Semiconductor laser-pumped solid-state laser

Abstract

In an LD-pumped solid-state laser, where a solid-state laser crystal is excited by excitation light emitted from an LD to cause laser oscillation, and the resulting laser oscillation light of two frequencies is converted into a sum frequency, stable operation and cost reduction are achieved. [Solution] In an LD-pumped solid laser 1 comprising a solid laser crystal 19, an LD 11 that emits excitation light to excite the solid laser crystal 19, a resonator that resonates the light emitted from the solid laser crystal 19, and an optical wavelength conversion element 22 that converts the wavelength of solid laser oscillation light L21 and L22, a multiplexing means 21 is provided that receives the two solid laser oscillation light L21 and L22 from different directions and combines them into one, and the optical wavelength conversion element 22 converts the combined solid laser oscillation light L21 and L22 into a sum frequency.

Description

[Technical Field]

[0001] This invention relates to a semiconductor laser-pumped solid-state laser, more specifically, to a solid-state laser in which a solid laser crystal, as a laser medium, is excited by excitation light emitted by a semiconductor laser to cause laser oscillation, and the resulting laser oscillation light of two frequencies is converted into a sum frequency. [Background technology]

[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:YLF (hereinafter referred to as Pr:YLF crystal), is excited by excitation light emitted by 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 solid-state laser crystals, Nd(Nd(Nd(Nd(N))) as shown in Patent Document 2) 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 442nm, 444nm, 469nm, and 479nm, and can generate laser oscillations in the 479-720nm range. 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 0.5-1nm 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 5-10 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 LD 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 an oscillation wavelength that matches 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. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2001-36176 [Patent Document 2] Japanese Patent Publication No. 2001-36175 [Patent Document 3] Japanese Patent Publication No. 2006-66436 [Overview of the Initiative] [Problems that the invention aims to solve]

[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 that excites a solid laser crystal with excitation light emitted from a semiconductor laser to cause laser oscillation, and converts the resulting laser oscillation light of two frequencies into a sum frequency. [Means for solving the problem]

[0009] The LD-pumped solid-state laser according to the present invention is Solid-state laser crystals such as Pr:YLF crystals, An LD such as a GaN-based LD that emits excitation light to excite the solid laser crystal, A resonator that resonates the light emitted from the solid laser crystal after it has been excited, A wavelength conversion element that converts the wavelength of solid-state laser light, In a semiconductor laser-pumped solid-state laser having, A multiplexing means is provided that receives multiple solid-state laser oscillating beams, for example two, from different directions and combines them into one beam. The optical wavelength conversion element converts the combined solid-state laser oscillation light into a sum frequency. It is characterized by the following:

[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 mentioned above. This external resonator has a transmission / reflection mirror that transmits the excitation light emitted from the semiconductor laser toward the solid laser crystal and reflects it toward the semiconductor laser. This transmissive and reflective mirror is preferably formed from two glass plates joined together.

[0011] In that case, the two glass plates may be joined to each other by optical contact, or metal plating may be formed in the vicinity of the periphery of each glass plate, and they may be joined to each other by heating and welding the metal platings, or metal plating and a metal plate overlapping the metal plating may be formed in the vicinity of the periphery of each glass plate, and they may be joined to each other by heating and welding the metal plates through the metal platings, or those joined to each other by melting a low melting point glass arranged in the vicinity of the periphery of each glass plate can be preferably used.

[0012] In the above configuration, the solid laser oscillation light consists of two beams with different polarization directions from each other, and these solid laser oscillation lights are incident on the multiplexing means in directions orthogonal to each other. It is desirable that the multiplexing means multiplexes the solid laser oscillation light into one using the difference in polarization direction. In that case, the wavelengths of the two solid laser oscillation lights are each in the range of 500 to 750 nm, and it is desirable that the wavelength of the sum frequency is in the range of 250 to 375 nm.

[0013] Also, in the above configuration, it is desirable that wavelength control means for making the oscillation wavelength of the excitation light by the LD substantially coincide with the absorption peak wavelength of the solid laser crystal is provided. Specifically, as such wavelength control means, a band-pass filter arranged in the resonator and narrowing the wavelength of the resonating light can be used.

Advantages of the Invention

[0014] According to the LD-excited solid laser of the present invention, since, by the multiplexing means as described above, for example, two solid laser oscillation lights are multiplexed into one, unlike the case of performing the coaxial propagation described above, it is not necessary to difficultly adjust the positions of the excitation LD, the solid laser crystal, the resonator for the solid laser, the optical wavelength conversion element for sum frequency generation, etc., and cost reduction is achieved from that point.

Brief Description of the Drawings

[0015] [Figure 1]Schematic configuration diagram showing the LD-pumped solid-state laser according to the first embodiment of the present invention [Figure 2] Schematic configuration diagram showing the LD-pumped solid-state laser according to the second embodiment of the present invention [Figure 3] Schematic configuration diagram showing the LD-pumped solid-state laser according to the third embodiment of the present invention [Figure 4] Schematic configuration diagram showing the LD-pumped solid-state laser according to the fourth embodiment of the present invention [Figure 5] Schematic configuration diagram showing the LD-pumped solid-state laser according to the fifth embodiment of the present invention [Figure 6] Schematic configuration diagram showing the LD-pumped solid-state laser according to the sixth embodiment of the present invention [Figure 7] Schematic configuration diagram showing the LD-pumped solid-state laser according to the seventh embodiment of the present invention [Figure 8] Schematic side view showing the state before assembly of the main parts in the apparatus of FIG. 7 [Figure 9] Schematic side view showing the state after assembly of the main parts shown in FIG. 7 [Figure 10] Schematic side view showing the deposits formed on the transmissive plane mirror of the LD-pumped solid-state laser [Figure 11] Schematic plan view showing an example of the beam spot of the excitation light affected by the deposits [Figure 12] Schematic diagram showing an example of the normal beam profile of the excitation light [Figure 13] Schematic diagram showing an example of the abnormal beam profile of the excitation light [Figure 14] Schematic side view showing the state before assembly of the main parts of the apparatus according to the fifth embodiment of the present invention [Figure 15] Schematic side view showing the state after assembly of the main parts shown in FIG. 14 [Figure 16] Schematic side view showing the state before assembly of the main parts of the apparatus according to the sixth embodiment of the present invention [Figure 17] Schematic side view showing the state after assembly of the main parts shown in FIG. 16 [Figure 18] Schematic side view showing the state before assembly of the main parts of the apparatus according to the seventh embodiment of the present invention [Figure 19]Schematic side view showing the assembled state of the main parts as shown in Figure 18. [Modes for carrying out the invention]

[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 a 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 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, similar to the above, arranged from bottom to top in the figure. The elements 11 to 19 arranged from bottom to top in the figure 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 through 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 LD11 of the second excitation / oscillation system 32 also generates its own laser oscillation, 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 a 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 tilted at 45° with respect to the propagation direction of the solid-state laser oscillation light L21 and the propagation direction of 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 polarizing 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 incident on a nonlinear optical material, a BBO crystal (β-BaB2O4 crystal) 22, and are wavelength-converted by the BBO crystal 22 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 outside the LD-pumped solid-state laser 1 as usable light. The concave surface 20a of the concave mirror 20, that is, the surface facing the planar mirror 18, is coated with an AR (anti-reflective) coating for light with a wavelength of 325 nm.

[0021] When the BBO crystal 22 is used as a nonlinear optical material, if its cut angle θ = 52.1°, the BBO crystal 22 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. On the other hand, if the cut angle θ = 57.3° of the BBO crystal 22, 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.

[0022] In addition to the BBO crystal 22 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 performs wavelength conversion by treating 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.

[0023] ≪Second Embodiment≫ Next, a second embodiment of the present invention will be described with reference to Figure 2. Figure 2 shows a schematic configuration of the LD-pumped solid-state laser 2, which is this second embodiment. Note that this LD-pumped solid-state laser 2 has a configuration that is largely the same as the LD-pumped solid-state laser 1 of the first embodiment shown in Figure 1. Therefore, the following will mainly describe the differences from the LD-pumped solid-state laser 1, but the parts not described are basically the same as the LD-pumped solid-state laser 1, so redundant explanations of those parts will be omitted (the same applies to the third embodiment which will be described later).

[0024] In the LD-pumped solid-state laser 2 shown in Figure 2, a saturable absorber 25 is placed 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 polarizing beam splitter 21. In addition, a saturable absorber 26 is placed 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 polarizing beam splitter 21.

[0025] In the LD-pumped solid-state laser 2 having the above configuration, the action of the saturable absorbers 25 and 26 enables Q-switched oscillation of the solid-state laser light L21 and L22. Specifically, the saturable absorbers 25 and 26 are Cr 4+ :YAG(Cr 4+ :Y3Al5O 12 ) Crystals, CO 2+ :MALO(CO 2+ Crystals such as MgAl2O4 can be used. Furthermore, to achieve Q-switched oscillation, acousto-optic elements or electro-optic elements can be used instead of saturable absorbers.

[0026] ≪Third Embodiment≫ Next, a third embodiment of the present invention will be described with reference to Figure 3. Figure 3 shows a schematic configuration of the LD-pumped solid-state laser 3, which is 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 differ from those of the LD-pumped solid-state laser 1 and LD-pumped solid-state laser 2 described earlier. Specifically, in the first excitation / oscillation system 31 of the LD-pumped solid-state laser 3, a collimating lens 12, a narrow-band BPF (bandpass filter) 13, a focusing lens 14, and a transmission plane mirror 15 are arranged between the excitation LD 11 and the collimating lens 16, similar to those described above.

[0027] The excitation light L emitted from the excitation LD11 in a divergent state is made into parallel light by the collimating lens12, 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 lens14. This incident parallel light is focused by the converging lens14 so as to converge at the front end face of the transmission plane mirror15, and then passes through the mirror15. The excitation light L that has passed through the transmission plane mirror15 is incident on the collimating lens16, 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 crystal19.

[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 focusing lens 17. This incident parallel light is focused by the focusing lens 17 so as to converge within the Pr:YLF crystal 19 and then transmitted 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 coincides with its optical axis. A BBO (β-BaB2O4) crystal 52 is positioned between the concave mirror 20 and the planar mirror 51 so that their optical axes pass through it. The BBO crystal 52 is a nonlinear optical material that 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 into 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. Furthermore, 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 355 nm for wavelength conversion.

[0034] In addition to the BBO crystal mentioned above, CLBO crystals and other nonlinear optical materials can also be used. 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 the extraordinary light, the solid-state laser oscillation light L22 with a wavelength of 607 nm as the ordinary light, and the sum frequency L23 with a wavelength of 355 nm as the extraordinary light for 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 emitted light L21 and L22. This saturable absorber 25 is the same as the saturable absorbers 25 and 26 arranged in the second embodiment. By arranging 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 The system 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 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 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 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 LD11, collimating lens12, and narrowband BPF13 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 this 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 (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 is then 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 mutually orthogonal directions 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 wavelengths are converted 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, with reference to Figure 7, a seventh embodiment of the present invention will be described. Figure 7 shows a schematic configuration of the 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 transmission-reflection 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-reflection 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-reflection coating film HR is, for example, HfO 2、The film is composed of a multilayer structure made of Ta2O5, TiO2, etc., and the anti-reflective coating films AR1 and AR2 are made of, for example, an SiO2 film. The anti-reflective coating film AR1 is designed and manufactured so that its reflectivity is 0.5% or less after the glass plate bonding 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 depositing 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 that constitutes 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, prolonged energization of the excitation LD11 will trigger a photochemical reaction 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 schematic side shape of the deposit T is shown in Figure 10, and an example of the schematic planar shape of the beam spot BS affected by this deposit T is shown in Figure 11. Furthermore, 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. Moreover, 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, an 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 in other respects, 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 arranged near the inner peripheral side of the periphery. FIG. 14 schematically shows the state before the metals M are welded, and FIG. 15 schematically shows the state after the welding. As shown in those figures, a high-reflection coating film HR is applied to the inner peripheral side of the annular metal M on one surface of the glass plate 115a, and an antireflection coating film AR2 is applied to the inner peripheral side of the annular metal M on one surface of another glass plate 115b. Antireflection coating films AR1 are applied to the other surfaces of the glass plates 115a and 115b, respectively.

[0054] The above high-reflection coating film HR is composed of, for example, a multilayer film of HfO 2、 Ta2O5, TiO2, etc., and the antireflection coating films AR1 and AR2 are composed of, for example, SiO2 films. The antireflection coating film AR1 is designed and formed so that the reflectance is 0.5% or less in air, and the antireflection coating film AR2 is designed and formed so that the reflectance is 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 on the peripheral portions (a predetermined range from the periphery to the center side) of the glass plates 115a and 115b, and AuSn (80% by weight of Au) is plated thereon until the thickness reaches 10 μm. This plated portion is shown as the metal M in FIGS. 14 and 15.

[0056] When the glass plates 115a and 115b are overlapped so that the above plated portions overlap and heated to 280°C or higher, the melting point of AuSn, AuSn melts and the glass plates 115a and 115b are joined (the state in FIG. 15). This joining by melting is preferably performed in an inert gas such as dry N2 with a dew point temperature of -50°C or lower. In addition to dry N2, argon, etc. can also be applied as the inert gas.

[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 (see Figure 10) caused by organic matter be formed. 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, a 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 glass plates 115a and 115b are each coated with the anti-reflective coating film AR1.

[0061] The above high-reflection coating film HR is, for example, HfO 2、The film is composed of a multilayer structure made of Ta2O5, TiO2, etc., and the anti-reflective coating films AR1 and AR2 are made of, for example, an SiO2 film. 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 depositing 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), 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 (as 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), the glass plates 115a and 115b are joined together via the molten metal M (as shown in Figure 17).

[0064] The above joining is preferably carried out in an inert gas such as dry N2 with a dew point temperature of -50°C or lower. In addition to dry N2, argon and other gases can also be used as the inert gas. In such a case, a hermetically sealed void of inert gas will be formed between the glass plate 115a and the glass plate 115b.

[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 (e.g., the ratio of Au to Sn) and contrasting 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-reflection coating film HR is, for example, HfO 2、 The coatings are composed of multilayer films made of Ta2O5, TiO2, etc., and the anti-reflective coating film AR1 is composed of, for example, an SiO2 film. 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 coating film HR described above, the low-melting-point glass G is melted, and the glass plates 115a and 115b are joined together (as shown in Figure 19). As the low-melting-point glass G, a mixture of powdered glass of lead-free glass Ta2O5 (tellurium dioxide) and MoO3 (molybdenum trioxide) is used. This mixture is applied to the outer periphery of each glass plate 115a and 115b, and the applied portion is heated to its melting point = 380°C or higher to melt and join the low-melting-point glass G together. In this way, glass plate 115a and glass plate 115b are joined together, but a gap sealed with inert gas is formed between them.

[0070] In addition, a mixture consisting of PbO·B2O3·SiO2 can be used as the powdered glass mixture described above. In that case, the 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-pumped solid-state 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-state 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-state laser crystal. For example, if one wants to obtain an LD-pumped solid-state 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-state 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 in Figure 7, a similar transmission-reflection mirror 115 may also be applied to the second excitation / oscillation system 32. [Explanation of Symbols]

[0073] 1, 2, 3, 4, 5, 6, 7 LD-pumped solid-state lasers 11 Excitation LD 12 Remade Lenses 13 Narrowband BPF 14. Converging lens 15. Transparent Planar Mirror 16 Collimating lenses 17. Converging lens 18, 51 Flat mirror 19 Pr:YLF crystal 20 Concave mirrors 20a Concave surface of concave mirror 21, 91, 92 Polarizing Beam Splitter 21a Dielectric multilayer film 22 BBO crystals 25, 26 Saturable absorbers 31 First excitation / oscillating system 32 Second excitation / oscillating system 52 BBO crystals 61 First Excitation System 62 Second Excitation System 63 Third Excitation System 64 Fourth Excitation System 65 Mirror 66, 67 wavelength multiplex mirror

Claims

1. Solid-state laser crystals and, A semiconductor laser that emits excitation light to excite the solid laser crystal, A resonator that resonates the light emitted from the solid laser crystal after it has been excited, A wavelength conversion element that converts the wavelength of solid-state laser light, In a semiconductor laser-pumped solid-state laser having, The system is provided with a wave-combining means that receives two solid-state laser oscillation beams with different frequencies from different directions and combines them into one beam. A semiconductor laser-pumped solid-state laser, wherein the optical wavelength conversion element converts the two solid-state laser oscillations into a sum frequency and emits the sum frequency in a direction different from that of at least one of the solid-state laser oscillations.

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

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

4. An external resonator is provided to resonate the excitation light from the semiconductor laser, This external resonator has a transmission / reflection mirror that transmits the excitation light emitted from the semiconductor laser toward the solid laser crystal and reflects it toward the semiconductor laser. The semiconductor laser-pumped solid-state laser according to claim 1, wherein the 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 wavelengths of the two solid-state lasers mentioned above are each in the range of 500 to 750 nm. The wavelength of the sum frequency is in the range of 250 to 375 nm. A semiconductor laser-pumped solid-state laser according to claim 1 or 2.

10. The aforementioned solid laser crystal is Pr ３＋ A semiconductor laser-pumped solid-state laser according to claim 1 or 2, wherein the laser 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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