Semiconductor laser-excited solid-state laser

Abstract

To provide a semiconductor laser-excited solid-state laser which offers high output and stable operation.SOLUTION: An LD-excited solid-state laser 10 provided herein comprises a solid-state laser crystal 19 such as Pr:YLF crystal, an LD 11 configured to emit excitation light L for exciting the laser crystal 19, and a resonator for resonating light emitted from the solid-state laser crystal 19, and is also provided with wavelength control means, such as a narrow bandpass filter 13, configured to cause an oscillation wavelength of the excitation light L of the LD 11 to substantially coincide with an absorption peak wavelength of the solid-state laser crystal 19.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor laser pumped solid-state laser, and more particularly to a solid-state laser in which a solid-state laser crystal serving as a laser medium is pumped by pumping light emitted from a semiconductor laser to produce laser oscillation. [Background technology]

[0002] For example, as shown in Patent Document 1, for example, Pr 3+ A conventionally known LD-pumped solid-state laser is one in which a solid-state laser crystal, such as a YLF crystal doped with Nd (hereinafter referred to as Pr:YLF crystal), is pumped by pumping light emitted from a semiconductor laser (laser diode, hereinafter referred to as LD), and the light emitted from the pumped solid-state laser crystal is resonated by a resonator. 3+ A YAG crystal doped with Nd (hereinafter referred to as Nd:YAG crystal) can also be used.

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

[0004] However, commercially available GaN-based pump laser diodes capable of emitting light in the 400 nm band, the absorption wavelength band of Pr:YLF crystals, have a 5–10 nm variation in their oscillation wavelengths. Selecting an LD with an oscillation wavelength that matches this absorption wavelength band results in a yield of only a few percent. Considering that the unit price of an LD is typically around 100,000 yen, the price of the LD alone exceeds 1 million yen. This makes industrial mass production extremely difficult. Furthermore, the oscillation wavelength width is approximately 2 nm wider than the absorption wavelength width of Pr:YLF crystals, resulting in reduced absorption efficiency even when the wavelengths match. Furthermore, LDs have the characteristic of varying their oscillation wavelength depending on optical output and temperature, making it extremely difficult to mass-produce LDs that match the absorption wavelength of Pr:YLF crystals.

[0005] Non-Patent Document 1 shows that LDs are selected and used so that their oscillation wavelength matches the absorption wavelength of the Pr:YLF crystal. However, even when LDs are selected and used in this way, if the LD oscillation wavelength fluctuates depending on the temperature, it becomes impossible to achieve stable, high-power laser oscillation.

[0006] To match the oscillation wavelength of the pump LD with the absorption wavelength of the Pr:YLF crystal, it is possible to use a broad-area LD, which has a relatively wide oscillation wavelength range. However, although broad-area LDs have high output, they have the drawback of poor spatial coherence due to their multi-transverse mode. Therefore, even if an external resonator is formed to control the oscillation wavelength and feedback is provided to the LD, optical loss increases, making it difficult to control the oscillation wavelength of the pump LD to the desired value. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-36176 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-36175 [Non-Patent Document 1] Applied Physics, Vol. 85, pp. 857-858 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and aims to achieve high output and stable operation in an LD-pumped solid-state laser in which a solid-state laser crystal such as a Pr:YLF crystal is pumped by an LD. [Means for solving the problem]

[0009] The LD-pumped solid-state laser according to the present invention has the following features: A solid-state laser crystal such as a Pr:YLF crystal, an LD that emits excitation light to excite the solid-state laser crystal; a resonator for resonating light emitted from the solid-state laser crystal upon excitation; In an LD pumped solid state laser having A wavelength control means is provided for making the oscillation wavelength of the excitation light from the semiconductor laser approximately coincident with the absorption peak wavelength of the solid-state laser crystal.

[0010] Specifically, it is preferable to use a bandpass filter disposed within the resonator as the wavelength control means, which narrows the wavelength of the light to be resonated.

[0011] In addition, in the LD pumped solid state laser according to the present invention, an external resonator is provided to configure the wavelength control means; the 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; The transmission-reflection mirror is preferably formed from two glass plates bonded together.

[0012] In this case, the two glass plates can be suitably joined together by optical contact, by forming metal plating near the periphery of each glass plate and then heating and welding the metal plating together, by forming metal plating and a metal plate overlapping the metal plating near the periphery of each glass plate and then heating and welding the metal plates together via the metal plating, or by melting low-melting point glass arranged near the periphery of each glass plate.

[0013] On the other hand, the resonator preferably includes a diffraction grating that selects the wavelength of light to be resonated. It is also preferable that the resonator further includes a VBG (Volume Bragg Grating) that selects the wavelength of light to be resonated. It is also preferable that the resonator further includes a confocal optical system.

[0014] It is preferable to use a GaN-based LD as the pumping LD, and it is preferable that this pumping LD be a multi-transverse mode LD. The LD-pumped solid-state laser according to the present invention may further include an optical wavelength conversion element that shortens the wavelength of the laser oscillation light. [Effects of the Invention]

[0015] According to the LD-pumped solid-state laser of the present invention, the oscillation wavelength of the pumping light from the LD can be made to approximately coincide with the absorption peak wavelength of the solid-state laser crystal using the wavelength control means as described above, thereby dramatically improving the yield of applicable LDs. Since the oscillation wavelength of the pumping LD is stabilized relative to the absorption wavelength of the solid-state laser crystal, the optical output of the solid-state laser is also stabilized. Furthermore, even if the oscillation wavelength fluctuates due to changes in the drive current value of the pumping LD or the outside temperature, the oscillation wavelength remains stable relative to the absorption wavelength of the solid-state laser crystal, so the optical output and related performance of the LD-pumped solid-state laser remain stable.

[0016] Although not limited to this, Nd:YAG lasers are often used as pumping LDs. In Nd:YAG lasers, the oscillation wavelength can deviate from the absorption wavelength of the solid-state laser crystal depending on factors such as the ambient temperature. To prevent this, it is possible to fix the oscillation wavelength by adjusting the temperature of the pumping LD. Meanwhile, the resonator of a solid-state laser is often also temperature-adjusted to stabilize the optical output and oscillation mode. The temperature adjustment of this resonator is generally different from the temperature adjustment of the pumping LD. In this case, a separate temperature adjustment function is required, which further increases the size and cost of the LD-pumped solid-state laser. The LD-pumped solid-state laser of the present invention does not require a separate temperature adjustment function, thereby avoiding this increase in size and cost. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic side view showing an LD-pumped solid-state laser according to a first embodiment of the present invention; [Figure 2] A diagram showing the optical spectrum of the pumping LD for each drive current value in the configuration of Figure 1. [Figure 3] A diagram showing the optical spectrum of the pumping LD for each drive current value in the configuration of Figure 1. [Figure 4] A graph showing the oscillation wavelength in the configuration of Figure 1 with and without wavelength control. [Figure 5] A graph showing the oscillation wavelength width in the configuration of Figure 1 with and without wavelength control. [Figure 6] A diagram showing the schematic configuration of the LD in the solid-state laser of Figure 1. [Figure 7] Graph showing the light intensity distribution in the fast axis direction of the excitation light in the solid-state laser of FIG. 1 [Figure 8] Graph showing the light intensity distribution in the slow axis direction of the excitation light in the solid-state laser of FIG. [Figure 9] FIG. 2 is a diagram showing the optical spectrum of the excitation light in the solid-state laser of FIG. 1 for each drive current value. [Figure 10] Graph showing the transmission characteristics of solid-state laser crystals [Figure 11]Graph showing oscillation characteristics of a solid-state laser according to the present invention [Figure 12] 1 is a schematic side view showing a LD-pumped solid-state laser according to a second embodiment of the present invention; [Figure 13] 13 is a side view showing a part of the LD-pumped solid-state laser of FIG. [Figure 14] FIG. 13 is a diagram showing the spectrum of excitation light wavelength-controlled in the device of FIG. 12; [Figure 15] 1 is a schematic side view showing an LD-pumped solid-state laser according to a third embodiment of the present invention; [Figure 16] FIG. 10 is a diagram showing the spectrum of excitation light when wavelength control is performed by the device of the present invention. [Figure 17] FIG. 10 is a diagram showing the spectrum of excitation light when wavelength control is not performed in the device of the present invention. [Figure 18] Absorption and oscillation characteristics of Pr:YLF crystal [Figure 19] A graph showing the relationship between the drive current value and the oscillation wavelength with and without wavelength control. [Figure 20] A graph showing the relationship between the drive current value and the oscillation wavelength width with and without wavelength control. [Figure 21] 1 is a schematic side view showing an LD-pumped solid-state laser according to a fourth embodiment of the present invention; [Figure 22] 10 is a schematic side view showing an LD-pumped solid-state laser according to a fifth embodiment of the present invention. [Figure 23] 10 is a schematic side view showing an LD-pumped solid-state laser according to a sixth embodiment of the present invention. [Figure 24] 10 is a schematic side view showing an LD-pumped solid-state laser according to a seventh embodiment of the present invention. [Figure 25] 10 is a schematic side view showing an LD-pumped solid-state laser according to an eighth embodiment of the present invention. [Figure 26] 13 is a schematic side view showing an LD-pumped solid-state laser according to a ninth embodiment of the present invention. [Figure 27] 10 is a schematic side view showing an LD-pumped solid-state laser according to a tenth embodiment of the present invention. [Figure 28] Graph showing examples of optical output and wavelength of wavelength-converted wave obtained in the present invention. [Figure 29] 11 is a schematic side view showing an LD-pumped solid-state laser according to an eleventh embodiment of the present invention. [Figure 30] 12. A schematic side view showing an LD-pumped solid-state laser according to a twelfth embodiment of the present invention. [Figure 31] FIG. 31 is a schematic side view showing the state before assembly of the main parts of the device of FIG. 30. [Figure 32] 33 is a schematic side view showing the state after assembly of the main parts shown in FIG. 32. [Figure 33] Schematic side view showing deposits on the transmission flat mirror of a LD-pumped solid-state laser [Figure 34] Schematic plan view showing an example of an excitation light beam spot affected by deposits [Figure 35] Schematic diagram showing an example of a normal beam profile of excitation light [Figure 36] Schematic diagram showing an example of an abnormal beam profile of the excitation light [Figure 37] 13 is a schematic side view showing the state before assembly of the main parts of the device of the present invention. [Figure 38] 38 is a schematic side view showing the main part shown in FIG. 37 in a state before assembly. [Figure 39] 14 is a schematic side view showing the state before assembly of the main parts of the device of the present invention. [Figure 40] FIG. 40 is a schematic side view showing the main parts shown in FIG. 39 in an assembled state. [Figure 41] 15th embodiment of the present invention is a schematic side view showing the state before assembly of the main parts of the device. [Figure 42] 42 is a schematic side view showing the main parts shown in FIG. 41 in an assembled state. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First Embodiment FIG. 1 shows a schematic configuration of an LD-pumped solid-state laser 10 according to a first embodiment of the present invention. This LD-pumped solid-state laser 10 is composed of elements ranging from a pumping LD 11 to a resonator concave mirror 20 arranged in front of (to the right in the drawing) the pumping LD 11 along its optical axis. These elements will be described in order below. The pumping LD 11 performs laser oscillation by itself and emits pumping light L in a diverging state. This pumping light L is collimated by a collimating lens 12, and the collimated light passes through a narrow-band BPF (bandpass filter) 13, which serves as wavelength control means, before entering a converging lens 14. The incident collimated light is condensed by the converging lens 14 so as to converge at the front end face of a transmitting flat mirror 15, and then passes through the mirror 15.

[0019] The excitation light L transmitted through the transmitting flat mirror 15 is collimated by the collimating lens 16, and the collimated light is focused by the converging lens 17. After transmitting through the flat mirror 18, the focused excitation light L is incident on a rod-shaped Pr:YLF crystal 19 and focused within the crystal 19. The direction of travel of the excitation light incident on the Pr:YLF crystal 19 in the above-mentioned collimated state is particularly shown as L1 in the figure, and the wavelength of this excitation light L1 has been controlled to a narrow band of mainly 444 nm by passing through the above-mentioned narrow-band BPF 13.

[0020] When the Pr:YLF crystal 19 receives excitation light L1, the wavelength of which is controlled mainly to 444 nm, it emits light L2, which has an output peak at a wavelength of 640 nm or the like, by stimulated emission. This light L2 resonates within the solid-state laser resonator, which is composed of the transmitting flat mirror 18 and concave mirror 20, and becomes high-intensity solid-state laser oscillation light L3, which is output from the concave mirror 20. The concave surface of the concave mirror 20, i.e., the surface facing the flat mirror 18, is coated with a coating 21 that transmits part of the light with a wavelength of 640 nm and reflects the remainder. In this way, high-intensity laser oscillation light L3 is stably output from the LD-pumped solid-state laser 10. In FIG. 1, the solid-state laser resonator range is indicated by a dashed double-headed arrow, and the resonator range for wavelength control is indicated by a solid double-headed arrow (same below).

[0021] Figure 2 shows the optical spectrum of a GaN-based broad-area LD with an emission wavelength of around 444 nm, as measured by a measuring instrument. The optical spectra are shown at drive currents of 300 mA, 500 mA, 1000 mA, 1500 mA, and 2000 mA (from top to bottom). The wavelength shifts from 443.76 nm to 447.27 nm as the current increases. The wavelength shift is 3.51 nm. In contrast, wavelength control using the BPF13 shown in Figure 1 results in the optical spectrum shown in Figure 3. These optical spectra are also shown at currents of 300 mA, 500 mA, 1000 mA, 1500 mA, and 2000 mA (from top to bottom). The emission wavelength changed only slightly from 443.95 nm to 444.19 nm. The wavelength shift was 0.24 nm. In other words, the wavelength shift relative to the current change was approximately 1 / 15 of that observed without wavelength control. In this way, it was found that wavelength control can provide a characteristic that can stably excite the Pr:YLF crystal 19 without causing a large wavelength shift even when the drive current value is increased or decreased.

[0022] Furthermore, when the drive current is 2000 mA, the oscillation wavelength is 444.19 nm with wavelength control compared to 447.27 nm without wavelength control, a difference of approximately 3 nm. Generally, the larger this difference, the easier it is to control the wavelength. Being able to control the wavelength even at a distance of approximately 3 nm means that LDs with a center wavelength of 444 nm up to ±3 nm can be used. This means that nearly 100% of commercially available LDs can be used, increasing the LD yield.

[0023] On the other hand, Figure 4 shows a comparison of the oscillation wavelength with and without wavelength control. With wavelength control, the wavelength fluctuation is smaller than without. Figure 5 also shows a comparison of the oscillation wavelength width with and without wavelength control. With wavelength control, the oscillation wavelength width is smaller than without, at 0.4 nm or less. With this value, there is almost no decrease in the absorption efficiency of the Pr:YLF crystal 19, so many LDs can be used for pumping.

[0024] The LD-pumped solid-state laser 10 shown in FIG. 1 has a resonator with an optical system called a confocal optical system. That is, in this LD-pumped solid-state laser 10, a resonator is formed between the pumping LD 11 and the front end face of the transmitting flat mirror 15. The pumping light L emitted from the pumping LD 11 is collimated by the collimating lens 12, and the collimated light is then focused by the converging lens 14 so as to converge on the front end face of the transmitting flat mirror 15, which has a reflectance of 35%. A resonator with such a confocal optical system is characterized by its robustness against mechanical system fluctuations due to factors such as ambient temperature, and its ability to maintain stable optical output. For example, even if the position or angle of the mirror 15 deviates slightly from the design values, almost all of the reflected light from the mirror 15 returns to the pumping LD 11, realizing a stable resonator.

[0025] Figure 6 shows the schematic configuration of the pump LD 11. The pump light L emitted from it has spatial coherence in the fast axis direction (vertical direction in Figure 1), resulting in a Gaussian beam. On the other hand, the slow axis direction, perpendicular to the fast axis, has multiple transverse modes, resulting in poor spatial coherence and a distorted intensity rather than a Gaussian beam. Figures 7 and 8 show the above diagrams. Figure 7 shows the intensity distribution of a Gaussian beam in the fast axis direction. Figure 8 shows the intensity distribution in the slow axis direction, showing fluctuations in beam intensity and poor spatial coherence. Thus, even if a resonator is formed for the pump light L with poor spatial coherence in multiple transverse modes and wavelength control is attempted, wavelength control is considered difficult because the beam from the resonator does not efficiently return to the pump LD 11. In fact, we attempted wavelength control by applying an LD with an output wavelength of 808 nm and a multi-transverse mode slow axis to the same optical system as Figure 1, but wavelength control was not possible. Considering that wavelength control is possible for LDs with a single mode slow axis, it is presumed that the reason for the difficulty in wavelength control as mentioned above is that the transverse mode is multimode. On the other hand, it was confirmed for the first time that wavelength control is possible for GaN-based LDs with an oscillation wavelength of 444 nm, even though they are multitransverse modes. The detailed reasons for this are unknown, but it may be due to the structure of the GaN-based LD.

[0026] The configuration of FIG. 1 will be explained in more detail. The Pr:YLF crystal 19 used here is Pr 3+ The doping amount is 0.5% and the crystal length is 6 mm. This Pr:YLF crystal 19 has the spectral characteristics shown in Figure 10. The vertical axis in the figure is transmittance and the horizontal axis is wavelength. π represents the characteristics when the polarization direction of the Pr:YLF crystal 19 is parallel to the crystal c-axis, and σ represents the characteristics when it is perpendicular. As can be seen, the absorption linewidth of the Pr:YLF crystal 19 is narrow and the tip is sharp rather than flat, so it can be seen that the narrower the oscillation wavelength width, the higher the absorption efficiency of the crystal 19.

[0027] Figure 9 shows the excitation light spectrum when the wavelength is controlled by varying the drive current value (300 mA, 500 mA, 1000 mA, 1500 mA, and 2000 mA) when the half-width of the BPF 13 in Figure 1 is 1 nm. In each column for each drive current, the upper value below the drive current is the oscillation wavelength, and the lower value is the oscillation wavelength width. It can be seen that this is narrower than a BPF with an oscillation wavelength width of 5 nm. For example, at a drive current of 2000 mA, the oscillation wavelength width is 0.08 nm. On the other hand, when the half-width of the BPF 13 is 1 nm (see Figure 3), it is 0.407 nm, indicating that the BPF 13 with a half-width of 1 nm has a narrower oscillation wavelength width. Furthermore, the absorption efficiency of the BPF 13 with a half-width of 1 nm in the Pr:YLF crystal 19 is higher than that of the BPF 13 with a half-width of 5 nm. It was confirmed that the wavelength of BPF13 can be controlled not only with a half-width of 5 nm, but also with a half-width of 1 nm or 2 nm.

[0028] As mentioned above, the Pr:YLF crystal 19 has the spectral characteristics shown in Figure 10, and the absorption characteristics of the crystal 19 can be seen from the transmittance on the vertical axis of the figure. Considering this absorption characteristic, there is an absorption peak at a wavelength of 444 nm, and approximately 90% of the pumping light L of this 444 nm wavelength is absorbed by the Pr:YLF crystal 19. Since the solid-state laser is designed to oscillate at a wavelength of 640 nm within the oscillation line of the Pr:YLF crystal 19 shown in Figure 18, the absorbed energy causes the solid-state laser to oscillate at a wavelength of 640 nm. Figure 11 shows the oscillation characteristics of this solid-state laser. The horizontal axis represents the drive current value (A) of the pumping LD 11, and the vertical axis represents the optical output (mW) of the solid-state laser oscillation light L3 with a wavelength of 640 nm. When the drive current value of the pumping LD 11 was 1.7 A, an optical output value of 332 mW of the solid-state laser oscillation light L3 was obtained. Because wavelength control is performed, the wavelength of the pumping LD 11 does not change with the drive current value and falls within the absorption line width of the Pr:YLF crystal 19, and it was confirmed that the optical output of the solid-state laser oscillation light L3 increases linearly in proportion to an increase in the drive current value. If wavelength control is not performed, the oscillation wavelength shifts as the drive current value increases, causing the optical output to saturate or decrease, but this did not occur with the LD-pumped solid-state laser 10 of this embodiment.

[0029] FIG. 18 shows the absorption and oscillation characteristics of the Pr:YLF crystal 19. The typical absorption line is 444 nm. The typical oscillation lines are 523 nm, 607 nm, 640 nm, 698 nm, and 721 nm. While the above design is for solid-state laser oscillation at a wavelength of 640 nm, solid-state laser oscillation at wavelengths other than 640 nm is also possible. Furthermore, when generating SHG (second harmonic), when the solid-state laser oscillation lines are 523 nm, 607 nm, 640 nm, 698 nm, and 721 nm, second harmonics with wavelengths of 262 nm, 304 nm, 320 nm, 349 nm, and 361 nm can be obtained, respectively.

[0030] Second Embodiment Next, an LD-pumped solid-state laser 30 according to a second embodiment of the present invention will be described with reference to Figures 12 and 13. Figure 12 shows a schematic configuration of this LD-pumped solid-state laser 30. In the following figures, elements equivalent to those described so far will be designated by the same reference numerals as those already used, and their description will be omitted unless particularly necessary. In this LD-pumped solid-state laser 30, elements equivalent to those in the LD-pumped solid-state laser 10 shown in Figure 1 are arranged in front of the collimating lens 16 (to the right in the figure).

[0031] A mirror moving means 31 serving as a wavelength control means is connected to the transmitting plane mirror 15 disposed between the converging lens 14 and the collimating lens 16. This mirror moving means 31 is composed of a drive source such as a motor and a drive force transmission mechanism such as a rack and pinion interposed between the drive source and the mirror 15. When the drive source is operated, the transmitting plane mirror 15 is moved between the lenses 14 and 16 in the direction of arrow A parallel to their optical axes.

[0032] FIG. 13 illustrates the focusing lens 14, the transmitting flat mirror 15, the collimating lens 16, and the mirror moving means 31, and also explains the effect of the above-described movement of the transmitting flat mirror 15. Specifically, when the movement position of the mirror 15 is set so that the pumping light L collected by the focusing lens 14 converges at the output end face of the transmitting flat mirror 15, the pumping light L with longer wavelengths converges farther (farther right in FIG. 9 ) due to wavelength dispersion of the focusing lens 14, and the pumping light L with shorter wavelengths converges closer (farther left in FIG. 13 ). Thus, by adjusting the movement position of the transmitting flat mirror 15, the wavelength of the pumping light L incident on the Pr:YLF crystal 19 (see FIG. 1 ) can be adjusted to a narrow band of 444 nm, even without the narrow-band BPF 13 shown in FIG. 1 . After adjustment, the mirror 15 is fixed at the position where it oscillates at 444 nm, and the mirror moving means 31 is further separated from the mirror 15, resulting in a laser module suitable for practical use.

[0033] Figure 14 shows the spectrum of the pump LD 11 when the oscillation wavelength is controlled to, for example, 444 nm by the mirror moving means 31 as wavelength control means. This display is the same as in Figure 3, and from top to bottom, the optical spectra are for drive current values ​​of 300 mA, 500 mA, and 1000 mA. At these times, the oscillation wavelength is controlled to 443.96 nm, 444.07 nm, and 443.98 nm, respectively. Furthermore, the oscillation wavelength widths (half-widths) are 0.27 nm, 0.033 nm, and 0.486 nm, respectively, which are less than 0.5 nm narrower than when wavelength control is not performed, and therefore the absorption of the pump light L in the Pr:YLF crystal 19 is favorable.

[0034] Third Embodiment Next, with reference to FIG. 15 , an LD-pumped solid-state laser 40 according to a third embodiment of the present invention will be described. FIG. 15 shows the configuration of the wavelength control means and its surroundings of the LD-pumped solid-state laser 40. In this embodiment, a diffraction grating 41 is used as the wavelength control means. That is, in comparison with the configuration shown in FIG. 1 , the LD-pumped solid-state laser 40 of this embodiment uses a diffraction grating 41 instead of the narrow-band BPF 13. The diffraction grating 41 has 600 grooves / mm. In the configuration shown in FIG. 15 , the pumping light L emitted from the pumping LD 11 is collimated by the collimating lens 12, and the collimated pumping light L enters the diffraction grating 41. The pumping light L is diffracted by the diffraction grating 41, and the diffracted light (−1st-order diffracted light) returns to the pumping LD 11. At this time, an external resonator is formed between the pumping LD 11 and the diffraction grating 41, and the wavelength of the pumping light L is controlled. In this case, the control wavelength can be selected by rotating the diffraction grating (around an axis perpendicular to the display surface of FIG. 14).

[0035] 16 and 17 show the optical spectra of the pump light L when the wavelength control is performed (shown as "wavelength locked" in FIG. 16) and when it is not performed (shown as "wavelength not locked" in FIG. 17), respectively. In the optical spectrum when wavelength control is performed, shown in FIG. 16, the oscillation wavelengths are 444.8 nm, 444.8 nm, 444.8 nm, and 444.85 nm when the drive current of the pump LD 11 is 300 mA, 500 mA, 700 mA, and 1000 mA, respectively, and the oscillation wavelength widths (half-width) are 0.06 nm, 0.08 nm, 0.083 nm, and 0.13 nm, respectively. This shows that the oscillation wavelength does not shift significantly even when the drive current value is increased.

[0036] 17, the optical spectrum without wavelength control shows that the oscillation wavelengths when the drive current of the pumping LD 11 is 300 mA, 500 mA, 700 mA, and 1000 mA are 444.73 nm, 444.2 nm, 444.74 nm, and 444.74 nm, respectively, and the oscillation wavelength widths (half widths) are 0.25 nm, 0.53 nm, 0.21 nm, and 1.11 nm, respectively. Thus, the oscillation wavelength changes with the drive current value, and the oscillation wavelength width (half width) also changes with an increase in the drive current value.

[0037] Figure 19 is a graph showing the results when the number of measurement points is increased even more than in Figures 16 and 17. Here, the horizontal axis shows the drive current value (mA) of the pumping LD 11, and the vertical axis shows the oscillation wavelength (nm) of the pumping LD 11. As shown in the figure, the oscillation wavelength fluctuates more significantly with changes in the drive current value when the wavelength is not controlled than when the wavelength is controlled. Figure 20 also shows the change in the oscillation wavelength width of the pumping LD 11 when the drive current value of the pumping LD 11 is changed. In this figure, the horizontal axis shows the drive current value (mA) of the pumping LD 11, and the vertical axis shows the oscillation wavelength width (nm) of the pumping LD 11. It can be seen that the oscillation wavelength width (half-width) also changes significantly with changes in the drive current value. As explained above, by controlling the oscillation wavelength of the LD, it is possible to match the oscillation wavelength of the LD with the absorption wavelength of the Pr:YLF crystal 19, even when the drive current value of the LD is changed.

[0038] Fourth Embodiment Next, with reference to Fig. 21, an LD-pumped solid-state laser 50 according to a fourth embodiment of the present invention will be described. Fig. 21 shows a schematic configuration of this LD-pumped solid-state laser 50. Compared with the LD-pumped solid-state laser 10 shown in Fig. 1, this LD-pumped solid-state laser 50 is fundamentally different in that the solid-state laser oscillation light L3 is made shorter in wavelength by a nonlinear optical material. That is, in this LD-pumped solid-state laser 50, the concave mirror 20 is disposed at an angle with respect to the optical axis of the plane mirror 18, and a plane mirror 51 is disposed so that the reflection axis of the concave mirror 20 coincides with the optical axis of the plane mirror 51. An LBO crystal 52 is disposed between the concave mirror 20 and the plane mirror 51 so that their optical axes pass through each other. The LBO crystal (LiBO 15 The crystal 52 is a nonlinear optical material that converts the incident laser oscillation light L3 of 640 nm wavelength into second harmonic L4, which has half the wavelength. Almost all of this second harmonic L4 laser light passes through the concave mirror 20 and is emitted outside the LD-pumped solid-state laser 50. The light incident surface of the flat mirror 18 is coated with a coating that has a reflectivity of 99.9% for light of 640 nm wavelength. The concave mirror 20 has a curvature of 75 mm, and its reflective surface is coated with a coating that has a reflectivity of 99% for light of 640 nm wavelength. With the above configuration, solid-state laser oscillation with an oscillation wavelength of 640 nm is realized.

[0039] The second harmonic wave L4, with a wavelength of 320 nm, is output from the concave mirror 20 and used as the light to be used. Almost all of the output is output from the concave mirror 20. In this LD-pumped solid-state laser 50, a pumping LD 11 with an output of 3.5 W was used, and wavelength conversion was performed using an LBO crystal 52 with a total length of 10 mm, resulting in a second harmonic wave L4 with an optical output of approximately 250 mW. Note that, in addition to the above-mentioned LBO, crystals such as BBO (β-BaB2O4) and PPSLT (Periodically Poled Stoichiometric Lithium Tantalite) can also be used as the nonlinear optical material for wavelength conversion.

[0040] Fifth Embodiment Next, with reference to FIG. 22, an LD-pumped solid-state laser 60 according to a fifth embodiment of the present invention will be described. As shown in the schematic configuration of FIG. 22, this LD-pumped solid-state laser 60 includes a pumping LD 11, a collimating lens 12, a narrow-band BPF 13, a converging lens 17, a plane mirror 18, a Pr:YLF crystal 19, and a concave mirror 20, similar to those shown in FIG. 1. A transmission mirror 95 is disposed between the Pr:YLF crystal 19 and the concave mirror 20 as a wavelength control means. The input surface of this transmission mirror 95 has a reflectivity of 99% or more for light with a wavelength of 444 nm, allowing the pumping light L with a wavelength of 444 nm to be returned to the pumping LD 11. Thus, within the resonator formed by the plane mirror 18 and the concave mirror 20 (the range of which is indicated by the dashed double-headed arrow in the figure), the pumping light L can be selected and oscillated primarily at a wavelength of 444 nm.

[0041] Furthermore, the pumping light L with a wavelength of 444 nm can be absorbed by the Pr:YLF crystal 19 on both sides, and the reflectivity of the plane mirror 95 for light with a wavelength of 444 nm is 99% or more, so there is little loss of the pumping light L, and a solid-state laser 60 capable of oscillating with high efficiency is obtained. On the other hand, the resonator of the solid-state laser has a transmittance of 99% or more for light with a wavelength of 640 nm, so there is little loss for the light with a wavelength of 640 nm, and a solid-state laser without a decrease in optical output is obtained. Note that the Pr:YLF crystal 19 is made of Pr 3+ By adjusting the doping amount and crystal length, for example, the transmittance for 444 nm light can be set to 50%, and 75% of the 444 nm light can be absorbed in the round trip, with the remaining 25% available for wavelength control.

[0042] The reflection and transmission characteristics of the input and output surfaces of the plane mirror 95 are summarized below. Input surface: 99% or more transmittance for wavelength 444nm Transmittance of 99% or more for wavelengths of 640 nm Emission surface: Reflectance of 99% or more for wavelengths of 444 nm Transmittance of 99% or more for wavelengths of 640 nm

[0043] Sixth Embodiment Next, an LD-pumped solid-state laser 70 according to a sixth embodiment of the present invention will be described with reference to Fig. 23. As shown in the schematic configuration of Fig. 23, this LD-pumped solid-state laser 70 has a configuration in which the transmission mirror 95 and the plane mirror 18 are omitted from the configuration of the fifth embodiment shown in Fig. 22. The reflection and transmission characteristics of the input and output surfaces of the Pr:YLF crystal 19 are as follows: Input surface: 99% or more transmittance for wavelength 444nm Reflectance of 99% or more for wavelengths of 640 nm Emission surface: Reflectance of 99% or more for wavelengths of 444 nm Transmittance of 99% or more for wavelengths of 640 nm The above configuration can achieve the same functions and effects as the configuration in Fig. 5. Furthermore, compared to the configuration in Fig. 5, further miniaturization and a reduction in the number of parts can be achieved, making it possible to make the LD-pumped solid-state laser 70 more affordable.

[0044] Seventh Embodiment Next, an LD pumped solid state laser 80 according to a seventh embodiment of the present invention will be described with reference to Fig. 24. As shown in the schematic configuration of Fig. 24, this LD pumped solid state laser 80 has the same configuration as Fig. 5 except that the transmission mirror 95 is omitted and instead a VBG (Volume Bragg Grating) is used as a wavelength control means. The VBG 96 is provided with a VBG. The VBG has the function of diffracting only specific wavelengths and returning them to the original optical path, and in this embodiment, it returns only the wavelength of 444 nm. Therefore, the oscillation wavelength of the pumping LD 11 is 444 nm. The reflection and transmission characteristics of the input and output surfaces of this VBG 96 are as follows: Input surface: 99% or more transmittance for wavelength 444nm Transmittance of 99% or more for wavelengths of 640 nm Exit surface: Transmittance of 99% or more for wavelength 444nm Transmittance of 99% or more for wavelengths of 640 nm The above configuration can achieve the same effects as the configuration in FIG.

[0045] Eighth Embodiment Next, an LD-pumped solid-state laser 90 according to an eighth embodiment of the present invention will be described with reference to Fig. 25. Fig. 25 shows a schematic configuration of this LD-pumped solid-state laser 90, which is fundamentally different from the previously described embodiments in that a plurality of solid-state laser crystals and a plurality of LDs for pumping them are provided. This point also applies to the ninth to eleventh embodiments described later.

[0046] 25, the LD-pumped solid-state laser 90 according to the eighth embodiment has a total of four pumping systems, each having a pumping LD 11, a collimating lens 12, and a narrow-band BPF 13, arranged from top to bottom in the figure as a first pumping system 61, a second pumping system 62, a third pumping system 63, and a fourth pumping system 64. The first pumping system 61, the second pumping system 62, the third pumping system 63, and the fourth pumping system 64 each have an appropriate pumping LD 11 selected and the pass band of each narrow-band BPF 13 set appropriately, so that the pumping light L emitted by each of them mainly has wavelengths of 479 nm, 469 nm, 444 nm, and 442 nm, respectively.

[0047] The pumping light L emitted by the first pumping system 61 is reflected by a mirror 65 and then multiplexed with the pumping light L emitted by the second pumping system 62 by a wavelength multiplexing mirror 66 that transmits wavelengths of 479 nm and reflects wavelengths of 469 nm. The multiplexed pumping light L is then multiplexed with the pumping light L emitted by the third pumping system 62 and the pumping light L emitted by the fourth pumping system 64 by a wavelength multiplexing mirror 67 that reflects wavelengths of 469 nm and 479 nm and transmits wavelengths of 444 nm and 442 nm. The pumping light L emitted by the third pumping system 63 and the pumping light L emitted by the fourth pumping system 64 are multiplexed by a polarizing beam splitter 68 before entering the wavelength multiplexing mirror 67.

[0048] 21, a plane mirror 18, a Pr:YLF crystal 19, a concave mirror 20, a plane mirror 51, and an LBO crystal 52 are arranged. The functions of these elements are the same as those in the LD-pumped solid-state laser 50.

[0049] This will be explained in more detail below. As shown in Figure 10, the Pr:YLF crystal 19 has a total of four absorption lines: three with a polarization of π and one with a polarization of σ. The pumping LD 11 of the first pumping system 61 in Figure 25 has an output of 1 W and is controlled to an oscillation wavelength of 479 nm, which coincides with one absorption line of the Pr:YLF crystal 19. Similarly, the pumping LD 11 of the second pumping system 62 has an output of 5 W and is controlled to an oscillation wavelength of 469 nm, the pumping LD 11 of the third pumping system 63 has an output of 5 W and is controlled to an oscillation wavelength of 444 nm, and the pumping LD 11 of the fourth pumping system 64 has an output of 5 W and is controlled to an oscillation wavelength of 442 nm. The polarization direction of the pumping light L from the fourth pumping system 64 is rotated by 90° by the polarizing beam splitter 68, and the pumping light L is combined with the pumping light L from the third pumping system 63. Since the wavelengths of all the pumping lights L emitted from the four pumping LDs 11 described above are controlled by the narrow-band BPF 13, an absorption of about 90% is achieved in the Pr:YLF crystal 19.

[0050] In the LD-pumped solid-state laser 90 configured as described above, when the output of the pumping LD 11 in the first pumping system 61 was 1 W and the pumping light L therefrom was controlled to a wavelength of 479 nm, the solid-state laser oscillated at a wavelength of 640 nm. Second harmonics were then generated by the LBO crystal 52, resulting in an optical output of 0.1 W at a wavelength of 320 nm. Similarly, when the output of the pumping LD 11 in the second pumping system 62 was 5 W and the pumping light L therefrom was controlled to a wavelength of 469 nm, the solid-state laser oscillated at a wavelength of 320 nm, resulting in an optical output of 0.3 W. Similarly, when the output of the pumping LD 11 in the third pumping system 63 was 5 W and the pumping light L therefrom was controlled to a wavelength of 444 nm, the solid-state laser oscillated at a wavelength of 320 nm, resulting in an optical output of 0.3 W. The pumping light L polarized and combined by the polarizing beam splitter 68 had an optical output of 5 W and a wavelength of 444 nm. If the optical output of the polarized combined pumping light L is 5 W and the wavelength is controlled to 442 nm, it is possible to obtain solid-state laser light with a wavelength of 320 nm with an optical output of 0.3 W. Furthermore, it is also possible to obtain solid-state laser light of about 1.0 W by pumping the Pr:YLF crystal 19 with high-intensity pumping light obtained by combining all of the pumping lights L from the first pumping system 61 to the fourth pumping system 64.

[0051] In this embodiment, the Pr:YLF crystal 19 used has a Pr doping amount of 0.5% and a total length of 10 mm to increase absorption efficiency for all wavelengths. The number of multiplexed pump light beams L is not limited to four, but may be two or three. Furthermore, the wavelength control means is not limited to a narrowband BPF, but may be one that has a second confocal point and does not require a BPF, or one that uses a third diffraction grating. Furthermore, a wavelength control means using a VBG (Volume Bragg Grating: volume holographic diffraction grating) may also be used.

[0052] Ninth Embodiment Next, with reference to Fig. 26, an explanation will be given of an LD-pumped solid state laser 100 according to a ninth embodiment of the present invention. As shown in the schematic configuration of Fig. 26, this LD-pumped solid state laser 100 has a configuration in which the plane mirror 51 and the LBO crystal 52 have been removed from the LD-pumped solid state laser 90 shown in Fig. 25. The concave mirror 20, including the coating applied to its concave surface (not shown), is the same as that in the LD-pumped solid state laser 90. Therefore, in this LD-pumped solid state laser 100 as well, light with a wavelength of 640 nm is output from the concave mirror 20. This light output is, for example, 1.2 W.

[0053] Tenth Embodiment Next, an LD-pumped solid state laser 110 according to a tenth embodiment of the present invention will be described with reference to Fig. 27. As shown in the schematic configuration of Fig. 27, this LD-pumped solid state laser 110 is configured to combine laser oscillation light L21 having a wavelength of 721 nm generated in a first excitation / oscillation system 81 and laser oscillation light L22 having a wavelength of 698 nm generated in a second excitation / oscillation system 82 using a polarizing beam splitter 83.

[0054] The laser oscillation light L21 with a wavelength of 721 nm generated in the first excitation / oscillation system 81 and the laser oscillation light L22 with a wavelength of 698 nm generated in the second excitation / oscillation system 82 have electric field vibration directions that are orthogonal to each other, and these laser oscillation lights L21 and L22 are combined by a polarizing beam splitter 83. The combined laser oscillation lights L21 and L22 are incident on a BBO crystal (β-BaB2O4 crystal) 84, which is a nonlinear optical material, and are wavelength-converted by the BBO crystal 84 to a sum frequency light L23 with a wavelength of 355 nm. This sum frequency light L23 passes through a concave mirror 20 and is emitted from the LD-pumped solid-state laser 110 as usable light.

[0055] The above configuration will be described in more detail below. The optical system in which pumping light L emitted from pumping LD 11 is wavelength-controlled by narrow-band BPF 13 and enters Pr:YLF crystal 19 is common to the first pumping and oscillation system 81 and the second pumping and oscillation system 82. The pumping light L, whose wavelength is controlled to 444 nm by first pumping and oscillation system 81, passes through plane mirror 18 and is absorbed by Pr:YLF crystal 19. The light generated from Pr:YLF crystal 19 by this absorption is resonated between plane mirror 18 and concave mirror 20, generating laser oscillation light L21 with a wavelength of 721 nm. At this time, laser oscillation light L21 with the above wavelength can be obtained by designing the reflective coating of plane mirror 18 to have a reflectivity of 99.9% or higher for light with a wavelength of 721 nm.

[0056] This 721 nm wavelength laser oscillation light L21 is oscillated as P-polarized light, with its polarization direction parallel to the display surface of Figure 27. Similarly, the coating of the plane mirror 18 of the second excitation / oscillation system 82 is designed to have a reflectivity of 99.9% or more for light with a wavelength of 698 nm, thereby obtaining laser oscillation light L22 with the above wavelength. This 698 nm wavelength laser oscillation light L22 is oscillated as S-polarized light, with its polarization direction perpendicular to the display surface of Figure 27. At this time, polarizing beam splitters 83 are placed in both resonators, so that the 721 nm wavelength laser oscillation light L21 and the 698 nm wavelength laser oscillation light L22 can be oscillated simultaneously. The polarizing beam splitter 83 is coated to transmit 721 nm wavelength light with a transmittance of 99.9% or more and reflect 698 nm wavelength light with a reflectance of 99.9% or more, thereby ensuring almost no propagation loss for the laser oscillation lights L21 and L22 of each wavelength.

[0057] Examples of the optical output and wavelength of the second harmonic and sum frequency obtained by wavelength conversion in the present invention will be described below with reference to Figure 28. In the figure, the black dots indicate examples of the optical output and wavelength of the second harmonic, and the black dots surrounded by circles indicate examples of the optical output and wavelength of the sum frequency.

[0058] Eleventh Embodiment Next, an LD-pumped solid state laser 120 according to an eleventh embodiment of the present invention will be described with reference to Fig. 29. As shown in the schematic configuration of Fig. 29, this LD-pumped solid state laser 120 is configured to combine laser oscillation light L1 having a wavelength of 721 nm generated in a first pumping and oscillation system 81 and laser oscillation light L2 having a wavelength of 698 nm generated in a second pumping and oscillation system 82 using a polarizing beam splitter 83. The first pumping and oscillation system 81 is equivalent to that shown in Fig. 26 and includes a first pumping system 61, a second pumping system 62, a third pumping system 63 and a fourth pumping system 64.

[0059] The first excitation / oscillation system 81 will now be described in detail. The first excitation system 61 is composed of an excitation LD 11, a collimating lens 12, a narrow-band BPF 13, a converging lens 14, a transmitting flat mirror 15, a collimating lens 16, and a mirror 65, arranged in this order from left to right along an optical axis extending horizontally in FIG. 29. The second excitation system 62 is composed of the same excitation LD 11, collimating lens 12, narrow-band BPF 13, a converging lens 14, a transmitting flat mirror 15, and a collimating lens 16 as above, plus a wavelength multiplexing mirror 66. The third excitation system 63 is composed of the same excitation LD 11, collimating lens 12, narrow-band BPF 13, a converging lens 14, a transmitting flat mirror 15, and a 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 by providing a polarization beam splitter 91 in addition to the excitation LD 11, collimator lens 12, and narrow-band BPF 13 similar to those described above.

[0060] Similarly, the second excitation / oscillation system 82 also 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 / oscillation system 82 will be described below. The first excitation system 61 is composed of an excitation LD 11, a collimating lens 12, a narrow-band BPF 13, a converging lens 14, a transmission flat mirror 15, a collimating lens 16, and a mirror 65, which are arranged in this order from bottom to top along an optical axis extending vertically in the figure. The second excitation system 62 is composed of the same excitation LD 11, collimating lens 12, narrow-band BPF 13, converging lens 14, transmission flat mirror 15, and collimating lens 16 as above, as well as a wavelength multiplexing mirror 66. The third excitation system 63 is configured by providing a wavelength multiplexing mirror 67 in addition to the same excitation LD 11, collimating lens 12, narrow-band BPF 13, converging lens 14, transmitting plane mirror 15, and collimating lens 16 as above (these elements are shared with the fourth excitation system 64 described below). The fourth excitation system 64 is configured by providing a polarizing beam splitter 92 in addition to the same excitation LD 11, collimating lens 12, and narrow-band BPF 13 as above.

[0061] The action of the above-mentioned first excitation / oscillation system 81 will be explained. The excitation light L1 emitted by the first excitation system 61 is reflected by a mirror 65 and then multiplexed with the excitation light L1 emitted by the second excitation system 62 by a wavelength multiplexing mirror 66. After being multiplexed, the excitation light L1 emitted by the second excitation system 62 and the excitation light L1 emitted by the fourth excitation system 64 are multiplexed by a wavelength multiplexing mirror 67. Note that the excitation light L1 emitted by the third excitation system 62 and the excitation light L1 emitted by the fourth excitation system 64 are multiplexed by a polarizing beam splitter 91 before entering the wavelength multiplexing mirror 67.

[0062] As described above, high-intensity pumping light L1, which is emitted from a total of four pumping systems and then combined into one beam, is incident from two directions on each of the two Pr:YLF crystals 19, so that pumping is performed well and high-intensity laser oscillation light L2 can be obtained. If this is the case, it is possible to obtain high-intensity wavelength-converted light even when this laser oscillation light L2 is wavelength-converted to a second harmonic wave, sum frequency wave, etc.

[0063] The laser oscillation light L1 with a wavelength of 721 nm generated in the first excitation / oscillation system 81 and the laser oscillation light L2 with a wavelength of 698 nm generated in the second excitation / oscillation system 82 have electric field vibration directions that are orthogonal to each other, and these laser oscillation lights L21 and L22 are combined by a polarizing beam splitter 83. The combined laser oscillation lights L21 and L22 are incident on a BBO crystal (β-BaB2O4 crystal) 84, which is a nonlinear optical material, and are wavelength-converted by the BBO crystal 84 to a sum frequency light L23 with a wavelength of 355 nm. This sum frequency light L23 passes through a concave mirror 20 and is emitted from the LD-pumped solid-state laser 120 as usable light.

[0064] As mentioned above, by utilizing wavelength conversion using nonlinear optical crystals, it is possible to generate various laser beams with wavelengths shorter than the fundamental wave. Below are examples in the order of the wavelength of the laser beam to be generated, the wavelength (type) of the laser beam that is the source, and the wavelength conversion method used. In the wavelength conversion methods, "SHG" stands for second harmonic generation, and "SFG" stands for sum frequency generation. ·262nm / 523nm (fundamental wave) / SHG 281nm / 607nm (fundamental wave) and 532nm (fundamental wave) / SFG 288nm / 639nm (fundamental wave) and 532nm (fundamental wave) / SFG 299nm / 698nm (fundamental wave) and 532nm (fundamental wave) / SFG ·303nm / 721nm (fundamental wave) and 532nm (fundamental wave) / SFG ·304nm / 607nm (fundamental wave) / SHG 311nm / 639nm (fundamental wave) and 607nm (fundamental wave) / SFG ·320nm / 639nm (fundamental wave) / SHG 325nm / 698nm (fundamental wave) and 607nm (fundamental wave) / SFG 330nm / 721nm (fundamental wave) and 607nm (fundamental wave) / SFG 334nm / 698nm (fundamental wave) and 639nm (fundamental wave) / SFG 339nm / 721nm (fundamental wave) and 639nm (fundamental wave) / SFG ·349nm / 698nm (fundamental wave) / SHG 355nm / 721nm (fundamental wave) and 698nm (fundamental wave) / SFG ·361nm / 721nm (fundamental wave) / SHG

[0065] In each of the above-described embodiments, an LD that generates laser oscillation by itself is used as the excitation LD 11, but instead, an LD that does not generate laser oscillation by itself, that is, an LD that has an AR (anti-reflection) coating applied to the output end surface, may be used.

[0066] Twelfth Embodiment Next, an LD-pumped solid state laser 130 according to a twelfth embodiment of the present invention will be described with reference to Fig. 30. As shown in the schematic configuration of Fig. 30, this LD-pumped solid state laser 130 differs from the configuration shown in Fig. 1 in that a transmission-reflection mirror 115 is provided instead of the transmission flat mirror 15, but other points are basically the same as the configuration in Fig. 1. Therefore, in the following, a description of the same configuration as the configuration in Fig. 1 will be omitted, and the differences will be mainly described.

[0067] As shown in detail in Figure 31, the transmission-reflection mirror 115 is formed by joining two parallel glass plates 115a and 115b, each of which is rectangular or circular. One surface of the glass plate 115a is coated with an anti-reflection coating AR2, and the other surface is coated with a high-reflection coating HR. One surface and the other surface of the other glass plate 115b are coated with anti-reflection coatings AR1 and AR2, respectively.

[0068] The high-reflection coating film HR is, for example, HfO 2、 It is composed of a multilayer film made of Ta2O5, TiO2, etc., and the anti-reflection coating films AR1 and AR2 are composed of, for example, an SiO2 film. The anti-reflection coating film AR1 is designed and deposited so that the reflectance is 0.5% or less after the glass plates are bonded as described below, and the anti-reflection coating film AR2 is designed and deposited so that the reflectance is 0.5% or less in air.

[0069] After forming the anti-reflection coating films AR1 and AR2 and the high-reflection coating film HR as described above, the surfaces of the anti-reflection coating film AR1 and the high-reflection coating film HR were activated by ozone treatment, plasma treatment, or ultraviolet light treatment. Then, the surfaces were overlapped to bond the two glass plates 115a and 115b (see Figure 32). The bonding was performed in air or vacuum. In this case, the two glass plates 115a and 115b were bonded by so-called optical contact. After bonding, the reflectance of the bonded portion was measured using a laser beam for reflectance measurement, and the reflectance was found to be 30%. This reflectance measurement could also be performed using the excitation light L in the configuration shown in Figure 30, and in this case, the reflectance was also found to be 30%. Furthermore, this reflectance can also be measured using a commonly used spectrometer.

[0070] The two glass plates 115a and 115b are bonded together and arranged as a transmission-reflection mirror 115 as shown in Fig. 30 to form an LD-pumped solid-state laser 130 according to the fifth embodiment. In this configuration, the pumping light L is condensed by the converging lens 14 so as to converge at the bonding surface of the two glass plates 115a and 115b. 70% of the pumping light L is transmitted through the transmission-reflection mirror 115, and the remaining 30% is reflected at the bonding surface (more specifically, by the high-reflection coating film HR) and returns toward the pumping LD 11 (see Fig. 32).

[0071] In this embodiment, the portion where the condensed excitation light L converges is sandwiched between both glass plates 115a and 115b, so that it is possible to maintain a normal beam profile of the excitation light L at the convergence position. This beam profile will be described in detail below.

[0072] First, as in the configuration shown in Figure 1, when the excitation light L is converged on one surface of the transmitting flat mirror 15 and energized for a long time, the beam profile changes abnormally over time. This tendency is particularly pronounced when a confocal optical system is used and the oscillation wavelength is controlled, as in the configuration shown in Figure 1. In other words, on the mirror surface that constitutes the external resonator (the resonator range is indicated by the solid double-headed arrow in Figure 1), the beam spot of the converged excitation light L is small, so the optical power density is high. When the optical power density is high, the beam profile is more likely to become abnormal. Note that long-term energization here refers to operation at a constant optical output for several hundred hours or more, or continuous operation for several thousand hours or more.

[0073] For example, if the excitation light L is a short wavelength blue to violet light with a high optical output of several hundred mW to over 1 W, a photochemical reaction will occur at the convergence point of the excitation light L if the excitation LD 11 is energized for a long period of time. This will cause organic matter floating in the surrounding atmosphere to gradually deposit on the mirror surface. Due to the influence of this deposit, the beam profile of the excitation light L converging on the mirror surface will gradually change from a normal Gaussian beam shape and become abnormal.

[0074] Here, in the configuration shown in Figure 1, if the above-mentioned deposits occur on one surface of the transmitting flat mirror 15, an example of the schematic side shape of the deposit T is shown in Figure 33, and an example of the schematic planar shape of the beam spot BS affected by the deposit T is shown in Figure 34. Furthermore, Figure 35 shows a Gaussian beam shape, which is the normal beam profile of the pump light L, and Figure 36 shows an example of an abnormal beam profile. The abnormal beam profile shape varies from the profile shown in Figure 36 to various other irregular shapes depending on the operating environment conditions. Because this is significantly different from the Gaussian beam shape used in normal optical design, the reflected light does not return normally to the pump LD 11, and wavelength control becomes insufficient. Furthermore, because the pump light L1 beam also has an abnormal beam profile shape, the beam cannot be focused as designed within the YLF crystal 19, resulting in problems such as normal laser oscillation. Note that the beam profiles in Figures 35 and 36 are represented by position on the horizontal axis and light intensity on the vertical axis.

[0075] 30, in this embodiment, the position where the condensed excitation light L converges is sandwiched between both glass plates 115a and 115b, which prevents the deposition of organic matter floating in the atmosphere around the glass plates 115a and 115b. As a result, the beam profile of the excitation light L does not become abnormal due to the influence of deposits, and the normal Gaussian beam shape is maintained.

[0076] Thirteenth Embodiment Next, a thirteenth embodiment of the present invention will be described. Compared with the LD-pumped solid state laser 130 of the fifth embodiment shown in Fig. 30, the LD-pumped solid state laser of this thirteenth embodiment differs in the configuration of the transmission-reflection mirror 115 (and therefore the manufacturing method), but other points are basically the same as the configuration of Fig. 30. Therefore, the following will mainly describe the points that differ from the configuration of Fig. 30, but this also applies to the seventh and eighth embodiments described later.

[0077] In this embodiment, two glass plates 115a and 115b are joined by welding metal plates arranged near the inner peripheries of their peripheries. Fig. 37 shows the state before the metal plates M are welded, and Fig. 38 shows the state after welding. As shown in these figures, a high-reflection coating film HR is applied to the inner periphery of the annular metal M on one surface of the glass plate 115a, and an anti-reflection coating film AR2 is applied to the inner periphery of the annular metal M on one surface of the other glass plate 115b. An anti-reflection coating film AR1 is applied to the other surface of each of the glass plates 115a and 115b.

[0078] The high-reflection coating film HR is, for example, HfO 2、 It is composed of a multilayer film made of Ta2O5, TiO2, etc., and the anti-reflection coating films AR1 and AR2 are composed of, for example, SiO2 films. The anti-reflection coating film AR1 is designed and deposited so that its reflectance in air is 0.5% or less, and the anti-reflection coating film AR2 is designed and deposited so that its reflectance in inert gas is 0.5% or less.

[0079] After the above coating films HR, AR1, and AR2 are formed, a base of NiCr or Cr is deposited on the peripheral portions of the glass plates 115a and 115b (a predetermined area from the periphery toward the center), and then AuSn (80% Au by weight) is plated on top of that to a thickness of 10 μm. This plated portion is shown as metal M in Figures 37 and 38.

[0080] When glass plates 115a and 115b are placed together so that the plated portions overlap, they are heated to a temperature above the melting point of AuSn, 280°C, causing the AuSn to melt and bond glass plates 115a and 115b together (the state shown in Figure 38). This bonding by melting is preferably performed in an inert gas such as dry N2 with a dew point of -50°C or less; in addition to dry N2, argon or other inert gases can also be used.

[0081] The above-described transmission-reflection mirror 115 made of glass plates 115a and 115b was applied to the configuration shown in Fig. 1 to obtain an LD-pumped solid-state laser according to the sixth embodiment. In this sixth embodiment, too, the beam profile at the convergence position of the pumping light L is maintained normal. This is thought to be because, in this embodiment as well, the convergence portion of the pumping light L is sandwiched between the glass plates 115a and 115b, and in this case, both glass plates are joined via welded metal.

[0082] That is, in this case, the portion sandwiched between the two glass plates 115a and 115b is highly airtight, and even if anything is present there, it is only inert gas, so that organic matter or the like does not invade this portion, and deposits (see FIG. 33) caused by organic matter or the like do not form. Therefore, the beam profile of the excitation light L does not become abnormal due to the influence of deposits caused by long-term application of power, and is maintained normal.

[0083] Fourteenth Embodiment Next, a fourteenth embodiment of the present invention will be described. In this fourteenth embodiment, as in the thirteenth embodiment, two glass plates 115a, 115b are joined by welding metals near their peripheries, but the method for producing the joining metal is different from that in the thirteenth embodiment. The production of this joining metal will be described below.

[0084] Fig. 39 schematically shows the state before the joining metal M is welded, and Fig. 40 schematically shows the state after welding. As shown in these figures, a high-reflection coating film HR is applied to the inner periphery of the ring-shaped metal M on one surface of glass plate 115a, and an anti-reflection coating film AR1 is applied to the inner periphery of the ring-shaped metal M on one surface of another glass plate 115b. The other surfaces of glass plates 115a and 115b are each applied with an anti-reflection coating film AR1.

[0085] The high-reflection coating film HR is, for example, HfO 2、It is composed of a multilayer film made of Ta2O5, TiO2, etc., and the anti-reflection coating films AR1 and AR2 are composed of, for example, SiO2 films. The anti-reflection coating film AR1 is designed and deposited so that its reflectance in air is 0.5% or less, and the anti-reflection coating film AR2 is designed and deposited so that its reflectance in inert gas is 0.5% or less.

[0086] After the above coating films HR, AR1, and AR2 are formed, NiCr or Cr is deposited as a base on the peripheral portions of the glass plates 115a and 115b (a predetermined area from the periphery toward the center), and then AuSn (80% Au by weight) is plated on top of that to a thickness of 10 μm. Note that this plated portion is omitted in Figures 39 and 40.

[0087] After the plating, when the glass plates 115a and 115b are heated to a temperature above 280°C, the melting point of AuSn, the AuSn melts, bonding the glass plates 115a and the metal M together, and bonding the glass plates 115b and the metal M together (the state shown in FIG. 39). Next, when the glass plates 115a and 115b are overlapped so that the metal M overlaps, the metal M is further heated to a temperature above 280°C, the melting point of AuSn, and the glass plates 115a and 115b are joined via the molten metal M (the state shown in FIG. 40).

[0088] The above bonding is preferably performed in an inert gas such as dry N2 with a dew point temperature of -50°C or lower, and in addition to dry N2, argon or the like can also be used as the inert gas. In this case, a hermetically sealed air gap is formed between the glass plates 115a and 115b by the inert gas.

[0089] After the glass plate 115a and the metal M and the glass plate 115b and the metal M are bonded as shown in Fig. 39, Au diffuses into the AuSn, and the melting point of AuSn becomes high. Therefore, when the glass plates 115a and 115b are bonded together as shown in Fig. 40, the AuSn melts, preventing the previously bonded portions from peeling. Alternatively, AuSn with different composition ratios (e.g., Au and Sn composition ratios) and melting points can be used for the bonding and bonding operations to prevent this peeling.

[0090] Fifteenth Embodiment Next, a fifteenth embodiment of the present invention will be described. In this fifteenth embodiment, two glass plates 115a and 115b are bonded together using low-melting-point glass. This bonding will be described below with reference to Figures 41 and 42.

[0091] Figure 41 schematically shows the state before glass plates 115a and 115b are joined, and Figure 42 schematically shows the state after welding. As shown in these figures, a high-reflection coating film HR is applied to the inner peripheral side of an annular low-melting-point glass G on one surface of glass plate 115a, and an anti-reflection coating film AR1 is applied to the inner peripheral side of an annular low-melting-point glass G on one surface of another glass plate 115b. The other surfaces of glass plates 115a and 115b are each applied with an anti-reflection coating film AR1.

[0092] The high-reflection coating film HR is, for example, HfO 2、 It is composed of a multilayer film made of Ta2O5, TiO2, etc., and the anti-reflection coating film AR1 is composed of, for example, an SiO2 film. The high-reflection coating film HR is designed and deposited so that the reflectance in an inert gas is 30%, and the anti-reflection coating film AR1 is designed and deposited so that the reflectance in an inert gas is 0.5% or less.

[0093] After the above coating film HR is formed, the low-melting-point glass G is melted, bonding the glass plates 115a and 115b together (the state shown in FIG. 42). A mixture of powdered lead-free glass, Ta2O5 (tellurium dioxide) and MoO3 (molybdenum trioxide), is used as the low-melting-point glass G, which is applied to the outer periphery of each of the glass plates 115a and 115b. The applied portions are then heated to a melting point of 380°C or higher, melting and bonding the low-melting-point glass G together. In this way, the glass plates 115a and 115b are bonded together, and a gap hermetically sealed with an inert gas is formed between them.

[0094] The powdered glass mixture may also be a mixture of PbO·B2O3·SiO2. In this 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 to bond the glass plates 115a and 115b to form the LD-pumped solid-state laser 130 shown in Figure 30, the Gaussian beam profile of the pumping light L at the convergence point can be maintained as normal, as in the previously described embodiment. Therefore, it is believed that the generation of deposit T due to long-term power supply, as shown in Figure 33, is also suppressed in this case. [Explanation of symbols]

[0095] 10, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 130 LD-pumped solid-state laser 11. Excitation LD 12 Remate Lens 13 Narrowband BPF 14 Converging Lens 15. Transmissive flat mirror 16 Collimating Lens 17 Converging Lens 18 Plane Mirror 19 Pr:YLF crystal 20 Concave mirror 21 Coating 31 Mirror movement means 41 Diffraction Grating 51 Plane Mirror 52 LBO crystal 61 First excitation system 62 Second excitation system 63 Third excitation system 64 Fourth excitation system 65 Mirror 66, 67 Wavelength multiplexing mirror 68, 83 Polarizing beam splitter 81 First excitation and oscillation system 82 Second excitation and oscillation system 115 Transflective mirror 115a, 115b glass plates

Claims

1. a solid-state laser crystal; a semiconductor laser that emits excitation light for exciting the solid-state laser crystal; a resonator for resonating light emitted from the solid-state laser crystal upon excitation; In a semiconductor laser pumped solid-state laser having A semiconductor laser pumped solid-state laser provided with wavelength control means for making the oscillation wavelength of the pumping light from the semiconductor laser approximately coincide with the absorption peak wavelength of the solid-state laser crystal.

2. 2. A diode-pumped solid-state laser according to claim 1, wherein said wavelength control means comprises a band-pass filter disposed within said resonator for narrowing the wavelength of light to be resonated.

3. 3. A diode-pumped solid-state laser according to claim 1, wherein the resonator further includes a diffraction grating for selecting a wavelength of light to be resonated.

4. 3. A semiconductor laser pumped solid-state laser according to claim 1, wherein the resonator further includes a VBG (Volume Bragg Grating) for selecting a wavelength of light to be resonated.

5. 3. The diode-pumped solid-state laser according to claim 1, wherein the resonator further includes a confocal optical system.

6. an external resonator is provided to configure the wavelength control means; the 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; 3. A diode-pumped solid-state laser according to claim 1, wherein said transmission-reflection mirror is formed from two glass plates bonded together.

7. 7. A diode-pumped solid-state laser according to claim 6, wherein the two glass plates are joined together by optical contact.

8. 7. The semiconductor laser pumped solid-state laser according to claim 6, 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 plating together.

9. 7. The semiconductor laser pumped solid-state laser according to claim 6, 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 heating and welding the metal plates together via the metal plating.

10. 7. A diode-pumped solid-state laser according to claim 6, wherein the two glass plates are joined together by melting low-melting-point glass disposed near the periphery of each glass plate.

11. The solid-state laser crystal is Pr ３＋ 3. The semiconductor laser pumped solid-state laser according to claim 1, wherein the laser is doped with:

12. 3. A diode-pumped solid-state laser according to claim 1, wherein the semiconductor laser is a GaN-based semiconductor laser.

13. 3. A semiconductor laser pumped solid-state laser according to claim 1, wherein the semiconductor laser is a multi-transverse mode semiconductor laser.

14. 3. The semiconductor laser pumped solid state laser according to claim 1, further comprising an optical wavelength conversion element for converting the wavelength of the solid state laser oscillation light into a shorter wavelength.

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