JPWO2017138373A1 - Laser equipment - Google Patents

Abstract

This laser device is a “wa” -shaped or “7” -shaped folded arrangement type, and includes a pair of terminal mirrors 10, 12, a laser medium 14, a Q switch 16, an aperture unit 18, a nonlinear optical crystal 20, and harmonic separation. A mirror 22 and an intermediate mirror 24 are arranged. The pump unit 30 includes a fiber coupling type optical fiber 32, an output unit 34 for guiding pumping LD light extracted from the optical fiber 32 to both end faces of the laser medium 14, a beam splitter 38, first and second half pumps. Optical units 40 and 42 are provided.

Description

  The present invention relates to a laser device using a crystal doped with active ions in a laser medium of a solid-state laser.

  Conventionally, solid-state lasers are often used for laser processing such as laser welding and laser marking. A general solid-state laser uses a block-shaped crystal (typically a rectangular parallelepiped shape or a rod-shaped crystal) doped with active ions such as rare earth elements as an active medium, and irradiates the side surface or end surface of the crystal with excitation light. The active element is optically pumped, and a laser beam is extracted after resonance oscillation amplification of a predetermined wavelength emitted from the crystal in the optical axis direction is performed in an optical resonator (for example, FIG. 1).

  In addition, the optical resonator is composed of a pair of terminal mirrors or total reflection mirrors, a non-linear optical crystal and a harmonic separation mirror are arranged together with an active medium on the optical path in the optical resonator, and harmonics are separated by the harmonic separation mirror. A laser beam is also taken out (for example, FIG. 3 of Patent Document 2).

  In the past, a lamp was mainly used as the excitation light source, but now a semiconductor laser, that is, a laser diode (LD), has become the mainstream. Among the LD excitation methods, the end face excitation method (Patent Document 1) is now the mainstream instead of the original side surface excitation method (Patent Document 2).

JP 2006-5212 A JP 2005-209965 A

  By the way, in the recent precision laser processing field, a solid-state laser capable of obtaining a high-power single-mode laser beam is required in terms of processing capability, processing accuracy, and cost. The single mode is a mode in which the beam shape is circular and the power density is concentrated at the center, has excellent light collecting properties, and is suitable for precision processing.

In this regard, the YVO ₄ laser using a YVO ₄ crystal doped with Nd ions as an active medium is more recently used than the YAG laser using a YAG crystal doped with Nd ions as an active medium. It has excellent excitation efficiency and is suitable for obtaining a single-mode laser beam, particularly a Q-switch pulse laser beam.

However, the YVO ₄ laser has a problem in that the average laser output is greatly reduced in a region (˜20 kHz) where the repetition frequency (Q switch frequency) where high peak power is obtained is low. This is because if the repetition frequency is lowered, heat is generated inside the YVO ₄ crystal, and the so-called thermal lens effect is likely to occur.

In the conventional YVO ₄ laser, in order to improve the average laser output, it is not effective to increase the output of pumping LD light excessively. In the conventional end face excitation method, even if the output of the excitation LD light is sufficiently high, very strong absorption occurs near the crystal end face where the LD excitation light is incident, and a thermal lens is likely to be generated locally. Laser power does not increase as expected. Rather, the YVO ₄ crystal is easily damaged by the high density incidence of the LD excitation light. As long as the air-cooled YVO ₄ laser that generates the second harmonic (SHG) laser beam of the Q-switch pulse in single mode, the oscillation specifications (performance) of the conventional apparatus generally has a repetition frequency of 40 kHz or more and an average laser output. Is 8 W or less, and the pulse energy is 200 μJ or less.

  On the other hand, low-power seed light generated by a solid-state laser is passed through an active fiber for laser amplification using an optical fiber doped with active ions in the core, and the core of the active fiber is excited by pumping LD light. Among them, a so-called MOPA type fiber laser, which amplifies the output of seed light and extracts a high-power laser beam, has recently become widespread. However, the MOPA fiber laser is considerably large. Also, the generation of abnormal pulses due to stimulated Brillouin scattering (SBS), which is one of the nonlinear optical phenomena of the optical fiber itself, hinders the improvement of peak power, and the generation threshold is proportional to the core cross-sectional area of the optical fiber. Another problem is that peak power during pulse amplification is limited by stimulated Raman scattering (SRS) inversely proportional to the fiber length. In general, the conventional pulse oscillation type MOPA fiber laser has a peak power of 10 kW and a pulse energy of 100 μJ or less.

  The present invention has been made in view of such problems of the prior art, and in a facet-pumped solid-state laser, the generation of a thermal lens effect can be effectively suppressed to obtain a low-order mode high-power laser beam. A laser apparatus is provided.

  A laser device according to a first aspect of the present invention includes an optical resonator having a first termination mirror and a second termination mirror that are optically opposed to each other, and an active medium portion made of a crystal doped with active ions. A non-active portion made of a crystal that is made of the same material as the active medium portion and is not doped with active ions, and is coupled to opposite end faces of the active medium portion. In order to generate a fundamental wave laser beam having a fundamental wavelength, a laser medium arranged with the active medium part and the inactive part aligned on the path, both sides of the laser medium on the optical path in the optical resonator An excitation unit for irradiating an end surface with an excitation laser beam, an aperture unit disposed on an optical path in the optical resonator to reduce the beam diameter of the fundamental laser beam, and a fundamental wavelength of the fundamental laser beam for In order to generate a harmonic laser beam having a harmonic wavelength, a nonlinear optical crystal disposed on an optical path in the optical resonator and the harmonic laser beam are separated from the fundamental laser beam and output. And a harmonic separation mirror disposed on the optical path in the optical resonator, and the beam diameter of the excitation laser beam incident on both end faces of the laser medium is the fundamental laser beam of the aperture unit. The structure is larger than the opening.

  In the above-described apparatus configuration, heat is generated by the combined or synergistic action of the structure of the laser medium composed of the active medium part and the inactive part, the both-ends end excitation method by the excitation part, and the beam stop function of the aperture unit. Generation of a lens effect can be effectively suppressed, and a high-power harmonic laser beam can be obtained in a low-order mode close to a single mode.

  A laser device according to a second aspect of the present invention includes an optical resonator having optically opposed total reflection mirrors and partial transmission mirrors, an active medium portion made of a crystal doped with active ions, and the active medium. A non-active part made of a crystal made of the same material as that of the active part and not doped with active ions, and inactive parts connected to opposite opposite end faces of the active medium part, and the active part on the optical path in the optical resonator In order to generate a laser beam having a predetermined wavelength and a laser medium arranged with the medium part and the inactive part aligned, both end surfaces of the laser medium are irradiated with an excitation laser beam on the optical path in the optical resonator. And an aperture unit disposed on the optical path in the optical resonator for narrowing the beam diameter of the laser beam, and the excitation laser beam incident on both end faces of the laser medium. Beam diameter, and an opening greater than the configuration for passing the laser beam of the aperture unit.

  In the above-described apparatus configuration, heat is generated by the combined or synergistic action of the structure of the laser medium composed of the active medium part and the inactive part, the both-ends end excitation method by the excitation part, and the beam stop function of the aperture unit. Generation of a lens effect can be effectively suppressed, and a high-power fundamental laser beam can be obtained in a low-order mode close to a single mode.

  According to the laser apparatus of the present invention, it is possible to effectively suppress the generation of the thermal lens effect in the end face excitation type solid-state laser and obtain a low-order mode high-power laser beam by the configuration and operation as described above. it can.

1 is a schematic plan view showing a configuration of a laser device according to an embodiment of the present invention. It is a figure which shows the structural example of the beam splitter used for the excitation part of the said laser apparatus. It is a figure which shows the structure of the laser medium in the said laser apparatus, and the effect | action of a both-ends end surface excitation system. It is a figure which compares and shows an Example and a comparative example about the excitation LD drive current value dependence of the average laser output of a 2nd harmonic. It is a figure which shows the position adjustment of each part at the time of performing high-order mode adjustment in the said laser apparatus. It is a schematic plan view which shows the 2nd Example regarding the arrangement configuration of the optical system in the excitation part of the said laser apparatus. It is a schematic plan view which shows the 3rd Example regarding the arrangement configuration of the optical system of the excitation part in the said laser apparatus. It is a schematic side view which shows the arrangement configuration of the optical system of the excitation part which concerns on the said 3rd Example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a configuration of an optical system of a laser apparatus according to an embodiment of the present invention. This laser device is configured as an air-cooled YVO ₄ laser that generates a second harmonic (SHG) laser beam of a Q switch pulse in a low-order mode close to a single mode. This YVO ₄ second harmonic (SHG) laser can be applied to various laser processing, and in particular, laser marking or laser for copper-based, metal-based metal workpieces and non-metal workpieces such as silicon and ceramics. It is suitable for use in laser surface removal processing such as trimming.

[Layout of optical resonator and internal configuration]
In this laser apparatus, as a layout of a laser oscillator, a “wa” -shaped or “7” -shaped folded arrangement as shown in plan view is arranged on a base or a support base (not shown) having a substantially flat upper surface. A pair of terminal mirrors 10 and 12, a laser medium 14, a Q switch 16, an aperture unit 18, a nonlinear optical (wavelength conversion) crystal 20, and intermediate mirrors 22 and 24 are arranged.

  Both terminal mirrors 10 and 12 are optically opposed to each other via intermediate mirrors 22 and 24 to constitute an optical resonator 13. On the other hand (on the left side in the figure), the reflecting surface of the terminal mirror 10 is coated with a highly reflective film for the fundamental wave (1064 nm) generated in the optical resonator 13. The reflecting surface of the other end mirror 12 (on the right side of the figure) is coated with two types of films that are highly reflective to the fundamental wave and the second harmonic (532 nm) generated in the optical resonator 13, respectively. Has been.

The laser medium 14 has a rectangular parallelepiped active medium portion 14a made of a YVO ₄ crystal doped with Nd ions as active ions (Nd: YVO ₄ crystal), and diffuses on both end surfaces of the active medium portion 14a facing each other in the axial direction. It has a pair of inactive part 14b couple | bonded by joining. Here, the inactive portion 14b is made of a YVO ₄ crystal (undoped YVO ₄ crystal) made of the same material as the active medium portion 14a and not doped with any active ions. As a whole, the laser medium 14 is configured as a solid or crystal body having a rectangular parallelepiped shape having parallel both end faces (left end face and right end face in FIG. 1). As an example, in the axial direction, the length of the active medium portion 14a is 10 mm, the lengths of the inactive portions 14b on the left and right sides are 2 mm, and the total length of the laser medium 14 is 14 mm.

  In the laser medium 14, the active medium portion 14a and the inactive portion 14b are aligned between the intermediate mirrors 22 and 24 on the fundamental optical path FH in the optical resonator 13 (the optical axis of the crystal is overlapped with the optical path). Arranged). Note that the fundamental wave optical path FH in the optical resonator 13 is set between the both end mirrors 10 and 12 via the intermediate mirrors 22 and 24.

  The Q switch 16 is composed of, for example, an acousto-optic Q switch, and is driven to be switched at a constant repetition frequency by a Q switch driver (not shown) when performing laser oscillation. In this embodiment, the repetition frequency can be selected in a wide range, and a low frequency region of 30 kHz or less or 20 kHz or less can be selected as well as a conventional high frequency region of 40 kHz or more. The aperture unit 18 is made of, for example, a metal plate, and forms an opening 18a having a predetermined diameter (for example, φ1 to φ1.2 mm) for narrowing the beam diameter of the fundamental laser beam generated in the optical resonator 13. Yes.

  The Q switch 16 and the aperture unit 18 are arranged side by side between the laser medium 14 and the left intermediate mirror 24 on the fundamental wave path FH in the optical resonator 13. The intermediate mirror 24 has a reflection surface coated with a highly reflective film with respect to the fundamental wave so that the fundamental wave path FH in the optical resonator 13 is folded back at an acute angle (usually 30 ° to 60 °). It is arranged at an angle. The fundamental laser beam that is incident on the intermediate mirror 24 from the laser medium 14 side and turned back is incident perpendicularly to the termination mirror 10 disposed near the aperture unit 18, where it is totally reflected and terminated on the opposite side. Return to the mirror 12.

  The nonlinear optical crystal 20 is made of, for example, a rectangular parallelepiped LBO crystal, and is disposed on the fundamental / second harmonic optical path FH / SH set between the terminal mirror 12 and the intermediate mirror 22. The nonlinear optical crystal 20 is optically coupled to a fundamental wave mode that is excited or amplified in the optical resonator 13, and generates a second harmonic by nonlinear interaction with the fundamental wavelength.

  The intermediate mirror 22 is a harmonic separation mirror. The harmonic separation mirror 22 is composed of a dichroic mirror having a film highly reflective to the fundamental wave and a film transmissive to the second harmonic, and the incident and reflection angles of the fundamental wave are acute angles. It functions as a folding mirror (usually 30 ° to 60 °) and functions as an output mirror for the second harmonic.

The fundamental-wave laser beam incident on the harmonic separation mirror 22 from the laser medium 14 side and turned back there passes through the nonlinear optical crystal 20 and then enters the termination mirror 12 perpendicularly, where it is totally reflected and the same. The light propagates in the reverse direction along the optical path FH. Further, the second harmonic wave coming out from the nonlinear optical crystal 20 toward the terminal mirror 12 is totally reflected by the terminal mirror 12 and enters the nonlinear optical crystal 20. The second harmonic emitted from the nonlinear optical crystal 20 toward the harmonic separation mirror 22 is transmitted through the harmonic separation mirror 22 and output as a second harmonic laser beam LB _SH .

[Configuration of excitation unit]
This laser apparatus includes a pumping unit 30 as described below in order to pump the laser medium 14 in the optical resonator 13 having the above-described configuration.

  The pump unit 30 includes a fiber coupling type optical fiber 32 that transmits pumping LD light from an LD (not shown) of a pumping light source to the front of the optical resonator 13 and pumping LD light extracted from the optical fiber 32. An optical system leading to the laser medium 14, that is, an emission unit 34, a beam splitter 38, and first and second semi-excitation optical units 40 and 42 are provided.

  The optical fiber 32 is attached so that the tip end of the fiber is inserted into an optical connector or a receptacle (not shown) of the emission unit 34. The optical fiber 32 has a core with a diameter of, for example, φ0.4 mm. A collimating lens 36 is provided in the emission unit 34. The pumping LD light EB emitted from the end of the optical fiber 32 at a certain spread angle is collimated into parallel light by passing through the collimating lens 36.

The beam splitter 38 is, for example, a cube-type beam splitter (FIG. 2A) or a plate-type beam splitter (FIG. 2B) configured by two right-angle prisms, and is excited from the output unit 34. The LD light EB is divided into two, that is, first and second half-pumped LD lights EB _h1 and EB _h2 . The first half-pumped LD light EB _h1 is emitted as transmitted light from the beam splitter 38 toward the first half-pump optical unit 40. On the other hand, the second half-pumped LD light EB _h2 is emitted as reflected light from the beam splitter 38 toward the second half-pump optical unit 42.

  The first semi-pumping optical unit 40 includes a folding mirror 44 and a condensing lens 46 arranged on the same line as the fundamental wave path FH in the optical resonator 13 (in a line in the X direction in the figure). The condenser lens 46 optically has an optically constant distance (usually a focal length or a distance close to this) from one end face (right side of the drawing) of the laser medium 14 via the harmonic separation mirror 22. Opposite parallel and spaced apart.

The folding mirror 44 receives the first half-pumped LD light EB _h1 from the beam splitter 38 and reflects it at a right angle toward the laser medium 14. The first half-pumped LD light EB _h1 turned back by the turning mirror 44 enters the right end surface of the laser medium 14 through the condenser lens 46 and the harmonic separation mirror 22. The harmonic separation mirror 22 is coated with a film that is transmissive to the wavelength of the excitation LD light EB (for example, 880 nm).

  The second semi-pumping optical unit 42 includes a folding mirror 48, a condensing lens 50, and a folding mirror 52 that are arranged in a line in the Y direction in the figure perpendicular to the fundamental wave path FH in the optical resonator 13. Yes. Here, the folding mirror 52 is disposed at an oblique angle on the fundamental wave path FH in the optical resonator 13 between the laser medium 14 and the Q switch 16. The condenser lens 50 is optically opposed in parallel to the left end surface of the laser medium 14 via the folding mirror 52 at a certain optical distance (usually a focal length or a distance close thereto). .

The folding mirror 48 receives the second half-pumped LD light EB _h2 from the beam splitter 38 and reflects it at a right angle toward the folding mirror 52 at the subsequent stage. The second half-pumped LD light EB _h2 folded by the folding mirror 48 is incident on the folding mirror 52 through the condenser lens 50, is folded at a right angle, and is incident on the left end surface of the laser medium 14. The folding mirror 52 is formed of a dichroic mirror, and includes a film that is transmissive to the fundamental wave and a film that is highly reflective to the wavelength of the excitation LD light EB.

[Laser oscillation operation (action)]
When the laser device performs a laser oscillation operation, under the control of a control unit (not shown), the LD of the excitation light source is driven to emit light by a drive circuit, and the Q switch 16 is driven to be switched by a Q switch driver.

The excitation LD light output from the LD of the excitation light source is transmitted to the emission unit 34 via the optical fiber 32 by a fiber coupling method. The excitation LD light emitted from the end of the optical fiber 32 in the emission unit 34 is collimated into parallel light by the collimating lens 36, and the parallel excitation light is converted by the beam splitter 38 into the first and second semi-excitation LD light EB _h1. , EB _h2 . Then, the first half-pumped LD light EB _h1 is condensed and applied to the right end surface of the laser medium 14 via the first half-pump optical unit 40. On the other hand, the second half-pumped LD light EB _h2 is condensed and applied to the left end surface of the laser medium 14 via the second half-pump optical unit 42.

In this embodiment, a large core diameter (φ0.4 mm) is selected in the fiber coupling type optical fiber 32 as described above, and, as shown in FIG. And the second half-pumped LD light beams EB _h1 and EB _h2 have beam diameters D ₁ and D ₂ (for example, φ1...) Larger than the apertures (φ1 to φ1.2 mm) of the openings 18a of the aperture unit 18 (32 mm). Incidentally, the one-side end face excitation type excitation LD light incident beam diameter in the conventional single mode oriented device is φ0.6 to 0.9 mm.

In the laser medium 14, the first and second half-pumped LD light beams EB _h1 and EB _{h2 focused} and incident on the outer end surfaces of the inactive portions 14b on both the left and right sides with the large beam diameters D ₁ and D ₂ as described above are It is introduced into the inner active medium part 14a through the inactive part 14b and excites active atoms in the active medium part 14a. By this pumping, the active medium portion 14a generates heat by absorbing the laser energy of the half-pumped LD light EB _h1 and EB _h2 supplied from both the left and right sides. On the other hand, the undoped non-active part 14b does not absorb the half-pumped LD light EB _h1 and EB _h2 incident from the outside, but passes it through the active medium part 14a as it is, and hardly generates heat.

Therefore, as shown in FIG. 3, in the laser medium 14, the vicinity of the interface between the active medium part 14a and the non-active part 14b is the absorption start point, and a considerable amount of heat generated in the active medium part 14a is indicated by an arrow. As indicated by H, it diffuses into the inactive portion 14b. In this case, the active medium portion (Nd: YVO ₄ crystal) 14a and the non-active portion (undoped YVO ₄ crystal) 14b are crystals of the same material, have the same thermal expansion coefficient, and are coupled to each other by diffusion bonding. Therefore, stable and good physical and thermal integrity is maintained between the two.

During the Q switching off period, pumping is continuously performed, and energy is stored in the laser medium 14 or the optical resonator 13. In this case, in the laser medium 14, as described above, heat escapes from the active medium part 14a to the inactive part 14b. Therefore, heat is not trapped in the active medium part 14a due to the effect of this heat pulling, and the thermal lens effect. Is suppressed. When the Q switch 16 is turned on at a constant timing, giant pulse oscillation occurs in the optical resonator 13, and the Q-pulse pulse fundamental wave laser beam LB _FH with extremely high peak power is generated.

The nonlinear optical crystal 20 is optically coupled with the fundamental laser beam LB _FH that passes through the crystal, and generates a second-order harmonic laser beam LB _SH in a low-order mode in the same manner as the fundamental laser beam LB _FH due to the nonlinear optical effect. Generate. The second harmonic laser beam LB _SH generated by the nonlinear optical crystal 20 is taken out of the optical resonator 13 through the harmonic separation mirror 22.

When the laser apparatus of this embodiment is applied to a laser processing apparatus such as a laser marking apparatus or a laser trimming apparatus, an emission unit (not shown) is connected to the optical resonator 13 via a transmission optical fiber (not shown), for example. ) Are optically connected. The emission unit incorporates an optical system such as a collimator lens, a galvano scanner, and a condenser lens, and receives a second harmonic laser beam LB _SH received from the optical resonator 13 via an optical fiber (not shown). Condensed and irradiated.

In general, in Q-switched pulse type solid-state lasers, the lower the Q switch frequency, that is, the repetition frequency, the greater the energy stored in the optical resonator during the switching-off time. Becomes higher. However, on the other hand, the heat trapped in the laser medium within one period also increases, so that the thermal lens effect is likely to occur. In particular, in the YVO ₄ laser of the one-side end face excitation type, very strong absorption occurs near the end face of the laser medium on which the LD excitation light is incident, and a thermal lens is likely to be generated locally.

In this embodiment, the special structure (Nd: YVO ₄ crystal 14a / undoped YVO ₄ crystal 14b) of the laser medium 14 as described above, both-side end face excitation method by the excitation unit 30, and the beam stop of the aperture unit 18 described later. The above trade-off is solved by a combined or synergistic action with the function.

According to the Q switch pulse type YVO ₄ second harmonic (SHG) laser in this embodiment, M ² (em square value) of the second harmonic laser beam LB _SH is 1 under the condition of a repetition frequency of 20 kHz. Experiments have confirmed that various characteristics such as .3 or less, average laser output of 10 W or more, peak output of 45 kW or more, and pulse energy of 500 μJ or more can be obtained.

FIG. 4 shows the above-described embodiment of the present invention and the laser regarding the dependency of the second harmonic average laser output on the excitation LD drive current value in the Q-switch pulse type YVO ₄ second harmonic (SHG) laser of the end face excitation type. A case where the medium 14 is composed of a single Nd: YVO ₄ crystal (comparative example) is shown in comparison. A half mirror was used as the beam splitter 38 of the excitation unit 30.

  As shown in the figure, in the embodiment, when the excitation LD drive current is increased from about 1.5 A to 6.6 A, the average laser output of the second harmonic (SHG) is proportionally increased from 0 W to about 10.5. It increases linearly up to 5W. On the other hand, in the comparative example, when the excitation LD drive current is increased, the average laser output also increases linearly in proportion thereto, but the maximum value (about 8.1 W) when the excitation LD drive current is about 5.5 A. ), Even if the excitation LD drive current is further increased, the average laser output is rather lowered. Such characteristics of the comparative example are considered to be caused by the thermal lens effect.

[High-order mode adjustment in the embodiment]
In the laser apparatus of this embodiment, the laser output has the above characteristics (repetition frequency 20 kHz, M ² <1.3, average laser output 10 W or more, peak output 45 kW or more, pulse energy 500 μJ or more). In order to realize efficiently, the aperture unit 18 is detachably attached to the optical resonator 13. Then, with the aperture unit 18 removed from the optical resonator 13, harmonics and second harmonics are generated in the high-order mode in the optical resonator 13, and the beam profile (especially M ² ) is adjusted for the high-order mode. I do.

In this higher-order mode adjustment, as shown in FIG. 5, the position and / or inclination of each optical system or optical component is adjusted in the optical resonator 13 and the excitation unit 30. In particular, in order to obtain stable optical resonance, and in order to optimize the incident beam diameters D ₁ and D ₂ of the half-pumped LD light beams EB _h1 and EB _{h2 in} the both-side end face pumping method with respect to the laser medium 14, both end mirrors are used. The optical distance between 10 and 12, the distance between both terminal mirrors 10 and 12 and the laser medium 14 or the nonlinear optical crystal 20, the position of the condensing lenses 46 and 50, etc. are adjusted.

The adjustment of the higher-order mode is monitored by the laser measuring instrument 54 taking out the second harmonic laser beam LB _SH outside the optical resonator 13 and measuring its M ² (em square value). Then, when the measured value of M ² falls within a predetermined range, preferably 3 <M ² <4, the high-order mode adjustment is terminated. After this, an aperture unit 18 having an aperture diameter (φ1 mm to 1.2 mm) smaller than the excitation LD light incident beam diameters D ₁ and D ₂ (φ1.3 mm) is inserted into the optical resonator 13. This is the device state of FIG.

[Other Embodiments Regarding Arrangement of Optical System of Excitation Unit]
In the laser apparatus of this embodiment, as described above, the layout of the optical resonator 13 is a folded arrangement type of “W” shape or “7” shape in plan view. Realization of space saving or space saving. On the other hand, the optical system of the excitation unit 30 is disposed around the optical resonator 13.

  With respect to the arrangement of the optical system of the excitation unit 30, the embodiment of FIG. 1 is arranged in the same two-dimensional direction (on the XY plane) as the optical resonator 13 in the emission unit 34, beam splitter 38, first and second half. All of the excitation optical units 40 and 42 are deployed and arranged.

In this case, since the optical fiber 32 of the fiber coupling is drawn from the Y direction so as to be orthogonal to the fundamental wave path FH of the optical resonator 13 extending in the X direction, the entire apparatus is in either the X direction or the Y direction. Is also widening and has a relatively large device area. Note that the second harmonic laser beam is placed before the optical path of the first half-pumped LD light EB _h1 set between the beam splitter 38 and the first half-pump optical unit 40 when viewed from the harmonic separation mirror 22. A folding mirror 55 that directs LB _SH in an appropriate direction may be arranged.

The second embodiment shown in FIG. 6 is characterized in that a fiber coupling optical fiber 32 is drawn in the same direction (X direction) as the fundamental wave optical path FH of the optical resonator 13. According to this layout, the apparatus size can be reduced in the Y direction, and the area of the entire apparatus can be reduced. The beam splitter 38 may be a plate type as illustrated. However, in the plate type, since the optical axis of the transmitted light EB _h1 is offset as shown in detail in FIG. 2B, it is necessary to adjust the arrangement position of the surrounding optical system in consideration of this point. . The beam splitter 38 provided in the laser apparatus of this embodiment is preferably a half mirror (a mirror having reflected light and transmitted light intensity of approximately 1: 1), regardless of whether it is a cube type or a plate type. be able to.

In the second embodiment, the first half-pumped LD light EB _h1 obtained as the partially transmitted light from the beam splitter 38 is the first half-pump optical unit 40 (condensing lens 46) and the harmonic separation mirror. 22 is focused and incident on the right end surface of the laser medium 14. On the other hand, the second half-pumped LD light EB _h2 obtained as partially reflected light from the beam splitter 38 _{passes through} the folding mirror 45 and the second half-pumping optical unit 42 (the folding mirror 48, the condenser lens 50, and the folding mirror 52). Then, the light is focused on the left end surface of the laser medium 14.

7 and 8 show the arrangement of the optical system of the excitation unit 30 according to the third embodiment. In the third embodiment, in addition to drawing the optical fiber 32 of the fiber coupling in the same direction (X direction) as the fundamental wave optical path FH of the optical resonator 13 as in the second embodiment, As shown in FIG. 8 (substantially side view), the optical path of the laser medium 14 or the fundamental wave light of the optical resonator 13 passes through the entire optical path of the first half-pumped LD light EB _h1 in the half-pump optical unit 40. The optical path of the second half-pumped LD light EB _h1 in the second half-pump optical unit 42 is set on the same line as the path FH, as shown in FIG. 7 (substantially plan view). It is characterized in that it is set in a vertical plane overlapping the fundamental wave optical path FH of the optical resonator 13.

  FIG. 8 shows each part located on a vertical plane (XZ plane) including the optical axis of the laser medium 14. Since the end mirrors 10 and 12 and the nonlinear optical crystal 20 are located outside the vertical plane (XZ plane), they are not shown in FIG.

  According to the layout of the third embodiment, the influence on the size of the optical system itself of the excitation unit 30 and the size of the entire apparatus in the Y direction can be reduced as much as possible. It is possible to maximize the advantages of the optical resonator 13 that adopts the “shaped” or “7” shaped folded arrangement type.

[Other Embodiments or Modifications]
The present invention is not limited to the Q-switch pulse type air-cooled YVO ₄ second harmonic (SHG) laser as in the above embodiment, but can be applied to other types of solid-state lasers. The present invention can also be applied to a YVO ₄ laser of the formula, a Q switch pulse type or a continuous oscillation type YAG laser.

  The excitation unit 30 in the above embodiment uses a single or common fiber coupling LD for the first and second half-pumping optical units 40 and 42 in the both-side end face excitation system for the laser medium 14, thereby improving efficiency and reducing costs. I am trying sex. However, the first and second semi-pumping optical units 40, 42 can be filled with separate fiber coupling LDs or other types of pumping LDs.

The above embodiments were those according to the second harmonic laser beam LB _SH laser device which oscillates output. However, as can be easily understood, the present invention is also applicable to a laser apparatus that oscillates and outputs the fundamental laser beam LB _FH . For example, in the laser device of the above embodiment, the nonlinear optical crystal 20 is removed from the optical resonator 13, and the terminal mirror 12 is replaced with a partially transmissive mirror (output mirror) having both transparency and reflectivity with respect to the fundamental wave. Thus, a fundamental wave laser device can be obtained.

10, 12 Terminal mirror 13 Optical resonator 14 Laser medium 16 Q switch 18 Aperture unit 20 Nonlinear optical crystal 22 Intermediate mirror (harmonic separation mirror)
24 Intermediate mirror (total reflection mirror)
DESCRIPTION OF SYMBOLS 30 Excitation part 32 Optical fiber 34 Output unit 38 Beam splitter 40 1st half excitation optical unit 42 2nd half excitation optical unit

In this regard, in a recent single-mode oriented laser apparatus, a YVO ₄ laser using a YVO ₄ crystal doped with Nd ions as an active medium is more preferable than a YAG laser using a YAG crystal doped with Nd ions as an active medium. However, it has excellent absorption efficiency and excitation efficiency in the crystal and is said to be suitable for obtaining a single-mode laser beam, particularly a Q-switch pulse laser beam.

A laser device according to a first aspect of the present invention includes an optical resonator having a first termination mirror and a second termination mirror that are optically opposed to each other, an active medium portion made of a crystal doped with active ions, The active medium portion is made of a crystal that is not doped with active ions, and has a pair of inactive portions coupled to opposite end faces of the active medium portion. In order to generate a fundamental laser beam having a fundamental wavelength, a laser medium arranged with the active medium part and the inactive part aligned on the optical path, both sides of the laser medium on the optical path in the optical resonator An excitation unit that irradiates an end surface with an excitation laser beam with the same light intensity; an aperture unit disposed on an optical path in the optical resonator to reduce a beam diameter of the fundamental laser beam; and the fundamental laser. beam In order to generate a harmonic laser beam having a harmonic wavelength with respect to the fundamental wavelength, a nonlinear optical crystal disposed on an optical path in the optical resonator, and the harmonic laser beam from the fundamental laser beam A harmonic separation mirror disposed on an optical path in the optical resonator for separation and output, and an incident beam diameter of the excitation laser beam with respect to both end faces of the laser medium is set to rather larger than the opening through which the fundamental wave laser beam, and has a larger configuration than the incident beam diameter to obtain a fundamental wave laser beam of single mode.

A laser device according to a second aspect of the present invention includes an optical resonator having optically opposed total reflection mirrors and partial transmission mirrors, an active medium portion made of a crystal doped with active ions, and the active medium. A pair of inactive portions that are made of a crystal that is the same material as the portion and is not doped with active ions, and that are coupled to opposite end faces of the active medium portion, on the optical path in the optical resonator In order to generate a laser beam having a predetermined wavelength and a laser medium arranged with the active medium part and the inactive part aligned, excitation laser beams are applied to both end faces of the laser medium on the optical path in the optical resonator. an excitation section that irradiates with the same light intensity, in order to narrow the beam diameter of the laser beam, and a aperture unit disposed on an optical path within the optical resonator, the relative side end face of said laser medium Incident beam diameter of the raised laser beam, and with the fundamental wave laser beam rather larger than the opening through which, and greater configuration than the incident beam diameter to obtain a fundamental wave laser beam of a single mode of the aperture unit.

In this embodiment, a large core diameter (φ0.4 mm) is selected in the fiber coupling type optical fiber 32 as described above, and, as shown in FIG. And the second half-pumped LD light beams EB _h1 and EB _h2 have beam diameters D ₁ and D ₂ (for example, φ1...) Larger than the apertures (φ1 to φ1.2 mm) of the openings 18a of the aperture unit 18 (32 mm). Incidentally, the incident beam diameter of the pumping LD light with respect to the end face of the laser medium of the one-side end face pumping method in the conventional single mode oriented apparatus is φ0.6 to 0.9 mm .

In this regard, recently, than YAG laser used a YAG crystal doped with Nd ions in the active medium, towards a YVO ₄ laser using a YVO ₄ crystal doped with Nd ions in the active medium, Ya absorption efficiency in the crystal It has excellent excitation efficiency and is suitable for obtaining a single-mode laser beam, particularly a Q-switch pulse laser beam.

The present invention has been made in view of the problems of the prior art , and effectively suppresses the generation of the thermal lens effect in a solid-state laser of both-ends excitation type even in the air-cooling type. A laser apparatus capable of generating a beam is provided.

The laser apparatus of the present invention is an air-cooled type, and includes an optical resonator having a first end mirror and a second end mirror that are optically opposed to each other, and an active medium portion made of a crystal doped with active ions. A pair of inactive portions made of a crystal that is made of the same material as the active medium portion and is not doped with active ions, and is coupled to opposite opposite end faces of the active medium portion, and in the optical resonator In order to generate a fundamental wave laser beam having a fundamental wavelength, and a laser medium in which the active medium portion and the inactive portion are arranged on the optical path of the optical resonator, the laser medium An excitation unit that irradiates both end faces with an excitation laser beam ; an aperture unit disposed on an optical path in the optical resonator to reduce a beam diameter of the fundamental laser beam; and a fundamental wavelength of the fundamental laser beam Against To generate a higher harmonic wave laser beam having a wavelength of the harmonic, and a non-linear optical crystal disposed in the optical path in the optical resonator, the fundamental wave laser beam and the higher harmonic wave laser beam of a constant repetition frequency Q to generate a switch pulse, a Q-switch disposed on the light path in the optical resonator, the higher harmonic wave laser beam to output separate from said fundamental wave laser beam, in the optical resonator A harmonic separation mirror disposed on the optical path between the laser medium and the first terminal mirror, and the excitation unit emits an original laser beam for excitation outside the optical resonator An excitation original laser beam emitting unit, a beam splitter for dividing the original laser beam for excitation from the excitation original laser beam emitting unit into first and second excitation laser beams, and The first excitation laser beam obtained from the beam splitter is passed through a first condenser lens disposed outside the optical resonator, and the first excitation laser beam transmitted through the first condenser lens is passed through the first condenser lens. A first half-pumping optical unit that is guided to one end face of the laser medium via a harmonic separation mirror and condensed, and the second pumping laser beam obtained from the beam splitter is placed outside the optical resonator. The second excitation laser beam that has passed through the second condensing lens disposed and transmitted through the second condensing lens is reflected by a folding mirror disposed on the optical path in the optical resonator, and the laser and a second half excitation optical unit for condensing light is guided to the other end face of the medium, the laser medium is made from the YVO ₄ crystal active medium portion is doped with Nd ions, the inactive portion Becomes sex ions from all doped non YVO ₄ crystal, wherein the end surfaces of the active medium portion inactive portion are joined by diffusion bonding, the active medium portion is long in the axial direction than the non-active portion, the The active medium part and the inactive part as a whole have a rectangular parallelepiped shape, and suppress the thermal lens effect according to the adjustment of the output of the excitation source laser beam emitting part, and the harmonic laser beam with a repetition frequency of 20 kHz or less. The average output can be increased substantially linearly from 0 W to at least 10 W, and the beam diameter of the excitation laser beam incident on both end faces of the laser medium is larger than the aperture through which the fundamental laser beam of the aperture unit passes. It has a large configuration.

In the above apparatus configuration, the first and second excitation laser beams obtained by dividing one original laser beam emitted from the excitation original laser beam emitting section into two by the beam splitter are respectively the first and second half lasers. The both end surfaces of the laser medium are irradiated with a beam diameter larger than the aperture of the aperture unit through the excitation optical unit, and the laser medium is excited by the both end surface excitation method. Here, the laser medium used the present invention may consist of the active medium portion YVO ₄ crystal doped with Nd ions, it becomes inactive portion of the active ions from YVO ₄ crystal undoped at all, both end surfaces of the active medium portion The active medium part is longer in the axial direction than the inactive part, the active medium part and the inactive part have a rectangular parallelepiped shape as a whole, and the output of the excitation laser beam emitting part is The average output of the harmonic laser beam can be increased substantially linearly from 0 W to at least 10 W at a repetition frequency of 20 kHz or less while suppressing the thermal lens effect according to the adjustment. As a result, a harmonic laser beam having a low-order mode close to a single mode can be obtained at a high output by a combined or synergistic action with the beam stop function of the aperture unit.

In a preferred embodiment of the present invention, a straight line of the optical axis of the laser medium is used as a reference while adopting a both-ends excitation method using an excitation original laser beam emitting portion, a beam splitter, and first and second semi-excitation optical units. Excitation optical system (beam splitter, first and second semi-excitation optical units) and wavelength conversion optical system (non-linear optics) in the first plane (XZ plane) and the second plane (XY plane) orthogonal to each other as lines A crystal, a resonator mirror, and a harmonic separating mirror). With this layout configuration, it is possible to provide a small-sized and small-area air-cooled laser apparatus that can obtain a high-power low-order mode harmonic laser beam without the thermal lens effect.

According to the laser apparatus of the present invention, with the configuration and operation as described above, the generation of the thermal lens effect in the double-sided excitation type solid-state laser is effectively suppressed even in the air cooling type, and the high-output low-order mode harmonic laser A beam can be generated .

In this embodiment, a large core diameter (φ0.4 mm) is selected in the fiber coupling type optical fiber 32 as described above, and, as shown in FIG. And the second half-pumped LD light beams EB _h1 and EB _h2 have beam diameters D ₁ and D ₂ (for example, φ1...) Larger than the apertures (φ1 to φ1.2 mm) of the openings 18a of the aperture unit 18 (32 mm). Incidentally, the one-side end face excitation type excitation LD light incident beam diameter in the conventional single mode oriented device is φ0.6 to 0.9 mm .

Claims (11)

An optical resonator having a first termination mirror and a second termination mirror that are optically opposed to each other;
An active medium portion made of a crystal doped with active ions, and a pair of non-active materials that are made of the same material as the active medium portion and not doped with active ions and are coupled to opposite opposite end faces of the active medium portion. A laser medium having an active part, and arranged with the active medium part and the inactive part aligned on an optical path in the optical resonator;
An excitation unit that irradiates both end faces of the laser medium on the optical path in the optical resonator to generate a fundamental laser beam having a fundamental wavelength; and
An aperture unit disposed on the optical path in the optical resonator to reduce the beam diameter of the fundamental laser beam;
A nonlinear optical crystal disposed on an optical path in the optical resonator to generate a harmonic laser beam having a harmonic wavelength with respect to a fundamental wavelength of the fundamental laser beam;
A harmonic separation mirror disposed on an optical path in the optical resonator for separating and outputting the harmonic laser beam from the fundamental laser beam;
A beam diameter of the excitation laser beam incident on both end faces of the laser medium is larger than an aperture through which the fundamental laser beam of the aperture unit passes;
Laser device. The excitation unit is
An excitation original laser beam emitting unit for emitting an original laser beam for excitation outside the optical resonator;
A beam splitter that divides the original laser beam for excitation from the excitation original laser beam emitting unit into first and second excitation laser beams;
The first excitation laser beam obtained by the beam splitter is passed through a first condenser lens disposed outside the optical resonator, and is transmitted through the first condenser lens. A first half-pumping optical unit that guides light to one end face of the laser medium and collects the light,
The second excitation laser beam obtained by the beam splitter is passed through a second condenser lens disposed outside the optical resonator, and transmitted through the second condenser lens. 2. The laser device according to claim 1, further comprising: a second half-pumping optical unit that guides the light to the other end face of the laser medium and focuses the light.   The second semi-pumping optical unit has a folding mirror disposed on an optical path in the optical resonator, and the second excitation laser beam transmitted through the second condenser lens is reflected by the folding mirror. The laser device according to claim 2, wherein the laser device is reflected and guided to the other end face of the laser medium. In the first semi-pumping optical unit, the optical path of the second excitation laser beam is set on the same line as the optical axis of the laser medium throughout the entire section.
In the second semi-pumping optical unit, an optical path of the second excitation laser beam is set in a vertical plane overlapping with an optical axis of the laser medium.
The laser device according to claim 2. The excitation source laser beam emitting section is
An optical fiber that transmits the original laser beam for excitation generated by the laser diode for excitation by a fiber coupling method and emits it from the end face of the end; and
The laser device according to claim 2, further comprising: a collimating lens that collimates the excitation original laser beam emitted from the end face of the optical fiber into parallel light.   The laser apparatus according to claim 2, wherein the beam splitter includes a half mirror. In the laser medium,
The active medium part is made of YVO ₄ crystal doped with Nd ions,
The inactive part is made of YVO ₄ crystal not doped with any active ions, and is bonded to both end faces of the active medium part by diffusion bonding.
The laser device according to claim 1.   2. The laser device according to claim 1, further comprising a Q switch disposed on an optical path in the optical resonator in order to generate the fundamental laser beam and the harmonic laser beam as pulses having a constant repetition frequency. In the optical resonator,
In a state where the aperture unit is removed, the fundamental laser beam is in a higher order mode, and its M ² is 3 or more.
In the state where the aperture unit is inserted, the fundamental laser beam is in a low-order mode, and its M ² is 1.3 or less.
The laser device according to claim 1. In the optical resonator, a first intermediate mirror that reflects the fundamental laser beam, the fundamental laser beam is reflected between the first termination mirror and the second termination mirror, and the harmonic is reflected. A second intermediate mirror for transmitting the wave laser beam,
The first terminal mirror, the first intermediate mirror, the Q switch, and the laser medium are disposed between the first terminal mirror and the second intermediate mirror,
The nonlinear optical crystal is disposed between the second terminal mirror and the second intermediate mirror,
An optical path connecting the first terminal mirror and the second terminal mirror via the first and second intermediate mirrors is formed in a “wa” shape or a “7” shape,
The laser device according to claim 1. An optical resonator having optically opposed total reflection mirrors and partial transmission mirrors;
A pair of active medium portions made of crystals doped with active ions, and crystals made of the same material as the active medium portions and not doped with active ions, which are coupled to opposite opposite end faces of the active medium portions. A laser medium having a non-active part, and arranged with the active medium part and the non-active part aligned on an optical path in the optical resonator;
An excitation unit that irradiates both end faces of the laser medium on the optical path in the optical resonator to generate a laser beam of a predetermined wavelength; and
An aperture unit disposed on the optical path in the optical resonator in order to reduce the beam diameter of the laser beam;
Have
A beam diameter of the excitation laser beam incident on both end faces of the laser medium is larger than an aperture through which the laser beam of the aperture unit passes;
Laser device.

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