JP2006135262A - Solid state laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state laser device wherein excitation light absorption ratio is high in solid state laser medium. <P>SOLUTION: The solid state laser device 1 is provided with the solid state laser medium 2, an excitation light supply 8, and a re-incident optical system 10. The solid state laser medium 2 is arranged between a first reflecting surface and a second reflecting surface of a resonator 4. The excitation light supply part 8 supplies first excitation light l<SB>1</SB>from the first reflecting surface of the resonator 4 to the inside of the resonator. At this time, the first excitation light l<SB>1</SB>enters slantingly to an optical axis A<SB>x</SB>of the resonator 4. The re-injected optical system 10 changes polarization direction of the first excitation light l<SB>1</SB>outputted from the resonator 4 in a surface perpendicular to the optical axis, and makes the light l<SB>1</SB>enter the inside of the resonator 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state laser device.

There is an end face excitation type as a configuration in the solid-state laser device. In the edge-pumped solid-state laser device, excitation light emitted from an excitation light source is irradiated from the end face of the solid-state laser medium, the solid-state laser medium is excited to generate laser light, which is emitted after being resonated. In the solid-state laser device of the end face excitation type, the optical path of the laser beam and the excitation light in the solid-state laser medium is in the same direction, so that the excitation efficiency is good and the quality of the obtained laser light is good (Non-Patent Document 1).
Kobayashi Goro, “Solid-State Laser”, Spectroscopic Society of Japan, Measurement Method Series, Japan Society Publishing Center, 1997, pages 124-127

  In a crystal, which is a laser medium of a solid-state laser device, when excitation light is incident, an absorption coefficient generally differs depending on the polarization direction of light due to the relationship with the axial direction of the crystal. Therefore, depending on the type of crystal, the wavelength of the excitation light, etc., the excitation light of one polarization component is difficult to be absorbed by the crystal, and the contribution to the excitation of the crystal may be small. On the other hand, for example, when a fiber coupling LD is used as an excitation light source, the polarization direction of the excitation light is random. For this reason, when the absorption coefficient is low for one polarization component as described above, the absorptance of the excitation light as a whole is lowered, which may cause a decrease in excitation efficiency. Further, if the absorption rate of the excitation light is low, the excitation efficiency is reduced.

  In addition, when using an excitation light supply means that supplies random light with a polarization direction like the above-described fiber coupling LD, the excitation light that has not been absorbed by the crystal becomes return light, which may damage the fiber or the like. There is.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a solid-state laser device having a high excitation light absorption rate in a solid-state laser medium.

  In order to achieve such an object, a solid-state laser device according to the present invention includes a solid-state laser medium disposed between a first reflecting surface and a second reflecting surface of a resonator, and the first reflecting surface of the resonator. The pumping light supply means for entering the first pumping light into the resonator from the first and the second pumping light by changing the polarization direction in the plane perpendicular to the optical axis of the first pumping light emitted from the resonator And a re-incident optical system that makes the second excitation light enter the resonator.

  The above-described solid-state laser device has an end-face excitation configuration in which the first excitation light is incident on the solid-state laser medium from the first reflection surface of the resonator. In such a configuration, since the optical paths of the laser light and the excitation light in the solid-state laser medium are in the same direction, high excitation efficiency is realized. Further, the solid-state laser device re-enters the first pumping light emitted from the resonator without being absorbed by the solid-state laser medium as a second pumping light by changing its polarization direction and entering again into the resonator. An optical system is provided. As a result, it is possible to polarize the excitation light emitted from the solid laser medium with a low absorption coefficient in a direction with a high absorption coefficient and to enter the solid laser medium again. As a result, in this solid-state laser device, a high pumping light absorption rate is realized in the solid-state laser medium. It is particularly preferable that the re-incidence optical system changes the first excitation light emitted from the resonator into the second excitation light by changing the polarization direction by 90 ° in a plane perpendicular to the optical axis. By rotating the polarization direction by 90 °, the excitation light absorptance is effectively improved from the relationship with the axial direction of the crystal.

  The first excitation light is preferably incident on the resonator obliquely with respect to the optical axis of the resonator. By making the first excitation light incident obliquely with respect to the optical axis of the resonator in this way, it is possible to prevent the first excitation light from returning to the excitation light supply means and damaging it. Furthermore, according to such a configuration, the re-incident optical system and the like can be easily installed.

  In addition, it is preferable that the re-incidence optical system includes a reflection unit and a quarter-wave plate disposed between the reflection unit and the resonator. In such a configuration, the first excitation light emitted from the resonator can be rotated into the polarization direction by 90 ° to be the second excitation light, and can enter the resonator.

  In addition, it is preferable to further include a spot diameter adjusting optical system that adjusts the spot diameter of the second excitation light from the re-incidence optical system to the solid laser medium so as to be substantially the same as the spot diameter of the first excitation light. . Thereby, the mode matching efficiency achieved when supplying the first excitation light can be achieved even when the second excitation light is incident.

The solid-state laser medium is preferably made of Nd: GdVO ₄ crystal. According to the examination result by the present inventor, the Nd: GdVO ₄ crystal has an absorption coefficient different depending on the polarization direction of light. Therefore, by applying the above configuration to such a crystal, it becomes possible to improve the pumping light absorption rate in the solid-state laser medium. Furthermore, by using the Nd: GdVO ₄ crystal as a solid-state laser medium, a solid-state laser device having high output, stability, and cost efficiency can be realized.

  According to the present invention, it is possible to provide a solid-state laser device having a high excitation light absorption rate in a solid-state laser medium.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

  FIG. 1 is a perspective view schematically showing a schematic configuration of a solid-state laser device according to this embodiment, and FIG. 2 is a cross-sectional view. The solid-state laser device 1 includes a resonator 4, a solid-state laser medium 2, an excitation light supply unit 8, a re-incidence optical system 10, and condensing optical systems 16 and 18. The solid-state laser device 1 is of an end face excitation type, and is excited by irradiating excitation light having a predetermined wavelength from the end face of the solid-state laser medium 2. Laser light having a wavelength different from that of the excitation light is generated by the excited solid-state laser medium 2, and is emitted after being resonated by the resonator 4.

The solid-state laser medium 2 included in the solid-state laser device 1 is composed of GdVO ₄ (Nd: GdVO ₄ ), which is a vanadate material to which Nd ions (Nd ³⁺ ) are added. The Nd: GdVO ₄ crystal that is the solid-state laser medium 2 absorbs light with wavelengths of 808 nm and 880 nm, and generates light with a wavelength of 1063 nm. In the solid-state laser device 1 according to the present embodiment, the solid-state laser medium 2 is excited using light having a wavelength of 880 nm as excitation light l ₁ and l ₂ , and laser light l ₃ having a wavelength of 1063 nm is output. FIG. 3 shows the properties of the Nd: GdVO ₄ crystal in detail.

The Nd: GdVO ₄ crystal is an anisotropic crystal having three crystal axes a-axis, b-axis, and c-axis orthogonal to each other, and the light absorption coefficient differs depending on the axial direction. FIG. 4 is a graph showing the absorption coefficient of the Nd: GdVO ₄ crystal with respect to light polarized in the respective directions of the a-axis and c-axis, ie, light whose electric field directions are the a-axis and c-axis directions. Graph A represents the absorption coefficient of Nd: GdVO ₄ crystal of light polarized in the a-axis direction, and graph B represents the absorption coefficient of Nd: GdVO ₄ crystal of light polarized in the c-axis direction. These graphs are the results of measurement using a cubic Nd: GdVO ₄ crystal having a Nd ion (Nd ³⁺ ) concentration of 0.5 at% and a side length of 3 mm. As can be seen from these graphs, the Nd: GdVO ₄ crystal has an absorption wavelength band centered on 808 nm and 878.8 nm (hereinafter, discussed as 880 nm). In any absorption wavelength band, the absorption coefficient of light polarized in the a-axis direction is smaller than the absorption coefficient of light polarized in the c-axis direction. However, in the absorption wavelength band having a central wavelength of 808 nm, the absorption coefficient of the light polarized in the a-axis direction has a certain size, so that there is little problem with the light that is not absorbed by the crystal. On the other hand, in the absorption wavelength band centered at 880 nm, the absorption coefficient of light polarized in the a-axis direction is very small, and the spectrum width is also narrow. Therefore, when light having a wavelength of 880 nm that is polarized in a random direction is used as excitation light, a component that is polarized in the a-axis direction is not absorbed, and a problem that does not occur with light having a wavelength of 808 nm also occurs. In addition, not only light polarized in the a-axis direction but also light polarized in any direction as long as the direction is perpendicular to the c-axis, the same absorption coefficient as the absorption coefficient shown in the graph A is shown. .

The solid-state laser medium 2 is formed in a rectangular parallelepiped shape as shown in FIG. As shown in FIGS. 1 and 2, the solid-state laser medium 2 has a first surface 2a and a second surface 2b facing each other. In the solid-state laser device 1, the solid-state laser medium 2 is arranged so that the c-axis of the Nd: GdVO ₄ crystal is perpendicular to the plane including the optical axes of the pumping light l ₁ and l ₂ . The a-axis of the Nd: GdVO ₄ crystal only needs to be parallel to a plane perpendicular to the c-axis. For example, the solid-state laser medium 2 is arranged so as to be parallel to any of the a _{1 to} a ₃ axes shown in FIG. You may arrange. A specific example of the solid-state laser medium 2 includes a configuration using a cubic crystal having a side length of 3 mm, for example.

On the first surface 2a of the solid-state laser medium 2, in order to transmit more pumping lights l ₁ and l ₂ , reflection of light in a predetermined wavelength band (for example, 800 nm to 900 nm) including the pumping wavelength (for example, 880 nm) is prevented. An antireflection coating (AR coating) 22A is applied. Additionally, on the first surface 2a, to more reflecting the laser beam l _3, high-reflection coating (HR coat) is a high reflectance with respect to light of a predetermined wavelength band including an oscillation wavelength (e.g., 1063 nm) 22H is given.

Further, on the second surface 2b of the solid-state laser medium 2, in order to reflect more of the first pumping light ₁₁ that has not been absorbed by the solid-state laser medium 2, a predetermined wavelength band including an excitation wavelength (for example, 880 nm) ( For example, a high reflection coat (HR coat) 24H having a high reflectivity is applied to light of 800 nm to 900 nm. In addition, on the second surface 2b, for transmitting a laser beam l _3, anti-reflection coating (AR coating) 24A for preventing reflection of light in a predetermined wavelength band including an oscillation wavelength (e.g., 1063 nm) is performed Yes.

Further, the solid-state laser device 1 has a high-reflection coating (HR) on the first surface 2a at a position away from the second surface 2b along the normal direction of the first surface 2a and the second surface 2b of the solid-state laser medium 2. Coat) An output mirror 6 is provided so as to constitute the resonator 4 together with 22H. That is, the first surface 2 a of the solid-state laser medium 2 functions as a first reflecting surface of the resonator 4, and the output mirror 6 functions as a second reflecting surface of the resonator 4. Accordingly, as understood from FIGS. 1 and 2, the solid-state laser medium 2 is disposed between the first reflection surface and the second reflection surface of the resonator 4. The output mirror 6 is disposed in parallel with the first surface 2 a and the second surface 2 b of the solid-state laser medium 2. Therefore, the optical axis A _x of the resonator 4 is perpendicular to the first surface 2a and second surface 2b of the solid-state laser medium 2. The optical axis _{A x} and Nd resonator 4: in a relationship perpendicular to the c axis of GdVO ₄ crystal. The output mirror 6, transmits a portion of the laser beam l ₃ for generating a partial transmission mirror that reflects the rest.

The solid-state laser apparatus 1, a first condensing optical system 16 for adjusting the first spot diameter of the excitation light l ₁ with respect to the excitation light supply unit 8 and the solid-state laser medium 2 and outputs a first excitation light l ₁ Prepare. Pumping light supply section 8, a first excitation light l _1, incident on the resonator 4 from the first reflecting surface of the cavity 4. At this time, the first excitation light l ₁ is incident on the resonator 4 obliquely to the optical axis A _x of the resonator 4. Thus, the incident direction of the first excitation light l ₁ forms an angle θ with the optical axis A _x of the resonator 4. For example, when the solid laser medium 2 having a side length of 3 mm is used, the angle θ = 2.77 °. The pumping light supply unit 8 includes a semiconductor laser element 8a that is a pumping light source and an optical fiber 8b. First excitation light l ₁ outputted from the semiconductor laser element 8a passes through the optical fiber 8b is incident on the solid-state laser medium 2.

Further, the solid-state laser device 1 changes the polarization direction with respect to the first excitation light l ₁ that is not absorbed by the solid-state laser medium 2 but is reflected by the second surface 2 b and emitted from the resonator 4. A re-incidence optical system 10 that is l ₂ and enters the resonator 4 is provided. The re-incidence optical system 10 includes a mirror 14 and a quarter-wave plate 12 that are reflection means in order to change the polarization direction of the _first excitation light ₁₁ in a plane perpendicular to the optical axis. The mirror 14 is provided with a high reflection coat (HR coat) having a high reflectivity with respect to light in a predetermined wavelength band (for example, 800 nm to 900 nm) including an excitation wavelength (for example, 880 nm).

In addition, the solid-state laser apparatus 1 comprises a second condensing optical system 18 is a second excitation light l ₂ of the image transfer lens to be incident on the resonator 4 emitted from the re-incident optical system 10. Second condensing optical system 18, the second excitation light l spot diameter of ₂ adjusted so that the first substantially the same spot diameter as the excitation beam l ₁ of from re-entering the optical system 10 with respect to the solid-state laser medium 2 Functions as a spot diameter adjusting optical system, and is constituted by one or a plurality of lenses, for example. The second condensing optical system 18 is disposed between the re-incident optical system 10 and the resonator 4 so that the optical axis thereof coincides with the optical axis of the re-incident optical system 10. Here, in the present specification, the spot diameter refers to the spot diameter of the excitation light when the second surface 2b of the solid-state laser medium 2 is incident.

  Next, the laser oscillation operation of the solid state laser device 1 will be described.

First, the first pumping light ₁₁ having a wavelength of 880 nm is output from the semiconductor laser element 8a and is incident on the optical fiber 8b. Then, the first excitation light ₁₁ is incident on the solid-state laser medium 2 from the optical fiber 8b via the first condensing optical system 16, and the solid-state laser medium 2 is excited. At this time, considering the mode matching efficiency, the first excitation light ₁₁ is condensed by the first condensing optical system 16 so as to have a predetermined spot diameter. For example, at a cooling temperature of 15 ° C. (however, variable between 12 ° C. and 20 ° C.), the amount of Nd ions (Nd ³⁺ ) added is 0.5 at%, and the length of one side is 3 mm. was a Nd: using GdVO ₄ crystal as the solid-state laser medium 2, when the resonator length was set to 120mm, the spot diameter of the first excitation light _{l 1} is preferable to the 400 [mu] m, the cavity length Can be increased to 800 μm. In addition, when entering the resonator 4, the first excitation light ₁₁ is incident obliquely with respect to the optical axis A _x of the resonator 4 by an angle θ.

Since the first pumping light ₁₁ is supplied via the optical fiber 8b, it is polarized in a random direction. Further, in the Nd: GdVO ₄ crystal, which is the solid-state laser medium 2, the light absorption coefficient varies greatly depending on the polarization direction, as shown in FIG. That is, while the absorption coefficient of light polarized in the c-axis direction is large, the absorption coefficient of light polarized in the direction perpendicular to the c-axis direction such as the a-axis direction is very small. Therefore, in the first excitation light ₁₁ , the component polarized in the c-axis direction of the crystal is absorbed in the crystal, but the component polarized in the direction perpendicular to the c-axis direction (for example, the a-axis direction) is difficult to be absorbed. .

Further, as shown in FIG. 5, the first excitation light l ₁ enters the resonator 4 at an angle θ with respect to the optical axis A _{x of} the resonator 4. Therefore, the first excitation light l ₁ which is not absorbed by the solid-state laser medium 2, the second surface 2b of the solid-state laser medium 2 which has been subjected to high-reflection coating (HR coating) 24H, resonator 4 optical axis A _x Are reflected at an angle θ in the opposite direction to the incident direction, and are emitted from the resonator 4.

First excitation light l ₁ emitted from the resonator 4, as shown in FIGS. 1 and 2 and enters the re-incidence optical system 10. First excitation light l ₁ incident on re-entering the optical system 10 is reflected by the mirror 14 passes through the quarter-wave plate 12 twice. Thereby, the first excitation light l ₁ becomes the second excitation light l ₂ whose polarization direction is rotated by 90 ° in a plane perpendicular to the optical axis. Since the first excitation light l ₁ which is not absorbed by the solid-state laser medium 2 is polarized mainly to the c-axis perpendicular direction (e.g., the a-axis direction), the second excitation light l ₂ is mainly c-axis Polarize in direction.

Second excitation light l ₂ emitted from the re-incident optical system 10, the second condensing optical system 18 is focused on the first reflective surface of the cavity 4 (the first surface 2a of the solid-state laser medium 2) , Enters into the resonator 4. The solid laser medium 2 is excited by the incident first and second pumping lights l ₁ and l _{2 in} such a manner that laser oscillation is possible, and laser light l ₃ is generated. Laser beam l ₃ generated after being laser cavity between the first reflecting surface 2a and the second reflecting surface 6 of the cavity 4, is outputted from the output mirror 6.

  Next, effects of the solid-state laser device 1 according to the present embodiment will be described.

The solid-state laser device 1 has a configuration of end-face excitation that supplies pumping lights l ₁ and l ₂ from the first reflecting surface of the resonator 4 (first surface 2 a of the solid-state laser medium 2) to the solid-state laser medium 2. In such a configuration, since the optical paths of the laser beam l ₃ and the pumping beams l ₁ and l ₂ in the solid-state laser medium 2 are substantially in the same direction, high pumping efficiency is realized. In addition, since the oscillation region and the excitation region in the solid-state laser medium 2 easily match, high mode matching efficiency can be obtained.

The solid-state laser apparatus 1, a first excitation light l _1, re-enters the optical system to be incident on the second excitation light l ₂ and to the resonator 4 changes its polarization direction to be emitted into the resonator 4 10 Is provided. As a result, the excitation light component emitted from the resonator 4 having a low absorption coefficient in the first excitation light l ₁ is also incident on the solid laser medium 2 again by rotating the polarization direction in the direction of the high absorption coefficient. Can be made. As a result, a high pumping light absorption rate is realized in the solid-state laser medium 2.

Further, it is preferable to rotate the polarization direction of the excitation light by 90 ° by the re-incident optical system 10. The difference in the absorption coefficient depending on the polarization direction is due to the relationship with the axial direction of the crystal, and the crystal axes of the Nd: GdVO ₄ crystal are orthogonal to each other. It is because it can plan.

The effect of improving the excitation light absorptance will be specifically described using an Nd: GdVO ₄ crystal. As shown in FIG. 4, the absorption coefficient of the Nd: GdVO ₄ crystal varies greatly depending on the polarization direction of the excitation light. That is, the absorption coefficient of the polarization component in the c-axis direction is large, whereas the absorption coefficient of the component polarized in the direction perpendicular to the c-axis such as the a-axis direction is very small. Therefore, the c-axis direction polarization component of the first excitation light l ₁ is absorbed, but the component polarized in the direction perpendicular to the c-axis (for example, the a-axis direction) is hardly absorbed and emitted from the resonator 4. Is done. The first excitation light l ₁ emitted in this way is rotated by 90 ° in the polarization direction by the re-incidence optical system 10 and becomes the second excitation light l ₂ polarized in the c-axis direction. Further, since the second excitation light l ₂ obtained in this way is mainly polarized in the c-axis direction having a large absorption coefficient, it is re-incident into the resonator 4, so that the absorption rate of the excitation light is increased. Improvement is achieved. Thus, the solid-state laser device 1 can function as a single-polarization double-pass excitation optical mechanism.

  Further, when excitation light is supplied by an optical fiber as in the present embodiment, the degree of improvement in absorption rate is particularly large. This is because the excitation light supplied via the optical fiber is randomly polarized and therefore contains a polarization component having a low absorption coefficient.

  It is shown by calculation that the above-described effect can be obtained. If the spectral distribution of a semiconductor laser that is an excitation light source is a Gaussian distribution, the distribution can be expressed by the following equation (1).

Here, λ is the wavelength (nm) of the excitation light, λ ₀ is the center wavelength (878.8 nm) of the semiconductor laser spectrum, and λ _x is the displacement amount when deviating from the center wavelength λ ₀ (878.8 nm) ( nm), and Δλ represents the spectrum width (nm) of the full width at half maximum. Using the spectral distribution I (λ _x , λ) obtained by the equation (1), the excitation light absorption rate A (λ _x , λ) of the Nd: GdVO ₄ crystal can be expressed by the following equation (2).

Here, α (λ) is Nd: a quantification for the absorption coefficient spectra of GdVO ₄ crystal, t is Nd: represents the thickness of GdVO ₄ crystal (mm), respectively. Therefore, 2t represents the length of the optical path when the excitation light reciprocates in the crystal. The thus calculated excitation light absorptance A (λ _x , λ) of the Nd: GdVO ₄ crystal is graphically represented in FIGS. 6 and 7 for the c-axis component and the a-axis component perpendicular to the c-axis, respectively. Figure 6 represents the absorptance A of the c-axis component of the excitation light (λ _{x, λ),} Fig. 7 represents the absorptivity A (λ _x, λ) of the a-axis component. Further, in FIG. 6 and FIG. 7, it represents the graph for each case where a semiconductor laser having different spectral width as an excitation light source, a case graph C _a and C _c is due to the excitation light source spectral width [Delta] [lambda] = 1 nm, graph D _a and When D _c is based on an excitation light source having a spectral width Δλ = 1.5 nm, graphs E _a and E _c are based on an excitation light source having a spectral width Δλ = 2.0 nm, and graphs F _a and F _c are based on a spectral width Δλ = 2. The case with an excitation light source of .5 nm is shown. 6 and 7, it can be seen that the component polarized in the a-axis direction has an absorptance of nearly ½ compared to the component polarized in the c-axis direction.

Further, the results of calculating the absorption rate A (λ _x , λ) of the entire excitation light including all polarization components are shown in FIGS. 8 shows a case where randomly polarized excitation light is supplied to a solid-state laser device without a re-incident optical system, and FIG. 9 shows randomly polarized excitation light applied to the solid-state laser device 1 having the configuration shown in FIG. Each case is shown. 8 and 9, the graphs C ₁ and C ₂ are obtained by using an excitation light source having a spectral width Δλ = 1 nm, and the graphs D ₁ and D ₂ are obtained by using an excitation light source having a spectral width Δλ = 1.5 nm. E ₁ and E ₂ represent the case of an excitation light source having a spectral width Δλ = 2.0 nm, and graphs F ₁ and F ₂ represent the case of an excitation light source having a spectral width Δλ = 2.5 nm. When corresponding to the solid-state laser device 1 according to the present embodiment, FIG. 8 shows the pumping light absorption rate A (λ _x , λ) of the solid-state laser medium 2 when only the first pumping light ₁₁ is supplied, and FIG. This corresponds to the pumping light absorption rate A (λ _x , λ) of the solid-state laser medium 2 when the first pumping light ₁₁ and the second pumping light ₁₂ are supplied. When the spectral width Δλ = 2.0 nm and FIG. 8 and FIG. 9 are compared at the center wavelength match (λ _x = 0.0 nm), the absorptance in the case of random polarization (FIG. 8) is 67.8%. On the other hand, in the case of having the configuration shown in FIG. 1 (FIG. 9), it can be seen that the absorption rate is improved by 97% to nearly 30%. As the absorption rate is improved, the excitation wavelength spectrum width becomes wider. Specifically, FIG. 9 shows that the absorption rate of 90% or more can be maintained even when a wavelength shift of ± 1 nm occurs. For this reason, even if a slight change in excitation wavelength occurs, it is estimated that the solid laser device having the configuration shown in FIG. 1 has an absorptance of 90% or more. As described above, FIG. 8 and FIG. 9 show that the excitation light absorptance is greatly improved by re-entering the excitation light that has not been absorbed by changing the polarization direction.

  Furthermore, with the improvement of the absorption rate of the excitation light in the solid-state laser medium 2, the wavelength band that can be excited is broadened. That is, since a high absorptance is maintained in a wide wavelength range, a high absorptance can be realized even if a wavelength shift from the center wavelength occurs as shown in FIG. Therefore, it is possible to use a light source having a broad spectrum width, and it is possible to reduce the cost applied to the excitation light source.

  In addition, the pumping light absorptance in the solid laser medium is thus improved, so that the pumping efficiency of the solid laser device is also improved.

Also, pumping light supply section 8 is arranged so as to enter the first excitation light l ₁ obliquely to the optical axis A _x of the resonator 4. Therefore, the first excitation light l ₁ returns to the excitation light supply unit 8 which is not absorbed by the solid-state laser medium 2, without injuring the excitation light source 8a and the optical fiber 8b. In particular, when light having a wavelength of 880 nm is incident as excitation light, the absorption coefficient of the component polarized in the direction perpendicular to the c-axis such as the a-axis direction is extremely small as shown in FIG. For example, most of the components polarized in the a-axis direction) are emitted from the resonator 4. Therefore, the optical fiber 8b and the like may be damaged by the return light. However, in the case where the first excitation light l ₁ as the solid-state laser apparatus 1 is incident obliquely to the optical axis A _x of the resonator 4, the excitation light which is not absorbed is different from the pumping light supply section Since the light is emitted in the direction, the excitation light supply unit is not damaged.

Furthermore, since the first excitation light l ₁ is incident obliquely with respect to the optical axis A _x of the resonator 4, the first excitation light l ₁ is emitted from the resonator without being absorbed with the first excitation light l ₁ incident on the resonator 4. The optical path is different from that of the first excitation light. Therefore, the re-incident optical system 10 can be easily installed by this arrangement.

The re-incidence optical system 10 includes a quarter-wave plate 12 and a mirror 14, and the quarter-wave plate 12 is connected to the first reflecting surface of the resonator 4 (the first surface 2 a of the solid-state laser medium 2). It is arranged between the mirror 14. Therefore, the first excitation light l ₁ emitted from the resonator 4 is reflected by the mirror 14, passes through the 1/4-wavelength plate 12 twice. As a result, the polarization direction of the _first excitation light 11 can be rotated by 90 °. As a result, as described above, the pumping light absorption rate in the solid-state laser medium can be improved efficiently.

Further, the solid-state laser apparatus 1 in the second condensing optical system 18, a second spot diameter of the excitation light l _2, is substantially the same as the first spot diameter of the excitation light l _1. Therefore, the mode matching efficiency achieved when supplying the _first excitation light l ₁ can be achieved even when the second excitation light l _{2 is} incident.

The solid-state laser medium 2 is made of Nd: GdVO ₄ crystal. Since the Nd: GdVO ₄ crystal has an absorption coefficient that differs depending on the polarization direction of the light, the pumping light component polarized in the direction with a low absorption coefficient can be used by using the Nd: GdVO ₄ crystal in the solid laser device 1, thereby improving the excitation efficiency. It becomes possible.

Furthermore, the Nd: GdVO ₄ crystal has a broad stimulated emission cross section at the lasing wavelength, a high absorption coefficient at a wide excitation wavelength band, a wide absorption band at the excitation wavelength, a high thermal conductivity, a high slope efficiency, and a high laser induced damage threshold. It has the characteristic of having. Therefore, by using the Nd: GdVO ₄ crystal, it is possible to realize a solid-state laser device that is stable at a high output and further reduced in cost. In addition, the Nd: GdVO ₄ crystal shows a large birefringence optically in one axis, and enables powerful polarized laser oscillation. Furthermore, the Nd: GdVO ₄ crystal has low dependence on the excitation wavelength and is optimal for single mode output. In addition, since the Nd: GdVO ₄ crystal has high thermal conductivity and can obtain high output, it has excellent thermal lens characteristics. Further, the device can be downsized due to high slope efficiency. As described above, the Nd: GdVO ₄ crystal has excellent characteristics as a medium for a high-power DPSS (Diode Pumped Solid-State) laser. In addition, when light having a wavelength of 880 nm is used as excitation light for an Nd: GdVO ₄ crystal, direct excitation to a laser upper level with less thermal problems such as thermal birefringence and thermal lens effect becomes possible.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the solid-state laser medium is not limited to an Nd: GdVO ₄ crystal, but may be an Nd: YVO ₄ crystal or an Nd: YLF crystal. For example, the Nd: YVO ₄ crystal, like the Nd: GdVO ₄ crystal, has a different absorption coefficient of the polarization component of light depending on the crystal axis direction. Therefore, the absorptance can be improved by applying the solid-state laser device according to the present invention to the Nd: YVO ₄ crystal. Further, in the Nd: YVO ₄ crystal, as in the case of the Nd: GdVO ₄ crystal, when light having a wavelength of 880 nm is used as excitation light, the direct laser directing to the laser upper level has few thermal problems such as thermal birefringence and thermal lens effect. Excitation is possible. When the Nd: YVO ₄ crystal is used, the dimensions and the excitation method of the pumping optical system of the solid-state laser device are the same vanadate-based medium, and therefore the Nd: GdVO ₄ crystal including the size of the crystal is used as the solid-state laser medium. It is the same as the case where it used as. When a different crystal is used as the solid-state laser medium, it is preferable to use the center wavelength of the absorption wavelength band of the crystal.

Further, the size and shape of the crystal may not be a cube having a side of 3 mm as in the Nd: GdVO ₄ crystal in the present embodiment. For example, the solid-state laser medium 2A which is a rectangular parallelepiped having an addition amount of Nd ions (Nd ³⁺ ) of 1.0 at% and a size of 3 × 3 × 1 (mm) is used, and the first excitation light ₁₁ is supplied. The state is shown in FIG. In this case, for example, the angle θ can be set to 26 °. Since the mode matching efficiency between the excitation light and the laser beam l _3, and the optical axis of the excitation light and the optical axis of the laser beam in the crystal because it is better to meet with no gap, the angle θ is preferably small. The Nd: GdVO ₄ crystal is preferably arranged so that the c-axis of the Nd: GdVO ₄ crystal and the plane including the optical axis of the excitation light are orthogonal from the viewpoint of oscillation efficiency. Absent.

  The spot diameter ω of the excitation light when the length of the solid-state laser medium in the optical axis direction of the resonator is changed is calculated by the following equation (3).

Here, M ² is the beam quality, λ _p is the excitation light center wavelength, L is the solid laser medium length, and n is the refractive index of the solid laser medium.

  In the solid-state laser device 1, the re-incident optical system 10 rotates the polarization direction of the excitation light by 90 °, but the rotation angle is not limited to 90 °. However, it is preferably between 72 ° and 108 °.

  Further, when an optical fiber is used in the pumping light supply unit, the degree of freedom of the position of the pumping light source in the solid-state laser device is increased, and the space in the solid-state laser device 1 can be effectively used. Therefore, the size of the solid-state laser device can be reduced. However, the excitation light may be directly supplied from the excitation light source to the solid-state laser medium without using an optical fiber. Further, the wavelength of the excitation light is not limited to 880 nm, and may be, for example, 808 nm. The solid-state laser device according to the present invention can be applied to CW oscillators such as CW green laser, far-infrared CW laser, and blue CW laser, pulse oscillators such as near-infrared and green, and mode lock oscillators, for example. Is possible.

  The present invention can be used as a solid-state laser device having a high excitation light absorption rate in a solid-state laser medium.

It is a perspective view which shows the structure of the solid-state laser apparatus which concerns on embodiment. It is a transverse cross section showing typically the composition of the solid-state laser device concerning an embodiment. Nd: is a table showing characteristics of a GdVO ₄ crystal. Nd: is a graph showing the absorption coefficient for the wavelength of GdVO ₄ crystal. It is a figure showing a mode that 1st excitation light is supplied to a crystal | crystallization. It is the graph showing the absorptivity characteristic of the c-axis direction polarization | polarized-light component of excitation light. It is the graph showing the absorptivity characteristic of the a-axis direction polarization | polarized-light component of excitation light. The calculation result of the absorptivity characteristic in the whole excitation light polarized in a random direction is shown. The result of having calculated the absorptivity characteristic in the whole excitation light at the time of making incident light which was not absorbed again is shown. It is a figure showing a mode that 1st excitation light is supplied to a crystal | crystallization.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solid laser apparatus, 2A ... Solid laser medium, 2a ... 1st surface, 2b ... 2nd surface, 4 ... Resonator, 6 ... Output mirror, 8 ... Excitation light supply part, 8a ... Semiconductor laser element, 8b DESCRIPTION OF SYMBOLS Optical fiber, 10 ... Re-incidence optical system, 12 ... 1/4 wavelength plate, 14 ... Mirror, 16 ... 1st condensing optical system, 18 ... 2nd condensing optical system, 22A, 24A ... Antireflection coating, 22H , 24H ... highly reflective coating, the optical axis of the a x _... resonator, l 1 _... first excitation light, l 2 _... first excitation light, l 3 _... laser beam

Claims (5)

A solid-state laser medium disposed between the first reflecting surface and the second reflecting surface of the resonator;
Excitation light supply means for entering first excitation light into the resonator from the first reflecting surface of the resonator;
The first pumping light emitted from the resonator is changed into a second pumping light by changing the polarization direction in a plane perpendicular to the optical axis, and the second pumping light is incident on the resonator. Re-incidence optics,
A solid-state laser device comprising:   2. The solid-state laser device according to claim 1, wherein the first excitation light is incident on the resonator obliquely with respect to the optical axis of the resonator.   3. The solid-state laser device according to claim 1, wherein the re-incidence optical system includes a reflecting unit, and a quarter-wave plate disposed between the reflecting unit and the resonator. .   A spot diameter adjusting optical system for adjusting the spot diameter of the second excitation light from the re-incidence optical system with respect to the solid-state laser medium so as to be substantially the same as the spot diameter of the first excitation light; The solid-state laser device according to any one of claims 1 to 3, wherein: 5. The solid-state laser device according to claim 1, wherein the solid-state laser medium is made of Nd: GdVO ₄ crystal.

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