JP2013235930A - Sunlight-pumped laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sunlight-pumped laser oscillator which can enhance conversion efficiency of sunlight into laser light, and durability of a laser medium.SOLUTION: A sunlight-pumped laser oscillator 1 comprises: a rod-like laser medium 31 being pumped with sunlight to output laser light; and first reflection surface 22a and second reflection surface 22b for reflecting sunlight located on the side of the laser medium 31 for the longitudinal axis X thereof, while having different tilt angles for the axis X. From a position of the laser medium 31 on the output end side toward a position on the side opposite from the output end of the laser medium 31, the first reflection surface 22a is tilted away from the axis X.

Description

  The present invention relates to a solar light excitation laser oscillation device excited by sunlight.

  Effective use of sunlight is considered to solve global environmental problems. As an example, there is a laser oscillation device excited by sunlight. In such a solar-excited laser oscillation apparatus, as a method of concentrating sunlight on the laser medium, a tapered reflecting surface extending in a direction away from the longitudinal axis of the laser medium from the output end of the rod-shaped laser medium is used. There is a method of reflecting sunlight and condensing it on a laser medium (see, for example, Patent Document 1).

International Publication No. 2009/128510

  However, in the condensing method using a tapered reflecting surface as described in Patent Document 1, sunlight is concentrated and concentrated near the output end of the laser medium and absorbed by the laser medium. As a result, only that portion becomes significantly large, and as a result, the distortion of the laser medium in the vicinity of the output end portion becomes large and may be damaged.

  The present invention has been made in view of such problems, and an object thereof is to provide a solar light excitation laser oscillation device capable of improving the conversion efficiency from sunlight to laser light and the durability of the laser medium. To do.

In order to achieve the above object, the laser oscillation device of the present invention comprises:
A rod-shaped laser medium that emits laser light when excited by sunlight; and
A plurality of reflecting surfaces that are located laterally of the laser medium with respect to the longitudinal axis of the laser medium, have different inclination angles with respect to the axis, and reflect the sunlight;
With
The plurality of reflecting surfaces are separated from the longitudinal axis of the laser medium from the position on the output end side of the laser medium toward the position on the end side opposite to the output end of the laser medium. Including an outwardly inclined surface inclined with respect to the axis,
It is characterized by that.

The outwardly inclined surface is
A first outwardly inclined surface inclined at a first angle with respect to the axis;
A second outwardly inclined surface that is inclined with respect to the axis at a second angle smaller than the first angle;
A third outward direction that is located on the output end side of the laser medium with the second outwardly inclined surface sandwiched between the second outwardly inclined surface and that is inclined at a third angle larger than the second angle with respect to the axis. An inclined surface;
May be included.

  You may further provide the prism which covers at least one part of the said laser medium through a medium, and has a refractive index larger than the said medium.

Further comprising a glass tube containing the laser medium and water;
The prism may be disposed on an outer side surface of the glass tube.

  The plurality of reflection surfaces approach the longitudinal axis of the laser medium from the position on the output end side of the laser medium toward the position on the end side opposite to the output end of the laser medium. In addition, an inwardly inclined surface that is inclined with respect to the axis may be further included.

A glass window disposed opposite to the end opposite to the output end of the laser medium,
The medium and the laser medium are accommodated in a space formed by the glass window and the plurality of reflecting surfaces,
The prism may be disposed on a surface of the glass window opposite to a surface forming the space.

  The reflective surface may be formed by subjecting a glass material to a surface treatment that reflects the sunlight.

  The reflective surface may be formed by subjecting a resin material to a surface treatment that reflects the sunlight.

  ADVANTAGE OF THE INVENTION According to this invention, the sunlight excitation laser oscillation apparatus which can improve the conversion efficiency from sunlight to a laser beam and durability of a laser medium can be provided.

It is a schematic diagram which shows the schematic structural example of the sunlight excitation laser oscillation apparatus which concerns on Embodiment 1 of this invention. It is a top view of a Fresnel lens. It is a schematic diagram which shows the mode of condensing by a Fresnel lens. FIG. 3 is a schematic diagram illustrating a light guide and a laser cavity according to the first embodiment. (A) And (b) is a schematic diagram which shows the mode of condensing in the conventional light guide. 6 is a schematic diagram illustrating a light guide and a laser cavity according to a modification of the first embodiment. FIG. It is a schematic diagram which shows the light guide and laser cavity which concern on Embodiment 2. (A) And (b) is a schematic diagram which shows the mode of condensing in the light guide which concerns on Embodiment 2. FIG. It is a schematic diagram which shows the light guide and laser cavity which concern on Embodiment 3. 10 is a diagram illustrating a path of light incident on a prism piece according to a third embodiment. FIG. (A) And (b) is a schematic diagram which shows the light guide and laser cavity which concern on Embodiment 4. FIG. FIG. 10 is a schematic diagram illustrating a light guide and a laser cavity according to a fifth embodiment.

(Embodiment 1)
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating a schematic configuration example of a solar light pumped laser oscillation device 1 according to the present embodiment. FIG. 2 is a plan view of the Fresnel lens 10 used in the sunlight-excited laser oscillation device 1. FIG. 3 is a schematic diagram showing a state of light collection by the Fresnel lens 10. FIG. 4 is a schematic diagram showing the light guide 20 and the laser cavity 30 of the solar light pumped laser oscillation device 1.

  As shown in FIG. 1, a sunlight-excited laser oscillation device 1 includes a Fresnel lens 10 that condenses sunlight, a light guide 20 that guides the collected sunlight as laser excitation light, and a laser that resonates laser light. And a cavity 30. And the sunlight excitation laser oscillation apparatus 1 irradiates the generated laser beam to magnesium oxide (MgO) which is an example of the target 2, generates magnesium (Mg) vapor, and obtains magnesium from the magnesium oxide. The target 2 may be a metal or plastic for processing with generated laser light, or an oxide material such as magnesium oxide for purification by heating to high temperature and reduction.

  As shown in FIG. 2, the Fresnel lens 10 is a four-split Fresnel lens configured by combining four split lenses 11 of 1 to 2 m square. The Fresnel lens 10 has a groove 11a as shown in FIG. 2 on one surface of plastic in order to collect sunlight by a refraction method. The groove 11a is formed on the exit surface of the split lens 11 so as to reduce the reflection loss. The entrance / exit surface of the split lens 11 is subjected to surface treatment using an excimer lamp that emits light in the deep ultraviolet wavelength region so that the scattering loss is several percent or less. In addition, a dielectric optical thin film is vapor-deposited on the surface of the splitting lens 11 using the patented technology for forming an optical thin film (Japanese Patent No. 3,905,035) so that the reflectance is several percent or less. . As described above, the surface of the Fresnel lens 10 is modified by deep ultraviolet light. The number of divisions of the Fresnel lens 10 is not limited to four, and the shape of the division lens 11 is not limited to a square, and the division lens 11 may be combined to produce the effect of the Fresnel lens 10.

  As shown in FIG. 3, the light guide 20 is arranged so that the vicinity of the end of the laser cavity 30 is located at the focal position of the Fresnel lens 10 having a focal length f. And the Fresnel lens 10 condenses sunlight S to the center part (center part of a laser housing) of the light guide 20. FIG. The optical axis of the Fresnel lens 10 is parallel to the longitudinal axis X of the laser medium 31 (the optical axis of the laser medium 31). Details of the laser medium 31 will be described later. Thus, the Fresnel lens 10 functions as an example of a condensing unit that condenses the sunlight S and makes it incident on the light guide 20.

  Next, as shown in FIG. 4, the light guide 20 includes a sunlight incident window 21 that transmits the concentrated sunlight Sf and a plurality of reflecting surfaces that reflect the sunlight Sf and guide it to the laser medium 31. 22 (22a, 22b) and a laser housing 23 for housing the laser cavity 30. In addition, since the condensing diameter of the sunlight Sf condensed by the Fresnel lens 10 is about 50 mm near the focal point, it is essential to provide the light guide 20. The light guide 20 serves to guide the sunlight Sf collected by the Fresnel lens 10 to the laser cavity 30 with high efficiency.

  The sunlight incident window 21 is disposed perpendicular to the vertically incident light Sf1 incident in parallel to the optical axis of the Fresnel lens 10, and is formed of a plate-shaped transparent material such as glass. Thus, the surface of the incident window of the light guide 20 that takes in the sunlight Sf is arranged perpendicular to the optical axis of the Fresnel lens 10.

  The reflection surface 22 is located on the side of the laser medium 31 with respect to the longitudinal axis X of the laser medium 31 and is formed on the inner surface of the laser housing 23. On the reflective surface 22, a highly reflective metal film is corroded by cooling water, and a dielectric multilayer film that does not absorb sunlight is deposited in order to prevent a decrease in reflectance. For example, an Al or Ag mirror with a water-resistant thin film or a reflective mirror in which a dielectric multilayer film is coated on an Al or Ag film is used as the reflecting surface, and the reflectance is 95% or more. Moreover, you may form the reflective surface 22 by giving the surface treatment which reflects sunlight to a glass material or a resin material. By forming the reflecting surface 22 by surface-treating such an inexpensive material, low cost can be realized.

  Next, a specific shape of the reflecting surface 22 will be described. The reflecting surface 22 according to the present embodiment has a two-step tapered reflecting surface, that is, a first reflecting surface 22a, so as to extend from the output end of the laser medium in a direction away from the longitudinal axis X of the laser medium. The second reflecting surface 22b.

The first reflecting surface 22a is inclined with respect to the axis X so as to move away from the axis X from the position on the output end side of the laser medium 31 toward the position of the end opposite to the output end of the laser medium. It is a surface to do. That is, the first reflecting surface 22a is an outwardly inclined surface that inclines so that the surface faces in the direction (outward) from the laser housing 23 toward the sunlight incident window 21. The first reflecting surface 22a is inclined with respect to the axis X by an angle θ ₁ .

Here, the angle θ _1, which is an inclination angle of the first reflecting surface 22 a with respect to the axis X, has a conventional reflecting surface 220 formed in a one-step tapered shape as shown in FIGS. It is larger than the inclination angle of the reflection surface 220 of the solar light excitation laser oscillation device.

  The second reflecting surface 22b is a reflecting surface formed so as to continuously extend from the end of the first reflecting surface 22a on the output end side of the laser medium 31 to the output end of the laser medium 31. The second reflecting surface 22b is a surface substantially parallel to the axis X.

  Next, the laser housing 23 has a space 24 formed by the sunlight incident window 21 and the reflecting surface 22, and the space is filled with cooling water. The laser housing 23 has a cooling water inlet 25 and a cooling water outlet 26, and is configured so that cooling water can be supplied to the space 24 from the outside and discharged. The cooling water inlet 25 and the cooling water outlet 26 penetrate the laser housing 23 and reach the space 24 so as to be connected to the space 24 from the outside. The material of the laser housing 23 is metal, plastic, glass, ceramic, or the like.

  Next, as shown in FIGS. 1 and 4, the laser cavity 30 is a laser medium 31 that is excited by sunlight and outputs laser light, an end of the laser medium 31, and the sunlight entrance window 21. The highly reflective film 32 formed on the opposing surface, the antireflection film 33 formed on the surface of the output end that is the end of the laser medium 31 that outputs laser light, and the output end of the laser medium 31 are opposed to each other. And an output mirror 34 installed at a position where

The material of the laser medium 31 is YAG (Y ₃ Al ₅ O ₁₂ ), GSGG (Gd ₃ Ac ₂ Al ₃ O ₁₂ ), in which Nd and Cr are added together, or YAG, GSGG, GGG (in which high concentration Nd is added). Solid laser crystal (or ceramic) such as Gd ₃ Ga ₅ O ₁₂ ). The laser medium 31 has a rod shape with a circular cross-sectional shape. However, the cross-sectional shape of the laser medium 31 is not limited to a circle, and may be appropriately determined according to the shape of the light guide 20, for example.

  The high reflection film 32 is formed by vapor-depositing a dielectric multilayer film that highly reflects at the oscillation wavelength of the laser medium 31. For example, when a YAG crystal is used, a highly reflective film (with a reflectance of 99% or more) for a wavelength of 1.064 μm is formed by vapor deposition. The highly reflective film 32 reflects only the light having a wavelength of 1.064 μm excited in the laser medium 31, and the light having other wavelengths, that is, the sunlight entering through the sunlight incident window 21. Most of the light passes through the highly reflective film 32 and enters the laser medium 31.

  The antireflection film 33 is formed by depositing an antireflection film having a wavelength of 1.064 μm (reflectance: 0.2% or less). The antireflection film 33 prevents reflection loss in the laser cavity 30 and oscillation of other modes.

  As shown in FIG. 4, the output mirror 34 has a concave surface 34 a that faces the output end of the laser medium 31. The concave surface 34 a of the output mirror 34 has an effect of correcting the thermal lens effect of the laser medium 31. Laser light grown in the laser cavity 30 is output from the output mirror 34 to the outside. Since the output of the laser light greatly depends on the curvature radius and the reflectance of the concave surface 34a of the output mirror 34, the output mirror 34 has a configuration that can be easily adjusted.

  The laser medium 31 is optically pumped by sunlight. The sunlight that has passed through the highly reflective film 32 enters the laser medium 31 to excite the laser medium 31 (axial excitation), and the sunlight reflected by the reflecting surface 22 of the light guide 20 enters the laser medium 31. Incident light excites the laser medium 31 (side excitation).

  Next, as an operation example of the sunlight-excited laser oscillation device 1, focusing on the light guide 20 will be described in comparison with the reflection surface 220 of the light guide 200 of the conventional solar-excitation laser oscillation device. The conventional solar pumped laser device is different from the solar pumped laser device 1 according to the present embodiment in that the reflecting surface 220 of the light guide 200 is formed in a substantially conical shape, that is, a one-step tapered shape. Differently, the other configurations are the same.

  FIGS. 5A and 5B are schematic views showing the state of light collection in the light guide 200. FIG. 5A shows a case where light is reflected near the end face of the reflecting surface 220 in the light guide 200, and FIG. 5B shows a case where light is reflected behind the reflecting surface 220 in the light guide 200.

  As shown in FIG. 1, sunlight S is collected by the Fresnel lens 10 and passes through the sunlight incident window 21 as sunlight Sf and enters the light guide 20. The condensed incident light is reduced in the diameter of sunlight until it becomes substantially equal to the diameter of the laser medium 31, and is incident from the end of the laser medium 31 where the highly reflective film 32 is formed. Excited in the axial direction. Other sunlight is reflected by the reflecting surface 22 of the light guide 20 and enters the laser medium 31 from the side surface of the laser medium 31 to excite the laser medium 31 on the side surface.

  Next, the sunlight Sf reflected by the reflection surface 220 of the light guide 200 in the conventional sunlight-excited laser oscillation device will be described.

  As shown in FIG. 5A, out of the sunlight Sf incident near the end surface of the reflection surface 220 in the conventional solar light pumped laser oscillation device, the light is incident perpendicularly to the sunlight incident window 21 or the end surface of the laser medium 31. The normal incident light Sf1 is gathered relatively toward the bottom of the light guide 200 (near the output end of the laser medium 31) for both the first reflected light and the second reflected light. Further, the oblique incident light Sf2 also has its optical path reaching the bottom of the light guide 200 due to the first reflection. The oblique incident light Sf2 shown in FIGS. 5A and 5B is an example of oblique incident light having various angles.

  Next, as shown in FIG. 5B, when the light is reflected by the reflection surface 220 near the bottom of the light guide 200, the vertically incident light Sf <b> 1 and the obliquely incident light Sf <b> 2 reach the bottom of the light guide 200. Yes. As shown in FIGS. 5A and 5B, the sunlight reflected by the reflecting surface 220 tends to gather near the bottom of the light guide 200. Therefore, the sunlight reflected by the reflecting surface 220 is likely to excite the vicinity of the output end of the laser medium 31.

  Further, in the conventional solar-pumped laser oscillation device, the mode volume in the laser medium 31 is large near the output end of the laser medium 31 due to the concave surface 34 a of the output mirror 34. Therefore, the sunlight reflected by the reflecting surface 220 of the light guide 200 gathers near the output end where the mode volume of the laser medium 31 is large, and the conversion efficiency from sunlight to laser light can be further improved. However, the sunlight concentrates in the vicinity of the output end of the laser medium 31 in this way, and the energy of the sunlight absorbed by the laser medium 31 is greatly increased only by that portion. As a result, the laser medium 31 near the output end There is a risk of damage due to increased distortion.

With respect to the reflection surface 220 in such a conventional solar-pumped laser oscillation device, the first reflection surface 22a of the reflection surface 22 according to the present embodiment is inclined with respect to the axis X relative to the reflection surface 220 as shown in FIG. θ ₁ is large, that is, the length L in the axis X direction is short. Therefore, the sunlight incident on the vicinity of the bottom portion of the light guide 200 is reduced, and it is possible to prevent the sunlight from being concentrated near the output end portion of the laser medium 31 as compared with the conventional solar light excitation laser device.

As shown in FIG. 6, when the first reflecting surface 22a is larger than the inclination angle θ ₁ of the first reflecting surface 22a shown in FIG. 4, that is, when the length L in the axis X direction is further shortened, The sunlight reflected by the reflecting surface 22 a does not go to the laser medium 31 and almost goes outside the light guide 20. Therefore, the inclination angle θ ₁ of the first reflecting surface 22a, that is, the length L in the axis X direction of the first reflecting surface 22a, and the degree of concentration of sunlight near the output end of the laser medium 31, It is preferable to set an appropriate value in consideration of a trade-off with the degree to which the sunlight reflected by the one reflecting surface 22a goes out.

  As described above, the solar light excitation laser oscillating device 1 according to this embodiment includes a rod-shaped laser medium 31 that is excited by sunlight and outputs laser light, and the longitudinal direction of the laser medium 31 from the output end of the laser medium 31. A first reflection surface 22a and a second reflection surface 22b that are positioned on the side of the laser medium 31 with respect to the axis X, have different inclination angles with respect to the axis X, and reflect sunlight; The one reflecting surface 22a is a reflecting surface that is inclined outward. Therefore, it is possible to improve the conversion efficiency from sunlight to laser light while preventing the sunlight from being concentrated near the output end of the laser medium 31 near the output end of the laser medium 31.

(Embodiment 2)
In the first embodiment, the example in which the plurality of reflecting surfaces 22 are configured by the first reflecting surface 22a inclined outward and the second reflecting surface substantially parallel to the axis X has been described. However, the configuration of the plurality of reflecting surfaces is not limited to this. In the second embodiment, an example in which a plurality of reflecting surfaces is configured by three reflecting surfaces will be described. In the second embodiment, the configuration other than the plurality of reflecting surfaces is assumed to be the same as that of the first embodiment, and detailed description thereof is omitted.

FIG. 7 is a schematic diagram showing the light guide 20 and the laser cavity 30 in the present embodiment. In the present embodiment, the light guide 20 includes a reflecting surface 42 instead of the reflecting surface 22 in the first embodiment. The reflective surface 42 has a three-stage tapered reflective surface, that is, a first reflective surface 42a and a second reflective surface so as to extend from the output end of the laser medium 31 in a direction away from the longitudinal axis X of the laser medium. The surface 42b is comprised from the 3rd reflective surface 42c. The first reflecting surface 42 a is a reflecting surface that is inclined with respect to the axis X at an angle θ _a1 . The second reflecting surface 42b is a reflecting surface that is inclined with respect to the axis X at an angle θ _a2 smaller than the angle θ _a1 . The third reflecting surface 42c is located on the output end side of the laser medium 31 with the first reflecting surface 42a and the second reflecting surface 42b interposed therebetween, and is inclined with respect to the axis X at an angle _θa3 larger than the angle _θa2 . It is a reflective surface. Specifically, the third reflecting surface 42c inclined at an angle _θa3 extends so as to spread outward from the output end of the laser medium 31 about the axis X, and further spreads outward from the third reflecting surface 42c. the second reflecting surface 42b extends inclined at an angle theta _a2, the first reflecting surface 42a inclined at an angle theta _a1 to extend further outwardly from the second reflecting surface 42b extends. Thus, the first reflecting surface 42a, the second reflecting surface 42b, and the third reflecting surface 42c continuously extend from the output end of the laser medium 31 so as to surround the laser medium 31 to form the reflecting surface 42. ing.

Here, the angle θ _a3, which is an inclination angle of the third reflecting surface 42c with respect to the axis X, has a conventional reflecting surface 220 formed in a one-step tapered shape as shown in FIGS. It is larger than the inclination angle of the reflection surface 220 of the solar light excitation laser device. That is, the sunlight incident on the vicinity of the bottom of the light guide 20 is reflected upward (in the direction of the sunlight incident window 21) by the third reflecting surface 42c.

  Next, the optical path of the sunlight Sf reflected by the reflecting surface 42 of the light guide 20 in the sunlight-excited laser oscillation device 1 according to this embodiment, and the light collection on the light guide 20 will be described.

  FIGS. 8A and 8B are schematic views showing the state of light collection in the light guide 20. 8A shows a case where light is reflected near the end face of the reflecting surface 42 in the light guide 20, and FIG. 8B shows a case where light is reflected behind the reflecting surface 42 in the light guide 20.

  As shown in FIG. 8A, out of sunlight Sf incident on the vicinity of the end surface of the reflecting surface 42 (specifically, the first reflecting surface 42 a) with respect to the sunlight incident window 21 or the end surface of the laser medium 31. The vertically incident light Sf1 and the obliquely incident light Sf2 that are perpendicularly incident are relatively near the upper part from the central part of the light guide 20 (both from the central part to the upper part of the laser medium 31). ).

  Next, as shown in FIG. 8B, when reflected by the reflecting surface 42 (specifically, the third reflecting surface 42c) near the bottom of the light guide 20, the vertically incident light Sf1 and the obliquely incident light Sf2 are The optical path does not reach the bottom of the light guide 20 and is reflected upward. Therefore, as shown in FIGS. 5A and 5B, the sunlight reflected by the reflecting surface 22 is not concentrated near the bottom of the light guide 20, and the laser medium 31 is excited substantially uniformly in the longitudinal direction. Easy to make.

Thus, according to the present embodiment, the rod-shaped laser medium 31 that is excited by sunlight and outputs laser light, and extends from the output end of the laser medium 31 in a direction away from the longitudinal axis X of the laser medium 31. A reflective surface 42 that reflects sunlight, and the reflective surface 42 is inclined with respect to the axis X at an angle θ _{a1 and} an angle θ smaller than the angle θ _a1 with respect to the axis X. _An angle greater than the angle θ _{a2 with} respect to the axis X, located on the output end side of the laser medium 31 with the second reflection surface 42b inclined at _a2 and the second reflection surface 42b together with the first reflection surface 42a By including the third reflecting surface 42c inclined at θ _a3 , sunlight is not concentrated near the output end of the laser medium 31 and the laser medium 31 is excited substantially uniformly in the longitudinal direction thereof, Sunlight to laser -The conversion efficiency to light can be improved.

(Embodiment 3)
In Embodiments 1 and 2 described above, the effect of dispersing sunlight over the entire output end portion of the laser medium 31 without concentrating sunlight can be expected. However, the amount of sunlight escaping to the outside of the light guide 20 may increase by dispersing sunlight throughout. In the present embodiment, an example will be described in which a configuration for further confining sunlight that has entered the light guide 20 so as not to escape to the outside of the light guide 20 is added to the configurations of the first and second embodiments.

  In FIG. 9, the schematic diagram which shows the light guide 20 and the laser cavity 30 of the sunlight excitation laser oscillation apparatus 1 which concerns on this embodiment is shown. The solar light pumped laser oscillation device 1 according to the present embodiment further includes a glass tube 50 and a prism 60 in addition to the solar light pumped laser oscillation device 1 according to the first embodiment.

  The glass tube 50 accommodates the laser cavity 30 and water. The water cools the laser cavity 30, and the glass tube 50 has a cooling water inlet and a cooling water outlet (not shown), and is configured so that cooling water can be supplied into the glass tube 50 from the outside and discharged. ing. In the first embodiment, the cooling water is supplied into the space 24. However, in this embodiment, the cooling water is supplied into the glass tube 50, and the space 24 is filled with air.

  The prism 60 has a refractive index larger than that of the glass tube 50 and is made of, for example, quartz glass. The prism 60 includes a plurality of triangular pyramid-shaped prism pieces 61 and is disposed so as to cover the outer side surface of the glass tube 50. In the present embodiment, the prism 60 functions to prevent the sunlight that has entered the prism 60 from the space 24 from entering the space 24 again due to the property of total reflection.

  Here, total reflection of sunlight in the prism 60 will be described.

In general, the incident angle θ _A and the refraction angle θ _B of light passing through the two media A and B having the refractive indexes N _A and N _B have the following relationship according to Snell's law.

例えば、媒質Ａが石英ガラスであるとすると、屈折率Ｎ_A＝１．５４であるから、θ_A≧４０度となる。すなわち、θ_A＝４０度よりも大きい角度で入射した光は、媒質Ｂへ入射できずに反射（すなわち、全反射）する。 Assuming that N _A > 1 and N _B = 1, there is θ _A that can be θ _B = 90 degrees (sin θ _B = 1) from the following equation (2).

For example, if the medium A is quartz glass, the refractive index N _A = 1.54, so θ _A ≧ 40 degrees. That is, light incident at an angle larger than θ _A = 40 degrees cannot be incident on the medium B and is reflected (that is, totally reflected).

となる。しかし、この数３式を満たすθ_Bは存在しない。すなわち、媒質Ｂが空気の場合、媒質Ａから入射する光には全反射する角度が存在するが、媒質Ｂ（空気）からの光は必ず透過する。この性質を利用したのがプリズムである。 If θ _A = 90 degrees (sinθ _A = 1) under the same conditions, Equation 2 is

It becomes. However, there is no θ _B that satisfies this equation (3). That is, when the medium B is air, the light incident from the medium A has a totally reflected angle, but the light from the medium B (air) is always transmitted. A prism uses this property.

  FIG. 10 shows a path of light incident on the prism piece 61. As shown in FIG. 10, the light L1 that has entered the prism piece 61 having a refractive index greater than 1 from the inside of the glass tube 50 enters the glass tube 50 again through the path indicated by the solid line in FIG. Further, the light L2 incident on the prism piece 61 from the air passes through the path indicated by the chain line in FIG. 10, but may be totally reflected at the boundary between the glass tube 50 and the prism piece 61. In order to prevent this, it is necessary that the bottom surface of the prism piece 61 is in contact with a medium having a similar refractive index. In the present embodiment, the laser medium 31 is accommodated in the glass tube 50 with the periphery surrounded by water, and a prism piece 61 is disposed on the outer side surface of the glass tube 50. Therefore, the light L2 incident on the prism piece 61 from the air enters the laser medium 31 through the prism piece 61, the glass tube 50, and water. The light that has not been absorbed by the laser medium 31 enters the prism piece 61 opposite to the incident prism piece 61 and is totally reflected at the boundary between the prism piece 61 and air. Therefore, the totally reflected light does not escape into the air but travels again toward the laser medium 31.

Specifically, when the material of the prism piece 61 is quartz glass, since the refractive index N _A = 1.54, the critical angle θ _m is expressed by the equation (2) from sin θ _m = 1 / 1.54, θ _m = 40 degrees. That is, the light traveling from the prism piece 61 into the air is totally reflected when the incident angle is 40 degrees or more. Therefore, it is considered that the light traveling from the prism piece 61 into the air has a higher probability of total reflection at the boundary than the probability of transmission into the air.

On the other hand, since the refractive index of water is N = 1.33, if N _A = 1.54 and N _B = 1.33 in Equation 2, the critical angle θ _m is sinθ _m = 1.33 / From 1.54, θ _m = 60 degrees. That is, the light traveling from the prism piece 61 to the water is totally reflected when the incident angle is 60 degrees or more. Therefore, it is considered that the light traveling from the prism piece 61 to the water has a higher probability of transmitting into the water than the probability of total reflection at the boundary.

Further, in the present embodiment, a glass tube 50 is interposed between the prism piece 61 and water. If the refractive index of the glass tube 50 is N = 1.46, at the boundary between the prism piece 61 and the glass tube 50, if N _A = 1.54 and N _B = 1.46 in Equation 2, The critical angle θ _m is θ _m = 71 degrees from sin θ _m = 1.46 / 1.54. That is, the light traveling from the prism piece 61 to the glass tube is totally reflected when the incident angle is 71 degrees or more. Further, at the boundary between the glass tube 50 and the water, if N _A = 1.46 and N _B = 1.33 in the formula 2, the critical angle θ _m is from sin θ _m = 1.33 / 1.46. , Θ _m = 66 degrees. That is, by interposing the glass tube 50 between the prism piece 61 and water, it is possible to increase the probability that light incident on the prism piece 61 from the air reaches the water without being reflected.

  In this way, by interposing a medium having a different refractive index little by little in the light path from the prism 60 to the laser medium 31, the effect of confining the light once incident on the prism 60 so as not to escape into the air is increased. be able to. Thereby, the absorption efficiency of the light to the laser medium 31 can be raised.

(Embodiment 4)
In the third embodiment, the prism 60 is described as being disposed on the outer side surface of the glass tube 50 in which the laser medium 31 is accommodated, but the arrangement of the prism 60 is not limited thereto. For example, the prism 60 may be disposed outside the laser housing 23.

  11A and 11B are schematic views showing the light guide 20 and the laser cavity 30 of the solar light pumped laser oscillation device 1 according to this embodiment. The solar light pumped laser oscillation device 1 according to the present embodiment further includes a prism 70 in addition to the solar light pumped laser oscillation device 1 according to the first embodiment.

  In the example shown in FIG. 11A, the prism 70 is composed of one prism piece arranged on the sunlight incident window 21. With this configuration, sunlight incident from above in FIG. 11A enters the prism 70, the sunlight incident window 21, and the water in the space 24 without being reflected at the boundary between the prism 70 and the air. Further, the light exiting from the inside of the laser housing 23 is totally reflected at the boundary between the prism 70 and the air, and therefore travels inward again.

  In the example illustrated in FIG. 11B, the prism 70 includes a plurality of prism pieces 71 arranged on the sunlight incident window 21. In the example shown in FIG. 11A, since the volume of one prism piece constituting the prism 70 is large, there is a possibility that thermal destruction may occur due to sunlight absorbed by slight impurities in the prism 70. Therefore, by arranging a plurality of small prism pieces 71 on the sunlight incident window 21 as shown in FIG. 11B, the possibility of thermal destruction can be reduced.

(Embodiment 5)
In FIG. 12, the schematic diagram which shows the light guide 20 and the laser cavity 30 of the sunlight excitation laser oscillation apparatus 1 which concerns on this embodiment is shown. The sunlight-excited laser oscillation device 1 according to the present embodiment includes a reflection surface 82 instead of the reflection surface 22 in the light guide 20 of the sunlight-excitation laser oscillation device 1 according to the third embodiment. In the fifth embodiment, the configuration other than the reflection surface is the same as that of the third embodiment, and the detailed description thereof is omitted.

  The reflecting surface 82 is composed of a plurality of reflecting surfaces 82a to 82g. The reflection surface 82a is a surface substantially parallel to the longitudinal axis X of the laser medium.

  The reflecting surfaces 82b, 82d, 82f, and 82g are arranged so as to move away from the axis X from the position on the output end side of the laser medium 31 toward the position of the end opposite to the output end of the laser medium. It is a surface inclined with respect to. That is, the reflecting surfaces 82b, 82d, 82f, and 82g are outward inclined surfaces that are inclined so that the surfaces face in the direction (outward) from the laser housing 23 toward the sunlight incident window 21.

  The reflection surfaces 82c and 82e are inclined with respect to the axis X so as to approach the axis X from the position on the output end side of the laser medium 31 toward the end on the opposite side to the output end of the laser medium. It is a surface to do. That is, the reflecting surfaces 82c and 82e are inwardly inclined surfaces that are inclined so that the surfaces face in the direction (inward) from the laser housing 23 toward the output end of the laser medium 31.

  Next, light collection in the light guide 20 in the present embodiment will be described.

  As shown in FIG. 12, sunlight Sf3 incident on the reflecting surfaces 82b, 82d, 82f, and 82g (only the sunlight incident on the reflecting surface 82b is shown in FIG. 12) is relatively reflected by the central portion of the laser medium 31. Condensed from near to the top. Therefore, the sunlight is prevented from being collected near the output end of the laser medium 31. Further, the reflective surfaces 82b, 82d, and 82f are shorter in length in the direction perpendicular to the axis X than the first reflective surface 22a as shown in FIG. Therefore, the reflective surfaces 82b, 82d, and 82f have a smaller amount of blocking sunlight toward the back of the light guide 20 than the first reflective surface 22a as shown in FIG.

  As shown in FIG. 12, the reflecting surfaces 82c and 82e receive sunlight Sf4 reflected from the back of the light guide 20 and traveling outward (only sunlight incident on the reflecting surface 82c is shown in FIG. 12). Reflects in the direction toward. Loss of light incident on the light guide 20 can be reduced.

  In the present embodiment, the reflective surface 82 including the four outwardly inclined surfaces of the reflective surfaces 82b, 82d, 82f, and 82g and the two inwardly inclined surfaces of the reflective surfaces 82c and 82e has been described. The number of outwardly inclined surfaces and inwardly inclined surfaces included is not limited to this.

DESCRIPTION OF SYMBOLS 1 Sunlight excitation laser apparatus 10 Fresnel lens 11 Split lens 11a Groove 20 Light guide 21 Sunlight incident window 22 Reflective surface 22a First reflective surface 22b Second reflective surface 23 Laser housing 24 Space 25 Cooling water inlet 26 Cooling water outlet 30 Laser cavity 31 Laser medium 32 High reflection film 33 Antireflection film 34 Output mirror 42 Reflection surface 42a First reflection surface 42b Second reflection surface 42c Third reflection surface 50 Glass tube 60 Prism 61 Prism piece 70 Prism 71 Prism piece 82 (82a to 82g) Reflective surface 200 Conventional light guide 220 Conventional reflective surface 2 Target

Claims (8)

A rod-shaped laser medium that emits laser light when excited by sunlight; and
A plurality of reflecting surfaces that are located laterally of the laser medium with respect to the longitudinal axis of the laser medium, have different inclination angles with respect to the axis, and reflect the sunlight;
With
The plurality of reflecting surfaces are separated from the longitudinal axis of the laser medium from the position on the output end side of the laser medium toward the position on the end side opposite to the output end of the laser medium. Including an outwardly inclined surface inclined with respect to the axis,
A solar-excited laser oscillation device characterized by that. The outwardly inclined surface is
A first outwardly inclined surface inclined at a first angle with respect to the axis;
A second outwardly inclined surface that is inclined with respect to the axis at a second angle smaller than the first angle;
A third outward direction that is located on the output end side of the laser medium with the second outwardly inclined surface sandwiched between the second outwardly inclined surface and that is inclined at a third angle larger than the second angle with respect to the axis. An inclined surface;
including,
The solar light excitation laser oscillating device according to claim 1. Covering at least a part of the laser medium via a medium, further comprising a prism having a refractive index larger than that of the medium;
The solar light excitation laser oscillating device according to claim 1 or 2. Further comprising a glass tube containing the laser medium and water;
The prism is disposed on an outer side surface of the glass tube.
The solar light excitation laser oscillating device according to claim 1 or 2. The plurality of reflection surfaces approach the longitudinal axis of the laser medium from the position on the output end side of the laser medium toward the position on the end side opposite to the output end of the laser medium. Further including an inwardly inclined surface inclined with respect to the axis,
The solar-pumped laser oscillation device according to claim 4. A glass window disposed opposite to the end opposite to the output end of the laser medium,
The medium and the laser medium are accommodated in a space formed by the glass window and the plurality of reflecting surfaces,
The prism is disposed on a surface opposite to a surface forming the space of the glass window.
The solar-pumped laser oscillation device according to claim 3. The reflective surface is formed by subjecting a glass material to a surface treatment that reflects the sunlight.
The solar light pumped laser oscillation device according to any one of claims 1 to 6. The reflective surface is formed by applying a surface treatment that reflects the sunlight to a resin material.
The solar light pumped laser oscillation device according to any one of claims 1 to 6.

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