaped laser crystal, turned into parallel rays by the parabolic mirror or spherical mirror, and the parallel rays are turned back by a plane mirror to be multiplexed. An edge-pumped fine rod-type laser gain module characterized by forming an optical path. 4. The end-pumped fine rod-type laser gain module according to claim 3, wherein a continuous wave from a second pumping light device is also provided on the second end face side of the fine rod-shaped laser crystal instead of the folding mirror. Arranging means for irradiating the excitation light through a parabolic mirror or a spherical mirror and a plane mirror, the excitation light in the laser crystal is greatly expanded by multiple reflections on both inner surfaces of the fine rod-shaped laser crystal, An edge-excited fine rod type laser gain module, wherein a parallel beam is formed by the parabolic mirror or the spherical mirror, and the parallel beam is folded by a plane mirror to form a multiple optical path.

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