JP2016012682A - Mode lock laser device and measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mode lock laser device capable of satisfactorily outputting a first laser beam and a second laser beam of which the center wavelengths are different from each other.SOLUTION: The mode lock laser device includes a gain medium, an excitation light source, an optical path branch mechanism and a beam waist adjustment mechanism. The gain medium is positioned on an optical path of the first laser beam reciprocating between a first mirror and an output coupler and on an optical path of the second laser beam reciprocating between a second mirror and the output coupler and within the gain medium, beam waists of the first laser beam and the second laser beam are positioned. The beam waist adjustment mechanism adjusts a position of at least one of the beam waist of the first laser beam and the beam waist of the second laser beam in such a manner that an area within a focal depth of the first laser beam and an area within a focal depth of the second laser beam are separated from each other.

Description

  The present invention relates to a mode-locked laser device and a measurement device.

  Nonlinear optical measurement devices that identify or observe substances using nonlinear optical effects such as stimulated Raman scattering, fluorescence due to two-photon absorption, and anti-Stokes Raman scattering are useful in medical and industrial fields. ing.

  Since the nonlinear optical effect becomes stronger as the peak power of the irradiation light is higher, the light source used in the nonlinear optical measurement apparatus is required to output a pulse beam having a higher peak power.

  A mode-locked solid-state laser device (mode-locked laser device) is known as one of light sources that can output a pulse beam with high peak power. The mode-locked laser device includes a resonator that resonates a laser beam, a gain medium that gives optical energy to the laser beam, and an excitation light source that excites the gain medium. The gain medium is disposed inside the resonator and is excited by the excitation light output from the excitation light source. The excited gain medium provides optical energy to the laser beam that resonates in the resonator via a stimulated emission process.

  The mode-locked laser device includes a modulator (mode locker) that periodically turns on / off the resonance of the laser beam. In general, the modulation period of the mode locker is adjusted to coincide with the reciprocal of the time (round trip time) in which the laser beam reciprocates through the resonator. When the modulation period of the mode locker matches the reciprocal of the round trip time, an oscillating laser beam is output from the resonator as a pulse train. The pulse width of such a laser beam is, for example, 1 nanosecond or less. The repetition period of the pulse train output from the resonator is equal to the modulation period of the mode locker, that is, the reciprocal of the round trip time. Such a pulse train generation mechanism is called mode lock.

  The mode-locked laser device can appropriately set the pulse width and the repetition period by appropriately setting the optical path length of the laser beam in the resonator. The pulse width of the laser beam can be appropriately set within a range of several fs to 1 ns, for example. Further, the repetition period of the laser beam can be appropriately set within a range of 1 MHz to 1 GHz, for example. The laser beam generated in this way has a peak power of, for example, 1 kW or more. Therefore, the mode-locked laser device is suitable as a light source for the nonlinear optical measurement device.

  Recently, a mode-locked laser apparatus that can output two types of pulsed laser beams having different center wavelengths has been proposed (see Non-Patent Document 1).

M. R. X. de Barros and P. C. Becker, “Two-color synchronously mode-locked femtosecond Ti: sapphire laser”, Optics Letters, Vol. 18, Issue 8, pp. 631-633 (1993).

  However, a mode-locked laser device that outputs two types of pulsed laser beams having different center wavelengths may not always obtain a satisfactory output.

  An object of the present invention is to provide a mode-locked laser device capable of outputting a good first laser beam and a second laser beam having different center wavelengths, and a measuring device using the mode-locked laser device. is there.

  According to an aspect of the present invention, the first mirror, the second mirror, the output coupler, and the optical path of the first laser beam that reciprocates between the first mirror and the output coupler. And a gain medium positioned on the optical path of the second laser beam having a center wavelength different from the center wavelength of the first laser beam, and reciprocating between the second mirror and the output coupler. A gain medium in which a beam waist of the first laser beam and a beam waist of the second laser beam are located inside, an excitation light source for exciting the gain medium, and the first laser An optical path branching mechanism that is arranged on the optical path of the beam and the optical path of the second laser beam and divides the optical path of the first laser beam and the optical path of the second laser beam; Thus, between the output coupler and the optical path branching mechanism, the optical path of the first laser beam and the optical path of the second laser beam coincide with each other, and the optical path branching mechanism and the optical path branching mechanism The optical path of the first laser beam between the first mirror and the optical path of the second laser beam between the optical path branching mechanism and the second mirror are different from each other. The beam waist of the first laser beam and the second so that the mechanism and the region within the focal depth of the first laser beam and the region within the focal depth of the second laser beam are separated from each other. And a beam waist adjusting mechanism that adjusts the position of at least one of the beam waists of the laser beam.

  According to the present invention, the region within the focal depth of the first laser beam and the region within the focal depth of the second laser beam are separated from each other. Since the energy is not divided into the first laser beam and the second laser beam at the same location in the gain medium, a high-power first laser beam and second laser beam can be obtained. In addition, since energy contention does not occur at the same location in the gain medium 4, even if the excitation threshold of the first laser beam and the excitation threshold of the second laser beam are different, stable output can be obtained. A first laser beam and a second laser beam are obtained. As described above, according to the present invention, it is possible to provide a mode-locked laser device that can favorably output the first laser beam and the second laser beam having different center wavelengths.

FIG. 1A is a schematic diagram showing the configuration of the mode-locked laser device according to the first embodiment, and FIG. 1B shows the beam shape of the first laser beam and the second laser inside the gain medium. It is a figure which shows notionally the beam shape of a beam. FIG. 2 is a diagram illustrating an example of a beam waist adjusting mechanism. FIG. 3A is a diagram showing a configuration of the mode-locked laser device according to the second embodiment, and FIG. 3B is a diagram showing the beam diameters of the first laser beam and the second laser beam inside the gain medium. It is a graph showing the simulation value of D. FIG. 4 is a diagram showing the configuration of the mode-locked laser device according to the third embodiment. FIG. 5 is a diagram showing the configuration of the mode-locked laser device according to the fourth embodiment. FIG. 6A is a diagram showing the configuration of the mode-locked laser device according to the fifth embodiment, and FIG. 6B is a diagram showing the beam diameters of the first laser beam and the second laser beam inside the gain medium. It is a graph which shows the simulation value of D. FIG. 7 is a diagram showing the configuration of the mode-locked laser device according to the sixth embodiment. FIG. 8 is a diagram showing the configuration of the measuring apparatus according to the seventh embodiment. FIG. 9 is a cross-sectional view showing a diffraction grating. FIG. 10A is a schematic diagram showing a configuration of a mode-locked laser device according to a reference example, and FIG. 10B is a diagram conceptually showing a beam shape of a laser beam inside a titanium sapphire crystal. FIG. 10C is a graph showing the cross-sectional intensity distribution of the laser beam.

  In order to improve the measurement accuracy in the nonlinear optical measurement apparatus, it is preferable to use two types of ultrashort pulse laser beams having different center wavelengths. For example, in stimulated Raman scattering, pump light that is a pulse laser beam having a center wavelength of λp and Stokes light that is a pulse laser beam having a center wavelength of λs can be used. When the subject is irradiated with the pump light pulse and the Stokes light pulse at the same time, a part of the energy of the pump light pulse is converted into the Stokes light pulse due to the nonlinear optical effect generated in the subject. By measuring the energy of the pump light pulse after conversion, the magnitude of the nonlinear optical effect generated in the subject can be measured. In order to reduce the size of the nonlinear optical measurement device, it is desirable that two types of pulse trains having different wavelengths are output from one light source.

  FIG. 10A is a schematic diagram showing the configuration of a mode-locked laser device according to a reference example.

  The mode-locked laser device according to the reference example includes a mirror 91 and a concave mirror 92 that constitute a resonator, and an output coupler 93 that extracts a part of the optical energy of the laser beam 95 as an output. The mode-locked laser device according to the reference example is made of a titanium sapphire crystal, and a gain medium 94 that gives optical energy to the laser beam 95, an excitation light source 96 for exciting the gain medium 94, and a saturable absorption as a mode locker. And a body 97. Further, the mode-locked laser device according to the reference example includes a prism pair 98 and a double slit 99 for selecting the center wavelength of the laser beam.

  In the mode-locked laser device according to the reference example, the laser beam 95 that has passed through the prism pair 98 is separated into a laser beam 95a having a center wavelength of λA and a laser beam 95b having a center wavelength of λB. The double slit 99 is inserted on the optical path of the laser beam 95a and on the optical path of the laser beam 95b. The double slit 99 has two openings, that is, an opening A and an opening B. The laser beam 95 is separated into a laser beam 95a and a laser beam 95b by the prism pair 98, the laser beam 95a passes through the opening A, and the laser beam 95b passes through the opening B. The laser beam 95 resonates between the mirror 91 and the partial reflection mirror 93 and oscillates. The round trip times of the laser beam 95a and the laser beam 95b are substantially equal since the lengths of the resonators are equal. Therefore, the laser beam 95a and the laser beam 95b are pulse trains having the same repetition frequency. The optical axis of the laser beam 95 a and the optical axis of the laser beam 95 b coincide between the prism pair 98 and the partial reflection mirror 93. As a result, the mode-locked laser device according to the reference example can output the laser beams A and B having different center wavelengths λA and λB from the output coupler 93 as a pulse train having the same optical axis.

  However, in the mode-locked laser device according to the reference example, the energy of the output pulse train becomes low. Hereinafter, this point will be described.

  FIG. 10B conceptually shows the beam shapes of the laser beams 95a and 95b inside the gain medium 94. As shown in FIG. The left-right direction in FIG. 10B corresponds to the traveling direction of the laser beams 95a and 95b. The solid line in FIG. 10B indicates the contour shape 100a of the laser beam 95a. The broken line in FIG. 10B shows the contour shape 100b of the laser beam 95b.

FIG. 10C is a graph showing the cross-sectional intensity distribution of the laser beam, that is, the intensity distribution of the laser beam 95 per unit area. A position d 0 in FIG. 10C represents the center of the laser beam 95. Further, a position d1 and a position d2 in FIG. 10C indicate positions where the intensity decreases to 1 / e ² with respect to the intensity at the center of the laser beam 95. What connects the positions d 1 and d 2 along the traveling direction of the laser beam 95 corresponds to the side shape of the laser beam 95. A distance D between the position d1 and the position d2 corresponds to the beam radius of the laser beam 95.

  As can be seen from FIG. 10B, the laser beam 95a and the laser beam 95b form a beam waist 100 having a minimum beam radius inside the gain medium 94.

  Further, as can be seen from FIG. 10B, the beam waist position WA of the laser beam 95a and the beam waist position WB of the laser beam 95b substantially coincide.

  The energy (excitation energy) of the excitation light absorbed by the gain medium 94 becomes optical energy through the stimulated emission process and is given to the laser beam 95a and the laser beam 95b. Since the intensity of the stimulated emission process is proportional to the cross-sectional intensity of the laser beams 95a and 95b, the excitation energy absorbed in the vicinity of the beam waist of the laser beams 95a and 95b is substantially the light energy of the laser beams 95a and 95b. . That is, since the beam waists of the laser beam 95a and the laser beam 95b overlap, the excitation energy absorbed at the same position is divided into the laser beam 95a and the laser beam 95b as light energy. As a result, the mode-locked laser device according to the reference example almost halves the energy of the output pulse train as compared with the mode-locked laser device that emits one type of center wavelength laser beam.

  Further, in the mode-locked laser device according to the reference example, the positions of the beam waists of the laser beams 95a and 95b coincide with each other, so that a competition for excitation energy occurs between the laser beams 95a and 95b. When the excitation threshold of one laser beam is lower than the excitation threshold of the other laser beam, the energy of the laser beam having a low excitation threshold tends to be high. The excitation threshold of the laser beam is affected by the wavelength dependence of the optical component characteristics. Since the wavelength dependency of the optical component characteristics also changes depending on the environmental temperature or the like, as a result, the outputs of the two types of laser beams 95a and 95b having different center wavelengths become unstable.

  As described above, the mode-locked laser apparatus according to the reference example cannot always output two types of laser beams having different center wavelengths.

[First Embodiment]
A mode-locked laser device according to a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1A is a schematic diagram showing the configuration of the mode-locked laser device according to the present embodiment.

  The mode-locked laser device according to the present embodiment is a solid-state laser device that emits pulse laser beams having two different wavelengths having different center wavelengths at a predetermined repetition period, that is, a two-wavelength morrodoc solid-state laser device. The center wavelength here refers to the wavelength at the center of the half width of the pulsed light.

  The mode-locked laser device according to this embodiment includes mirrors 21 and 22, concave mirrors 23 and 24, an output coupler 25, an optical path branching mechanism 111, and a beam waist adjusting mechanism 12, which are in phase. As a result, a resonator (optical resonator) 3 is formed.

  The first laser beam 1 reciprocates between an output coupler 25 composed of a partially transmissive mirror and a mirror 21 which is a highly reflective flat mirror. The mirror 21 is located at one end of the optical path of the first laser beam 1. The second laser beam 2 reciprocates between an output coupler 25 made up of a partially transmissive mirror and a mirror 22 that is a highly reflective flat mirror. The mirror 22 is located at one end of the optical path of the second laser beam 2. The center wavelength λ1 of the first laser beam 1 and the center wavelength λ2 of the second laser beam 2 are different from each other. The center wavelength λ1 of the first laser beam 1 is, for example, about 750 nm. The center wavelength λ2 of the second laser beam 2 is about 850 nm, for example. The output coupler 25 has a function of reflecting the first laser beam 1 and the second laser beam 2 and also has a function of extracting a part of the first laser beam 1 and the second laser beam 2 as outputs. Have. In the present invention, the partial transmission mirror refers to a mirror having a reflectance of 70% or more and less than 99% at the oscillation wavelength, and the high reflection mirror refers to a mirror having a reflectance of 99% or more at the oscillation wavelength.

  The first laser beam 1 and the second laser beam 2 reciprocating in the resonator 3 are modulated by a lens effect (Kerr lens effect) generated in the gain medium 4 when passing through a gain medium 4 described later. Due to the Kerr lens effect, the first laser beam 1 and the second laser beam 2 are turned on / off at a period equal to the reciprocal of the round trip time of the first laser beam 1 and the second laser beam 2. As a result, the first laser beam 1 and the second laser beam 2 are mode-locked, and the first laser beam 1 and the second laser beam 2 are output at the repetition frequency equal to the reciprocal of the round trip time. Are repeatedly emitted in pulses. The outputs of the first laser beam 1 and the second laser beam 2 that are repeatedly output are also referred to as pulse trains.

  The optical path branching mechanism 111 branches the optical path of the first laser beam 1 and the optical path of the second laser beam 2. The optical path branching mechanism 111 is disposed on the optical path of the first laser beam 1 and on the optical path of the second laser beam 2. Between the optical path branching mechanism 111 and the output coupler 25, the optical path (optical axis) of the first laser beam 1 and the optical path (optical axis) of the second laser beam 2 coincide. On the other hand, the optical path (optical axis) of the first laser beam 1 between the optical path branching mechanism 111 and the mirror 21 and the optical path (optical axis) of the second laser beam 2 between the optical path branching mechanism 111 and the mirror 22. Are different from each other.

  The first laser beam 1 and the second laser beam 2 reaching the concave mirror 23 from the output coupler 25 are reflected by the concave mirror 23 and further reflected by the concave mirror 24 to reach the optical path branching mechanism 111. Concave mirrors 23 and 24 are arranged.

  The mode-locked laser apparatus according to the present embodiment further includes a gain medium 4 that applies optical energy to the first laser beam 1 and the second laser beam 2 and amplifies the first laser beam 1 and the second laser beam 2. Have. The gain medium 4 is located on the optical path of the first laser beam 1 and on the optical path of the second laser beam 2. More specifically, the gain medium 4 is disposed on the optical path of the first laser beam 1 and the optical path of the second laser beam 2 between the concave mirror 23 and the concave mirror 24. The first laser beam and the second laser beam reaching the concave mirror 23 from the output coupler 25 are reflected by the concave mirror 23, further reflected by the concave mirror 24 through the gain medium 4, and transmitted to the optical path branching mechanism 111. The gain medium 4 is arranged so as to reach. The beam waist of the first laser beam 1 and the beam waist of the second laser beam 2 are located inside the gain medium 4.

  The mode-locked laser device according to the present embodiment further includes an excitation light source 6 for exciting the gain medium 4. Excitation light emitted from the excitation light source 6 enters the gain medium 4.

  The mode-locked laser device according to the present embodiment further includes a beam waist adjusting mechanism 12. The beam waist adjusting mechanism 12 adjusts the position of at least one of the beam waist of the first laser beam 1 and the beam waist of the second laser beam 2. The beam waist adjusting mechanism 12 is disposed on the optical path of the first laser beam 1 branched by the optical path branching mechanism 111, for example.

  Here, the case where the beam waist adjusting mechanism 12 is arranged on the optical path of the first laser beam 1 branched by the optical path branching mechanism 111 will be described as an example, but the present invention is not limited to this. For example, the beam waist adjusting mechanism 12 may be arranged on the optical path of the second laser beam 2 branched by the optical path branching mechanism 111.

  When the optical path length of the first laser beam 1 and the optical path length of the second laser beam 2 are equal to each other, the position W1 of the beam waist of the first laser beam 1 and the beam waist of the second laser beam 2 The position W2 is shifted in the following cases. That is, the position W1 of the beam waist of the first laser beam 1 and the position W2 of the beam waist of the second laser beam 2 are the curvature of the wavefront of the first laser beam 1 when entering the gain medium 4 and the first. This occurs when the curvatures of the wavefronts of the two laser beams 2 are different from each other. Therefore, the beam waist adjusting mechanism 12 may be any mechanism that can change the curvature of the wavefront of at least one of the first laser beam 1 and the second laser beam 2.

  FIG. 2 is a diagram illustrating an example of a beam waist adjusting mechanism.

  FIG. 2A is a diagram showing a case where the beam waist adjusting mechanism 12 is constituted by a concave mirror 12a.

  Reference numeral 115a conceptually shows the shape of the wavefront before the first laser beam 1 and the second laser beam 2 enter the concave mirror 12a. Reference numeral 115b conceptually shows the shape of the wavefront at a stage after the first laser beam 1 and the second laser beam 2 are reflected by the concave mirror 12a.

  In this way, the beam waist adjusting mechanism 12 may be configured by the concave mirror 12a.

  FIG. 2B is a diagram illustrating a case where the beam waist adjusting mechanism 12 is configured by a convex mirror 12b.

  Reference numeral 116a conceptually indicates the shape of the wavefront at the stage before the first laser beam 1 and the second laser beam 2 enter the convex mirror 12b. Reference numeral 116b conceptually shows the shape of the wavefront at a stage after the first laser beam 1 and the second laser beam 2 are reflected by the convex mirror 12b.

  As described above, the beam waist adjusting mechanism 12 may be configured by the convex mirror 12b.

  FIG. 2C is a diagram illustrating a case where the beam waist adjusting mechanism 12 is configured by a concave lens 12c.

  Reference numeral 117a conceptually indicates the shape of the wavefront at the stage before the first laser beam 1 and the second laser beam 2 enter the concave lens 12c. Reference numeral 117b conceptually shows the shape of the wavefront at a stage after the first laser beam 1 and the second laser beam 2 have passed through the concave mirror 12c.

  In this manner, the beam waist adjusting mechanism 12 may be configured by the concave lens 12c.

  FIG. 2D is a diagram illustrating a case where the beam waist adjusting mechanism 12 is configured by a convex lens 12d.

  Reference numeral 118a conceptually shows the shape of the wavefront at the stage before the first laser beam 1 and the second laser beam 2 enter the convex lens 12d. Reference numeral 118b conceptually shows the shape of the wavefront at a stage after the first laser beam 1 and the second laser beam 2 have passed through the convex mirror 12d.

  In this way, the beam waist adjusting mechanism 12 may be configured by the convex mirror 12d.

  FIG. 1B is a diagram conceptually showing the beam shape of the first laser beam 1 and the beam shape of the second laser beam 2 inside the gain medium 4. The left-right direction in FIG. 1B corresponds to the traveling direction of the first laser beam 1 and the second laser beam 2. Reference numeral 113 in FIG. 1B indicates the contour shape of the first laser beam 1. Reference numeral 114 in FIG. 1B indicates the contour shape of the second laser beam 2.

  Reference sign z <b> 1 in FIG. 1B indicates the depth of focus of the first laser beam 1. Reference sign z <b> 2 in FIG. 1B indicates the focal depth of the second laser beam 2. A symbol S <b> 1 in FIG. 1B indicates a region within the focal depth z <b> 1 of the first laser beam 1, that is, a Rayleigh region of the first laser beam 1. A symbol S <b> 2 in FIG. 1B indicates a region within the focal depth z <b> 2 of the second laser beam 2, that is, a Rayleigh region of the second laser beam 2. A symbol W <b> 1 in FIG. 1B indicates the position of the beam waist of the first laser beam 1. The symbol W2 in FIG. 1B indicates the position of the beam waist of the second laser beam 2. A symbol D1 in FIG. 1B indicates a beam diameter at the beam waist of the first laser beam 1. Reference sign D2 in FIG. 1B indicates the beam diameter at the beam waist of the second laser beam 1.

  The beam waist position w 1 of the first laser beam 1 and the beam waist position w 2 of the second laser beam 2 are located inside the gain medium 4.

The focal depth z1 of the first laser beam 1 is a distance between two points in the optical axis direction at which the beam diameter D is √2 times the beam diameter D1 of the beam waist. That is, the depth of focus z1 of the first laser beam 1 passes through the beam waist from the position where the beam diameter D is √2 times the beam diameter D1 of the beam waist, and further the beam diameter of the beam waist. This is the distance to the point where the beam diameter D is √2 times D1. In other words, the first focus depth z1 of the laser beam 1, beam cross-sectional area (= πD ^2/4) is twice the beam cross section at the beam waist, is the distance between two points in the optical axis direction . The focal depth is also referred to as the Rayleigh length (Rayleigh region, Rayleigh distance).

  The focal depth z2 of the second laser beam 2 is a distance between two points in the optical axis direction at which the beam diameter D is √2 times the beam diameter D2 of the beam waist. That is, the depth of focus z2 of the second laser beam 2 passes through the beam waist from the position where the beam diameter D is √2 times the beam diameter D2 of the beam waist, and further the beam diameter of the beam waist. This is the distance to the point where the beam diameter D is √2 times D2. In other words, the focal depth z2 of the second laser beam 2 is a distance between two points in the optical axis direction at which the beam cross-sectional area is twice the beam cross-sectional area at the beam waist.

When the cross-sectional intensity distribution of the first laser beam 1 can be approximated by a Gaussian distribution, the focal depth z1 of the first laser beam 1 is D1 as the beam diameter of the first laser beam 1, and the center of the first laser beam 1 When the wavelength is λ1, it is expressed by the following equation (1).
z1 = 2π (D1 / 2) ² / λ1 (1)

Further, when the cross-sectional intensity distribution of the second laser beam 2 can also be approximated by a Gaussian distribution, the focal depth z2 of the second laser beam 2 is D2 as the beam diameter of the second laser beam 2, and the second laser beam 2 Assuming that the center wavelength of λ2 is λ2, it is expressed by the following equation (2).
z2 = 2π (D2 / 2) ² / λ2 (2)

  The intensity of the stimulated emission process of the first laser beam 1 is inversely proportional to the beam cross-sectional area of the first laser beam 1 passing through the gain medium 4. The intensity of the stimulated emission process of the second laser beam 2 is inversely proportional to the beam cross-sectional area of the second laser beam 2 that passes through the gain medium 4. The beam cross-sectional area of the first laser beam 1 is sufficiently small in the region S1 within the focal depth z1 of the first laser beam 1. The beam cross-sectional area of the second laser beam 2 is sufficiently small in the region S2 within the focal depth z2 of the second laser beam 2. For this reason, the amplification of the first laser beam 1 is mainly performed in the region S <b> 1 within the focal depth of the first laser beam 1. The amplification of the second laser beam 2 is mainly performed in the region S2 within the focal depth of the second laser beam 2.

  In the present embodiment, the distance between the beam waist position W1 of the first laser beam 1 and the beam waist position W2 of the second laser beam 2 is 1/2 of the focal depth z1 of the first laser beam. And ½ of the focal depth z2 of the second laser beam. Therefore, the region S1 within the focal depth z1 of the first laser beam 1 and the region S2 within the focal depth z2 of the second laser beam 2 are separated from each other and do not overlap. For this reason, the first laser beam 1 and the second laser beam 2 are amplified by obtaining light energy from different portions of the gain medium 4. Since the optical energy from the same location in the gain medium 4 is not divided into the first laser beam 1 and the second laser beam 2, according to the present embodiment, the first laser beam 1 and the first laser beam 1 The output of the second laser beam 2 can be increased.

  In the present embodiment, the region S1 within the focal depth z1 of the first laser beam 1 and the region S2 within the focal depth z2 of the second laser beam 2 are separated from each other. For this reason, according to the present embodiment, it is possible to suppress the energy contention between the first laser beam 1 and the second laser beam 2. Therefore, according to the present embodiment, even when the excitation threshold of the first laser beam 1 and the excitation threshold of the second laser beam 2 are different from each other, the stable first laser beam 1 and second laser beam 1 are stable. The laser beam 2 can be output.

  The mode-locked laser device according to the present embodiment can output the first laser beam 1 and the second laser beam 2 having a pulse width of, for example, several fs to 1 ns in a pulse shape with a repetition period of, for example, about 1 MHz to 1 GHz. . The pulse width and repetition period of the first laser beam 1 and the second laser beam 2 are set to desired values by appropriately setting the optical path lengths of the first laser beam 1 and the second laser beam 2. obtain. The first laser beam 1 and the second laser beam 2 thus generated have a peak power of, for example, 1 kW or more. Therefore, the mode-locked laser device according to the present embodiment is very useful as a light source for a nonlinear optical measurement device.

  Thus, in the present embodiment, the region S1 within the focal depth z1 of the first laser beam 1 and the region S2 within the focal depth z2 of the second laser beam 2 are separated from each other. Since the energy is not divided into the first laser beam 1 and the second laser beam 2 at the same location in the gain medium 4, the first laser beam 1 and the second laser beam 2 with high output are obtained. be able to. In addition, since the energy contention does not occur at the same location in the gain medium 4, even when the excitation threshold of the first laser beam 1 and the excitation threshold of the second laser beam 2 are different, stable An output first laser beam 1 and second laser beam 2 are obtained. As described above, according to the present embodiment, it is possible to provide a mode-locked laser apparatus that can favorably output the first laser beam 1 and the second laser beam 2 having different center wavelengths.

[Second Embodiment]
A mode-locked laser device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 3A is a diagram showing the configuration of the mode-locked laser device according to the present embodiment. The same components as those of the mode-locked laser device according to the first embodiment shown in FIG. 1 and FIG.

  This embodiment shows a more specific aspect of the mode-locked laser device described above in the first embodiment.

  In this embodiment, as the mirrors 21 and 22, for example, highly reflective flat mirrors are used.

  In the present embodiment, as the concave mirrors 23 and 24, concave mirrors having a reflective surface with a curvature of, for example, about 5 cm are used. The distance between the concave mirror 23 and the concave mirror 24 is, for example, about 5.5 cm.

  In the present embodiment, a YAG laser double wave is used as the excitation light source 6.

  In the present embodiment, a titanium sapphire crystal is used as the gain medium 4. The gain medium 4 made of titanium sapphire crystal has a Kerr lens effect and can function as a mode locker. The thickness of the gain medium 4 is about 5 mm, for example. The incident angles of the first laser beam 1 and the second laser beam 2 to the gain medium 4 are set to be Brewster angles. The Brewster angle is about 60 °, for example.

  In the present embodiment, an optical path branching mechanism 111 is configured by a plurality of prisms (prism pairs) 11 a and 11 b for wavelength division and a prism mirror (total reflection prism) 13. The first laser beam 1 and the second laser beam 2 passing through the gain medium 4 and reflected by the concave mirror 24 pass through the prism 11a and further pass through the other prism 11b. .

  The first laser beam 1 and the second laser beam 2 have different center wavelengths. Specific numerical values described in the description of the present embodiment are design examples when the center wavelength of the first laser beam 1 is about 750 nm and the center wavelength of the second laser beam 2 is about 850 nm. The same applies to the third and subsequent embodiments. Since the refractive indexes in the prisms 11a and 11b differ depending on the wavelength of light, the directions of the first laser beam 1 and the second laser beam 2 that have passed through the prism pair 11a and 11b are different from each other. For this reason, the optical path of the first laser beam 1 and the optical path of the second laser beam 2 are first branched by the prism pairs 11a and 11b. The optical path of the first laser beam 1 and the optical path of the second laser beam 2 are further branched by reflection by the prism mirror 13. For example, the first laser beam 1 and the second laser beam 2 are reflected by the prism mirror 13 so as to travel in opposite directions.

  In the present embodiment, a beam waist adjusting mechanism is configured by the concave mirror 12a. The concave mirror 12 a is disposed on the optical path of the first laser beam 1 between the prism mirror 13 and the mirror 21. The curvature of the reflecting surface of the concave mirror 12a is about 13 cm, for example. The concave mirror 12 a is arranged so that the first laser beam 1 reaching the concave mirror 12 a from the prism mirror 13 is reflected by the concave mirror 12 a and reaches the mirror 21.

  The distance between the output coupler 25 and the concave mirror 23 is, for example, about 50 cm. The length of the optical path between the concave mirror 24 and the mirror 21 is, for example, about 60 cm. The length of the optical path between the concave mirror 24 and the mirror 22 is about 60 cm, for example. The distance between the concave mirror 12a and the mirror 21 is, for example, about 10 cm.

  Since the optical path length of the first laser beam 1 in the resonator 3 and the optical path length of the second laser beam 2 in the resonator 3 are equal to each other, the first laser beam 1 and the second laser beam 2 are It is emitted in the form of pulses at the same repetition period.

  FIG. 3B is a graph showing simulation values of the beam diameter D of the first laser beam 1 and the second laser beam 2 inside the gain medium 4. The horizontal axis in FIG. 3B indicates the position, and the vertical axis indicates the beam diameter D.

  As can be seen from FIG. 3B, the focal depth z1 of the first laser beam 1 is about 0.4 mm. Further, as can be seen from FIG. 3B, the focal depth z2 of the second laser beam 2 is about 1.2 mm. Therefore, the sum of 1/2 of the focal depth z1 of the first laser beam 1 and 1/2 of the focal depth z2 of the second laser beam 2 is about 0.8 mm.

  On the other hand, as can be seen from FIG. 3B, the distance between the beam waist position W1 of the first laser beam 1 and the beam waist position W2 of the second laser beam 2 is about 0.9 mm. .

  Accordingly, the distance between the beam waist of the first laser beam 1 and the beam waist of the second laser beam 2 is ½ of the focal depth z1 of the first laser beam 1 and the distance of the second laser beam 2. It is larger than the sum of 1/2 of the focal depth z2. Accordingly, the region S1 within the focal depth z1 of the first laser beam 1 and the region S2 within the focal depth z2 of the second laser beam 2 are separated from each other and do not overlap.

  Thus, in the present embodiment, the region S1 within the focal depth z1 of the first laser beam 1 and the region S2 within the focal depth z2 of the second laser beam 2 are separated from each other. Since the energy is not divided into the first laser beam 1 and the second laser beam 2 at the same location in the gain medium 4, the first laser beam 1 and the second laser beam 2 with high output are obtained. be able to. In addition, since the energy contention does not occur at the same location in the gain medium 4, even when the excitation threshold of the first laser beam 1 and the excitation threshold of the second laser beam 2 are different, stable An output first laser beam 1 and second laser beam 2 are obtained. As described above, according to the present embodiment, it is possible to provide a mode-locked laser apparatus that can favorably output the first laser beam 1 and the second laser beam 2 having different center wavelengths.

[Third Embodiment]
A mode-locked laser device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing the configuration of the mode-locked laser device according to the present embodiment. The same components as those of the mode-locked laser device according to the first and second embodiments shown in FIGS. 1 to 3 are denoted by the same reference numerals, and description thereof is omitted or simplified.

  In the present embodiment, a beam waist adjusting mechanism is configured by the convex lens 12d. Specific values are shown with the center wavelength of the first laser beam 1 being about 750 nm and the center wavelength of the second laser beam 2 being about 850 nm.

  As shown in FIG. 4, a convex lens 12 d as a beam waist adjusting mechanism is arranged on the optical path of the first laser beam 1. More specifically, the convex lens 12 d is disposed on the optical path of the first laser beam 1 between the prism mirror 13 and the total reflection mirror 21.

  The distance between the output coupler 25 and the concave mirror 23 is, for example, about 50 cm. The length of the optical path between the concave lens 24 and the mirror 21 is, for example, 60 cm. The length of the optical path between the concave mirror 24 and the mirror 22 is about 60 cm, for example. The distance between the convex lens 12d and the mirror 21 is, for example, 10 cm. The focal length of the convex lens 12d is, for example, 6.5 cm.

  In general, a concave mirror 12a with a curvature R of a reflecting surface arranged on the optical path of a laser beam and a convex lens 12d with a focal length f are equivalent in constructing a resonator when R / 2 = f. Can be considered. As described above, the focal length f of the convex lens 12d in the present embodiment is 6.5 cm. Further, as described above, the curvature R of the reflecting surface of the concave mirror 12a used in the second embodiment is 13 cm. Therefore, the convex lens 12d in the present embodiment and the concave mirror 12a in the second embodiment can be regarded as equivalent in configuring the resonator 30.

  Accordingly, also in the present embodiment, as in the second embodiment, the distance between the beam waist position W1 of the first laser beam 1 and the beam waist position W2 of the second laser beam 2 is about 0. 9 mm.

  Therefore, also in the present embodiment, the distance between the beam waist of the first laser beam 1 and the beam waist of the second laser beam 2 is ½ of the focal depth z1 of the first laser beam 1 and the first. It becomes larger than the sum of the focal depth z2 of the laser beam 2 of 2. The region within the focal depth z1 of the first laser beam and the region within the focal depth z2 of the second laser beam are separated from each other and do not overlap.

  Thus, also in the present embodiment, the region within the focal depth z1 of the first laser beam and the region within the focal depth z2 of the second laser beam are separated from each other. Also in this embodiment, the energy is not divided into the first laser beam 1 and the second laser beam 2 at the same location in the gain medium 4, and therefore the first laser beam 1 and the second laser beam 1 with the high output are not divided. The laser beam 2 can be obtained. In addition, since the energy contention does not occur at the same location in the gain medium 4, even when the excitation threshold of the first laser beam 1 and the excitation threshold of the second laser beam 2 are different, stable An output first laser beam 1 and second laser beam 2 are obtained. As described above, the present embodiment can also provide a mode-locked laser device that can favorably output the first laser beam 1 and the second laser beam having different center wavelengths.

[Fourth Embodiment]
A mode-locked laser device according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram showing the configuration of the mode-locked laser device according to the present embodiment. The same components as those of the mode-locked laser device according to the first to third embodiments shown in FIGS. 1 to 4 are denoted by the same reference numerals, and description thereof will be omitted or simplified.

  In the mode-locked laser device according to the present embodiment, the concave mirror 12a and the convex mirror 12b together constitute a beam waist adjusting mechanism.

  The concave mirror 12a is disposed on the optical path of the first laser beam 1, for example. The concave mirror 12 a is arranged so that the first laser beam 1 reaching the concave mirror 12 a from the prism mirror 13 is reflected by the concave mirror 12 a and reaches the mirror 21.

  The convex mirror 12b is disposed on the optical path of the second laser beam 2, for example. The convex mirror 12 b is arranged so that the second laser beam 2 reaching the convex mirror 12 b from the prism mirror 13 is reflected by the convex mirror 12 b and reaches the mirror 22.

  As described above with reference to FIG. 2, the concave mirror 12a and the convex mirror 12b change the curvatures of the wavefronts of the laser beams 1 and 2 in the opposite directions. For this reason, the beam waist position w1 of the first laser beam 1 and the beam waist position w2 of the second laser beam 2 are shifted in opposite directions within the gain medium 4. For this reason, in this embodiment, the distance between the beam waist position w1 of the first laser beam 1 and the beam waist position w2 of the second laser beam 2 can be further increased.

  Here, although the concave mirror 12a is disposed on the optical path of the first laser beam 1 and the convex mirror 12b is disposed on the optical path of the second laser beam 2, the present invention is not limited to this. The concave mirror 12a, the convex mirror 12b, the concave lens 12c, and the convex lens 12d are appropriately combined so that the curvature of the wavefront of the first laser beam 1 and the curvature of the wavefront of the second laser beam 2 change in opposite directions. Just do it. For example, when the concave mirror 12 a is disposed on the optical path of the first laser beam 1, the convex mirror 12 b or the concave lens 12 c may be disposed on the optical path of the second laser beam 2. Further, when the convex mirror 12 b is disposed on the optical path of the first laser beam 1, the concave mirror 12 a or the convex lens 12 d may be disposed on the optical path of the second laser beam 2. Further, when the concave lens 12 c is disposed on the optical path of the first laser beam 1, the concave mirror 12 a or the convex lens 12 d may be disposed on the optical path of the second laser beam 2. When the convex lens 12d is disposed on the optical path of the first laser beam 1, the convex mirror 12b or the concave lens 12c may be disposed on the optical path of the second laser beam 2.

  Thus, in this embodiment, the separation distance between the region S1 within the focal depth z1 of the first laser beam 1 and the region S2 within the focal depth z2 of the second laser beam 2 becomes larger. For this reason, according to the present embodiment, the first laser beam 1 and the second laser beam 2 with higher output can be obtained. Further, according to the present embodiment, the first laser beam 1 and the second laser beam 2 having more stable outputs can be obtained. Thus, according to the present embodiment, it is possible to provide a mode-locked laser apparatus that can better output the first laser beam 1 and the second laser beam having different center wavelengths.

[Fifth Embodiment]
A mode-locked laser device according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 6A is a diagram showing a configuration of the mode-locked laser device according to the present embodiment. The same components as those of the mode-locked laser devices according to the first to fourth embodiments shown in FIGS. 1 to 5 are denoted by the same reference numerals, and description thereof will be omitted or simplified.

  In the mode-locked laser device according to the present embodiment, a concave mirror 12a is used as a mirror disposed at one end of the optical path of the first laser beam 1, and a mirror disposed at one end of the optical path of the second laser beam 2. The convex mirror 12b is used.

  In the present embodiment, the first laser beam 1 reciprocates between the concave mirror 12a and the output coupler 25. That is, in the present embodiment, the concave mirror 12 a also serves as a mirror disposed at one end of the optical path of the first laser beam 1.

  In the present embodiment, the second laser beam 2 reciprocates between the convex mirror 12b and the output coupler 25. That is, in the present embodiment, the convex mirror 12 b also serves as a mirror disposed at one end of the optical path of the second laser beam 2.

  The concave mirror 12a and the convex mirror 12b together constitute a beam waist adjustment mechanism.

  The concave mirror 12 a is arranged so that the first laser beam 1 reaching the concave mirror 12 a from the prism mirror 13 is reflected by the concave mirror 12 a and folded back in the opposite direction to reach the prism mirror 13. The second laser beam 2 reaching the convex mirror 12 b from the prism mirror 13 is reflected by the convex mirror 12 b and folded back in the opposite direction, and the convex mirror 12 b is arranged so as to reach the prism mirror 13.

  Accordingly, the concave mirror 12a and the convex mirror 12b serve not only as a beam waist adjusting mechanism but also as a function of reflecting the first laser beam 1 and the second laser beam 2 back into the resonator 3.

  The curvature of the reflecting surface of the concave mirror 12a is about 23 cm, for example. The curvature of the reflecting surface of the convex mirror 12b is about 80 cm, for example.

  FIG. 6B is a graph showing simulation values of the beam diameter D of the first laser beam 1 and the second laser beam 2 inside the gain medium 4.

  As can be seen from FIG. 6B, the focal depth z1 of the first laser beam 1 is about 0.8 mm. As can be seen from FIG. 6B, the focal depth z2 of the second laser beam 2 is about 0.7 mm. 6B, the distance between the beam waist position W1 of the first laser beam 1 and the beam waist position W2 of the second laser beam 2 is about 1.0 mm. .

  Therefore, also in the present embodiment, the distance between the beam waist of the first laser beam 1 and the beam waist of the second laser beam 2 is ½ of the focal depth z1 of the first laser beam 1 and the first. It becomes larger than the sum of the focal depth z2 of the laser beam 2 of 2. The region within the focal depth z1 of the first laser beam and the region within the focal depth z2 of the second laser beam are separated from each other and do not overlap.

  Thus, also in the present embodiment, the region within the focal depth z1 of the first laser beam and the region within the focal depth z2 of the second laser beam are separated from each other. Also in this embodiment, the energy is not divided into the first laser beam 1 and the second laser beam 2 at the same location in the gain medium 4, and therefore the first laser beam 1 and the second laser beam 1 with the high output are not divided. The laser beam 2 can be obtained. In addition, since the energy contention does not occur at the same location in the gain medium 4, even when the excitation threshold of the first laser beam 1 and the excitation threshold of the second laser beam 2 are different, stable An output first laser beam 1 and second laser beam 2 are obtained. As described above, also in this embodiment, it is possible to provide a mode-locked laser apparatus that can favorably output the first laser beam 1 and the second laser beam having different center wavelengths.

[Sixth Embodiment]
A mode-locked laser device according to a sixth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram showing the configuration of the mode-locked laser device according to the present embodiment. The same components as those of the mode-locked laser devices according to the first to fifth embodiments shown in FIGS. 1 to 6 are denoted by the same reference numerals, and description thereof will be omitted or simplified.

  In the mode-locked laser device according to the present embodiment, an optical path branching mechanism is configured by one prism 11.

  In the second to fifth embodiments described above, the optical path branching mechanism is configured by the prism pairs 11a and 11b and the prism mirror 13. However, in this embodiment, the optical path branching mechanism is configured by one prism 11 for wavelength division. It is configured.

  The first laser beam 1 and the second laser beam 2 have different center wavelengths. Since the refractive index in the prism 11 varies depending on the wavelength of light, the directions of the first laser beam 1 and the second laser beam 2 that have passed through the prism 11 are different from each other. Therefore, the optical path of the first laser beam 1 and the optical path of the second laser beam 2 are branched by the prism 11.

  In the present embodiment, the concave mirror 12a is used as a mirror disposed at one end of the optical path of the first laser beam 1. In the present embodiment, the first laser beam 1 reciprocates between the concave mirror 12a and the output coupler 25. That is, in the present embodiment, the concave mirror 12 a also serves as a mirror disposed at one end of the optical path of the first laser beam 1. The concave mirror 12a is arranged so that the first laser beam reaching the concave mirror 12a from the prism 11 is reflected in the opposite direction by the concave mirror 12a and reaches the prism 11.

  At one end of the optical path of the second laser beam 2, a mirror 22 that is a highly reflective flat mirror is provided. The mirror 22 is arranged so that the second laser beam 2 reaching the mirror 22 from the prism 11 is reflected in the opposite direction by the mirror 22 and reaches the prism 11.

  Here, a case where a concave mirror 12a is arranged at one end of the optical path of the first laser beam 1 and a mirror 22 which is a highly reflective flat mirror is arranged at one end of the optical path of the second laser beam 2 will be described as an example. However, the present invention is not limited to this. For example, the concave mirror 12 a may be disposed at one end of the optical path of the first laser beam 1 and the convex mirror 12 b may be disposed at one end of the optical path of the second laser beam 2. Alternatively, the convex mirror 12 b may be disposed at one end of the optical path of the first laser beam 1 and the concave mirror 12 a may be disposed at one end of the optical path of the second laser beam 2. Alternatively, the convex mirror 12 b may be disposed at one end of the optical path of the first laser beam 1, and the highly reflective flat mirror 22 may be disposed at one end of the optical path of the second laser beam 2. The distance between the beam waists of the first laser beam 1 and the second laser beam 2 is 1/2 of the focal depth z1 of the first laser beam 1 and 1/2 of the focal depth z2 of the second laser beam 2. What is necessary is just to comprise a beam waist adjustment mechanism suitably so that it may become larger than the sum of.

  Thus, also in this embodiment, the area | region in the focal depth z1 of the 1st laser beam 1 and the area | region of the focal depth z2 of the 2nd laser beam 2 are mutually separated. Also in this embodiment, the energy is not divided into the first laser beam 1 and the second laser beam 2 at the same location in the gain medium 4, and therefore the first laser beam 1 and the second laser beam 1 with the high output are not divided. The laser beam 2 can be obtained. In addition, since the energy contention does not occur at the same location in the gain medium 4, even when the excitation threshold of the first laser beam 1 and the excitation threshold of the second laser beam 2 are different, stable An output first laser beam 1 and second laser beam 2 are obtained. As described above, also in this embodiment, it is possible to provide a mode-locked laser apparatus that can favorably output the first laser beam 1 and the second laser beam having different center wavelengths.

[Seventh Embodiment]
A measurement apparatus according to a seventh embodiment of the present invention will be described with reference to FIG. FIG. 8 is a diagram showing the configuration of the measuring apparatus according to the present embodiment. The same components as those of the mode-locked laser device according to the first to sixth embodiments shown in FIGS. 1 to 7 are denoted by the same reference numerals, and description thereof will be omitted or simplified.

  The measurement device (measurement device) according to the present embodiment is a measurement device (nonlinear optical measurement device) in which the mode-locked laser device according to any one of the first to sixth embodiments is used for the light source unit 150. Here, a case where the measurement device according to the present embodiment is a stimulated Raman scattering microscope will be described as an example, but the measurement device is not limited to the stimulated Raman scattering microscope. The mode-locked laser device described in the first to sixth embodiments can be used as appropriate for various measuring devices.

Pumping light (excitation light) P and Stokes light S are emitted from the light source unit 150. The center wavelength of the pump light P is lambda _p. The central wavelength of the Stokes light S is λ _s different from the central wavelength λ _p of the pump light. The pump light P corresponds to, for example, the first laser beam 1 described above in the first to sixth embodiments. The Stokes light S corresponds to, for example, the second laser beam 2 described above in the first to sixth embodiments. The optical axis of the pump light P coincides with the optical axis of the Stokes light S.

  The pump light P and the Stokes light S emitted from the light source unit 150 are condensed by the condensing optical system 154 and irradiated onto the subject 155. At the condensing point, the stimulated Raman scattering based on the molecular vibrations of the molecules constituting the subject 155 is generated by the pump light P and the Stokes light S. When stimulated Raman scattering occurs, the intensity of the pump light P and the intensity of the Stokes light S change.

  The pump light P and Stokes light S that have passed through the subject 155 are condensed by the condensing optical system 156 and are incident on the bandpass filter 157. The bandpass filter 157 transmits light in the wavelength region of the pump light P. The pump light P passes through the band pass filter 157 and is received by the light receiving element 158 as signal light.

  Information acquired by the light receiving element 158 is input to the information acquisition unit 159. The information acquisition unit 159 generates image information based on the information acquired by the light receiving element 158.

  The light receiving element 158 and the information acquisition unit 159 constitute a part of the detection unit of the measurement apparatus according to the present embodiment.

  The image information generated by the information acquisition unit 159 is displayed using the display unit 160 as necessary.

  The pump light P and Stokes light S output from the light source unit 150 may be scanned using a scanning unit (not shown). By appropriately scanning the condensing point, two-dimensional information and three-dimensional information of the subject 155 can be acquired.

  According to the present embodiment, since a mode-locked laser device that can emit stable high-power pump light and Stokes light is used in the light source unit 150, strong signal light can be stably obtained, and thus High-accuracy information about the subject 150 can be acquired.

  Moreover, since the excitation efficiency of the mode-locked laser device used in the light source unit 150 is high, the power consumption of the entire measuring device can be reduced.

[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications are possible.

  For example, in the above embodiment, the case of using the gain medium 4 made of a titanium sapphire crystal that can function as a mode locker has been described as an example, but other optical components that can function as a mode locker may be further used. For example, a mode locker of a saturable absorber whose transmittance varies depending on the intensity of the laser beam may be further used. Examples of such a saturable absorber include a dye, a semiconductor, a carbon nanotube, and graphene. Further, a mode locker composed of an AO element (Acousto Optical Element) may be further used. Such a mode locker may be appropriately disposed on the optical path of the first laser beam 1 or the optical path of the second laser beam 2.

  In the above embodiment, the prisms 11, 11a, and 11b for wavelength division are used for the optical path branching mechanism. However, the diffraction grating 14 may be used instead of the prisms 11, 11a, and 11b. FIG. 9 is a cross-sectional view showing a diffraction grating. Even when the diffraction grating 14 is used, the optical path of the first laser beam 1 and the optical path of the second laser beam 2 can be branched. For example, instead of the prism pairs 11a and 11b shown in FIGS. 3A, 3, 5, and 6, a diffraction grating pair including a pair of diffraction gratings 11 for wavelength division may be provided. Further, instead of one prism 11 shown in FIG. 7, one diffraction grating 14 for wavelength division may be arranged.

21, 22, 91 ... mirrors 23, 24, 12a, 92 ... concave mirror 12b ... convex mirror 12d ... convex lenses 25, 93 ... output coupler 111 ... optical path branching mechanism 12 ... beam waist adjusting mechanism 6, 96 ... excitation light source,
4, 94: Gain medium 1, 2, 95, 95a, 95b ... Laser beam 13: Prism mirror 11, 11a, 11b, 98 ... Prism 99 ... Double slit 97 ... Saturable absorber 115a-118a, 115b-118b ... Wave front DESCRIPTION OF SYMBOLS 100 ... Beam waist 113, 114 ... Beam outline shape 150 ... Light source part 154 ... Condensing optical system 155 ... Subject 156 ... Light condensing optical system 157 ... Band pass filter 158 ... Light receiving element 159 ... Information acquisition part

Claims (8)

A first mirror;
A second mirror;
An output coupler,
The first mirror is positioned on the optical path of the first laser beam that reciprocates between the first mirror and the output coupler, and reciprocates between the second mirror and the output coupler. A gain medium positioned on an optical path of a second laser beam having a center wavelength different from the center wavelength of the laser beam, wherein the beam waist of the first laser beam and the beam waist of the second laser beam are inside A gain medium located;
An excitation light source for exciting the gain medium;
Optical path branching arranged on the optical path of the first laser beam and on the optical path of the second laser beam and for branching the optical path of the first laser beam and the optical path of the second laser beam The optical path of the first laser beam and the optical path of the second laser beam coincide with each other between the output coupler and the optical path branching mechanism, and the optical path branching mechanism And the optical path of the first laser beam between the first mirror and the optical path of the second laser beam between the optical path branching mechanism and the second mirror are different from each other. An optical path branching mechanism;
The beam waist of the first laser beam and the second laser beam such that a region within the focal depth of the first laser beam and a region within the focal depth of the second laser beam are separated from each other. And a beam waist adjusting mechanism for adjusting a position of at least one of the beam waists. The beam waist adjustment mechanism is a concave mirror, a convex mirror, a concave lens, a convex lens, or a combination thereof,
The beam waist adjusting mechanism is disposed at least one of between the optical path branching mechanism and the first mirror and between the optical path branching mechanism and the second mirror. The mode-locked laser device according to claim 1. At least one of the first mirror and the second mirror is a concave mirror or a convex mirror,
The mode-locked laser device according to claim 1, wherein the concave mirror or the convex mirror also serves as the beam waist adjusting mechanism.   The mode-locked laser device according to claim 1, wherein the optical path branching mechanism includes a prism or a diffraction grating.   The mode-locked laser device according to any one of claims 1 to 3, wherein the optical path branching mechanism includes a prism pair or a diffraction grating pair.   6. The mode-locked laser device according to claim 4, wherein the optical path branching mechanism further includes a prism mirror. A light source unit that includes the mode-locked laser device according to any one of claims 1 to 6, and that emits the first laser beam and the second laser beam in a pulse shape,
A condensing optical system for condensing the first laser beam and the second laser beam and irradiating the subject;
And a detection unit that detects the first laser beam that has passed through the subject.   The measurement apparatus according to claim 7, wherein the measurement apparatus is a stimulated Raman scattering microscope that detects stimulated Raman scattering generated in the subject by the detection unit.

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