Patent Application
20140029640
The present invention relates to a solid-state laser device having a configuration in which a solid-state laser medium is excited by a plurality of excitation light sources.
In a conventional solid-state laser device, a configuration is employed in which a plurality of excitation modules are provided in the solid-state laser device and the excitation modules are arranged in series optically. Opening portions are provided for the respective excitation modules. For example, when there are two excitation units, opening portions are arranged in opposite directions each other, and when there are three or more excitation units, the respective directions of the opening portions are arranged to equally divide the circumference around the optical axis. Two excitation light sources are provided for each of the opening portions. In this way, excitation intensity is strengthened concentrating on an excitation area around the optical axis, so that the effect of thermal strain generated in the excitation modules is removed in total (for example, see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application Publication No. H5-335662 (Paragraphs [0024] through [0026],
In a conventional solid-state laser device, uniformity of an excitation distribution with respect to the axis of a solid-state laser medium is only considered, and symmetry of the excitation distribution in the optical axis direction of the solid-state laser device as a whole is not considered. Therefore, there has been a problem that it is difficult to generate a high-power and high-quality laser beam with high efficiency.
Excitation modules of an even number are provided near the center of a resonator along the optical axis of a laser beam, and excitation light sources and solid-state laser media provided in each of the excitation modules are arranged to be symmetrical with respect to a virtual symmetry plane located at a center gap between the excitation modules of the even number.
Excitation distributions and thermal lenses that a solid-state laser beam experiences when it passes through excitation portions of the solid-state laser media can be made substantially symmetrical with respect to the virtual symmetry plane. As a result, quality of high-power laser beam can be improved by suppressing generation of the following situation: if solid-state laser beam is influenced by thermal-strain asymmetry of the solid-state laser media when the beam passes through the media, symmetry of beam transmission is lost especially when a high-power laser beam is outputted, and thus, the solid-state laser beam is deformed and beam quality is deteriorated.
As shown in
The first excitation module 51 includes a first solid-state laser medium 11 of a rod type, and a plurality of semiconductor lasers 21-24, serving as excitation light sources for exciting the first solid-state laser medium from its lateral side, which are arranged along the optical axis of a laser beam 18 and each of which are configured with a semiconductor laser bar including a light emission unit and a heat sink. The four semiconductor lasers are provided, which are called as the first semiconductor laser 21, the second semiconductor laser 22, the third semiconductor laser 23, and the fourth semiconductor laser 24 from the total reflection mirror 13 side. In addition, there are provided four semiconductor laser bases 31-34 for supporting respectively the first through fourth semiconductor lasers 21-24 along with the first solid-state laser medium 11, and a first base 41 for supporting the semiconductor laser bases 31-34. The four semiconductor laser bases are called as the first semiconductor laser base 31, the second semiconductor laser base 32, the third semiconductor laser base 33, and the fourth semiconductor laser base 34, each of which corresponds to each of the four semiconductor lasers.
Similarly, the second excitation module 52 includes a second solid-state laser medium 12 of a rod type, fifth through eighth semiconductor lasers 25-28 serving as excitation light sources, fifth through eighth semiconductor laser bases 35-38 for supporting respectively the fifth through eighth semiconductor lasers 25-28 along with the second solid-state laser medium 12, and a second base 42 for supporting the semiconductor laser bases 35-38. The fifth semiconductor laser 25 through the eighth semiconductor laser 28 and the fifth semiconductor laser base through the eighth semiconductor laser base are arranged from the total reflection mirror 13 side.
Note that, as the excitation module in Embodiment 1 is set for each of the solid-state laser media, there exist two excitation modules since there are two solid-state laser media in
The total reflection mirror 13 and the partial reflection mirror 14 are fixed to a first holder 43 and a second holder 44, respectively.
The first and second solid-state laser media 11, 12 contains an active medium thereinside; are members each having a function for amplifying a beam by forming an inverted population triggered by an excitation light emission; are made of Nd:YAG
(Neodymium/Yttrium Aluminum Garnet), for example; and have a rod-type shape, preferably a cylindrical shape. Note that the first and second solid-state laser media 11, 12 are in the same shape (length, figure, etc.).
The first through eighth semiconductor lasers 21-28 each have a function to generate an excitation light for exciting the first solid-state laser media 11 or the second solid-state laser media 12, and a side excitation configuration is employed in the present invention, in which the excitation light is projected from a lateral side of the first and second solid-state laser media 11, 12.
The first through eighth semiconductor lasers 21-28, via the heat sinks thereof, are respectively fixed onto the first through eighth semiconductor laser bases 31-38. Between the first through eighth semiconductor lasers 21-28 and the first through eighth semiconductor laser bases 31-38, respectively, soft metals such as indium, resin sheets or ceramics having high heat conductivity, or the like are provided (not shown), so that the heat transfer can be improved between the heat sinks of the first through eighth semiconductor lasers and the first through eighth semiconductor laser bases 31-38, respectively.
The first through eighth semiconductor laser bases 31-38 are made of metal materials having high heat radiation performance such as copper. As shown in (a) through (h) in
As shown in (a) through (h) in
The first and second solid-state laser media 11, 12 are fixed in the cylindrical holes 71-78 respectively formed in the first through eighth semiconductor laser bases 31-38 with potting agents or adhesives, etc. (not shown) which are substantially transparent against the excitation light from the first through eighth semiconductor lasers 21-28. The potting agents or the adhesives, etc. have a function of, other than supporting the first and second solid-state laser media 11, 12, transferring heat generated in the first and second solid-state laser media 11, 12 to the first through eighth semiconductor laser bases 31-38.
The first through eighth semiconductor laser bases 31-38 are provided onto the first base 41 or the second base 42. Between the first through eighth semiconductor laser bases 31-38 and the first base 41 or the second base 42, soft metals such as indium, resin sheets or ceramics having high heat conductivity, or the like are provided (not shown), so that the heat transfer can be promoted between the first through eighth semiconductor laser bases 31-38 and the first base 41 or the second base 42.
The first and second bases 41, 42 are made of metal materials having high heat radiation performance such as copper, and are cooled by the water flowing therethrough or the thermoelectric cooling device (Peltier device) provided thereunder, so as to have a function of cooling heat generating members, i.e. the first through eighth semiconductor lasers 21-28 and the first and second solid-state laser media 11, 12, via the first through eighth semiconductor laser bases 31-38.
In this solid-state laser device, the solid-state laser beam 18 generated in the first and second excitation modules 51, 52 is amplified every time it passes through the first and second excitation modules 51, 52 while traveling back and forth in the resonator comprised with the total reflection mirror 13 and the partial reflection mirror 14. A part of the solid-state laser beam 18 traveling back and forth in the resonator transmits the partial reflection mirror 14 and is taken out to the outside of the solid-state laser device.
In the solid-state laser device in Embodiment 1, the first through fourth semiconductor lasers 21-24 and the fifth through eighth semiconductor lasers 25-28, which are provided in the first excitation module 51 and the second excitation module 52, respectively, are arranged to be symmetrical with respect to a virtual symmetry plane 61, which is perpendicular to the axis of the laser beam 18, located at the gap between the first excitation module 51 and the second excitation module 52. Since the first solid-state laser medium 11 and the second solid-state laser medium 12 have the same shape, the first solid-state laser medium 11 and the second solid-state laser medium 12 are configured to be symmetrical with respect to the virtual symmetry plane 61.
Mirrors having the same curvature are employed in the total reflection mirror 13 and the partial reflection mirror 14. The first excitation module 51 and the second excitation module 52 are arranged so that the virtual symmetry plane 61, which is located at the gap between the first excitation module 51 and the second excitation module 52, will be located at the optical center of the resonator comprised with the total reflection mirror 13 and the partial reflection mirror 14. In other words, the total reflection mirror 13, the partial reflection mirror 14, and the excitation modules 51, 52 configure a symmetrical resonator.
As shown in
As described above, in Embodiment 1, the excitation modules 51, 52 are arranged at around the center of the symmetrical resonator, and the excitation light sources 21-28, which are provided in the excitation modules 51, 52, are arranged to be symmetrical with respect to the virtual symmetry plane 61 located at the gap between the excitation modules 51, 52. Thus, since the excitation distributions and the thermal lenses that the solid-state laser beam 18 experiences when it passes through excitation portions of the solid-state laser media 11, 12 are symmetrical with respect to the virtual symmetry plane 61, it is possible to make the solid-state laser beam 18 to be ideally transmitted in the symmetrical resonator, i.e. to be transmitted symmetrical with respect to the virtual symmetry plane 61. As a result, quality of high-power laser beam can be improved by avoiding the following situation: if solid-state laser beam is influenced by thermal-strain asymmetry of the solid-state laser media when the beam passes through the media, symmetry of beam transmission is lost especially when a high-power laser beam is outputted, and thus, the solid-state laser beam is deformed and beam quality is deteriorated.
Because the excitation modules 51, 52 are arranged at around the center of the symmetrical resonator, the shape of the solid-state laser beam 18 which travels in the resonator, whose beam diameter becomes largest at the resonator center and becomes smallest both at the total reflection mirror 13 and the partial reflection mirror 14, can be centrosymmetric with respect to the optical axis direction, thereby making it possible to improve the utilization efficiency of the solid-state laser media 11, 12. As a result, it is possible to generate a high-power and high-quality laser beam with higher efficiency.
As shown in
As shown in
As shown in
Note that, as shown in
In addition, while a case is described in Embodiment 1 in which one excitation module is configured with four semiconductor lasers, an excitation module may be configured with two, three, or no less than five semiconductor lasers. Naturally, it is necessary to provide semiconductor lasers to be symmetrical with respect to the virtual symmetry plane 61. The same applies to other embodiments.
Also, the above-described configurations such as employing two or more different incident directions of the excitation light, providing excitation light sources on one side with respect to the first plane 62, and allocating one excitation light source at each spot, are employed so that the effect, obtained by configuring the excitation light sources to be symmetrical with respect to the virtual symmetry plane 61, will be further improved. Therefore, the above-described configurations are not mandatory in Embodiment 1, but just preferable ones. The same can be applied to other embodiments.
Furthermore, while the description on the symmetrical resonator is made in Embodiment 1, this is not a limitation and an oscillator other than the symmetrical type may be employed. In other words, it is mandatory to provide the excitation modules to be symmetrical with respect to the virtual symmetry plane 61 located at the center gap between the plurality of excitation modules which are arranged along the optical axis of the laser beam, but, for example, the curvature of the total reflection mirror 13 may differ from that of the partial reflection mirror 14, or the distance between the total reflection mirror 13 and one excitation module may differ from that between the partial reflection mirror 14 and another excitation module. In these cases, because the beam diameters at symmetrical positions with respect to the virtual symmetry plane 61 are not the same, the effect of getting the same thermal lens and thermal strain at symmetrical positions is a bit decreased. The same can be applied to other embodiments.
Still further, while the semiconductor lasers 21-28, the semiconductor laser bases 31-38, and the bases 41, 42 are configured by separate members in Embodiment 1, semiconductor laser bases and a base may be formed monolithically as one member for each excitation module, or semiconductor laser bases and bases for all excitation modules may be formed monolithically. In these cases, it is possible to generate, with high efficiency, a high-power and high-quality laser beam with a space-saving configuration. The same can be applied to other embodiments.
Next, specific Working Example 1 according to Embodiment 1 will be described.
The excitation modules 51, 52 are provided in the resonator, and the semiconductor lasers 21-24 and the semiconductor lasers 25-28 are arranged in the two excitation modules, respectively.
A concrete disposition of the semiconductor lasers 21-28 will be described with reference to
By employing this configuration, all the angles are set to be 90 degrees, i.e. the incident angle of the excitation light from the second semiconductor laser 22 with respect to the excitation light from the first semiconductor laser 21, the incident angle of the excitation light from the fourth semiconductor laser 24 with respect to the excitation light from the third semiconductor laser 23, the incident angle of the excitation light from the sixth semiconductor laser 26 with respect to the excitation light from the fifth semiconductor laser 25, and the incident angle of the excitation light from the eighth semiconductor laser 28 with respect to the excitation light from the seventh semiconductor laser 27.
As shown in
In
In Working Example 1, when one solid-state laser medium is excited by four semiconductor lasers, since the respective semiconductor lasers are arranged to have an angular deviation of 45 degrees with each other when viewed from the axial direction of the solid-state laser medium as shown in
In Working Example 1, as shown in
Embodiment 2 of the present invention. In
The 90-degree polarizing rotator 15 is fixed to a holder 45, arranged between the first excitation module 51 and the second excitation module 52, and configured so that the polarizing directions of the solid-state laser beam 18 will differ between the first excitation module 51 and the second excitation module 52 by 90 degrees.
As described above, since the 90-degree polarizing rotator 15 is arranged between two excitation modules and the polarizing directions of the solid-state laser beam 18 differ between two excitation modules by 90 degrees, the thermal lenses, which differ depending on the polarizing directions, of the solid-state laser media can be equalized throughout the resonator. As a result, a higher-quality laser beam with high power can be generated with high efficiency.
As described in Embodiment 1, note that a configuration including more than two excitation modules is possible as long as the number thereof is even. In this case, by locating the 90-degree polarizing rotator at a center gap between a plurality of arranged excitation modules, the polarizing directions of the solid-state laser beam 18 differ by 90 degrees between the excitation modules provided at the partial reflection mirror side and the excitation modules provided at the total reflection mirror side when viewed from the 90-degree polarizing rotator. Thus, the thermal lenses, which differ depending on the polarizing directions, of the solid-state laser media can be equalized throughout the resonator.
As for an arrangement of two lenses, two types of configuration could be considered depending on thermal lens intensity of the solid-state laser media. When the thermal lens effect is small, the focal length and the arrangement of the lenses 16, 17 are selected to have an optical system in which the center point of the first solid-state laser medium 11 is image-transcribed onto the center point of the second solid-state laser medium 12.
As described above, by arranging, between the excitation modules 51, 52, the optical system in which the center point of the first solid-state laser medium 11 is image-transcribed onto the center point of the second solid-state laser medium 12, the excitation distributions of one solid-state laser medium can be image-transcribed onto the other solid-state laser medium when the thermal lens effects of the solid-state laser media 11, 12 are small, thereby being able to make the excitation distributions at the respective cross sections in the solid-state laser media to be more equalized. As a result, when the excitation intensity is small, i.e. when low-powered, it is possible to generate a higher-quality laser beam with higher efficiency.
Meanwhile, as for a thermal lens which exceeds thermal lens intensity operable as a stable resonator in the above described configuration, an arrangement is employed in which only the distance between two lenses is shortened in the image transcription optical system configured with the lenses having the above-described focal length and arrangement. That is, while the distance between the first solid-state laser medium 11 and the first lens 16, and the distance between the second solid-state laser medium 12 and second lens 17 are the same with those in the image transcription optical system, the distance between the first lens 16 and the second lens 17 is shorter than that in the image transcription optical system.
As described above, by arranging, between the plurality of excitation modules, the optical system in which the distance between the lenses in the image transcription optical system is shortened, when the excitation intensity is large, i.e. when the thermal lens effects of the solid-state laser media are stronger, the excitation distributions of one solid-state laser medium can be image-transcribed onto the other solid-state laser medium, thereby being able to make the excitation distributions at the respective cross sections in the solid-state laser media to be more equalized. As a result, when the excitation intensity is large, i.e. when high-powered, it is possible to generate a higher-quality laser beam with higher efficiency.
As described in Embodiment 1, note that a configuration including more than two excitation modules is possible as long as the number thereof is even. In this case, by locating the lenses 16, 17 at a center gap between a plurality of arranged excitation modules, the excitation distributions of the solid-state laser medium provided at the partial reflection mirror side and the excitation distributions of the solid-state laser medium provided at the total reflection mirror side, when viewed from the lenses 16, 17, can be image-transcribed onto the solid-state laser medium provide at the opposite side. Thus, it is possible to make the excitation distributions to be more equalized.
Next, specific Working Example 2 according to Embodiment 3 will be described.
A configuration of a solid-state laser device in Working Example 2 is shown in
As for the arrangement of the lenses 16, 17, while the distance between the first solid-state laser medium 11 and the first lens 16, and the distance between the second solid-state laser medium 12 and second lens 17 are the same with those in the image transcription optical system, the distance between the first lens 16 and the second lens 17 is shorter than that in the image transcription optical system.
In this solid-state laser device, excitation distributions at cross sections of the solid-state laser media are the same with those shown in
By an optical system comprised with the lenses 16, 17, when high power is inputted, E-E cross section in
Because excitation distributions are also image-transcribed by image transcription, it can be considered that an excitation distribution at a position subjected to the image transcription is obtained by synthesizing an original excitation distribution at that position and an image-transcribed excitation distribution of its source position.
As shown in
In Embodiment 3, while the solid-state laser device is shown as an example, in which the 90-degree polarizing rotator 15 and the lenses 16, 17 are provided between the plurality of excitation modules, a solid-state laser device in which only the lenses 16, 17 are provided between the plurality of excitation modules may be possible, which has the effect same with that of the solid-state laser device in Embodiment 3.
The third excitation module 151 includes the third solid-state laser medium 111;
ninth through twelfth semiconductor lasers 121-124 serving as excitation light sources; ninth through twelfth semiconductor laser bases 131-134 for supporting the ninth through twelfth semiconductor lasers 121-124 and the third solid-state laser medium 111; and a third base 141 for supporting ninth through twelfth semiconductor laser bases 131-134. The ninth through twelfth semiconductor lasers 121-124 are arranged in directions that are the same with or corresponding to those of lasers in the first excitation module 51. The third excitation module is provided, adjacent to the first excitation module 51, between the first excitation module 51 and the total reflection mirror 13.
Similarly, the fourth excitation module 152 includes the fourth solid-state laser medium 112; thirteenth through sixteenth semiconductor lasers 125-128 serving as excitation light sources; thirteenth through sixteenth semiconductor laser bases 135-138 for supporting the thirteenth through sixteenth semiconductor lasers 125-128 and the fourth solid-state laser medium 112; and a base 142 for supporting thirteenth through sixteenth semiconductor laser bases 135-138. The thirteenth through sixteenth semiconductor lasers 125-128 are arranged in directions that are the same with or corresponding to those of lasers in the second excitation module 52. The fourth excitation module is provided, adjacent to the second excitation module 52, between the second excitation module 52 and the partial reflection mirror 14.
The first through fourth semiconductor lasers 21-24 provided in the first excitation module 51 and the fifth through eighth semiconductor lasers 25-28 provided in the second excitation module 52 are arranged to be symmetrical with respect to the virtual symmetry plane 61 located at the gap between the first excitation module 51 and the second excitation module 52. The ninth through twelfth semiconductor lasers 121-124 provided in the third excitation module 151 and the thirteenth through sixteenth semiconductor lasers 125-128 provided in the fourth excitation module 152 are arranged to be symmetrical with respect to the virtual symmetry plane 61 located at the gap between the first excitation module 51 and the second excitation module 52.
As described above, because a plurality of excitation light sources arranged in a plurality of excitation modules are provided to be symmetrical with respect to the virtual symmetry plane 61 located at the center gap between the plurality of excitation modules, the excitation distributions and the thermal lenses that the solid-state laser beam 18 experiences when it passes through excitation portions of the solid-state laser media 11, 12, 111, and 112 are symmetrical with respect to the virtual symmetry plane 61. Thus, it is possible to make the transmission of the solid-state laser beam 18 to be symmetrical with respect to the virtual symmetry plane 61. As a result, quality of high-power laser beam can be improved by avoiding the following situation: if solid-state laser beam is influenced by thermal-strain asymmetry of the solid-state laser media when the beam passes through the media, symmetry of beam transmission is lost especially when a high-power laser beam is outputted, and thus, the solid-state laser beam is deformed and beam quality is deteriorated.
While the solid-state laser device is shown as an example in Embodiment 4, in which the third excitation module 151 is provided—adjacent to the first excitation module 51—between the first excitation module 51 and the total reflection mirror 13, and the fourth excitation module 152 is provided—adjacent to the second excitation module 52—between the second excitation module 52 and the partial reflection mirror 14, this is not a limitation. For example, the fourth excitation module 152 may be provided, adjacent to the first excitation module 51, between the first excitation module 51 and the total reflection mirror 13; and the third excitation module 151 may be provided, adjacent to the second excitation module 52, between the second excitation module 52 and the partial reflection mirror 14. In short, the same effect is obtained as long as a plurality of excitation light sources provided in a plurality of excitation modules are arranged to be symmetrical with respect to the virtual symmetry plane 61 located at the center gap between the plurality of excitation modules.
In addition, while the solid-state laser device is shown in Embodiment 4 as an example, which includes four excitation modules each of which are provided with the same number of excitation light sources, this is not a limitation. For example, the number of excitation modules, each of which are provided with the same number of excitation light sources, may be six or eight, and the number of excitation light sources to be provided to the respective excitation modules may differ from with each other. In short, an equivalent effect is obtained as long as a plurality of excitation light sources are arranged to be symmetrical with respect to the virtual symmetry plane 61 located at the center gap between the plurality of excitation modules.
In
As shown in
The semiconductor lasers 221-224 provided in the one excitation module 251 and the semiconductor lasers 225-228 provided in the other excitation module 252 are arranged to be symmetrical with respect to the virtual symmetry plane 61 located at the gap between the one excitation module 251 and the other excitation module 252.
In this configuration, as shown in
The size of the semiconductor laser supporting unit 231b in the semiconductor laser base 231 is determined by the size capable of mounting the semiconductor laser 221, and the size of the solid-state laser medium supporting unit 231a in the semiconductor laser base 231 is determined as the width capable of transmitting the excitation light emitted by the semiconductor laser 221 to the solid-state laser medium 211. Therefore, the width in cross direction of the semiconductor laser supporting unit 231b in the semiconductor laser base 231 should be wider than the width of the heat sink 221b in the semiconductor laser 221, and the width in cross direction of the solid-state laser medium supporting unit 231a in the semiconductor laser base 231 should be wider than the width of the semiconductor laser bar 221a in the semiconductor laser 221. In general, the width of the semiconductor laser bar 221a is narrower than that of the heat sink 221b, and the semiconductor laser bar 221a having 10-mm width and the heat sink 221b having 25-mm width, for example, are often used. Thus, as shown in (b) in
In this configuration, the semiconductor lasers 221-224 and the semiconductor lasers 225-228 provided in the respective excitation modules are arranged in the axial direction of the solid-state laser media with a gap narrower than the width of the heat sinks of the semiconductor lasers 221-224 and the semiconductor lasers 225-228. In other words, the pitch of the semiconductor laser bases, i.e. the distance between A-A and B-B cross sections or between E-E and F-F cross sections in
As described above, because excitation light sources arranged in a plurality of excitation modules are provided to be symmetrical with respect to the virtual symmetry plane 61 located at the center gap between the plurality of excitation modules, and neighboring excitation light sources in one excitation module are more closely arranged in the optical axis direction of the laser beam 18, the solid-state laser media 11, 12 can be excited densely and the gain of the solid-state laser media 11, 12 can be increased. As a result, it is possible to further increase the efficiency of generating a high-power and higher-quality laser beam.
A configuration may be employed to Embodiment 5, in which the 90-degree polarizing rotator is arranged at the center gap between the plurality of excitation modules, as described in Embodiment 2; or the lenses 16, 17 are arranged at the center gap between the plurality of excitation modules, as described in Embodiment 3. In this case, the effect similar to that described in Embodiments 2 or 3 can be obtained.
As shown in
While this configuration is similar to that in Embodiment 1, shapes of four semiconductor laser bases in each of the excitation modules differ from those in Embodiment 1. Thus, the excitation light of the semiconductor lasers is projected to the solid-state laser media from the entire circumference direction. Specifically, as shown in
As a result, from among effects achieved by the solid-state laser device according to Embodiment 1, the effects that the solid-state laser device can be configured simply and its assembling can be simplified are lost. However, because the effect that the solid-state laser media are more uniformly excited is enhanced, it is possible to generate a higher-quality and high-power laser beam with high efficiency.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/002092 | 4/8/2011 | WO | 00 | 10/7/2013 |
