JPH0799357A - Semiconductor laser excited solid state laser system - Google Patents

Abstract

PURPOSE:To miniaturize the laser system for enhancing the reliability by integrating a wavelength control element with resonator mirrors within an SHG beam source using the wavelength variable solid laser used for laser printer etc. CONSTITUTION:A semiconductor laser 11 is focussed by a focussing optical system 12 to excite laser crystal 31. Next, Cr: LiSrAlF6 as the excited laser crystal raises basic waves 41 between resona-tor mirrors 21a-21c. At this time, the laser crystal 31 and a non-linear optical crystal KNbO332 are arranged between the reso-nator mirrors 21a, 21b formed on the front end face of the laser crystal 31. Furthermore, an optical axis bent by the resonator mirror 21-b, after transmitting the triangular wavelength dispersing prism 33, is reflected on the resonator mirror 21-c formed on the prism 33 outgoing end face so as to form the resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of optoelectronics, and more particularly to a visible laser light source and a laser printer device or stereolithography device using the visible laser light source.

[0002]

2. Description of the Related Art With the progress of the advanced information age, in the optical recording field such as an optical disk device and a laser printer device, there is an increasing demand for a shorter wavelength in order to satisfy the demands for higher recording density and higher speed printing. . However, gas laser devices such as He-Cd (helium-cadmium) laser devices and Ar (argon) laser devices are the only light sources that satisfy the blue-green region, which is a wavelength region that is highly demanded at the commercialization level. It was large and not suitable for mounting because of its large power consumption. Further, although it is installed in some laser printers, there is a possibility that it may be an obstacle to further miniaturization and lower power consumption in the future. On the other hand, optical second harmonic generation (SHG; Second Harmonic Gene)
ration) has been proposed to shorten the wavelength. The study of the practical application technology of the SHG light source has advanced along with the increase in the output of the semiconductor laser. Behind that, there was the possibility of realizing compactness and low power consumption without the need for discharge like conventional gas lasers. Next, SHG, which depends on the output stability and long life of pumping semiconductor lasers. High reliability of the light source (output stability, long life). As an SHG light source having an output wavelength equivalent to that of the gas laser, for example, a near-infrared semiconductor laser output is used as a first oscillating wave, that is, a fundamental wave, and it is resonated by an external resonator, in which a nonlinear optical crystal KN ( KNbO ₃ ; potassium niobate) has been proposed to obtain a second lasing wave, that is, an SH wave, a blue laser beam (W Jay Koslovsky, W. Lens, “Gallium Aluminium Arsenic”). 41m due to second harmonic of semiconductor laser
Generation of W Blue Light ”, Applied Physics Letters, Vol. 56, No. 23, p. 2291, 1990; WJKo
zlovsky and W. Lenth, "Generation of 41mW of blue ra
diation by frequency doubling of a GaAlAsdiode las
er ", Appl.Phys.Lett., vol.56, no.23, p2291, '90). However, in the SHG light source, the wavelength permissible width of KN (the wavelength at which the conversion efficiency is 1/2 or more of the maximum value) The range) is as narrow as 1 nm or less, and the semiconductor laser requires an optical isolator because it causes output instability when the oscillation wavelength fluctuates by several nm due to disturbance such as return light. LiSAF (Cr: LiSrAl) is a laser crystal that can achieve the same output wavelength as an external semiconductor laser.
F ₆ ; chromium-added lithium strontium aluminum fluoride) was proposed (USP 4,811,34)
9). In a semiconductor laser pumped solid-state laser device using the LiSAF crystal, a light source having a wavelength variable in the range of 860 to 920 nm for coupling an external resonator using a birefringent filter, and an SH using LiIO ₃ (lithium iodate)
A report on G has been made. For the former, Qui Zang, D. J. Dixon, B.H.Chai, P.N.Kean, "Electrically tuned semiconductor laser pumped Cr: LiSrAlF ₆ laser" Optics Letter, Volume 17, 1 No., p. 43, 1
992; Qi Zhang, GJDixon, BHChai, PNKea
n, "Electronically tuned diode-laser-pumped Cr: LiSr
AlF ₆ laser ", Opt.Lett., Vol.17, no.1, p43, '92, for the latter Francois Barembois, Patrick Georges, Francois Sari, Gerard Roger, Alan Brunn," Cr addition Blue light source with variable wavelength by internal resonant second harmonic of LiSrAlF ₆ laser
Physics Letter, Vol. 61, No. 20, pp. 2381,
1992; Francois Balembois, Patrick Georges,
Francois Salin, Gerard Roger, and Alain Brun, "Tunable blue light source by intracavi
ty frequency doublingof a Cr-doped LiSrAlF ₆ lase
r ", Appl. Phys. Lett., vol. 61, no. 20, p2381, '92. FIG. 4 is a diagram for explaining an SHG light source with a cavity structure using a tunable solid-state laser. The excitation light is condensed and excites the laser crystal 31. The excited laser crystal 31 generates a fundamental wave 41 between the resonator mirrors (M1, M2, M3). ),
A laser crystal 31 and a nonlinear optical crystal 32 are arranged between M2 (21-b). The resonated fundamental wave 41 is partially converted into the SH wave 42 in the nonlinear optical crystal 32 and emitted from the resonator mirror M2 (21-b). At this time, the output of the SH wave 42, that is, the conversion efficiency of the nonlinear optical crystal 32 changes depending on the oscillation wavelength of the fundamental wave 41. Therefore, it is necessary to control the wavelength in order to obtain a high output. Therefore, the resonator mirrors M2 (21-b) and M3 (2
A birefringent filter, which is the wavelength control element 33, is arranged between 1-c) to control the wavelength. A birefringent filter is generally made by laminating three quartz plates with different thicknesses, the incident surface is arranged at Brewster's angle with respect to the fundamental wave optical axis, and a precise rotation adjustment mechanism is required for wavelength control. To do. Further, as shown in FIG. 4, the reason why not all the optical components are arranged in one resonator is as follows. First, the beam waist diameter in one resonator is made small in order to increase the efficiency of generation of normal SH waves. Therefore, the beam divergence other than the beam waist becomes large, and it is difficult to construct a resonator having a long optical path length. Secondly, the wavelength control element such as the birefringence filter has a different selected wavelength depending on the incident angle of the beam. Therefore, if the optical path length of the birefringent filter is increased in order to obtain good selectivity, the partial divergence angle is different in the beam cross section, and the efficiency is lowered and the wavelength controllability is deteriorated. For these two reasons, a resonator for arranging a wavelength control element such as a bending type or a resonator coupling type in the beam waist is configured.

[0003]

Generally, there are two advantages of using a tunable solid-state laser as the fundamental wave of an SHG light source. First
In addition, the wavelength of the SH wave can be tuned within the wavelength tunable range of the fundamental wave. Secondly, the wavelength tolerance of the nonlinear optical crystal is narrow as described above, and maximum efficiency can be reliably obtained by controlling the fundamental wave wavelength. When the wavelength control element such as the birefringent filter is used in the internal resonance type SHG light source using the wavelength tunable solid state laser, it is necessary to form an adjustment mechanism such as a rotation mechanism for Brewster angle adjustment and wavelength control. It was For this reason, there is a problem in that the advantage of the semiconductor laser pumped SHG light source described above, which is the advantage of miniaturization, is greatly impaired.

[0004]

In the present invention, in the internal resonance type SHG light source using the wavelength tunable solid state laser, the device is downsized by devising the wavelength control element, and the problems of the prior art are solved. That is, a fundamental wave resonator mirror is formed on the wavelength dispersion prism used for the wavelength control element, and the resonator mirror and the wavelength control element are integrated. In the tunable solid-state laser, the wavelength width of spontaneous emission of the excited laser crystal has a wide tunable range. Further, in order to realize the SHG light source using the wavelength tunable solid-state laser by this method, it is sufficient that the resonator mirror adjustment mechanism is provided, and the adjustment of the wavelength control element which is required in the conventional device is not necessary. Become. Compared with the conventional method, the number of parts was reduced by integrating the wavelength control element and the resonator mirror, and the adjustment mechanism of the wavelength control element could be omitted. Therefore, the device can be downsized and the conventional problems can be solved. The invention also describes the following specific and distinct features. (1) A semiconductor laser, a laser crystal excited by the semiconductor laser, and a resonator structure including the laser crystal, and a variable oscillation wavelength width Δλ of a solid-state laser output generated by the resonator structure is 20 ≦. In the semiconductor laser pumped solid-state laser device in which Δλ ≦ 200 nm, a semiconductor laser-pumped solid-state laser device in which the wavelength is controlled by using a resonator mirror that selects the oscillation wavelength width Δλ to be 10 nm or less was proposed. (2) A semiconductor laser pumped solid-state laser device is proposed in which the resonator mirror is a wavelength dispersion prism, and a reflection film having a reflectance of 95% or more at the variable oscillation wavelength of the solid-state laser output is formed on one surface of the wavelength dispersion prism. . (3) A semiconductor laser pumped solid-state laser device having a nonlinear optical crystal for converting a first oscillation wave of the laser crystal into a second oscillation wave in the resonator structure has been proposed. (4) A semiconductor laser pumped solid-state laser using LiSAF (Cr: LiSrAlF ₆ ; chromium-added lithium strontium aluminum) as the laser crystal.
I proposed the device. (5) A semiconductor laser pumped solid-state laser device using KN as the nonlinear optical crystal was proposed. (6) A semiconductor laser pumped solid-state laser device using KLN (KLiNbO ₃ ; potassium lithium niobate) as the nonlinear optical crystal was proposed. (7) A semiconductor laser pumped solid-state laser device having means for controlling the temperature of a laser housing mounting the resonator structure was proposed. (8) A semiconductor laser pumped solid-state laser device is proposed in which the second oscillating wave is the second harmonic of the first oscillating wave. (9) A semiconductor laser pumped solid-state laser device in which the optical axis of the semiconductor laser and the optical axis of the second oscillating wave are parallel to each other has been proposed. (10) A laser printer device or a stereolithography device using the above-mentioned semiconductor laser pumped solid-state laser device has been proposed.

(Embodiment 1) FIG. 1 is a diagram for explaining an embodiment of the present invention. The semiconductor laser 11 is condensed by the condensing optical system 12 and excites the laser crystal 31. The excited laser crystal 31 is a resonator mirror 21 (M1, M
2 and M3), a fundamental wave 41 is generated. Laser crystal 31
Resonator mirror M1 (21-a) formed on the front end face of the
And M2 (21-b), a laser crystal 31 and a nonlinear optical crystal 32 are arranged. The optical axis is the resonator mirror M2
It is bent at (21-b), and after passing through the triangular prism wavelength dispersion prism 33, is reflected by the resonator mirror M3 (21-c) formed on the emission end face of the wavelength dispersion prism to form a resonator. The resonated fundamental wave 41 is the nonlinear optical crystal 3
In FIG. 2, a part of the SH wave 42 is converted to a resonator mirror M.
2 (21-b) is emitted. Excitation wavelength is 680n
m, fundamental wave wavelength is 860 nm, SH wave wavelength is 430 nm
And In this configuration, the excitation beam and the SH wave 42 output are parallel. Here, when spontaneous emission enters the wavelength dispersion prism 33 in the resonator, different wavelength components travel in different directions inside the wavelength dispersion prism 33. Further, the resonator mirror M3 (21-c) that reflects perpendicularly to the traveling direction of the beam 41 of the desired wavelength is provided with the wavelength dispersion prism 3.
If formed on the exit surface of 3, the beam travels in the opposite direction along the same optical axis. At this time, for the other wavelength components, the resonator mirror M3 (21-c) is not positioned vertically, so that the reflected light is reflected in a direction different from the traveling direction and resonance does not occur. Therefore, only the spontaneous emission beam having a desired wavelength is selected, the resonance condition is satisfied, and the wavelength can be controlled. In the present invention, a wavelength dispersion prism in which a wavelength change of 2 nm corresponds to an angle adjustment of 1 ° was used. The reflecting surface of the wavelength dispersion prism 33 is designed to be perpendicular to the optical axis at the fundamental wavelength. Under the design conditions, the oscillation wavelength of the fundamental wave 41 is 860 nm at the center, and the wavelength width Δλ is Δλ <2 nm. Δλ can be controlled to be 10 nm or less by adjusting the thickness in the optical axis direction of the wavelength dispersion prism. As the excitation semiconductor laser 11, a broad area type having an oscillation wavelength of 680 nm and an output of 500 mW was used. An anamorphic prism pair is used for the condensing optical system 12 to correct the distortion of the condensing shape so that the coupling with the fundamental wave resonance mode 41 in the laser crystal 31 is favorably performed. The condensing optical system 12 is all provided with antireflection (hereinafter simply referred to as AR; Anti-Reflection) coating so that the reflectance is 5% or less at the excitation wavelength. The Cr content in the laser crystal 31 is 5.5%
The LiSAF crystal of was used. Crystal size is 3x3x1
The thing of mm was used. The front end face of the crystal has an AR coating with a reflectance of 5% or less with respect to the excitation wavelength, and a total reflection with a reflectance of 99% or more with respect to the fundamental wavelength (hereinafter simply referred to as HR; High
-Reflection) coated resonator mirror M1
(21-a). The rear end surface of the laser crystal 31 was AR-coated with a reflectance of 5% or less for the fundamental wavelength. The resonator mirror M2 (21-b) was provided with an HR coating similar to M1 for the fundamental wavelength and an AR coating with a reflectance of 15% or less for the 42 SH wavelengths. Further, the incident surface of the wavelength dispersion prism 33 is AR coated with a reflectance of 5% or less for the fundamental wavelength,
An HR coating having a reflectance of 99% or more was applied to the reflecting surface. KN was used for the nonlinear optical crystal 32. Size 3
The thing of * 3 * 5 was used and it arranged so that the advancing direction of the fundamental wave beam 41 might become the a-axis direction of KN crystal. Both ends of the KN crystal were AR-coated with a reflectance of 5% or less for the fundamental wave 41 and the SH wave 42 wavelengths. Also, KN
The temperature of the crystal was controlled to 25 ° C. ± 0.2 to stabilize the phase matching condition of SHG. Furthermore, the temperature of the entire holder was controlled so that the distance between the optical components did not change thermally. In the present invention, each of the independent control elements 51 is used, but temperature control by the same control element is also possible. The reflectance of the HR coating may be 95% or more, particularly 99%.
There is no need to go above. The allowable wavelength range of absorption of LiSAF is as wide as about 100 nm, and the wavelength of the excitation semiconductor laser was not controlled by using a temperature control element or the like, but it may be controlled to match the maximum absorption wavelength. Also, KLN may be used instead of KN.

(Embodiment 2) FIG. 2 is a diagram for explaining an embodiment of the present invention. In this embodiment, each component is
Semiconductor laser 11, focusing optical system 12, resonator mirror M1
(21-a), laser crystal 31, nonlinear optical crystal 32,
The triangular prism wavelength dispersion prism 33, the resonator mirror M2 (21-b), SH formed on the emission end face of the wavelength dispersion prism.
It becomes the prism 34 for correcting the emission angle of the wave 42. The fundamental wave beam 41 oscillates so as to form a beam waist on the M2 side by the resonator mirror M1 (21-a) and the resonator mirror M2 (21-b). Here, what is different from the first embodiment is the coating specification. AR is provided on both end faces of the laser crystal 31 with respect to the fundamental wavelength, HR with respect to the fundamental wavelength on M2 (21-b), and AR with respect to the SH wavelength. Perform coating. In this configuration, the above-mentioned SH exit angle correction prism is provided so that the excitation beam and the output of the SH wave 42 are parallel.
The temperature control of the KN and the resonator are the same as in the first embodiment.

(Third Embodiment) FIG. 3 is a diagram for explaining one embodiment of the present invention. The SH wave 42 emitted from the SHG light source 100 described in the first or second embodiment is an acousto-optic (AO) modulator 20.
1, beam expander 202, rotary polygon mirror 203, f
The light passes through the θ lens 204 and is focused on the photosensitive drum 205. The AO modulator 201 modulates the SH wave 42 according to the image information, and the rotary polygon mirror 203 scans in the horizontal (inside the paper) direction. With this combination, the two-dimensional information is stored on the photosensitive drum 205.
Is recorded as a partial potential difference. Photosensitive drum 205
According to the potential difference, toner is attached and rotated to reproduce information on the recording paper.

[0008]

The effect obtained by the present invention is that the number of parts and part of the adjusting mechanism are omitted in the assembly of the SHG light source to realize miniaturization that can be mounted in an optical electronic device such as a laser printer device and an optical molding device. There is a point. In addition, since the size is reduced and the number of parts is reduced, SHG
Improves reliability against vibration of the light source.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining an example of the present invention.

FIG. 3 is a diagram for explaining an example of the present invention.

FIG. 4 S by internal resonance using a tunable solid-state laser
It is a figure for demonstrating an HG light source.

[Explanation of symbols]

11 semiconductor laser, 12 focusing optical system, 21 resonator mirror, 31 laser crystal, 32 nonlinear optical crystal, 3
3 wavelength control element, 34 SH wave exit angle correction prism,
41 fundamental wave, 42 SH wave, 51 temperature control element, 1
00 SHG light source, 201 AO modulator, 202 beam expander, 203 rotating polygon mirror, 204 fθ lens, 205 photosensitive drum

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication H01S 3/18

Claims (11)

[Claims] 1. A semiconductor laser, a laser crystal excited by the semiconductor laser, and a resonator structure including the laser crystal, wherein a variable oscillation wavelength width Δλ of a solid-state laser output generated by the resonator structure is 20 ≦ Δλ ≦ 200n
In the semiconductor laser pumped solid-state laser device of m, the wavelength is controlled by using a resonator mirror that selects an oscillation wavelength width Δλ of 10 nm or less. 2. The resonator mirror is a wavelength dispersion prism, and a reflection film having a reflectance of 95% or more at a variable oscillation wavelength of the solid-state laser output is formed on one surface of the wavelength dispersion prism. 1. A semiconductor laser pumped solid-state laser device according to 1. 3. A non-linear optical crystal for converting a first oscillating wave by the laser crystal into a second oscillating wave in the resonator structure. A semiconductor laser pumped solid-state laser device as described. 4. The laser crystal is LiSAF (Cr: LiSrA).
1F ₆ ; chromium-added lithium strontium aluminum fluoride).
The semiconductor laser pumped solid-state laser device according to any one of 1. 5. The nonlinear optical crystal is KN (KNbO ₃ ; potassium niobate), wherein the nonlinear optical crystal is KN (KNbO ₃ ; potassium niobate).
The semiconductor laser pumped solid-state laser device according to any one of 1. 6. The non-linear optical crystal is KLN (KLiNb
O ₃ ; potassium lithium niobate), The semiconductor laser pumped solid-state laser device according to claim 1. 7. The semiconductor laser pumped solid-state laser device according to claim 1, further comprising means for controlling a temperature of a laser housing on which the resonator structure is mounted. 8. The second oscillating wave is a second oscillating wave of the first oscillating wave.
The semiconductor laser pumped solid-state laser device according to claim 1, wherein the solid-state laser device is a harmonic. 9. The semiconductor laser pumped solid-state laser device according to claim 1, wherein an optical axis of the semiconductor laser and an optical axis of the second oscillating wave are parallel to each other. 10. A laser printer device using the semiconductor laser pumped solid-state laser device according to claim 1. Description: 11. An optical modeling apparatus using the semiconductor laser pumped solid-state laser device according to claim 1. Description: