Semiconductor laser-excited solid state laser

Abstract

[Problem] To achieve stable operation and cost reduction in an LD-excited solid-state laser in which a solid-state laser crystal is excited by an excitation light emitted from an LD, causing laser oscillation, and obtained laser oscillation lights of two frequencies are converted into a sum frequency. [Solution] An LD-excited solid-state laser (1) that is obtained by having: a solid-state laser crystal (19); an LD (11) that emits an excitation light for exciting the solid-state laser crystal (19); a resonator that causes light emitted from the solid-state laser crystal (19) to resonate; and a light wavelength conversion element (22) that performs wavelength conversion of solid-state laser oscillation lights (L21, L22), wherein a wave combining means (21) is provided that receives the two solid-state laser oscillation lights (L21, L22) from different directions from each other and combines the same into one, and the light wavelength conversion unit (22) converts the combined solid-state laser oscillation lights (L21, L22) into a sum frequency.　

Description

Semiconductor laser-pumped solid-state laser

[0001] This invention relates to a semiconductor laser-pumped solid-state laser, more specifically, to a solid-state laser that excites a solid laser crystal, which serves as a laser medium, with excitation light emitted by a semiconductor laser to cause laser oscillation, and converts the resulting laser oscillation light of two frequencies into a sum frequency.

[0002] For example, as detailed examples are shown in Patent Document 1, for example, Pr ３＋ Conventionally known solid-state lasers are in which a solid-state laser crystal, such as a YLF crystal doped with Pr (hereinafter referred to as Pr:YLF crystal), is excited by excitation light emitted from a semiconductor laser (laser diode; hereinafter referred to as LD), and the light emitted from the excited solid-state laser crystal is resonated by a resonator. As for the solid-state laser crystal, Nd(YLF) as shown in Patent Document 2 is a known example. ３＋ YAG crystals doped with Nd:YAG (hereinafter referred to as Nd:YAG crystals) can also be used.

[0003] Pr:YLF crystals are extremely attractive laser crystals because they absorb light at wavelengths of 442 nm, 444 nm, 469 nm, and 479 nm, and can generate laser oscillations at wavelengths of 479 to 720 nm. However, because Pr:YLF crystals have a narrow absorption wavelength range, when applied to semiconductor laser-pumped solid-state lasers, the oscillation wavelength of the excitation LD must match the absorption wavelength, and the oscillation wavelength range must be 0.5 to 1 nm or less for high-power and stable laser oscillations to be achieved. To explain the absorption and oscillation wavelengths in more detail and practical terms, they are not fixed at pinpoint locations, but rather have waveforms that extend over a certain range. When specific numerical values ​​are given for wavelengths, they refer to the peak wavelength (which may also be the center wavelength of the waveform) in that waveform.

[0004] However, commercially available GaN-based LDs for excitation that can emit light at 400 nm, the absorption wavelength band of Pr:YLF crystals, have an oscillation wavelength variation of 5 to 10 nm. If an LD with an oscillation wavelength that matches the absorption wavelength band is selected, the yield becomes only a few percent. Considering that the unit price of an LD is originally around 100,000 yen, the cost of the LDs alone would exceed 1 million yen. Therefore, it is extremely difficult to carry out mass production on an industrial level. Furthermore, the oscillation wavelength width is wider than the absorption wavelength width of the Pr:YLF crystal, by about 2 nm, so even if the wavelengths match, there is a problem of reduced absorption efficiency. In addition, LDs have the characteristic that their oscillation wavelength fluctuates depending on the light output and temperature, so it is extremely difficult to mass-produce LDs with oscillation wavelengths that match the absorption wavelength of the Pr:YLF crystal, taking these characteristics into account.

[0005] Furthermore, it has also been conventional to convert the laser oscillation light obtained as described above into a desired optical wavelength, and in particular, Patent Document 3 shows how to convert laser oscillation light of two wavelengths into a sum frequency of one wavelength.

[0006] However, the laser device described in the above-mentioned patent document propagates both wavelengths of laser light and the sum frequency coaxially (propagates in a common direction). Therefore, it is difficult to match the oscillation wavelength of the excitation LD with the absorption wavelength of the solid laser crystal in order to achieve stable operation. Furthermore, difficult alignment (position adjustment) of the excitation LD, solid laser crystal, solid laser resonator, and sum frequency generation optical wavelength conversion element is required to achieve coaxial propagation, which tends to make the device even more expensive.

[0007] Japanese Patent Publication No. 2001-36176, Japanese Patent Publication No. 2001-36175, Japanese Patent Publication No. 2006-66436

[0008] This invention has been made in view of the above circumstances, and aims to achieve stable operation and lower cost in an LD-pumped solid-state laser in which a solid-state laser crystal is excited by excitation light emitted by a semiconductor laser to cause laser oscillation, and the two resulting laser oscillations of different frequencies are converted into a sum frequency.

[0009] The LD-pumped solid-state laser according to the present invention comprises: a solid-state laser crystal such as a Pr:YLF crystal; an LD such as a GaN-based LD that emits excitation light to excite the solid-state laser crystal; a resonator that resonates the light emitted from the excited solid-state laser crystal; and an optical wavelength conversion element that converts the wavelength of the solid-state laser oscillation light. The semiconductor laser-pumped solid-state laser is characterized in that a multiple solid-state laser oscillation light is provided, which receives a plurality of solid-state laser oscillation light beams, for example two, from different directions and combines them into one beam, and the optical wavelength conversion element converts the multiple solid-state laser oscillation light beams into a sum frequency.

[0010] In the LD-pumped solid-state laser according to the present invention, an external resonator is provided to resonate the excitation light from the semiconductor laser, and this external resonator has a transmission-reflection mirror that transmits the excitation light emitted from the semiconductor laser toward the solid-state laser crystal and reflects it toward the semiconductor laser, and it is preferable that this transmission-reflection mirror is formed from two glass plates joined together.

[0011] In that case, the two glass plates can preferably be those joined together by optical contact, those joined by forming a metal plating near the edge of each glass plate and heating and welding the metal platings together, those joined by forming a metal plating and a metal plate overlapping the metal plating near the edge of each glass plate and heating and welding the metal plates together via the metal plating, or those joined by melting low-melting-point glass placed near the edge of each glass plate.

[0012] In the above configuration, it is desirable that the solid-state laser oscillation light consists of two beams with different polarization directions, and that these solid-state laser oscillation light beams are incident on the multiplexing means in directions perpendicular to each other, and that the multiplexing means combines the solid-state laser oscillation light beams into one beam by utilizing the difference in polarization directions. In that case, it is desirable that the wavelengths of the two solid-state laser oscillation light beams are each in the range of 500 to 750 nm, and the wavelength of the sum frequency is in the range of 250 to 375 nm.

[0013] Furthermore, in the above configuration, it is desirable to provide a wavelength control means that substantially matches the oscillation wavelength of the excitation light from the LD with the absorption peak wavelength of the solid laser crystal. Specifically, a bandpass filter can be used as such a wavelength control means, which is placed inside the resonator to narrow the wavelength of the resonating light.

[0014] According to the LD-pumped solid-state laser of the present invention, as described above, two solid-state laser oscillations are combined into one by the multiplexing means. Therefore, unlike the case of coaxial propagation described above, it is not necessary to perform difficult positional adjustments of the excitation LD, solid-state laser crystal, solid-state laser resonator, and sum-frequency generation optical wavelength conversion element, and thus cost reduction is achieved.

[0015] Schematic diagram showing an LD-pumped solid-state laser as the first embodiment of the present invention. Schematic diagram showing an LD-pumped solid-state laser as the second embodiment of the present invention. Schematic diagram showing an LD-pumped solid-state laser as the third embodiment of the present invention. Schematic diagram showing an LD-pumped solid-state laser as the fourth embodiment of the present invention. Schematic diagram showing an LD-pumped solid-state laser as the fifth embodiment of the present invention. Schematic diagram showing an LD-pumped solid-state laser as the sixth embodiment of the present invention. Schematic diagram showing an LD-pumped solid-state laser as the seventh embodiment of the present invention. Schematic side view showing the main parts of the apparatus in Figure 7 before assembly. Schematic side view showing the main parts shown in Figure 7 after assembly. LD-pumped solid-state laser A schematic side view showing deposits formed on a transmissive plane mirror. A schematic plan view showing an example of a beam spot of excitation light affected by deposits. A schematic diagram showing an example of a normal beam profile of excitation light. A schematic diagram showing an example of an abnormal beam profile of excitation light. A schematic side view showing the state of the main part of the eighth embodiment of the present invention before assembly. A schematic side view showing the state of the main part after assembly as shown in Figure 14. A schematic side view showing the state of the main part of the ninth embodiment of the present invention before assembly. A schematic side view showing the state of the main part after assembly as shown in Figure 16. A schematic side view showing the state of the main part of the tenth embodiment of the present invention before assembly. A schematic side view showing the state of the main part after assembly as shown in Figure 18.

[0016] Embodiments of the present invention will be described below with reference to the drawings. <<First Embodiment>> Figure 1 shows a schematic configuration of an LD-pumped solid-state laser 1, which is the first embodiment of the present invention. This LD-pumped solid-state laser 1 has a first excitation LD 11, a collimating lens 16, a focusing lens 17, a plane mirror 18, and a rod-shaped (shown as a rectangle in the figure) Pr:YLF crystal 19 arranged from left to right in the figure. The elements 11 to 19 arranged from left to right in the figure above are collectively referred to as the first excitation / oscillation system 31. The LD-pumped solid-state laser 1 also has a second excitation LD 11, a collimating lens 16, a focusing lens 17, a plane mirror 18, and a rod-shaped (shown as a rectangle in the figure) Pr:YLF crystal 19, which are arranged from bottom to top in the figure above. The elements 11 to 19 arranged from bottom to top in the figure above are collectively referred to as the second excitation / oscillation system 32.

[0017] The first excitation / oscillation system 31 will now be explained in detail. The first excitation LD 11 is a laser oscillator that emits excitation light L with a wavelength of 444 nm in a divergent state. This excitation light L travels to the right in the figure, is made into parallel light by the collimating lens 16, and enters the converging lens 17. This incident parallel light is focused by the converging lens 17 so as to converge within the Pr:YLF crystal 19, and then passes through the plane mirror 18. The Pr:YLF crystal 19, upon receiving the excitation light L, is excited by the excitation light L and emits light with a wavelength of 698 nm by stimulated emission. This light resonates in a solid-state laser resonator composed of the plane mirror 18 and the concave mirror 20, and solid-state laser oscillation light L21 with a wavelength of 698 nm is obtained.

[0018] The second excitation LD 11 of the second excitation / oscillation system 32 also generates a laser itself, emitting excitation light L with a wavelength of 444 nm in a divergent state. This excitation light L travels upward in the figure, is made into parallel light by the collimating lens 16, and enters the converging lens 17. This incident parallel light is focused by the converging lens 17 so as to converge within the Pr:YLF crystal 19, and then passes through the plane mirror 18. The Pr:YLF crystal 19, upon receiving the excitation light L, is excited by the excitation light L and emits light with a wavelength of 607 nm through stimulated emission. This light resonates within the solid-state laser resonator composed of the plane mirror 18 and the concave mirror 20, yielding solid-state laser oscillation light L22 with a wavelength of 607 nm. The surface of the plane mirror 18 facing the Pr:YLF crystal and the concave surface (inner surface) of the concave mirror 20 are coated with a coating (not shown) to constitute the solid-state laser resonator described above.

[0019] The Pr:YLF crystal 19 of the first excitation / oscillation system 31 and the Pr:YLF crystal 19 of the second excitation / oscillation system 32 are configured such that their c-axis extends in the direction shown in the figure. Therefore, the solid-state laser oscillation light L21 with a wavelength of 698 nm has an electric field oscillation direction in the vertical direction in the figure, and the solid-state laser oscillation light L22 with a wavelength of 607 nm has an electric field oscillation direction perpendicular to the plane of the paper in the figure, and these are incident on the polarization beam splitter 21. The polarization beam splitter 21 has a dielectric multilayer film 21a that is tilted at 45° with respect to the direction of propagation of the solid-state laser oscillation light L21 and the solid-state laser oscillation light L22. The solid-state laser oscillation light L21 is incident on this dielectric multilayer film 21a in a p-polarized state, and the solid-state laser oscillation light L22 is incident on it in an s-polarized state. For solid-state laser oscillation light L21 and L22 in such polarized states, the dielectric multilayer film 21a transmits the former with a transmittance of 99.5% or more and reflects the latter with a reflectance of 99.5% or more.

[0020] Thus, from the polarized beam splitter 21, the solid-state laser oscillation light L21 and solid-state laser oscillation light L22, which were propagating in different directions, are combined and emitted in a common unidirectional direction. These combined solid-state laser oscillation light L21 and solid-state laser oscillation light L22 are emitted from a nonlinear optical material, BBO crystal (β-BaB ２ O ４It is incident on the BBO crystal 22 and wavelength-converted by the BBO crystal 22 into a sum frequency wave L23 with a wavelength of 325 nm under the type-II phase matching condition. This sum frequency wave L23 passes through the concave mirror 20 and is emitted as useful light outside the LD-pumped solid-state laser 1. An AR (anti-reflection) coating for light with a wavelength of 325 nm is applied to the concave surface 20a of the concave mirror 20, that is, the surface facing the plane mirror 18.

[0021] When the BBO crystal 22 is used as the nonlinear optical material, if its cut angle θ = 52.1°, the BBO crystal 22 wavelength-converts the solid-state laser oscillation light L21 with a wavelength of 698 nm as the extraordinary light, the solid-state laser oscillation light L22 with a wavelength of 607 nm as the ordinary light, and the sum frequency wave L23 with a wavelength of 325 nm as the extraordinary light. On the other hand, if the cut angle θ of the BBO crystal 22 is 57.3°, the solid-state laser oscillation light L21 with a wavelength of 698 nm is used as the ordinary light, the solid-state laser oscillation light L22 with a wavelength of 607 nm is used as the extraordinary light, and the sum frequency wave L23 with a wavelength of 325 nm is wavelength-converted as the extraordinary light.

[0022] As the nonlinear optical material, in addition to the BBO crystal 22, a CLBO crystal or the like can also be used. When a CLBO crystal is used, if its cut angle θ = 71.4°, the CLBO crystal wavelength-converts the solid-state laser oscillation light L21 with a wavelength of 698 nm as the extraordinary light, the solid-state laser oscillation light L22 with a wavelength of 607 nm as the ordinary light, and the sum frequency wave L23 with a wavelength of 325 nm as the extraordinary light.

[0023] <<Second Embodiment>> Next, referring to FIG. 2, the second embodiment of the present invention will be described. FIG. 2 shows a schematic configuration of the LD-pumped solid-state laser 2 according to this second embodiment. The LD-pumped solid-state laser 2 has a configuration that is mostly common to the LD-pumped solid-state laser 1 of the first embodiment shown in FIG. 1. Therefore, hereinafter, mainly the differences from the LD-pumped solid-state laser 1 will be described, but the parts not described are basically the same as those of the LD-pumped solid-state laser 1, so the overlapping descriptions regarding those parts are omitted (the same applies to the third embodiment described later).

[0024] In the LD-pumped solid-state laser 2 shown in FIG. 2, a saturable absorber 25 is disposed in the optical path of the solid-state laser oscillation light L21 between the Pr:YLF crystal 19 of the first excitation / oscillation system 31 and the polarization beam splitter 21. Also, a saturable absorber 26 is disposed in the optical path of the solid-state laser oscillation light L22 between the Pr:YLF crystal 19 of the second excitation / oscillation system 32 and the polarization beam splitter 21.

[0025] In the LD-pumped solid-state laser 2 having the above configuration, Q-switch oscillation of the solid-state laser oscillation lights L21 and L22 becomes possible due to the action of the saturable absorbers 25 and 26. Specifically, as such saturable absorbers 25 and 26, Cr ４＋ :YAG (Cr ４＋ :Y ３ Al ５ O １２ ), crystals, CO ２＋ :MALO (CO ２＋ :MgAl ２ O ４ ), crystals, etc. can be used. Also, in order to realize Q-switch oscillation, an acousto-optic element or an electro-optic element can be used instead of using a saturable absorber.

[0026] <<Third Embodiment>> Next, referring to FIG. 3, a third embodiment of the present invention will be described. FIG. 3 shows a schematic configuration of an LD-pumped solid-state laser 3 according to this third embodiment. In this LD-pumped solid-state laser 3, the optical configurations of the first excitation / oscillation system 31 and the second excitation / oscillation system 32 are different from those in the LD-pumped solid-state laser 1 and the LD-pumped solid-state laser 2 described above. That is, in the first excitation / oscillation system 31 of the LD-pumped solid-state laser 3, between the excitation LD 11 and the collimating lens 16 similar to the above, a collimating lens 12, a narrow-band BPF (band-pass filter) 13, a converging lens 14, and a transmissive plane mirror 15 are arranged.

[0027] The excitation light L emitted from the excitation LD 11 in a divergent state is made into parallel light by the collimating lens 12, and this parallel light passes through the narrow-band BPF (bandpass filter) 13, which acts as a wavelength control means, and is incident on the converging lens 14. This incident parallel light is focused by the converging lens 14 so as to converge at the front end face of the transmission plane mirror 15, and then passes through the mirror 15. The excitation light L that has passed through the transmission plane mirror 15 is incident on the collimating lens 16, and thereafter proceeds in the same manner as in the LD-pumped solid-state laser 1 and the LD-pumped solid-state laser 2, and is used to excite the Pr:YLF crystal 19.

[0028] With the first excitation / oscillation system 31 configured as described above, the wavelength of the excitation light L is controlled to precisely match the absorption wavelength of the Pr:YLF crystal 19, thereby maintaining a high luminescence efficiency of the Pr:YLF crystal 19. The second excitation / oscillation system 32 is similar to that of the first excitation / oscillation system 31 described above, and can produce the same effects as the first excitation / oscillation system 31. In Figure 3, the solid-state laser resonator ranges for the first excitation / oscillation system 31 and the second excitation / oscillation system 32 are indicated by arrows A.

[0029] ≪Fourth Embodiment≫ Next, a fourth embodiment of the present invention will be described with reference to Figure 4. Figure 4 shows a schematic configuration of an LD-pumped solid-state laser 4, which is the fourth embodiment. In this LD-pumped solid-state laser 4, excitation light L with a wavelength of 444 nm emitted in a divergent state from the excitation LD 11 is made into parallel light by the collimating lens 16 and incident on the converging lens 17. This incident parallel light is focused by the converging lens 17 so as to converge within the Pr:YLF crystal 19 and then passes through the plane mirror 18. The Pr:YLF crystal 19, upon receiving the excitation light L, is excited by the excitation light L and emits light with a wavelength of 698 nm by stimulated emission. This light is reflected by the concave mirror 20, which serves as the first mirror, and incident on the plane mirror 51, which serves as the second mirror. It resonates in a solid-state laser resonator composed of the plane mirror 51 and the plane mirror 18, and solid-state laser oscillation light L21 with a wavelength of 698 nm is obtained.

[0030] Furthermore, the Pr:YLF crystal 19, upon receiving the excitation light L, is excited by the excitation light L and emits light with a wavelength of 607 nm through stimulated emission. This light is reflected by the concave mirror 20 and incident on the planar mirror 51, where it resonates within the solid-state laser resonator composed of the planar mirror 51, the concave mirror 20, and the planar mirror 18, thereby obtaining solid-state laser oscillation light L22 with a wavelength of 607 nm.

[0031] The concave mirror 20 is positioned at an angle to the optical axis of the planar mirror 18, and the planar mirror 51 is positioned so that the reflection axis of the concave mirror 20 and the optical axis are aligned. A BBO (β-BaB) is then placed between the concave mirror 20 and the planar mirror 51 so that their optical axes pass through it. ２ O ４ A crystal 52 is arranged. The BBO crystal 52 is a nonlinear optical material and wavelength-converts the incident solid-state laser oscillation light L21 with a wavelength of 698 nm and the solid-state laser oscillation light L22 with a wavelength of 607 nm to a sum frequency L23 with a wavelength of 325 nm under type II phase matching conditions. This sum frequency L23 passes through the concave mirror 20 and is emitted out of the LD-pumped solid-state laser 4. The concave surface 20a of the concave mirror 20, that is, the surface facing the planar mirror 51, is coated with an AR (anti-reflective) coating for light with a wavelength of 325 nm.

[0032] As described above, in this embodiment, the solid-state laser oscillation light L21 and solid-state laser oscillation light L22, which are traveling in different directions, are combined by the BBO crystal 52 into a state where they travel in a common unidirectional direction, and then wavelength-converted to a sum frequency L23. This sum frequency L23, in particular, travels along a different optical path from the solid-state laser oscillation light L21 and L22 after passing through the concave mirror 20.

[0033] When the BBO crystal 52 is used as a nonlinear optical material as described above, if its cut angle θ = 52.1°, the BBO crystal 52 uses the solid-state laser oscillation light L21 with a wavelength of 698 nm as extraordinary light, the solid-state laser oscillation light L22 with a wavelength of 607 nm as ordinary light, and the sum frequency L23 with a wavelength of 325 nm as extraordinary light for wavelength conversion. When the BBO crystal is used, if its cut angle θ = 57.3°, the solid-state laser oscillation light L21 with a wavelength of 698 nm as ordinary light, the solid-state laser oscillation light L22 with a wavelength of 607 nm as extraordinary light, and the sum frequency L23 with a wavelength of 325 nm as extraordinary light for wavelength conversion.

[0034] In addition to the BBO crystal mentioned above, CLBO crystals and the like can also be used as nonlinear optical materials. When a CLBO crystal is used, if its cut angle θ = 71.4°, the CLBO crystal uses the solid-state laser oscillation light L21 with a wavelength of 698 nm as extraordinary light, the solid-state laser oscillation light L22 with a wavelength of 607 nm as ordinary light, and the sum frequency L23 with a wavelength of 325 nm as extraordinary light to perform wavelength conversion.

[0035] <Fifth Embodiment> Next, a fifth embodiment of the present invention will be described with reference to Figure 5. Figure 5 shows a schematic configuration of the LD-pumped solid-state laser 5, which is this fifth embodiment. In this LD-pumped solid-state laser 5, a saturable absorber 25 is placed between the Pr:YLF crystal 19 and the concave mirror 20, in the optical paths of the solid-state laser oscillation light L21 and L22. This saturable absorber 25 is the same as the saturable absorbers 25 and 26 placed in the second embodiment. By placing such a saturable absorber 25, the same effects as those obtained in the second embodiment can be achieved in this embodiment as well.

[0036] <<Sixth Embodiment>> Next, a sixth embodiment of the present invention will be described with reference to Figure 6. Figure 6 shows a schematic configuration of the LD-pumped solid-state laser 6, which is this sixth embodiment. This LD-pumped solid-state laser 6 is configured to combine solid-state laser oscillation light L21 with a wavelength of 698 nm generated in the first excitation / oscillation system 31 and solid-state laser oscillation light L22 with a wavelength of 607 nm generated in the second excitation / oscillation system 32 using a polarizing beam splitter 21. The first excitation / oscillation system 31 includes a first excitation system 61, a second excitation system 62, a third excitation system 63, and a fourth excitation system 64.

[0037] The first excitation / oscillation system 31 will now be described in detail. The first excitation system 61 consists of an excitation LD 11, a collimating lens 12, a narrowband BPF 13, a focusing lens 14, a transmission plane mirror 15, a collimating lens 16, and a mirror 65, which are arranged sequentially from left to right along the optical axis extending horizontally in Figure 6. The second excitation system 62 consists of the same excitation LD 11, collimating lens 12, narrowband BPF 13, focusing lens 14, transmission plane mirror 15, and collimating lens 16 as described above, plus a wavelength multiplexing mirror 66. The third excitation system 63 consists of the same excitation LD 11, collimating lens 12, narrowband BPF 13, focusing lens 14, transmission plane mirror 15, and collimating lens 16 as described above (these elements are shared with the fourth excitation system 64, which will be described later), plus a wavelength multiplexing mirror 67. The fourth excitation system 64 is configured with the same excitation LD 11, collimating lens 12, and narrowband BPF 13 as described above, in addition to a polarizing beam splitter 91.

[0038] On the other hand, the second excitation / oscillating system 32 similarly has a first excitation system 61, a second excitation system 62, a third excitation system 63, and a fourth excitation system 64. The first excitation system 61 to the fourth excitation system 64 of the second excitation / oscillating system 32 will be described below. The first excitation system 61 consists of an excitation LD 11, a collimating lens 12, a narrowband BPF 13, a focusing lens 14, a transmission plane mirror 15, a collimating lens 16, and a mirror 65, which are arranged sequentially from bottom to top along the optical axis extending vertically in the figure. The second excitation system 62 consists of the same excitation LD 11, collimating lens 12, narrowband BPF 13, focusing lens 14, transmission plane mirror 15, and collimating lens 16 as above, plus a wavelength multiplexing mirror 66. The third excitation system 63 is configured with the same excitation LD 11, collimating lens 12, narrowband BPF 13, focusing lens 14, transmission plane mirror 15, and collimating lens 16 as described above (the above elements are shared with the fourth excitation system 64 described later), in addition to a wavelength multiplexing mirror 67. The fourth excitation system 64 is configured with the same excitation LD 11, collimating lens 12, and narrowband BPF 13 as described above, in addition to a polarizing beam splitter 92.

[0039] The operation of the first excitation / oscillation system 31 described above will now be explained. The excitation light L1 emitted by the first excitation system 61 is reflected by the mirror 65 and then combined with the excitation light L emitted by the second excitation system 62 by the wavelength multiplexing mirror 66. After combination, the excitation light L emitted by the second excitation system 62 and the excitation light L emitted by the fourth excitation system 64 are combined by the wavelength multiplexing mirror 67. The excitation light L emitted by the third excitation system 62 and the excitation light L emitted by the fourth excitation system 64 are combined by the polarization beam splitter 91 before being incident on the wavelength multiplexing mirror 67. In this manner, the Pr:YLF crystal 19 of the first excitation / oscillation system 31 is incident on the Pr:YLF crystal 19, which has been combined from a total of four excitation systems, resulting in good excitation and the acquisition of high-intensity solid-state laser oscillation light L21.

[0040] The same applies to the second excitation / oscillation system 32. In other words, the Pr:YLF crystal 19 of the second excitation / oscillation system 32 is also incident on it with high-intensity excitation light L that has been emitted from a total of four excitation systems and then combined into one, so that excitation is performed well and high-intensity solid-state laser oscillation light L22 can be obtained.

[0041] The solid-state laser light L21 has a wavelength of 698 nm, and the solid-state laser light L22 has a wavelength of 607 nm. They propagate in directions orthogonal to each other and are incident on the polarizing beam splitter 21, where they are combined into a single beam. The combined solid-state laser light L21 and L22 are incident on the BBO crystal 22, where the BBO crystal 22 converts their wavelength to a sum frequency L23 with a wavelength of 325 nm. The sum frequency L23 passes through the concave mirror 20 and is emitted outside the LD-pumped solid-state laser 6 as usable light.

[0042] <<Seventh Embodiment>> Next, a seventh embodiment of the present invention will be described with reference to Figure 7. Figure 7 shows a schematic configuration of an LD-pumped solid-state laser 7, which is the seventh embodiment. Compared to the LD-pumped solid-state laser 3 of the third embodiment shown in Figure 3, this LD-pumped solid-state laser 7 differs in that a transmission-reflection mirror 115 is provided instead of a transmission-plane mirror 15, and other aspects are basically the same as the configuration in Figure 3. Therefore, in the following, we will omit the explanation of configurations that are the same as those in Figure 3 and mainly explain the differences.

[0043] As shown in detail in Figure 8, the transmissive reflective mirror 115 is formed by joining two glass plates 115a and 115b, each being a parallel plate with a rectangular or circular shape. One surface of glass plate 115a is coated with an anti-reflective coating AR2, and the other surface is coated with a high-reflectivity coating HR. One surface and the other surface of another glass plate 115b are coated with anti-reflective coatings AR1 and AR2, respectively.

[0044] The above high-reflectance coating film HR is, for example, HfO ２、 Ta ２ O ５ , TiO ２ It is composed of a multilayer film made of the like, and the anti-reflective coating films AR1 and AR2 are for example SiO ２It is composed of films. The anti-reflective coating film AR1 is designed and manufactured so that its reflectivity is 0.5% or less after the glass plate is bonded as described below, and the anti-reflective coating film AR2 is designed and manufactured so that its reflectivity is 0.5% or less in air.

[0045] As described above, after fabricating the anti-reflective coating films AR1 and AR2 and the high-reflectivity coating film HR, the surfaces of the anti-reflective coating film AR1 and the high-reflectivity coating film HR were activated by ozone treatment, plasma treatment, or ultraviolet light treatment. Then, the two glass plates 115a and 115b were joined by overlapping their surfaces (see Figure 9). The joining was performed in air or vacuum. In this case, the two glass plates 115a and 115b were joined by so-called optical contact. After joining, the reflectivity of the joint was measured using a laser beam for reflectivity measurement, and the reflectivity was 30%. This reflectivity measurement can also be performed using the excitation light L in the configuration of Figure 7, and in that case as well, the reflectivity was 30%. Furthermore, this reflectivity can also be measured using a spectrometer, which is commonly used.

[0046] The two glass plates 115a and 115b are joined together and arranged as a transmission-reflection mirror 115 as shown in Figure 7 to form an LD-pumped solid-state laser 7 according to the seventh embodiment. In this configuration, the excitation light L is focused by the focusing lens 14 so as to converge at the joint surface of the two glass plates 115a and 115b. 70% of the excitation light L passes through the transmission-reflection mirror 115, and the remaining 30% is reflected at the joint surface (more specifically by the high-reflection coating film HR) and returns to the excitation LD 11 (see Figure 9).

[0047] In this embodiment, the portion where the focused excitation light L converges is sandwiched between the two glass plates 115a and 115b, so that the beam profile of the excitation light L at the convergence position can be maintained in a normal state. This beam profile will be described in detail below.

[0048] First, as shown in the configuration in Figure 3, when the excitation light L is focused on one surface of the transmission plane mirror 15 and energized for a long period of time, the beam profile will change abnormally over time. This tendency is particularly strong when a confocal optical system is present and the oscillation wavelength is also controlled, as in the configuration in Figure 3. In other words, on the mirror surface constituting the external resonator (shown by the solid double arrows indicating the resonator range in Figure 3), the beam spot of the focused excitation light L is small, resulting in a high optical power density. A high optical power density makes the beam profile more prone to becoming abnormal. Here, long-term energization refers to driving at a constant optical output for several hundred hours or more, or continuous driving for several thousand hours or more.

[0049] For example, if the excitation light L is a short-wavelength blue to violet light with a high output of several hundred mW to over 1 W, and the excitation LD 11 is energized for a long time, a photochemical reaction will occur in the focused portion of the excitation light L. As a result, organic matter floating in the surrounding atmosphere will gradually accumulate on the mirror surface. Due to the influence of this accumulation, the beam profile of the excitation light L focused on the mirror surface will gradually change from a normal Gaussian beam shape and become abnormal.

[0050] Here, in the configuration shown in Figure 3, if the above-mentioned deposit occurs on one surface of the transmission plane mirror 15, an example of the approximate side shape of the deposit T is shown in Figure 10, and an example of the approximate planar shape of the beam spot BS affected by this deposit T is shown in Figure 11. Also, the Gaussian beam shape, which is the normal beam profile of the excitation light L, is shown in Figure 12, and an example of an abnormal beam profile is shown in Figure 13. The abnormal beam profile shape changes to various disordered shapes, not limited to the profile shape in Figure 13, depending on the operating environment conditions. Because it is so different from the Gaussian beam shape used in normal optical design, the reflected light does not return to the excitation LD 11 normally, and wavelength control becomes insufficient. Furthermore, the beam of the excitation light L1 also has an abnormal beam profile shape, so the beam cannot be focused to the design value within the YLF crystal 19, resulting in a malfunction in which normal laser oscillation cannot be achieved. Note that the beam profiles in Figures 12 and 13 are represented by position on the horizontal axis and light intensity on the vertical axis.

[0051] In this embodiment, as shown in Figure 7, the position where the focused excitation light L converges is sandwiched between the two glass plates 115a and 115b, thus preventing the accumulation of organic matter floating in the surrounding atmosphere around the glass plates 115a and 115b. Therefore, the beam profile of the excitation light L is not abnormalized due to the influence of deposits, and a normal Gaussian beam shape is maintained.

[0052] <Eighth Embodiment> Next, the eighth embodiment of the present invention will be described. Compared to the LD-pumped solid-state laser 7 of the seventh embodiment shown in Figure 7, the LD-pumped solid-state laser of this eighth embodiment differs in the configuration of the transmission-reflection mirror 115 (and therefore in its manufacturing method), but other than that, it is basically the same as the configuration in Figure 7. Therefore, the following will mainly describe the differences from the configuration in Figure 7, but this is also true for the ninth and tenth embodiments which will be described later.

[0053] In this embodiment, two glass plates 115a and 115b are joined by welding metals positioned near the inner circumference of their periphery. Figure 14 schematically shows the state before the metals M are welded, and Figure 15 schematically shows the state after welding. As shown in these figures, a high-reflectivity coating film HR is applied to the inner circumference of the annular metal M on one surface of glass plate 115a, and an anti-reflective coating film AR2 is applied to the inner circumference of the annular metal M on one surface of the other glass plate 115b. The other surfaces of glass plates 115a and 115b are each coated with an anti-reflective coating film AR1.

[0054] The above high-reflectance coating film HR is, for example, HfO ２、 Ta ２ O ５ , TiO ２ It is composed of a multilayer film made of the like, and the anti-reflective coating films AR1 and AR2 are for example SiO ２ It is composed of films. The anti-reflective coating film AR1 is designed and manufactured to have a reflectivity of 0.5% or less in air, and the anti-reflective coating film AR2 is designed and manufactured to have a reflectivity of 0.5% or less in an inert gas.

[0055] After forming the above coating films HR, AR1, and AR2, NiCr or Cr is deposited as a base layer on the peripheral areas (a predetermined range from the periphery to the center) of the glass plates 115a and 115b, and then AuSn (80% Au by weight) is plated on top of it until it reaches a thickness of 10 μm. In Figures 14 and 15, this plated portion is shown as metal M.

[0056] When glass plates 115a and 115b are stacked so that the plated portions overlap, and heated to a temperature above the melting point of AuSn (280°C), the AuSn melts and the glass plates 115a and 115b are joined together (as shown in Figure 15). This joining by melting is performed on dry N2 with a dew point temperature of -50°C or lower. ２ It is preferable to carry out the procedure in an inert gas such as dry nitrogen. ２ In addition, argon and other gases can also be used.

[0057] The transmission-reflection mirror 115, consisting of the glass plates 115a and 115b described above, was applied to the configuration shown in Figure 7 to obtain an LD-pumped solid-state laser according to the eighth embodiment. In this eighth embodiment as well, the beam profile at the convergence position of the excitation light L is maintained normally. This is thought to be because, in this embodiment as well, the convergence portion of the excitation light L is sandwiched between the glass plates 115a and 115b, and in this particular case, the two glass plates are joined via welded metal.

[0058] In other words, in this case, the area sandwiched between the two glass plates 115a and 115b is highly airtight, and even if something is present there, it is only an inert gas. Therefore, organic matter cannot penetrate this area, nor can deposits caused by organic matter (see Figure 10) form. Consequently, the beam profile of the excitation light L is not abnormally altered by long-term energization due to the influence of deposits, and is maintained normally.

[0059] <<Ninth Embodiment>> Next, the ninth embodiment of the present invention will be described. In this ninth embodiment, as in the eighth embodiment, two glass plates 115a and 115b are joined by welding the metal near their peripheral edges together, but the method of producing the joining metal differs from that of the eighth embodiment. The production of this joining metal will be described below.

[0060] Figure 16 schematically shows the state before the joining metal M described above is welded, and Figure 17 schematically shows the state after welding. As shown in these figures, a high-reflectivity coating film HR is applied to the inner circumference of the annular metal M on one surface of the glass plate 115a, and an anti-reflective coating film AR1 is applied to the inner circumference of the annular metal M on one surface of the other glass plate 115b. The other surfaces of the glass plates 115a and 115b are each coated with an anti-reflective coating film AR1.

[0061] The above high-reflectance coating film HR is, for example, HfO ２、 Ta ２ O ５ , TiO ２ It is composed of a multilayer film made of the like, and the anti-reflective coating films AR1 and AR2 are for example SiO ２ It is composed of films. The anti-reflective coating film AR1 is designed and manufactured to have a reflectivity of 0.5% or less in air, and the anti-reflective coating film AR2 is designed and manufactured to have a reflectivity of 0.5% or less in an inert gas.

[0062] After forming the coating films HR and AR1 described above, NiCr or Cr is deposited as a base layer on the peripheral areas (a predetermined range from the periphery to the center) of the glass plates 115a and 115b, and then AuSn (80% Au by weight) is plated on top of that until it reaches a thickness of 10 μm. Note that this plating process is omitted in Figures 16 and 17.

[0063] After the above plating is applied, when heated to a temperature above the melting point of AuSn (280°C or higher), the AuSn melts and the glass plate 115a and the metal M are fixed together, and the glass plate 115b and the metal M are fixed together (the state shown in Figure 16). Next, with the glass plates 115a and 115b stacked on top of each other so that the portions of the metal M overlap, when the metal M is further heated to a temperature above the melting point of AuSn (280°C or higher), the glass plates 115a and 115b are joined together via the molten metal M (the state shown in Figure 17).

[0064] The above bonding is for dry N with a dew point temperature of -50°C or lower. ２ It is preferable to carry out the procedure in an inert gas such as dry nitrogen. ２In addition, argon and other gases can also be used. In such cases, a gap formed between the glass plate 115a and the glass plate 115b will be created by an airtightly sealed inert gas.

[0065] After the glass plate 115a and metal M are bonded together, and the glass plate 115b and metal M are bonded together, as shown in Figure 16, the melting point of AuSn is elevated because Au has diffused into the AuSn. Therefore, when joining glass plates 115a and 115b, as shown in Figure 17, the melting of AuSn and the subsequent delamination of the previously established bond are prevented. Alternatively, this delamination can be prevented by using AuSn with different composition ratios (for example, the ratio of Au to Sn) and different melting points for the bonding and bonding processes.

[0066] <Tenth Embodiment> Next, a tenth embodiment of the present invention will be described. In this tenth embodiment, two glass plates 115a and 115b are joined using low-melting-point glass. This joining will be described below with reference to Figures 18 and 19.

[0067] Figure 18 schematically shows the state of glass plates 115a and 115b before joining, and Figure 19 schematically shows the state after welding. As shown in these figures, a high-reflectivity coating film HR is applied to the inner circumference of the annular low-melting-point glass G on one surface of glass plate 115a, and an anti-reflective coating film AR1 is applied to the inner circumference of the annular low-melting-point glass G on one surface of the other glass plate 115b. The other surfaces of glass plates 115a and 115b are each coated with an anti-reflective coating film AR1.

[0068] The above high-reflectance coating film HR is, for example, HfO ２、 Ta ２ O ５ , TiO ２ It is composed of a multilayer film made of the like, and the anti-reflective coating film AR1 is for example SiO ２ It is composed of films. The high-reflectivity coating film HR is designed and manufactured to have a reflectivity of 30% in an inert gas, while the anti-reflective coating film AR1 is designed and manufactured to have a reflectivity of 0.5% or less in an inert gas.

[0069] After forming the above coating film HR, the low-melting-point glass G is melted, and the glass plates 115a and 115b are joined together (as shown in Figure 19). The low-melting-point glass G is lead-free glass Ta ２ O ５ (Tantalum pentoxide) and MoO ３ A mixture of powdered glass (molybdenum trioxide) was used and applied to the outer periphery of each glass plate 115a and 115b. The applied area was then heated to its melting point of 380°C or higher to melt and join the low-melting-point glass Gs together. In this way, glass plate 115a and glass plate 115b are joined, but a gap sealed with an inert gas is formed between them.

[0070] The aforementioned powdered glass mixture includes PbO·B ２ O ３ ・SiO ２ A mixture consisting of the above can also be used. In that case, the above heating is performed at 500°C, which is above the melting point of the mixture. When the low-melting-point glass G is melted in this way and the glass plates 115a and 115b are joined to form an LD-excited solid laser 1 as shown in Figure 7, the beam profile of the Gaussian beam shape at the convergence position of the excitation light L was able to be maintained as normal, similar to the embodiments described above. Therefore, in this case as well, it is considered that the generation of deposits T due to long-term current application as shown in Figure 10 is suppressed.

[0071] Although embodiments of the present invention have been described above, it goes without saying that the LD-pumped solid-state laser according to the present invention is not limited to these embodiments. Furthermore, the LD-pumped solid-state laser according to the present invention is not limited to these embodiments, but can be particularly suitably used in, for example, devices for measuring the photoluminescence of semiconductors, flow cytometry devices, devices for analyzing genomics such as DNA sequencers, exposure devices for performing mask writing, direct writing, beam interference, etc., semiconductor wafer inspection devices, semiconductor mask inspection devices, laser processing devices, etc.

[0072] Furthermore, the specific nm value to which the excitation wavelength of the semiconductor laser is controlled to approximate the absorption peak wavelength of the solid laser crystal is not limited to the values ​​(nm) mentioned in each embodiment described above, but can be set appropriately according to the absorption peak wavelength of the target solid laser crystal. For example, if one wants to obtain an LD-pumped solid laser having an oscillation wavelength similar to that of a He-Ne laser, which is a type of gas laser, then it is natural to control the wavelength to approximately match the absorption peak wavelength of the solid laser crystal used therein. In addition, although the above describes an embodiment in which a transmission-reflection mirror 115 is applied in the first excitation / oscillation system 31 of Figure 7, a similar transmission-reflection mirror 115 may also be applied to the second excitation / oscillation system 32.

[0073] 1, 2, 3, 4, 5, 6, 7 LD-pumped solid-state laser 11 Excitation LD 12 Remating lens 13 Narrowband BPF 14 Focusing lens 15 Transmitting plane mirror 16 Collimating lens 17 Focusing lens 18, 51 Planar mirror 19 Pr:YLF crystal 20 Concave mirror 20a Concave surface of concave mirror 21, 91, 92 Polarizing beam splitter 21a Dielectric multilayer film 22 BBO crystal 25, 26 Saturable absorber 31 First excitation / oscillation system 32 Second excitation / oscillation system 52 BBO crystal 61 First excitation system 62 Second excitation system 63 Third excitation system 64 Fourth excitation system 65 Mirror 66, 67 Wavelength multiplexing mirror

Claims

1. A semiconductor laser-pumped solid laser comprising: a solid laser crystal; a semiconductor laser emitting excitation light to excite the solid laser crystal; a resonator for resonating the light emitted from the excited solid laser crystal; and a wavelength conversion element for wavelength conversion of the solid laser oscillation light, wherein a multiplexing means is provided for receiving two solid laser oscillation lights of different frequencies from different directions and combining them into one, and the wavelength conversion element converts the two solid laser oscillation lights into a sum frequency and emits the sum frequency in a direction different from at least one of the solid laser oscillation lights.

2. The semiconductor laser-pumped solid-state laser according to claim 1, wherein the two solid-state laser oscillation beams have polarization directions orthogonal to each other, and these solid-state laser oscillation beams are incident on the multiplexing means, and the multiplexing means combines the two solid-state laser oscillation beams into one beam by utilizing the difference in their polarization directions.

3. The semiconductor laser-pumped solid laser according to claim 1, wherein the two solid-state laser oscillation beams are emitted from a single solid-state laser crystal and have mutually orthogonal polarization directions, these solid-state laser oscillation beams travel along a common optical path, the two solid-state laser oscillation beams traveling along this common optical path are reflected by a first mirror and incident on the optical wavelength conversion element, and the sum frequency whose wavelength has been converted by the optical wavelength conversion element is reflected by a second mirror so as to travel along an optical path different from the optical path of the two solid-state laser oscillation beams.

4. A semiconductor laser-pumped solid-state laser according to claim 1, wherein an external resonator is provided to resonate the excitation light from the semiconductor laser, and this external resonator has a transmission-reflection mirror that transmits the excitation light emitted from the semiconductor laser toward the solid-state laser crystal and reflects it toward the semiconductor laser, and this transmission-reflection mirror is formed from two glass plates joined together.

5. The semiconductor laser-pumped solid-state laser according to claim 4, wherein the two glass plates are joined to each other by optical contact.

6. The semiconductor laser-pumped solid-state laser according to claim 4, wherein the two glass plates are joined together by forming a metal plating near the periphery of each glass plate and heating and welding the metal platings together.

7. The semiconductor laser-pumped solid-state laser according to claim 4, wherein the two glass plates are joined together by forming a metal plating near the periphery of each glass plate and a metal plate overlapping the metal plating, and then heating and welding the metal plates to each other via the metal plating.

8. The semiconductor laser-pumped solid-state laser according to claim 4, wherein the two glass plates are joined together by melting low-melting-point glass placed near the periphery of each glass plate.

9. The semiconductor laser-pumped solid-state laser according to claim 1 or 2, wherein the wavelengths of the two solid-state laser oscillations are each in the range of 500 to 750 nm, and the wavelength of the sum frequency is in the range of 250 to 375 nm.

10. The solid laser crystal is Pr ３＋ A semiconductor laser-pumped solid-state laser according to claim 1 or 2, which is doped with [a specific substance].

11. The semiconductor laser-pumped solid-state laser according to claim 1 or 2, wherein the semiconductor laser is a GaN-based semiconductor laser.

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