JP2010109094A - Mode synchronous laser apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mode synchronous laser apparatus which outputs ultrashort pulses, with high heat radiation characteristic, having a stable structure. <P>SOLUTION: The mode synchronous laser apparatus 10 includes a resonator containing an SESAM (semiconductor saturable absorption mirror) 14 and a negative dispersion mirror 20 controlling group speed dispersion within the resonator, a solid laser medium 16 which is arranged in the resonator to output oscillation light when excitation light enters, an excitation optical system 12 which causes the excitation light to enter the solid laser medium 16, and a resonator holder 34 integrated with a first support body 35B, which is held between the SEASAM 14 and the solid laser medium 16 while supports the SEASAM 14 and the solid laser medium 16, and a second support body 35C protruding along the resonator axial direction from the first support body 35B. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a mode-locked laser device, and more particularly, to a mode-locked laser device that outputs ultrashort pulsed light.

  Conventionally, solid-state lasers using a semiconductor laser (LD) as an excitation light source and doped with rare earth ions (or transition metal ions) have been actively developed. Above all, ultra-short pulse lasers that generate so-called ultra-short pulse light in the femtosecond range have been explored, proposed, verified, and put into practical use in a wide variety of application fields such as medicine, biotechnology, mechanical industry, and measurement. Yes.

  This ultrashort pulse laser generates an ultrashort pulse by an operation called mode synchronization. In simple terms, mode synchronization means that the phases of many longitudinal modes are all synchronized in the frequency domain during laser oscillation (relative phase difference = 0). Therefore, due to multimode interference between longitudinal modes. This is a phenomenon that results in a very short pulse in the time domain.

  In general, a semiconductor saturable absorbing mirror (SESAM) is used as one of mirrors constituting a laser resonator, and a mode-synchronized operation is performed by the effect of pulse sharpening in the SESAM. Furthermore, in the femtosecond region, since the spectral band of the pulse is wide, it is necessary to compensate for the positive group velocity dispersion experienced when passing through the optical material (laser crystal, resonator mirror, etc.) in the resonator. .

  A method of obtaining a pulse in the femtosecond region by arranging SESAM as a resonator mirror, starting mode synchronization, and performing compensation of self-phase modulation effect and group velocity dispersion by a light pulse circulating in the resonator in the resonator. This is especially called soliton mode synchronization. This method has been widely adopted as an excellent practical method that can be self-started and is more resistant to misalignment than other methods (such as Kerr lens mode synchronization).

  Conventionally, not only soliton mode locking but a wide mode-locking laser has been reported that has a large repetition rate of a resonator length of 2 m class corresponding to a repetition frequency of 80 MHz (for example, see Patent Document 1).

The repetition frequency PRF is represented by PRF = C / 2L _cav when the speed of light is C and the resonator length is L _cav . When L _cav is 2 m, the PRF corresponds to 75 MHz. A large ultrashort pulse laser can provide a moderate repetition frequency (50 MHz to 100 MHz) and a relatively high peak power (100 kW to 1 MW). On the other hand, a mirror or the like for folding the resonator is required, and the resonator structure is complicated, which tends to increase the number of parts and increase the manufacturing cost. Furthermore, there is a concern that the output stability of a large laser is generally low. This is because as the size is increased, a slight mechanical variation (positional deviation) of the resonator mirror causes a large beam position variation and consequently an output variation. Ordinary ultrashort pulse lasers are operated on the premise of periodic mirror alignment. For example, the mirror needs to be optimally adjusted every day.

  Therefore, an ultrashort pulse laser that is low in cost and highly stable is expected by mounting the laser in a small size. By downsizing, the component cost can be reduced by reducing the number of components, and the output fluctuation due to the resonator length and the position change of the resonator mirror can be minimized. Specifically, if the resonator length is about 150 mm or less, preferably 75 mm or less, an integrated resonator structure described later can be adopted, and the stability can be increased.

  As a configuration of the resonator, by taking a linear structure, optical components for folding can be omitted, and the number of components can be minimized. For example, Patent Document 1 discloses a solid-state laser having such a structure. This is because the resonator is an integrally formed metal holder, mirror mounting surfaces are installed on both end faces, and the laser crystal and the resonator output mirror are made of an extremely thin layer (2 μm) with an adhesive having a volume shrinkage of 1% or less. The optical resonator is configured by bonding and fixing in the following). By doing so, a small and extremely stable output characteristic is realized. The adhesive surface is mirror-polished, and the thickness of the adhesive layer is strictly controlled. According to Patent Document 1, the change in resonator length was 0.02 μm after driving for 5000 h under general air conditioning.

  On the other hand, Patent Documents 2 to 4 disclose linear and small ultrashort pulse lasers. Each includes a semiconductor saturable absorption mirror (SESAM) necessary for mode locking as one end of the resonator mirror. By making SESAM and laser crystal close to each other or closely contacting each other and having a resonator waist on SESAM, it is possible to reduce the size of the linear type compared to the conventional case where resonator spots are separately formed on both SESAM and laser crystal. It is.

The ultrashort pulse laser described in Patent Document 2 is configured to realize a mode-locked laser having a high repetition frequency, specifically, a repetition frequency of 1 GHz or more. The object of the present invention is to realize a high repetition frequency. Since 1 GHz corresponds to a resonator length of 15 cm, it is possible to realize a small and high repetition frequency ultrashort pulse laser with a resonator length of 15 cm or less. Is equivalent to Patent Document 2 defines a stimulated emission cross-sectional area (> 0.8 × 10 ⁻¹⁸ cm ² ) of a laser medium, an absorption depth ΔR (<0.5%) of SESAM, and the like.

  Further, Patent Document 2 discloses a configuration of a linear laser resonator composed of SESAM arranged on the rear side of a laser crystal using a curvature mirror provided on the front end face of the laser crystal as an output mirror. Further, a configuration is disclosed in which dispersion compensation is performed by causing negative dispersion by a Gires-Tournois interferometer (GTI interference) by causing etalon interference between the SESAM and the laser crystal.

  Patent Document 3 discloses a small ultrashort pulse laser for the purpose of operating an ultrashort pulse laser at a high repetition frequency. Specifically, there is disclosed a linear mode-locked laser composed of a saturable absorber coated on the rear side end face of a laser crystal and a curved chirp mirror (negative dispersion mirror).

Further, Patent Document 4 discloses an extremely compact ultrashort pulse laser including a linear laser resonator composed of SESAM arranged close to a negative dispersion mirror and a laser crystal. By disposing SESAM, the negative dispersion output mirror, and the laser crystal separately, there are design freedom, thermal interference, and resonator length freedom, which can be said to be a suitable structure.
Japanese Patent No. 3378103 (FIG. 1) US Pat. No. 7,106,764 (FIG. 15) Japanese Patent Laid-Open No. 11-168252 (FIG. 3) Japanese Patent Laying-Open No. 2008-28379 (FIG. 1)

  However, the invention described in Patent Document 1 is focused on applying the integrated resonator structure to a semiconductor laser pumped solid-state laser. More specifically, the main object is to realize an internal resonator type second harmonic laser that is continuous operation and has a nonlinear optical crystal disposed inside the resonator in a small size, high stability, and low cost. Therefore, Patent Document 1 does not describe how to obtain an ultrashort pulse laser capable of being small, low cost, and highly stable when applied to an ultrashort pulse laser.

  The ultrashort pulse laser described in Patent Document 2 has a quasi-monolithic structure in which a laser resonator is joined to a laser crystal and SESAM, and there is no description of a resonator holder in which the laser crystal, SESAM, etc. are arranged, Patent Document 2 does not describe what kind of structure can be used to obtain an ultrashort pulse laser capable of small size, low cost, and high stable operation. This structure is suitable for the case where it is assumed that the driving is actually performed at a repetition frequency of about 10 GHz (monolithic structure having a resonator length of 1.5 cm), and conversely, 1 GHz (resonator length of 15 cm) to 5 GHz (resonance). In the case of a length of about 5 cm), it is difficult to realize a monolithic structure and it is difficult to apply.

  Further, in the ultrashort pulse laser described in Patent Document 3, the curved chirp mirror and the laser crystal are spatially separated from each other. However, Patent Document 3 does not describe a resonator holder that supports them. There is no description as to whether an ultrashort pulse laser capable of small size, low cost, and high stable operation can be obtained with such a structure.

  In addition, Patent Document 4 also does not describe a resonator holder for arranging optical components constituting the resonator so as to be separated from each other. What kind of structure can be used to achieve small size, low cost, and high stability operation. It is not described whether an ultrashort pulse laser can be obtained.

  As described above, Patent Documents 2 to 4 in which inventions related to ultrashort pulse lasers are disclosed do not disclose the configuration and structure of the resonator holder, and how to mount them can be reduced in size and cost. It is not disclosed whether a stable ultrashort pulse laser can be realized. In addition, stability is not taken into consideration, such as structure definition of the resonator and temperature control of the resonator length.

  Furthermore, an ultrashort pulse laser that can efficiently dissipate heat generated in SESAM or a solid laser medium and has a stable structure with high rigidity has not yet been proposed.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a mode-locked laser device that outputs an ultrashort pulse and has a high heat dissipation and a stable structure. To do.

  In order to solve the above-mentioned problem, the invention according to claim 1 is arranged in a resonator including a semiconductor saturable absorber mirror and a negative dispersion mirror for controlling group velocity dispersion in the resonator, It is sandwiched between a solid-state laser medium that outputs oscillation light when the excitation light is incident, excitation means that causes the excitation light to enter the solid-state laser medium, the semiconductor saturable absorption mirror, and the solid-state laser medium. And a first support that supports the semiconductor saturable absorption mirror and the solid-state laser medium, and a second support that protrudes from the first support in a direction intersecting the first support. And a resonator holder integrally formed.

  According to this invention, a resonator holder is sandwiched between the semiconductor saturable absorption mirror and the solid-state laser medium, and the first support that supports the semiconductor saturable absorption mirror and the solid-state laser medium; The second support that protrudes along the direction intersecting the first support from the first support is integrally formed, and the semiconductor is saturable so as to sandwich the first support The absorption mirror and the solid-state laser medium are supported. For this reason, while being able to improve the heat dissipation of a semiconductor saturable absorption mirror and a solid state laser medium, even when the first support is thin, the second support can increase the rigidity of the resonator holder. A stable structure can be obtained.

  Note that, as described in claim 2, it is preferable that a light incident surface of the semiconductor saturable absorbing mirror is attached to one surface of the first support. Thereby, compared with the case where the surface opposite to the light incident surface of the semiconductor saturable absorber mirror is attached to the resonator holder, the resonator holder can be easily manufactured at low cost and with high accuracy. Therefore, the semiconductor saturable absorber mirror can be easily and accurately attached to the resonator holder, and as a result, small size, low cost, and highly stable operation are possible.

  As described in claim 3, it is preferable that the length of the first support in the direction intersecting the first support is not more than half of the Rayleigh length. Thereby, the spot diameter of the oscillation light can be maintained satisfactorily.

  In addition, as described in claim 4, a length of the second support in a direction intersecting with the first support is a direction in which the first support intersects with the first support. It is preferable that the length is at least twice the length. Thereby, the rigidity of the resonator holder can be further increased.

  Further, as described in claim 5, the negative dispersion mirror may be attached to the resonator holder.

  According to the present invention, there is an effect that it is possible to provide a mode-locked laser device that outputs an ultrashort pulse and has a high heat dissipation property and a stable structure.

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

  1A is a schematic plan view of the mode-locked laser device 10, and FIG. 1B is a schematic side view. As shown in FIGS. 2A and 2B, the mode-locked laser device 10 includes an excitation optical system 12, a SESAM 14, a solid-state laser medium 16, a dichroic mirror 18, a negative dispersion mirror 20, a Peltier element 22, and a Peltier drive unit 24. , A beam splitter 40, a photodiode 42, and a control unit 44.

  As shown in FIG. 1A, the excitation optical system 12 includes a semiconductor laser 26 as a light source for excitation and a Selfoc lens 28. For example, the excitation optical system holder is composed of a member made of copper. It is fixed on 30 by, for example, adhesion.

  The dichroic mirror holder 32 to which the SESAM 14, the solid-state laser medium 16, the negative dispersion mirror 20, and the dichroic mirror 18 are attached is arranged on a straight line, that is, along the direction of the pulsed light L (resonator axial direction). For example, it is fixed to 34 by adhesion. The excitation optical system 12 is not shown in FIG.

  As shown in FIG. 1 (B), the resonator holder 34 has a basic support 35A along the resonator axial direction when viewed from the side, and is orthogonal to the resonator axial direction from the basic support 35A in the resonator axial direction. A substantially U-shape in which a first support 35B that protrudes in the direction in which the first support 35B projects, a second support 35C that protrudes along the resonator axis direction from the first support 35B, and a third support 35D are integrally formed. The shape of the mold. The first support 35B and the third support 35D are formed with holes 38A and 38B for allowing the pulsed light L to pass therethrough.

  The SEASAM 14 and the solid-state laser medium 16 are fixed to the first support 35B by, for example, adhesion so as to sandwich the first support 35B. In addition, the second support 35C protrudes from the first support 35B along the resonator axial direction. With such a configuration, even when the first support 35B is thin, the rigidity of the resonator holder 34 can be increased by the second support 35C, and the operation stability can be improved.

  The length (thickness) b of the first support 35B in the resonator axis direction is preferably less than or equal to half of the Rayleigh length, which is the distance at which the spot diameter of the oscillation light is maintained. Thereby, the spot diameter of the oscillation light can be maintained satisfactorily.

  In addition, the length a of the second support 35C in the resonator axial direction is preferably at least twice the length b of the first support 35B in the resonator axial direction. Thereby, the rigidity of the resonator holder 34 can be further increased.

  The resonator holder 34 is preferably made of a metal having high thermal conductivity and rigidity, and copper is preferable. Furthermore, considering the machinability, copper to which Te is added is more preferable.

  The excitation optical system holder 30 and the resonator holder 34 are fixed on a copper plate 36 shown in FIG.

  A Peltier element 22, which will be described later, provided on a substrate 46 is attached to the copper plate 36. The excitation optical system 12, SESAM 14, solid-state laser medium 16, dichroic mirror 18, negative dispersion mirror 20, Peltier element 22, beam splitter 40, and photodiode 42 are sealed on a substrate 46 by a sealing member 48. It is sealed and isolated from the outside world. The sealing member 48 is provided with a transmission window 48A for outputting the pulsed light L to the outside.

  In addition, as a sealing method of the sealing member 48 to the board | substrate 46, various well-known methods, such as welding, such as laser welding and electric welding, seam joining, soldering, adhesion | attachment with an adhesive agent, can be used, for example.

The SESAM 14 is a semiconductor saturable absorption mirror device. In the present embodiment, as an example, the modulation depth (ΔR) is 0.6%, and the saturation fluence is 70 μJ / cm ² .

  The SESAM 14 and the negative dispersion mirror 20 constitute a resonator. The resonator length of this resonator is preferably shorter as long as the resonator holder 34 that integrally supports the resonator and the solid-state laser medium 16 can be processed with sufficient accuracy. Specifically, considering the mechanical variation of the member due to temperature variation, the resonator length is preferably 150 mm or less, more preferably 75 mm or less.

The solid-state laser medium 16 is, for example, a solid-state laser crystal to which ytterbium (Yb) is added. Specifically, Yb: KYW (KY (WO ₄ ) ₂ ), Yb: KGW (KGd (WO ₄ ) ₂ ), Yb: _{YAG (Y 3 Al 5 O 12} ), Yb: YLF (LiYF 4), Yb: YVO 4 , and the like. Further, the present invention is not limited to this, but Nd-based (Nd: YAG, Nd: YVO ₄ , Nd: Glass), transition metal-based (Cr: LiSAF (LiSrAlF ₆ ), Cr: LiCAF (LiCaAlF ₆ ), Ti: Sapphire, etc.) May be used.

  The thickness and concentration of the solid-state laser medium 16 are set so that the excitation light can be sufficiently absorbed, for example, with an efficiency of 90%. In the present embodiment, as an example, the thickness is 1.5 mm and the additive concentration of Yb is 5 at%. Both surfaces of the solid-state laser medium 16 are optically polished to provide an antireflection coating having low reflection (for example, a reflectance of 0.5% or less) with respect to the wavelength of oscillation light (for example, 1045 nm) and the wavelength of excitation light (for example, 980 nm). Is given.

  Such a solid laser medium 16 is bonded to the resonator holder 34 by a method described in, for example, Japanese Patent No. 3450073.

  In FIG. 1, the solid-state laser medium 16 is arranged such that the light incident surface and the light emitting surface are orthogonal to the resonator axis, but several degrees ( For example, it may be arranged to be inclined. As a result, it is possible to suppress a component (satellite component) of the optical pulse that circulates around the resonator from remaining and reflecting at the boundary between the optical components. If tilted further, the beam shape may be distorted by astigmatism, and at the same time, an internal loss may occur due to the angular dependence of the reflectance of the non-reflective coating applied to the crystal.

  The dichroic mirror 18 folds the excitation light from the excitation optical system 12 toward the solid-state laser medium 16, and is highly reflective (for example, a reflectance of 95% or more) with respect to the wavelength of the excitation light, for example. A coating having a low reflection (for example, a reflectance of 0.2% or less) with respect to the wavelength is applied, thereby realizing high-efficiency excitation and low internal loss.

  The dichroic mirror 18 fixed to the dichroic mirror holder 32 is disposed in the resonator, that is, between the SESAM 14 and the negative dispersion mirror 20 so as to have a Brewster angle with respect to the optical axis of the resonator.

The negative dispersion mirror 20 plays a role of compensating for the group velocity dispersion in the resonator and also compensating for a positive chirp due to self-phase modulation generated in the solid-state laser medium 16 due to the high peak power of the optical pulse in the resonator. The amount of dispersion depends on operating conditions, but is preferably about 0 to -3000 fsec ² . In the present embodiment, the dispersion amount of the negative dispersion mirror 20 is set to −800 fsec ² as an example.

  Further, the transmittance T of the negative dispersion mirror 20 is 0.2% in the case of high reflection (as an example, the reflectance is 99.8%). By setting it to about ˜3%, optimum output extraction is possible. In this embodiment, the transmittance is 1.8% as an example.

  The radius of curvature of the negative dispersion mirror 20 is calculated by the Gaussian beam propagation design of the resonator. In order to make the resonator spot diameter as small as possible, the radius of curvature is approximately the same as the length of the resonator. Is preferable. As a result, the resonator spot can be suppressed to about 50 μm in diameter, and the Q-switch phenomenon associated with the short resonator can be avoided. At the same time, the spatial alignment with the spot diameter of the excitation light can be satisfactorily achieved, and high efficiency can be achieved. In the present embodiment, as an example, the resonator length is 50 mm, and the radius of curvature of the negative dispersion mirror 20 is also 50 mm, similar to the resonator length.

  The excitation optical system 12 outputs the excitation light toward the dichroic mirror 18 from an oblique direction with respect to the resonator axis, and the excitation light reflected by the dichroic mirror 18 is incident on the solid-state laser medium 16 to enter the solid state. The laser medium 16 is excited.

  As the semiconductor laser 26 of the excitation optical system 12, for example, a semiconductor laser that outputs excitation light having a wavelength of 980 nm, an emitter width of 50 μm, and an output of 2 W can be used.

  Further, the excitation light emitted from the semiconductor laser 26 is collected by the selfoc lens 28. The focused spot diameter is approximately 50 μmφ as an example. The thickness and concentration of the laser crystal are set so that the excitation light can be sufficiently absorbed, for example, with an efficiency of 90%.

  A Peltier element 22 is attached to a copper plate 36 to which a resonator holder 34 to which the SESAM 14, the solid-state laser medium 16, the negative dispersion mirror 20, and the dichroic mirror holder 32 are fixed and the excitation optical system holder 30 are fixed.

  The temperature of the resonator holder 34 and the excitation optical system holder 30 is adjusted by the Peltier element 22. The Peltier element 22 is driven by a Peltier drive unit 24.

  As described above, since the temperature of the resonator holder 34 can be adjusted, even if the temperature of the external environment fluctuates, the resonator is maintained at a constant temperature, and the variation in the resonator length and the position of each member such as a mirror can be changed. It can be minimized. As a result, it is possible to output ultrashort pulse light with extremely stable output.

  Further, since the temperature of the excitation optical system holder 30 can be adjusted, fluctuations in wavelength due to temperature fluctuations of the semiconductor laser 26, fluctuations in the relative position between the excitation optical system 12 and the resonator, and the like can be suppressed.

  Further, since the SESAM 14, the solid-state laser medium 16, the negative dispersion mirror 20, and the dichroic mirror holder 32 are fixed to one resonator holder 34, it is not necessary to prepare holders for each component, and A small structure can be obtained, and the device can be manufactured at low cost.

  A part of the light output from the resonator is reflected toward the photodiode 42 by the beam splitter 40, and the other light is output to the outside from the transmission window 48A.

  The photodiode 42 detects, for example, the intensity of the light reflected by the beam splitter 40, converts it into an electric signal, and outputs it to the control unit 44. The control unit 44 performs constant power control for controlling the semiconductor laser 26 so that the light intensity detected by the photodiode 42 is substantially constant. Thereby, the average output of the mode-locked laser device 10 can be maintained substantially constant.

  As shown in FIG. 1, the SESAM 14 is bonded to the resonator holder 34 by applying an adhesive to a portion other than a portion through which light is transmitted, on a light incident surface on which light transmitted through the solid laser medium 16 is incident. Is done. Thus, by adopting a configuration in which the light incident surface of the SESAM 14 is bonded to one end side of the resonator holder 34, heat generated in the SESAM 14 can be efficiently exhausted, and instability of the operation due to distortion caused by heat can be removed as much as possible. it can. As described in Patent Document 1 described above, the adhesive used when bonding SESAM 14 to resonator holder 34 has a layer thickness of 2 μm or less, and a change in hardening rate and a change in layer thickness due to stress of 1%. It is preferable to use the following adhesive.

  Incidentally, in the case where the surface (rear surface) opposite to the light incident surface (front surface) of SESAM 14 is attached to the resonator holder, for example, a structure as shown in FIG. 2 can be considered. However, in the case of the structure as shown in FIG. 2, in order to dispose the solid laser medium 16 in close proximity, it is necessary to shorten the distance between the supports 34A and 34B of the resonator holder 34 as much as possible. It is difficult to cut the resonator holder 34 into a shape as shown in FIG. 2 with high accuracy, and the manufacturing cost increases. In addition, it is extremely difficult to put the SESAM 14 in the gap between the very narrow supports 34A and 34B and to bond the SESAM 14 uniformly to the support 34A.

  Therefore, as in the mode-locked laser device 10 according to the present embodiment, the resonator holder 34 can be easily and highly accurately manufactured by bonding the front surface of the SESAM 14 to one end side of the resonator holder 34. , Can be bonded uniformly.

  Note that the shape of the resonator holder 34 is not limited to the U-shape shown in FIG. 1A, and in the direction intersecting at least the first support 35B in FIG. 1A, for example, a resonator. What is necessary is just the shape which the 2nd support body protruded in the axial direction.

  The inventor has confirmed that the mode-locked laser device 10 having the above configuration can output ultrashort pulse light having an average output of 600 mW, a pulse width of 200 fsec, a repetition of 2.9 GHz, and a peak power of 1 kW. When a long-term running test of this mode-locked laser apparatus 10 was performed, the output fluctuation was 10% even in a time-lapse test of 3000 h or more and a temperature cycle test (15 ° C. to 45 ° C.) without special power control. It was confirmed that the following can be suppressed. Further, like the mode-locked laser device 10 according to the present embodiment, the SEASAM 14 and the solid-state laser medium 16 are not supported by the first support 35B, but the first support 35B is not provided. When the above long-term running test was performed in the mode-locked laser device, the stability was 30% of the mode-locked laser device 10 according to the present embodiment, and it was confirmed that the stability was lowered.

  In this way, a stable output can be obtained without requiring constant power control as compared with a conventional large mode-locked laser apparatus that requires alignment adjustment every day.

  Further, a more stable output can be obtained by performing the above-described constant power control. When the present inventor conducted a 1000 h aging test when the constant power control was performed, the output fluctuation was ± 0.5%, and the output was more stable than the long-term running test in which the constant power control was not performed. It was confirmed that the performance was greatly improved.

  In addition, since the repetition frequency of the mode-locked laser device that outputs ultrashort pulse light is inversely proportional to the resonator length, the frequency can be kept extremely stable when the resonator length can be kept extremely stable. This is extremely effective when, for example, the mode-locked laser device 10 according to the present embodiment is used for precise clock light source, time-resolved measurement, and sampling measurement. In addition, by mode-synchronizing two mode-locked laser devices that output ultrashort pulsed light, it can be applied to nonlinear optical processes that mix two or more photons, such as coherent anti-Stokes Raman scattering. Become.

  Furthermore, the stability of the repetition frequency leads to the stability of jitter. Jitter is considered to be mainly caused by mechanical fluctuation of the mirror for a short time (frequency is 1 MHz or less), but the mode-locked laser device 10 according to the present embodiment operates stably as described above. Jitter can be effectively suppressed as compared with a large mode-locked laser apparatus. When the inventors measured the jitter by operating the mode-locked laser device 10 according to the present embodiment, a jitter of 120 fsec or less was obtained.

  In a mode-locked laser device that outputs ultrashort pulse light, an optical pulse that circulates inside the resonator is one of the pulses outside the resonator when the transmittance of the negative dispersion mirror 20 is T. Therefore, in the case of the mode-locked laser device 10 according to the present embodiment, an optical pulse having a peak power of 1 kW / (0.018) = 56 kW circulates. This is a strength capable of causing two-photon absorption with respect to various organic materials, for example, an outgas from an adhesive or a copper wire coating or an oil component in the atmosphere. The present inventor has observed in a long time test that a photochemical reaction occurs due to two-photon absorption and precipitates as a solid.

  On the other hand, in the mode-locked laser device 10 according to the present embodiment, the substrate 46 is sealed by the sealing member 48, so that each member is hermetically sealed off from the outside. Thereby, it is possible to prevent impurities from the external atmosphere from floating and mixed. Therefore, the output stability of the ultrashort pulse light can be improved. The inventor has confirmed that in such a mode-locked laser device 10 having a sealed structure, the output fluctuation is suppressed to 5% or less even when the above constant power control is not performed.

  In the present embodiment, the mode-locked laser device including the linear resonator in which the members constituting the resonator are arranged in a straight line has been described. However, the present invention is not limited thereto, and for example, a resonator as shown in FIG. The present invention can also be applied to a mode-locked laser device including a V-shaped resonator in which the members constituting the are arranged on a V-shape.

  A mode-locked laser device 10A shown in FIG. 3 includes an excitation optical system 12, a SEASAM 14, a solid-state laser medium 16, a dichroic mirror 18, a negative dispersion mirror 20, a cylindrical mirror 50, and an output mirror 52, each of which includes a semiconductor laser 26 and a Selfoc lens 28. It is comprised including. In this case, the resonator includes the SEASAM 14, the negative dispersion mirror 20, the cylindrical mirror 50, and the output mirror 52, and ultrashort pulse light is output to the outside from the output mirror. Also in this configuration, the SEASAM 14 and the solid-state laser medium 16 are arranged close to each other. As described above, the present invention can be applied to any configuration in which the SEASAM 14 and the solid-state laser medium 16 are arranged close to each other regardless of whether the resonator is a linear type or a V-shape.

(A) is a plan view of the mode-locked laser device, and (B) is a side view of (A). (A) is a top view of the resonator holder which concerns on a modification, (B) is a side view of (A). It is a schematic block diagram of the mode synchronous laser apparatus which concerns on a modification.

Explanation of symbols

10, 10A Mode-locked laser device 12 Excitation optical system 16 Solid laser medium 18 Dichroic mirror 20 Negative dispersion mirror 22 Peltier element 24 Peltier drive unit 26 Semiconductor laser 28 Selfoc lens 30 Excitation optical system holder 32 Dichroic mirror holder 34 Resonator holder 34A , 34B support 35A basic support 35B first support 35C second support 35D third support 36 copper plate 38A, 38B hole 40 beam splitter 42 photodiode 44 control unit 46 substrate 48 sealing member 48A transmission window 50 Cylindrical mirror 52 Output mirror

Claims (5)

A resonator comprising a semiconductor saturable absorber mirror and a negative dispersion mirror for controlling group velocity dispersion in the resonator;
A solid-state laser medium that is arranged in the resonator and outputs oscillation light when pumping light is incident;
Excitation means for causing the excitation light to enter the solid-state laser medium;
A first support that is sandwiched between the semiconductor saturable absorption mirror and the solid-state laser medium and supports the semiconductor saturable absorption mirror and the solid-state laser medium; and the first support from the first support A resonator holder integrally formed with a second support projecting along a direction intersecting the support;
A mode-locked laser device. The mode-locked laser device according to claim 1, wherein a light incident surface of the semiconductor saturable absorption mirror is attached to one surface of the first support. The mode-locked laser device according to claim 1, wherein a length of the first support in a direction intersecting with the first support is not more than half of a Rayleigh length. The length of the second support in the direction intersecting with the first support is at least twice the length of the first support in the direction intersecting with the first support. The mode-locked laser device according to any one of claims 1 to 3. The mode-locked laser device according to any one of claims 1 to 4, wherein the negative dispersion mirror is attached to the resonator holder.

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