JP2016053616A - Optical parametric oscillator, light source unit, and microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable more efficient and more stable wavelength conversion of pump light even if the pump light has limited intensity.SOLUTION: An optical parametric oscillator of the present invention includes; a nonlinear optical crystal unit comprising a plurality of nonlinear crystals for converting a wavelength of incident pump light into a different wavelength by means of angle phase matching; and at least two resonator mirrors that form a focused beam of light. The nonlinear optical crystal unit consists of the plurality of nonlinear optical crystals disposed on a movable unit that moves along a predetermined movable axis, each nonlinear optical crystal having at least two or more crystal surfaces assigned as reference surfaces that are positioned relative to the movable axis. A phase matching angle of each nonlinear optical crystal as measured from a reference surface thereof is different from those of other nonlinear optical crystals. By moving the movable unit, one of the plurality of nonlinear optical crystals is placed within a Rayleigh length from the waist of the focused beam.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an optical parametric oscillator, a light source unit, and a microscope.

  In living body observation using a fluorescence microscope, in recent years, fluorescence has been generated from an observation object by multiphoton excitation of a phosphor contained in the observation object. As a light source of such a multiphoton excitation fluorescence microscope, a short pulse light source capable of freely selecting a wavelength is desired. As a method for converting the wavelength of short pulse light obtained from a short pulse light source, there is a method of an optical parametric oscillator using a nonlinear optical crystal.

  There are various non-linear optical crystals used for wavelength conversion. However, when phase matching is performed by a quasi-phase matching method using a domain-inverted crystal, the time walk-off is large, which is inconvenient. Therefore, it is preferable to change the phase matching angle using a nonlinear optical crystal by the angle phase matching method. One optical parametric oscillator using a nonlinear optical crystal by the angle phase matching method is provided with a mechanism for changing the crystal angle as disclosed in Patent Document 1 below.

  Further, Patent Document 2 below discloses an optical parametric oscillator that uses a plurality of nonlinear optical crystals based on an angle phase matching method and replaces these nonlinear optical crystals to enable wavelength conversion.

JP-A-63-184382 JP 2006-173526 A Japanese Patent Laid-Open No. 9-61866 JP 2001-66654 A

  However, as in the optical parametric oscillator disclosed in Patent Document 1, if the crystal angle is changed as it is, the conditions of the resonator change, and even if the configuration of the optical parametric oscillator is devised, the mechanism is It becomes complicated.

  In addition, when a plurality of nonlinear optical crystals are used interchangeably as disclosed in Patent Document 2, the resonance condition becomes unstable due to a mechanical arrangement error of the nonlinear optical crystal or a phase matching angle shift. Or the oscillation wavelength may deviate from the desired wavelength.

  Furthermore, when downsizing the optical parametric oscillator, it is desired that the optical parametric oscillator can oscillate efficiently even with low-power pump light. However, the methods disclosed in Patent Document 3 and Patent Document 4 have many losses. I had to use high-power pump light.

  Therefore, in the present disclosure, in view of the above circumstances, an optical parametric oscillator capable of performing wavelength conversion of pump light more efficiently and more stably even with limited intensity of pump light, A light source unit and a microscope using such an optical parametric oscillator are proposed.

  According to the present disclosure, a nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of incident pump light into different wavelengths by the angle phase matching method is disposed, and at least two that form a light condensing state The nonlinear optical crystal unit, wherein each of the plurality of nonlinear optical crystals is disposed with respect to a movable portion that operates based on a predetermined movable axis, and each of the nonlinear optical crystals Using at least two crystal planes as reference planes, the reference planes are positioned with respect to the movable axis, and the phase matching angles measured from the reference planes of the respective nonlinear optical crystals are the plurality of nonlinear At least two of the optical crystals are different from each other, and the movable part is movable, so that one of the plurality of nonlinear optical crystals is in the focused state. Part is disposed Rayleigh the length of the optical parametric oscillator is provided.

  Further, according to the present disclosure, a nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of incident pump light into different wavelengths by an angular phase matching method is disposed, and at least a light condensing state is formed. The nonlinear optical crystal unit, wherein each of the plurality of nonlinear optical crystals is arranged with respect to a movable part that operates based on a predetermined movable axis, With at least two crystal planes of the optical crystal as reference planes, the reference plane is positioned with respect to the movable axis, and the phase matching angle measured from the reference plane of each of the nonlinear optical crystals is At least two of the plurality of nonlinear optical crystals are different from each other, and the movable portion is movable, so that one of the plurality of nonlinear optical crystals is in the condensed state. It is disposed Rayleigh the length of Esuto portion, and an optical parametric oscillator with respect to the optical parametric oscillator, a laser light source that emits pump light of a predetermined wavelength, the light source unit comprising a are provided.

  Further, according to the present disclosure, a nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of incident pump light into different wavelengths by an angular phase matching method is disposed, and at least a light condensing state is formed. The nonlinear optical crystal unit, wherein each of the plurality of nonlinear optical crystals is arranged with respect to a movable part that operates based on a predetermined movable axis, With at least two crystal planes of the optical crystal as reference planes, the reference plane is positioned with respect to the movable axis, and the phase matching angle measured from the reference plane of each of the nonlinear optical crystals is At least two of the plurality of nonlinear optical crystals are different from each other, and the movable portion is movable, so that one of the plurality of nonlinear optical crystals is in the condensed state. An optical parametric oscillator disposed within the Rayleigh length of the estimator, and a laser source that emits pump light of a predetermined wavelength to the optical parametric oscillator, and a light source unit that is emitted from the light source unit There is provided a microscope including a microscope optical system that guides illumination light to an observation object and guides light from the observation object to a light detection unit.

  According to the present disclosure, a plurality of nonlinear optical crystals having different crystal orientations are used, and the plurality of nonlinear optical crystals are positioned with respect to the movable portion. By operating the movable part, one nonlinear optical crystal is arranged at the position where the light is collected, and the pump light is changed to signal light of a predetermined wavelength according to the crystal orientation of the arranged nonlinear optical crystal. And wavelength conversion.

  As described above, according to the present disclosure, it is possible to perform wavelength conversion of pump light more efficiently and more stably even if the intensity of the pump light is limited.

  Note that the above effects are not necessarily limited, and any of the effects shown in the present specification, or other effects that can be grasped from the present specification, together with or in place of the above effects. May be played.

FIG. 3 is a schematic diagram schematically illustrating an example of a configuration of an optical parametric oscillator according to an embodiment of the present disclosure. It is the schematic diagram which showed typically an example of the nonlinear optical crystal unit which concerns on the same embodiment. It is the schematic diagram which showed typically an example of the nonlinear optical crystal unit which concerns on the same embodiment. It is explanatory drawing for demonstrating the refractive index ellipsoid in a nonlinear optical crystal. It is explanatory drawing for demonstrating the nonlinear optical crystal unit which concerns on the same embodiment. It is explanatory drawing for demonstrating the nonlinear optical crystal unit which concerns on the same embodiment. It is explanatory drawing for demonstrating the walk-off amount in a nonlinear optical crystal. It is explanatory drawing for demonstrating the walk-off amount in a nonlinear optical crystal. It is explanatory drawing for demonstrating the optical thin film provided in the nonlinear optical crystal which concerns on the embodiment. It is explanatory drawing for demonstrating the optical thin film provided in the nonlinear optical crystal which concerns on the embodiment. It is the schematic diagram which showed typically another example of the nonlinear optical crystal unit which concerns on the same embodiment. It is the schematic diagram which showed typically another example of the nonlinear optical crystal unit which concerns on the same embodiment. It is the block diagram which showed typically the structure of the light source unit which has the optical parametric oscillator which concerns on the embodiment. It is the block diagram which showed typically an example of the laser light source used with the light source unit which concerns on the embodiment. It is the block diagram which showed typically an example of the laser light source used with the light source unit which concerns on the embodiment. It is the block diagram which showed typically an example of the laser light source used with the light source unit which concerns on the embodiment. It is a block diagram showing typically an example of a microscope which has a light source unit concerning the embodiment. FIG. 3 is a block diagram schematically illustrating an example of a hardware configuration of a control unit according to an embodiment of the present disclosure. 5 is a schematic diagram schematically showing an optical system of an optical parametric oscillator in Example 1 and Example 3. FIG. 6 is a schematic diagram schematically illustrating an optical system of an optical parametric oscillator in Example 2. FIG.

  Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

The description will be made in the following order.
1. 1. First embodiment 1.1. Configuration of optical parametric oscillator 1.2. Configuration of light source unit 1.3. Structure of microscope 1.4. 1. Hardware configuration of control unit Example

(First embodiment)
<Configuration of optical parametric oscillator>
First, the configuration of the optical parametric oscillator 10 according to the first embodiment of the present disclosure will be described in detail with reference to FIGS. 1 to 9B.
FIG. 1 is a schematic diagram schematically showing an example of the configuration of the optical parametric oscillator according to the present embodiment. 2A to 2B are schematic views schematically showing an example of the nonlinear optical crystal unit according to the present embodiment. FIG. 3 is an explanatory diagram for explaining a refractive index ellipsoid in a nonlinear optical crystal. 4-5 is explanatory drawing for demonstrating the nonlinear optical crystal unit based on this embodiment. 6-7 is explanatory drawing for demonstrating the walk-off amount in a nonlinear optical crystal. 8A to 8B are explanatory views for explaining an optical thin film provided in the nonlinear optical crystal according to the present embodiment. 9A to 9B are schematic views schematically showing another example of the nonlinear optical crystal unit according to the present embodiment.

[Overall Configuration of Optical Parametric Oscillator 10]
The optical parametric oscillator 10 according to the present embodiment includes a nonlinear optical crystal unit 11 and a resonator optical system, as schematically shown in FIG. As shown in FIG. 1, the resonator optical system includes at least two resonator mirrors 13A and 13B, various optical elements such as a pump light input coupler IC, a dichroic mirror DM, an end mirror EM, a signal light output coupler OC, and the like. And is composed of. In addition to these optical elements, the resonator optical system may be provided with known optical elements such as various lenses, mirrors and filters.

  The light guided into the optical parametric oscillator 10 is condensed on the optical axis connecting these resonator mirrors 13A and 13B by at least two resonator mirrors 13A and 13B. In addition, one of the plurality of nonlinear optical crystals provided in the nonlinear optical crystal unit 11 is disposed within the Rayleigh length of the waist portion where the formed light is condensed.

Here, the waist part of the light condensing state is a position where the beam radius is minimum in the light condensing state formed by the resonator mirrors 13A and 13B (so-called beam waist). )). The Rayleigh length means the distance in the optical axis direction from the beam waist (beam radius W ₀ ) to the position where the beam radius expands to 2 ^0.5 W ₀ .

  The end mirror EM and the signal light output coupler OC of the optical parametric oscillator 10 according to the present embodiment are each provided with a drive unit 15.

  Further, the overall operation of the optical parametric oscillator 10 including the nonlinear optical crystal unit 11 and the drive unit 15 is comprehensively controlled by the control unit 17.

  Laser light emitted from a laser light source (not shown) is guided from the pump light input coupler IC to the inside of the optical parametric oscillator 10 as pump light (pumping light). Thereafter, the pump light is dichroic mirror DM, resonator mirror 13A, nonlinear optical crystal unit 11, resonator mirror 13B, end mirror EM, resonator mirror 13B, nonlinear optical crystal unit 11, resonator mirror 13A, dichroic mirror DM, Follow the optical path of pump light input coupler IC. Such a first optical path functions as a first resonator for amplifying the pump light.

  Further, when the pump light passes through one nonlinear optical crystal in the nonlinear optical crystal unit 11, light having a wavelength different from that of the excitation light, ie, signal light and idler light, is generated. The optical parametric oscillator 10 according to the present embodiment can extract signal light to the outside and use it as a light source, or can extract idler light to the outside and use it as a light source. Hereinafter, a case where signal light is extracted to the outside will be described as an example.

  The signal light generated from the nonlinear optical crystal in the nonlinear optical crystal unit 11 is a resonator mirror 13B, end mirror EM, resonator mirror 13B, nonlinear optical crystal unit 11, resonator mirror 13A, dichroic mirror DM, signal light output coupler. The optical path of OC, dichroic mirror DM, resonator mirror 13A, nonlinear optical crystal unit 11... The second optical path functions as a second resonator that generates output light (signal light in this description) and amplifies the intensity of the output light.

  Here, the nonlinear optical crystal unit 11 according to the present embodiment is provided with a plurality of nonlinear optical crystals, and when the movable unit 103 is driven under the control of the control unit 17, there is one nonlinear nonlinear crystal. An optical crystal is disposed in the light collection state. In the nonlinear optical crystal unit 11 according to this embodiment, the condition of the resonator is stabilized by disposing the nonlinear optical crystal in the light condensing state (more specifically, in the Rayleigh length of the waist portion). Can be maintained. The detailed configuration of the nonlinear optical crystal unit 11 will be described in detail later.

  Further, the resonator mirrors 13A and 13B (hereinafter collectively referred to as the resonator mirror 13), the pump light input coupler IC, the end mirror EM, and the signal light output coupler OC are not particularly limited, and are publicly known. You can use something. The dichroic mirror DM is not particularly limited as long as it has a low loss with respect to both the pump light and the output light, and a publicly known one can be used.

  Thus, the optical parametric oscillator 10 according to the present embodiment is a biaxial optical system having the two optical paths as described above. In addition, in the first resonator corresponding to the first optical path and the second resonator corresponding to the second optical path, one end of the optical element constituting each resonator is shared by the end mirror EM. The other end is a pump light input coupler IC in the case of the first resonator, and a signal light output coupler OC in the case of the second resonator.

  The optical parametric oscillator 10 according to the present embodiment introduces such a pan resonant system, so that the pump light and the OPO (Optical Parametric Oscillator) light (more specifically, two optical parametric oscillators) are provided inside the optical parametric oscillator 10. It is required to resonate at least one of the oscillation light. Here, for “resonance”, resonance is performed so that each light circulates in the resonator at a timing completely coincident with the oscillation period of a laser (for example, a semiconductor pulse laser) that is a light source of pump light. It is required to adjust the device length (that is, the optical path lengths of the two types of optical paths) (oscillation condition A).

  However, since the optical parametric oscillator 10 includes a nonlinear optical crystal as described later, the optical distance changes according to the wavelength of light due to chromatic dispersion of the crystal. As a result, it is effective to introduce the biaxial optical system as described above with different optical paths so that pump light and OPO light having different wavelengths satisfy the oscillation condition A.

  In order to adjust the optical path lengths of the two resonators, a drive unit 15 such as a servo mechanism is provided for the end mirror EM located at one end of the first optical path, and the other end of the second optical path. A drive unit 15 such as a servo mechanism is provided for the signal light output coupler OC located at the end of the signal light. Here, the drive units 15 provided in the end mirror EM and the signal light output coupler OC can be controlled independently of each other. By providing such a drive unit 15 and controlling the drive unit 15 by the control unit 17, it is possible to control the optical path length of the first optical path and the optical path length of the second optical path independently of each other. It becomes.

  Here, the control method of the optical path length of the first optical path by the drive unit 15 is not particularly limited. For example, the position of the end mirror EM that realizes an appropriate optical path length is stored in a data format such as a table. In addition, the position of the end mirror EM may be controlled so as to hold the position. It is also possible to use a known control method such as detecting the intensity of the reflected light of the pump light from the optical parametric oscillator 10 at any time and controlling the position of the end mirror EM according to the detected intensity of the reflected light. It is.

  Further, the method for controlling the optical path length of the second optical path by the driving unit 15 is not particularly limited. For example, an appropriate optical path length is set for each nonlinear optical crystal (in other words, for each wavelength of the signal light). The position of the signal light output coupler OC to be realized may be stored in a data form such as a table, and the position of the signal light output coupler OC may be controlled so as to hold the position. It is also possible to use a known control method such as detecting the intensity of the signal light inside the optical parametric oscillator 10 at any time and controlling the position of the signal light output coupler OC according to the detected intensity of the signal light. It is.

  The drive unit 15 as described above is not particularly limited, and a known drive mechanism such as a voice coil motor or a piezoelectric element can be used.

  In the above description, the case where the optical path length of the first optical path is adjusted by controlling the position of the end mirror EM with the drive unit 15 has been described. However, the end mirror EM is fixed and the pump light input coupler IC is fixed. These positions may be controlled by the drive unit 15.

  The control unit 17 is a unit realized by, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The control unit 17 is a processing unit that generally controls the operation of the optical parametric oscillator 10, and controls various units constituting the optical parametric oscillator 10. For example, the control unit 17 controls the movable unit 103 of the nonlinear optical crystal unit 11 to be described later in response to a user operation so that the nonlinear optical crystal that provides the signal light wavelength desired by the user enters the light collection state. And move. In addition, the control unit 17 controls the driving unit 15 provided in the optical element constituting the resonator optical system to maintain an appropriate optical path length for each of the pump light and the signal light.

  The control unit 17 may be realized by an information processing device such as a personal computer or various servers connected to the optical parametric oscillator 10, or may be an IC chip or an arithmetic processing board mounted in the optical parametric oscillator 10. Etc. may be realized. Moreover, the control part 17 can further control the function of various apparatuses (for example, a laser light source, a microscope unit, etc.) connected to the optical parametric oscillator 10 as needed.

  The overall configuration of the optical parametric oscillator 10 according to the present embodiment has been described above with reference to FIG.

  In FIG. 1, a so-called Bowtie type optical arrangement is shown as the resonator optical system, but the resonator optical system is not limited to the example shown in FIG. It may be an arrangement.

[Configuration of Nonlinear Optical Crystal Unit 11]
Next, the configuration of the nonlinear optical crystal unit 11 included in the optical parametric oscillator 10 according to the present embodiment will be described in detail with reference to FIGS.

  The nonlinear optical crystal unit 11 according to the present embodiment includes a plurality of nonlinear optical crystals 101 and a movable portion 103 as schematically shown in FIGS. 2A and 2B.

The nonlinear optical crystal 101 is a crystal that converts the wavelength of incident pump light into a different wavelength by the angle phase matching method. For such a nonlinear optical crystal 101, usable crystals are determined according to the wavelength of the pump light. For example, when blue light is used as pump light, the nonlinear optical crystal 101 includes BBO (β-BaB ₂ O ₄ ), LBO (LiB ₃ O ₅ ), BiBO (BiB ₃ O ₆ ), LN (LiNbO ₃ ), Known non-linear optical crystals for blue light such as LT (LiTaO ₃ ), KTP (KTiOPO ₄ ) and the like can be used. Further, when light other than blue light is used as the pump light, a known nonlinear optical crystal corresponding to the wavelength of the pump light may be used.

  The movable portion 103 is a member that can be operated based on a predetermined movable shaft. At least one surface of the movable portion 103 is processed to be a flat surface, and a plurality of nonlinear optical crystals 101 are disposed on the flat surface. The method for fixing the nonlinear optical crystal 101 on the flat surface is not particularly limited, and a known method can be used. Further, the shape of the movable portion 103 is not particularly limited, and may be a polygonal shape or a substantially circular shape as long as a plurality of nonlinear optical crystals 101 can be installed. Also good.

  Hereinafter, for the sake of convenience, description will be made assuming that the movable portion 103 has a rectangular parallelepiped shape as shown in FIGS. 2A and 2B. For convenience of explanation, the direction parallel to the traveling direction of the laser beam is defined as an a axis, the arrangement direction of the plurality of nonlinear optical crystals 101 (in other words, the longitudinal direction of the movable portion 103) is defined as the b axis, and the movable portion. Let the height direction of 103 be a c-axis.

  In the example shown in FIGS. 2A and 2B, the movable axis of the movable portion 103 is set to be parallel to the b-axis direction, and a plurality of nonlinear optical crystals 101 are arranged along the b-axis direction. Accordingly, when the movable portion 103 slides along the b-axis which is a movable axis, one of the plurality of nonlinear optical crystals 101 is selected, and laser light is incident.

  In the nonlinear optical crystal unit 11 according to this embodiment, each of the plurality of nonlinear optical crystals 101 has at least two crystal faces of the nonlinear optical crystal as reference planes, and the reference planes are positioned with respect to the movable shaft. Yes. In the case of the nonlinear optical crystal unit 11 shown in FIG. 2A and FIG. 2B, a bc plane defined by the b-axis and the c-axis and a plane parallel to the ac plane defined by the a-axis and the c-axis are used as two references. It is a surface. In addition, these reference planes in the plurality of nonlinear optical crystals 101 are positioned with respect to the b-axis which is a movable axis.

  By transmitting the pump light to the nonlinear optical crystal 101, output light having a wavelength different from that of the pump light can be obtained. In general, the wavelength of the output light generated by the nonlinear optical crystal 101 can be switched by controlling the installation angle or temperature of the nonlinear optical crystal. In the nonlinear optical crystal 101 according to the present embodiment, output light having a wavelength different from that of the pump light is generated from the incident pump light by controlling an angle related to the nonlinear optical crystal. Hereinafter, the wavelength conversion mechanism in the nonlinear optical crystal unit 11 according to the present embodiment will be specifically described with reference to FIGS.

  The nonlinear optical crystal 101 is a crystal having birefringence, and an index ellipsoid as shown in FIG. 3 can be considered to show the anisotropy of the refractive index. . Here, in FIG. 3, k is a wave vector, D is a vector representing the electric flux density, E is a vector representing the electric field, and S is a pointing vector representing the traveling direction of energy. .

  In the nonlinear optical crystal unit 11 according to the present embodiment, the crystal orientation of the nonlinear optical crystal 101 and the pump are changed by making the cut-out directions of the crystal orientation of the nonlinear optical crystal different from each other among at least two of the plurality of nonlinear optical crystals 101. The relative angular relationship with light is changed between at least two of the plurality of nonlinear optical crystals 101. Accordingly, as schematically shown in FIGS. 2A, 2B, and 4, even if the installation angle to the movable portion 103 is the same, the refractive index ellipsoid between at least two of the nonlinear optical crystals 101 is obtained. Will be different from each other. As a result, in the nonlinear optical crystal unit 11 according to the present embodiment, the phase matching angle measured from the reference plane (bc plane in FIG. 2A) of the nonlinear optical crystal 101 is between at least two of the plurality of nonlinear optical crystals 101. Different from each other. Thereby, in the nonlinear optical crystal unit 11 according to the present embodiment, the wavelength of the output light to be obtained can be made different between at least two of the plurality of nonlinear optical crystals 101 based on the phase matching condition. In the nonlinear optical crystal unit 11 according to the present embodiment, it is more preferable that the phase matching angles measured from the reference plane of the nonlinear optical crystal 101 are different from each other among all of the plurality of nonlinear optical crystals 101. Thereby, in the nonlinear optical crystal unit 11 according to the present embodiment, the wavelength of the output light obtained can be made different among all of the plurality of nonlinear optical crystals 101 based on the phase matching condition.

  Further, as schematically shown in FIGS. 2A and 2B, the crystal lengths (lengths in the a-axis direction) of the respective nonlinear optical crystals 101 are made equal to each other between the nonlinear optical crystals 101. Thereby, the cavity length of the resonator can be maintained at a certain length.

  Here, in the optical parametric oscillator 10 according to the present embodiment, as schematically shown in FIG. 5, the condensing angle of the pump light condensed on each nonlinear optical crystal 101 is the phase of the nonlinear optical crystal 101. The resonant optical system is adjusted so as to be larger than the matching allowable angle.

  In the conventional optical parametric oscillator, pump light with high intensity is used in consideration of the phase matching allowable angle (angle allowable width), and the light collecting angle of the pump light is made narrower than the allowable angle to condense shallowly. Has been done. In such a case, the conversion efficiency is maintained by increasing the length of the nonlinear optical crystal (the length along the optical axis of the pump light) in order to compensate for the narrowness of the light collection angle. However, when the length of the nonlinear optical crystal is increased, the beam pointing changes due to a slight structural accuracy error or a positional shift caused by a change in the walk-off between a plurality of nonlinear optical crystals. It becomes difficult to reproduce the oscillation state.

  On the other hand, in the optical parametric oscillator 10 according to the present embodiment, the condensing angle of the pump light is made larger than the allowable angle, contrary to the conventional case. As a result, the crystal length of the nonlinear optical crystal 101 can be made shorter than before, and optical parametric oscillation can be realized more stably and efficiently.

  Hereinafter, the advantages that can be obtained by making the collection angle of the pump light larger than the allowable angle will be described in detail with reference to FIGS. 6 and 7.

  As described above, when the cut-out angle of the crystal orientation of the nonlinear optical crystal 101 is changed in order to convert the wavelength of the pump light, the direction of the refractive index ellipsoid changes inside the crystal. On the other hand, if the wave vector k of the pump light incident on the nonlinear optical crystal 101 is always directed in the same direction, the nonlinear optical crystal 101 having different cut-out angles due to a change in the orientation of the refractive index ellipsoid with respect to the wave vector k. , The direction of the pointing vector S changes. Therefore, the magnitude of the walk-off angle φ (see FIG. 3) defined as the angle formed by the wave vector k and the pointing vector S differs between the nonlinear optical crystals 101. When the crystal length of the nonlinear optical crystal 101 is L and the walk-off angle is φ [rad], the walk-off amount d at the end of the nonlinear optical crystal is expressed by d = L · φ. Therefore, if the walk-off angle φ differs between the nonlinear optical crystals 101, a beam position shift corresponding to the walk-off amount d occurs between the crystals.

  Now, as schematically shown in FIG. 6, it is assumed that there are two nonlinear optical crystals 101 having different cutting angles in the crystal direction. In the nonlinear optical crystal A having a walk-off angle φ, if the crystal length is L2, the walk-off amount d2 = L2 · φ at a = L2. On the other hand, as in the nonlinear optical crystal unit 11 according to the present embodiment, when the condensing angle of the pump light is larger than the allowable angle, the light density in the nonlinear optical crystal 101 increases, and even if the crystal length is shortened, the light is stable. Wavelength conversion can be realized. Now, assuming that the crystal length of the nonlinear optical crystal A becomes L1 (<L2), the walk-off amount d1 = L1 · φ at a = L1, and the walk-off amount d is suppressed to a smaller value than the conventional nonlinear optical crystal. can do.

  On the other hand, in the nonlinear optical crystal B having a walk-off angle φ ′ (> φ), if the crystal length is L2, the walk-off amount d2 = L2 · φ ′ at a = L2 and the walk-off at a = L1. The quantity d1 = L1 · φ ′.

  As in the prior art, when the crystal length of the nonlinear optical crystal is L2, the deviation of the beam position between the nonlinear optical crystal A and the nonlinear optical crystal B at a = L2 can be expressed as a change in the walk-off amount d. The beam position deviation amount Δd = | d2 (A) −d2 (B) |. On the other hand, in the nonlinear optical crystal unit 11 according to the present embodiment, since the crystal length can be shortened, for example, when the crystal length can be reduced to L1 as shown in FIG. 6, the deviation amount Δd of the beam position. = | D1 (A) -d1 (B) | As a result, in the nonlinear optical crystal unit 11 according to the present embodiment, the deviation Δd of the beam position between the nonlinear optical crystals 101 can be suppressed to an extremely small value. Thereby, even if the allowable angle for phase matching and the beam radius of the pump light are reduced, it is possible to suppress the deviation Δd of the beam position between the nonlinear optical crystals 101.

  Here, it is assumed that when the Gaussian beam is formed in the resonator, a deviation of the beam position due to the walk-off as described above occurs, and the two Gaussian beams when the deviation amount is Δs. The magnitude of the overlap integral was calculated. The obtained results are shown in FIG.

As shown on the left side of FIG. 7, the beam radius r of the Gaussian beam is defined as a position where the beam intensity is 1 / e ² (about 13.5%) of the beam intensity at the center 0. As shown in the upper right part of FIG. 7, when Δs = r / 2, the magnitude of the overlap integral is about 80% or more, and the Gaussian beam after the shift almost overlaps the beam position before the shift. I understood it. This result means that wavelength conversion is efficiently realized when Δs = r / 2 or less.

  On the other hand, as shown in the lower right part of FIG. 7, when Δs = r, it was found that the size of the overlap integral is about 36%, and the beam mode becomes unstable. This result means that the efficiency of wavelength conversion decreases when Δs = r or more.

  From the results shown in FIG. 7, the beam shift is suppressed to ¼ of the beam diameter by making the deviation Δd of the beam position between the nonlinear optical crystals smaller than the half value of the beam radius r of the waist portion, and It can be seen that more than half of the intensity ratio overlaps the beam path before the shift. Therefore, by setting Δd ≦ r / 2 between the nonlinear optical crystals 101, a stable resonance state is maintained and wavelength conversion becomes possible.

  Actually, when the beam waist is located at the crystal center of the nonlinear optical crystal, the beam radius is expanded by defocus at the crystal end face. However, under the above condition (Δd ≦ r / 2), even if the beam waist is positioned on the end face of the nonlinear optical crystal 101, the path of the beam after the shift overlaps the path before the shift. Therefore, it is possible to perform wavelength conversion while maintaining a stable resonance state.

  Here, it is more preferable that the deviation Δd of the beam position between the nonlinear optical crystals is 10% or less of the half value of the beam radius r of the pump light. The wavelength conversion efficiency can be further improved by setting the amount of deviation Δd to 10% or less of the half value of the beam radius r of the pump light. Note that the lower limit value of the beam position deviation amount Δd is not particularly specified, and it is needless to say that the smaller the better, the smaller the lower limit value is.

  In the nonlinear optical crystal unit 11 according to the present embodiment, the resonator optical system is first adjusted for the nonlinear optical crystal 101 corresponding to the wavelength at which the signal light is less likely to oscillate among the plurality of nonlinear optical crystals 101. Select stable optical system conditions. At this time, the movable condition of the movable portion 103 is adjusted so that each nonlinear optical crystal 101 is disposed at the beam condensing position. Then, the resonator optical system is further adjusted while comparing whether or not wavelength conversion is realized in the nonlinear optical crystal 101 corresponding to the counter wavelength. Specifically, after determining the type and crystal length of the nonlinear optical crystal 101 to be used, the resonator optical system is first adjusted for wavelengths that are difficult to oscillate. Thereafter, the curvature of the mirror surfaces of the resonator mirrors 13A and 13B is adjusted and the distance between the resonator mirrors 13A and 13B is adjusted so that wavelength conversion is realized in the nonlinear optical crystal 101 corresponding to the counter wavelength. Thus, the resonator optical system is adjusted so that Δd ≦ r / 2 between all the nonlinear optical crystals 101.

  By adjusting the optical system as described above, each nonlinear optical crystal 101 is disposed at the beam condensing position, and the resonator conditions can be stably maintained. Further, by increasing the condensing angle of the pump light beyond the allowable angle of the nonlinear optical crystal 101, Δd, which is a conversion amount of the beam position shift amount, is reduced with a short crystal length, and each nonlinear optical crystal 101 is stabilized. A condition capable of oscillating signal light can be realized. Furthermore, by satisfying the condition of Δd ≦ r / 2, the oscillation state can be stably maintained even when the nonlinear optical crystal 101 is replaced by operating the movable portion 103.

  In order to realize more stable wavelength conversion, in each nonlinear optical crystal 101, the beam position shift amount due to the positioning error on the movable portion 103 in positioning is the beam position shift accompanying the walk-off as described above. It is preferable to be smaller than the amount of change Δd.

  The wavelength conversion mechanism in the nonlinear optical crystal unit 11 according to this embodiment has been specifically described above with reference to FIGS.

Here, in the nonlinear optical crystal 101 according to the present embodiment, in order to minimize the loss of efficiency and further reduce the oscillation threshold, as shown schematically in FIG. 8A, the optical functioning as an antireflection film is used. It is preferable to form the thin film 111. Here, regarding the refractive index n and the film thickness d _L of the optical thin film 111, optimum conditions are individually set according to the wavelength of the signal light corresponding to each nonlinear optical crystal 101.

  Further, as schematically shown in FIG. 8B, the optical thin film 111 may be composed of two thin films 111a and 111b, or may be composed of three or more thin films.

Next, a modification of the movable unit 103 according to the present embodiment will be briefly described with reference to FIGS. 9A and 9B.
In the above description, the case where the replacement of the plurality of nonlinear optical crystals 101 is realized by moving the rectangular movable unit 103 along the movable axis is taken as an example. Here, in the nonlinear optical crystal unit 11 shown in FIGS. 2A and 2B, a plurality of nonlinear optical crystals 11 are arranged along the c-axis direction, and the movable axis is set to be parallel to the c-axis direction. Needless to say, it's also good. Further, the shape of the movable portion 103 is not limited to that shown in FIGS. 2A and 2B, and may be a disk shape as shown in FIG. 9A.

  When the shape of the movable part 103 is a disk shape as shown in FIG. 9A, the movable axis of the movable part 103 is set to be coaxial with the central axis of the disk. In this case, when the movable portion 103 rotates around the movable shaft, one of the plurality of nonlinear optical crystals 101 disposed on the surface of the disk is disposed at the laser light condensing position. It will be.

  The method for fixing the nonlinear optical crystal 101 on the disk surface is not particularly limited. However, in order to fix the nonlinear optical crystal 101 more stably, as shown in FIG. 9B, the concave portion 105 is provided in the movable portion 103, and the nonlinear optical crystal 101 is fitted into the concave portion 105, so that the nonlinear optical crystal 101 is fixed. Is preferably fixed.

  The modification examples of the movable unit 103 according to the present embodiment have been briefly described above with reference to FIGS. 9A and 9B.

<About the configuration of the light source unit>
Next, the configuration of the light source unit having the optical parametric oscillator 10 as described above will be briefly described with reference to FIGS. 10 to 11C.
FIG. 10 is a block diagram schematically showing a configuration of a light source unit having the optical parametric oscillator according to the present embodiment. 11A to 11C are block diagrams schematically showing an example of a laser light source used in the light source unit according to the present embodiment.

  A light source unit can be realized using the optical parametric oscillator 10 as described above. As schematically shown in FIG. 10, the light source unit includes the optical parametric oscillator 10 described above and a laser light source 20 provided in the preceding stage of the optical parametric oscillator 10. In the light source unit 30, pump light having a predetermined wavelength emitted from the laser light source 20 is guided to the optical parametric oscillator 10 by optical elements (not shown) such as various lenses, mirrors, filters, and the like. Thereafter, the optical parametric oscillator 10 converts the light into a signal light having a wavelength different from that of the pump light, and the signal light is extracted outside the light source unit 30.

  Here, the laser light source 20 is not particularly limited, and may be a pulse laser or a CW laser as long as it has a laser power capable of realizing optical parametric oscillation. Also, the type of the laser light source 20 is not particularly limited, and may be various solid lasers, gas lasers, or various semiconductor lasers. However, since the optical parametric oscillator 10 according to the present embodiment can perform wavelength conversion efficiently and stably even with a smaller laser power, a light source unit can be obtained by using a semiconductor laser as the laser light source 20. 30 miniaturizations can be realized.

  Further, the laser light source 20 may further be provided with a control driver for controlling oscillation of pump light from the laser light source 20. The control unit 17 of the optical parametric oscillator 10 may also serve as a control driver for the laser light source 20.

  As an example of a semiconductor laser that can be used as the laser light source 20, for example, a semiconductor laser as shown in FIGS. 11A to 11C can be used.

  FIG. 11A schematically shows a main oscillator 201 composed of a semiconductor laser and a resonator, which is an example of a semiconductor laser applicable to a laser light source unit. The main oscillator 201 used as the laser light source 20 includes a semiconductor laser unit 203 capable of emitting laser light having a predetermined wavelength (for example, wavelength 405 nm), and a resonator unit for amplifying the laser light emitted from the semiconductor laser unit 203. 205.

  FIG. 11B is an example of a semiconductor laser applicable to the laser light source unit, and is a main oscillator composed of a semiconductor laser and a resonator, and an optical amplifier that amplifies laser light from the main oscillator. 1 schematically shows a light source having an oscillator output amplifier (MOPA). In such a light source, an optical amplifier 211 for further amplifying the emitted laser light is provided after the main oscillator 201 shown in FIG. 11A. As the optical amplifier 211, for example, a semiconductor optical amplifier (SOA) or the like can be preferably used.

  FIG. 11C schematically shows a light source having a main oscillator 201, an optical amplifier 211, and a beam shape correcting unit 213, which is an example of a semiconductor laser applicable to the laser light source unit. In such a light source, a beam shape correction unit 213 for correcting the beam shape of the laser light is provided after the optical amplifier 211 shown in FIG. 11B. By correcting the beam shape of the laser light by the beam shape correcting unit 213, the wavelength conversion efficiency in the optical parametric oscillator 10 can be further improved.

  The configuration of the light source unit 30 including the optical parametric oscillator 10 according to the present embodiment has been briefly described above with reference to FIGS. 10 to 11C.

<About the structure of the microscope>
Next, a configuration of a microscope using the light source unit 30 having the optical parametric oscillator 10 as described above will be briefly described with reference to FIG.
FIG. 12 is a block diagram schematically showing an example of a microscope having the light source unit according to the present embodiment.

  A microscope can be realized using the light source unit 30 having the optical parametric oscillator 10 as described above. As schematically shown in FIG. 12, the microscope guides the light source unit 30 having the optical parametric oscillator 10 and the laser light source 20, and the illumination light emitted from the light source unit 30 to the observation object. A microscope optical system 40 that guides light from the observation object to the light detection unit.

  The signal light emitted from the light source unit 30 is guided to the microscope optical system 40. In the microscope optical system 40, the signal light is guided to the XY-galvano mirror XY-gal via the lens L and the mirror M, and the sample (observation object) placed on the stage by the galvano mirror. The imaging position is controlled.

  The signal light that has passed through the galvanometer mirror is guided to the objective lens Obj through the relay lens RL, mirror M, and dichroic mirror DM, and the signal light that has passed through the objective lens Obj is irradiated onto the sample placed on the stage. Is done.

  Light emitted from the sample (for example, fluorescence generated by the interaction between the sample and signal light) is guided to the photodetector through the objective lens Obj, dichroic mirror DM, lens L, notch filter F, and the like. To be lighted.

  Here, the photodetector provided in the microscope optical system 40 is not particularly limited, and may be appropriately selected from known photodetectors according to the type of light to be observed. For example, when fluorescence generated from an observation object is an observation object, various detectors such as a CCD (Charge-Coupled Device) or a photomultiplier tube (PMT) may be used as the photodetector. Good.

  By using the microscope optical system 40 having such a configuration in combination with the light source unit 30, various microscopes 50 such as a multiphoton excitation fluorescence microscope can be realized.

<About hardware configuration>
Next, the hardware configuration of the control unit 17 according to the embodiment of the present disclosure will be described in detail with reference to FIG. In the following, the hardware configuration of the control unit 17 according to the embodiment of the present disclosure will be described in detail with an example in which the control unit 17 is realized by an information processing apparatus such as a personal computer or various servers. FIG. 13 is a block diagram for describing a hardware configuration of the control unit 17 according to the embodiment of the present disclosure.

  The control unit 17 mainly includes a CPU 901, a ROM 903, and a RAM 905. The control unit 17 further includes a host bus 907, a bridge 909, an external bus 911, an interface 913, an input device 915, an output device 917, a storage device 919, a drive 921, and a connection port 923. And a communication device 925.

  The CPU 901 functions as an arithmetic processing unit and a control unit, and controls all or a part of the operation in the control unit 17 according to various programs recorded in the ROM 903, the RAM 905, the storage device 919, or the removable recording medium 927. The ROM 903 stores programs used by the CPU 901, calculation parameters, and the like. The RAM 905 primarily stores programs used by the CPU 901, parameters that change as appropriate during execution of the programs, and the like. These are connected to each other by a host bus 907 constituted by an internal bus such as a CPU bus.

  The host bus 907 is connected to an external bus 911 such as a PCI (Peripheral Component Interconnect / Interface) bus via a bridge 909.

  The input device 915 is an operation unit operated by the user, such as a mouse, a keyboard, a touch panel, a button, a switch, and a lever. The input device 915 may be, for example, remote control means (so-called remote control) using infrared rays or other radio waves, or an external connection device 929 such as a mobile phone or a PDA corresponding to the operation of the control unit 17. It may be. Furthermore, the input device 915 includes an input control circuit that generates an input signal based on information input by a user using the above-described operation means and outputs the input signal to the CPU 901, for example. The user of the control unit 17 can input various data and instruct processing operations to the control unit 17 by operating the input device 915.

  The output device 917 is configured by a device capable of visually or audibly notifying acquired information to the user. Examples of such devices include CRT display devices, liquid crystal display devices, plasma display devices, EL display devices and display devices such as lamps, audio output devices such as speakers and headphones, printer devices, mobile phones, and facsimiles. The output device 917 outputs, for example, results obtained by various processes performed by the control unit 17. Specifically, the display device displays the results obtained by various processes performed by the control unit 17 as text or images. On the other hand, the audio output device converts an audio signal composed of reproduced audio data, acoustic data, and the like into an analog signal and outputs the analog signal.

  The storage device 919 is a data storage device configured as an example of a storage unit of the control unit 17. The storage device 919 includes, for example, a magnetic storage device such as an HDD (Hard Disk Drive), a semiconductor storage device, an optical storage device, or a magneto-optical storage device. The storage device 919 stores programs executed by the CPU 901, various data, various data acquired from the outside, and the like.

  The drive 921 is a recording medium reader / writer, and is built in or externally attached to the control unit 17. The drive 921 reads information recorded on a removable recording medium 927 such as a mounted magnetic disk, optical disk, magneto-optical disk, or semiconductor memory, and outputs the information to the RAM 905. In addition, the drive 921 can write a record on a removable recording medium 927 such as a magnetic disk, an optical disk, a magneto-optical disk, or a semiconductor memory. The removable recording medium 927 is, for example, a DVD medium, an HD-DVD medium, a Blu-ray (registered trademark) medium, or the like. Further, the removable recording medium 927 may be a CompactFlash (registered trademark) (CompactFlash: CF), a flash memory, an SD memory card (Secure Digital memory card), or the like. Further, the removable recording medium 927 may be, for example, an IC card (Integrated Circuit card) on which a non-contact IC chip is mounted, an electronic device, or the like.

  The connection port 923 is a port for directly connecting a device to the control unit 17. Examples of the connection port 923 include a USB (Universal Serial Bus) port, an IEEE 1394 port, a SCSI (Small Computer System Interface) port, and the like. As another example of the connection port 923, there are an RS-232C port, an optical audio terminal, a high-definition multimedia interface (HDMI) port, and the like. By connecting the external connection device 929 to the connection port 923, the control unit 17 acquires various data directly from the external connection device 929 or provides various data to the external connection device 929.

  The communication device 925 is a communication interface including a communication device for connecting to the communication network 931, for example. The communication device 925 is, for example, a communication card for a wired or wireless LAN (Local Area Network), Bluetooth (registered trademark), or WUSB (Wireless USB). The communication device 925 may be a router for optical communication, a router for ADSL (Asymmetric Digital Subscriber Line), or a modem for various communication. The communication device 925 can transmit and receive signals and the like according to a predetermined protocol such as TCP / IP, for example, with the Internet or other communication devices. The communication network 931 connected to the communication device 925 is configured by a wired or wireless network, and may be, for example, the Internet, a home LAN, infrared communication, radio wave communication, satellite communication, or the like. .

  Heretofore, an example of a hardware configuration capable of realizing the function of the control unit 17 according to the embodiment of the present disclosure has been shown. Each component described above may be configured using a general-purpose member, or may be configured by hardware specialized for the function of each component. Therefore, it is possible to change the hardware configuration to be used as appropriate according to the technical level at the time of carrying out this embodiment.

  Next, the optical parametric oscillator according to the embodiment of the present disclosure will be specifically described with reference to examples. Note that the following example is merely an example of the optical parametric oscillator according to the embodiment of the present disclosure, and the optical parametric oscillator according to the embodiment of the present disclosure is not limited to the following example.

<Example 1>
A Z-type arrangement shown in FIG. 14 was adopted as the resonator optical system, and an LBO (LiB ₃ O ₅ ) crystal having a crystal length of 8 mm was used as the nonlinear optical crystal 101.

  The concave mirrors used as the resonator mirrors 13A and 13B have a radius of curvature R = 30 mm so that the converging angle on the nonlinear optical crystal 101 is about 8 mrad, and the configuration of the cavity was examined. As a light source for pump light, a mode-locked light source having a wavelength of 405 nm shown in FIG. 11A was used.

  One LBO crystal is a nonlinear optical crystal 101A that oscillates light with wavelengths of 900 nm and 740 nm (matching angle 30.4 °), and another LBO crystal is a nonlinear optical that oscillates light with wavelengths of 1200 nm and 610 nm. Crystal 101 was obtained (matching angle 27.0 °). On top of that, light with wavelengths of 900 nm and 1200 nm was used as resonating signal light, and light with wavelengths of 740 nm and 610 nm was used as idler light.

  In the case of the LBO crystal having the matching angle as described above, the walk-off angles are 16.1 mrad and 15.0 mrad. Therefore, the deviation Δd of the beam position due to the walk-off is 9 μm when the crystal length is 8 mm. Therefore, in this embodiment, the resonator optical system is configured so that the half value of the beam radius at the waist is 13 μm. In this resonator optical system, the allowable angle for phase matching of the pump light is 3 mrad at full width at half maximum.

  Further, the non-linear optical crystal 101A and the non-linear optical crystal 101B were exchanged using a rotation mechanism as shown in FIG. 9A.

  At this time, even when the two nonlinear optical crystals 101A and 101B were exchanged by a rotation mechanism, stable oscillation was confirmed with signal lights having wavelengths of 900 nm and 1200 nm, respectively.

<Example 2>
As the resonator optical system, the Bowtie type arrangement shown in FIG. 15 was adopted, and as the nonlinear optical crystal 101, an LBO (LiB ₃ O ₅ ) crystal having a crystal length of 3 mm was used.

  The concave mirrors used as the resonator mirrors 13A and 13B have a radius of curvature R = 25 mm so that the converging angle on the nonlinear optical crystal 101 is about 10 mrad, and the configuration of the cavity was examined. In addition, a mode-locked light source having a wavelength of 405 nm shown in FIG. 11A was used as a light source for pump light.

  One LBO crystal is a nonlinear optical crystal 101A that oscillates light with wavelengths of 820 nm and 800 nm (matching angle 30.4 °), and another LBO crystal is a nonlinear optical that oscillates light with wavelengths of 1200 nm and 610 nm. Crystal 101 was obtained (matching angle 27.0 °). In addition, light having wavelengths of 820 nm and 1200 nm was used as resonating signal light, and light having wavelengths of 800 nm and 610 nm was used as idler light.

  In the case of the LBO crystal having the matching angle as described above, the walk-off angles are 16.2 mrad and 15.0 mrad. Accordingly, the deviation Δd of the beam position due to the walk-off is 4 μm when the crystal length is 3 mm. Therefore, in this embodiment, the resonator optical system is configured so that the half value of the beam radius at the waist is 11 μm. In this resonator optical system, the allowable angle for phase matching of the pump light is 4 mrad at full width at half maximum.

  The non-linear optical crystal 101A and the non-linear optical crystal 101B were exchanged using a slide mechanism as shown in FIG. 2A.

  In this example, three layers of optical antireflection films were formed on the respective nonlinear optical crystals 101A and 101B, and the combination of the refractive index and film thickness of the thin films was made different between the crystals.

  At this time, even when the two nonlinear optical crystals 101A and 101B were exchanged by the slide mechanism, stable oscillation was confirmed with signal lights having wavelengths of 820 nm and 1200 nm, respectively.

<Example 3>
A Z-type arrangement shown in FIG. 14 was adopted as the resonator optical system, and a BBO (β-BaB ₂ O ₄ ) crystal having a crystal length of 5 mm was used as the nonlinear optical crystal 101.

  The concave mirrors used as the resonator mirrors 13A and 13B have a radius of curvature R = 30 mm so that the converging angle on the nonlinear optical crystal 101 is about 8 mrad, and the configuration of the cavity was examined. In addition, a mode-locked light source having a wavelength of 405 nm shown in FIG. 11A was used as a light source for pump light.

  One of the LBO crystals is a nonlinear optical crystal 101A that oscillates light with wavelengths of 900 nm and 740 nm (matching angle 28.7 °), and the other LBO crystal is a nonlinear optical that oscillates light with wavelengths of 1100 nm and 640 nm. Crystal 101 was obtained (matching angle 27.9 °). Then, light having wavelengths of 900 nm and 1200 nm was used as resonating signal light, and light having wavelengths of 740 nm and 640 nm was used as idler light.

  In the case of the BBO crystal having the matching angle as described above, the walk-off angles are 67.3 mrad and 66.2 mrad. Accordingly, the deviation Δd of the beam position due to the walk-off is 6 μm when the crystal length is 5 mm. Therefore, in this embodiment, the resonator optical system is configured so that the half value of the beam radius at the waist is 13 μm. In this resonator optical system, the allowable angle for phase matching of the pump light is 0.8 mrad at full width at half maximum.

  Further, the non-linear optical crystal 101A and the non-linear optical crystal 101B were exchanged using a rotation mechanism as shown in FIG. 9A.

  At this time, even when the two nonlinear optical crystals 101A and 101B were exchanged by a rotating mechanism, stable oscillation was confirmed with signal lights having wavelengths of 900 nm and 1100 nm, respectively.

  The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, but the technical scope of the present disclosure is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field of the present disclosure can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that it belongs to the technical scope of the present disclosure.

  Further, the effects described in the present specification are merely illustrative or exemplary and are not limited. That is, the technology according to the present disclosure can exhibit other effects that are apparent to those skilled in the art from the description of the present specification in addition to or instead of the above effects.

The following configurations also belong to the technical scope of the present disclosure.
(1)
A nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of the incident pump light into different wavelengths by the angle phase matching method are disposed;
At least two resonator mirrors forming a light collection state;
With
The nonlinear optical crystal unit is:
Each of the plurality of nonlinear optical crystals is disposed with respect to a movable portion that operates based on a predetermined movable axis,
With at least two crystal planes of each of the nonlinear optical crystals as reference planes, the reference planes are positioned with respect to the movable shaft,
A phase matching angle measured from the reference plane of each of the nonlinear optical crystals is different between at least two of the plurality of nonlinear optical crystals;
An optical parametric oscillator in which one of the plurality of nonlinear optical crystals is disposed within the Rayleigh length of the waist portion in the condensed state by moving the movable portion.
(2)
The half value of the beam radius of the pump light at the condensing position in each nonlinear optical crystal is the amount of change in the position shift amount of the beam accompanying the walk-off that occurs in the entire crystal length between the respective nonlinear optical crystals. The optical parametric oscillator according to (1), which is larger than.
(3)
The optical parametric oscillator according to (2), wherein a change amount of the beam position shift amount is 10% or less of a half value of a beam radius of the pump light.
(4)
The light according to any one of (1) to (3), wherein a condensing angle of the pump light condensed on the nonlinear optical crystal is larger than an angle allowable half-value width of phase matching of the nonlinear optical crystal. Parametric oscillator.
(5)
At least one optical thin film is formed on the end face of each nonlinear optical crystal,
The optical parametric oscillator according to any one of (1) to (4), wherein a combination of a refractive index and a film thickness of the optical thin film is different between the respective nonlinear optical crystals.
(6)
With respect to each of the nonlinear optical crystals, the beam position shift amount due to the positioning error in the movable part in the positioning is smaller than the change in the beam position shift amount, any one of (2) to (5) An optical parametric oscillator according to claim 1.
(7)
The movable portion includes any one of (1) to (6) including a slide mechanism that realizes parallel movement along the movable axis, or a rotation mechanism that realizes rotation around the movable axis. The optical parametric oscillator described.
(8)
A nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of the incident pump light into different wavelengths by the angle phase matching method are disposed;
At least two resonator mirrors forming a light collection state;
Have
The nonlinear optical crystal unit is:
Each of the plurality of nonlinear optical crystals is disposed with respect to a movable portion that operates based on a predetermined movable axis,
With at least two crystal planes of each of the nonlinear optical crystals as reference planes, the reference planes are positioned with respect to the movable shaft,
A phase matching angle measured from the reference plane of each of the nonlinear optical crystals is different between at least two of the plurality of nonlinear optical crystals;
An optical parametric oscillator in which one of the plurality of nonlinear optical crystals is disposed within the Rayleigh length of the waist portion in the condensed state by moving the movable portion;
A laser light source for emitting pump light of a predetermined wavelength to the optical parametric oscillator;
A light source unit.
(9)
The laser light source includes a master oscillator composed of a semiconductor laser and a resonator, and an optical amplifier that amplifies the laser light from the master oscillator, and a master oscillator power amplifier (MOPA). The light source unit according to (8), which is a light source.
(10)
A nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of the incident pump light into different wavelengths by the angle phase matching method are disposed;
At least two resonator mirrors forming a light collection state;
Have
The nonlinear optical crystal unit is:
Each of the plurality of nonlinear optical crystals is disposed with respect to a movable portion that operates based on a predetermined movable axis,
With at least two crystal planes of each of the nonlinear optical crystals as reference planes, the reference planes are positioned with respect to the movable shaft,
A phase matching angle measured from the reference plane of each of the nonlinear optical crystals is different between at least two of the plurality of nonlinear optical crystals;
An optical parametric oscillator in which one of the plurality of nonlinear optical crystals is disposed within the Rayleigh length of the waist portion in the condensed state by moving the movable portion;
A laser light source for emitting pump light of a predetermined wavelength to the optical parametric oscillator;
A light source unit having
A microscope optical system that guides the illumination light emitted from the light source unit to the observation object, and guides the light from the observation object to the light detection unit,
A microscope.

DESCRIPTION OF SYMBOLS 10 Optical parametric oscillator 11 Nonlinear optical crystal unit 13 Resonator mirror 15 Drive part 17 Control part 20 Laser light source 30 Light source unit 40 Microscope optical system 50 Microscope 101 Nonlinear optical crystal 103 Movable part 105 Concave part 111 Optical thin film

Claims (10)

A nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of the incident pump light into different wavelengths by the angle phase matching method are disposed;
At least two resonator mirrors forming a light collection state;
With
The nonlinear optical crystal unit is:
Each of the plurality of nonlinear optical crystals is disposed with respect to a movable portion that operates based on a predetermined movable axis,
With at least two crystal planes of each of the nonlinear optical crystals as reference planes, the reference planes are positioned with respect to the movable shaft,
A phase matching angle measured from the reference plane of each of the nonlinear optical crystals is different between at least two of the plurality of nonlinear optical crystals;
An optical parametric oscillator in which one of the plurality of nonlinear optical crystals is disposed within the Rayleigh length of the waist portion in the condensed state by moving the movable portion.   The half value of the beam radius of the pump light at the condensing position in each nonlinear optical crystal is the amount of change in the position shift amount of the beam accompanying the walk-off that occurs in the entire crystal length between the respective nonlinear optical crystals. The optical parametric oscillator of claim 1, greater than.   3. The optical parametric oscillator according to claim 2, wherein a change in the position shift amount of the beam is 10% or less of a half value of a beam radius of the pump light.   2. The optical parametric oscillator according to claim 1, wherein a condensing angle of the pump light condensed on the nonlinear optical crystal is larger than an angle allowable half-value width of phase matching of the nonlinear optical crystal. At least one optical thin film is formed on the end face of each nonlinear optical crystal,
The optical parametric oscillator according to claim 1, wherein a combination of the refractive index and the film thickness of the optical thin film is different between the respective nonlinear optical crystals.   3. The optical parametric oscillator according to claim 2, wherein, for each of the nonlinear optical crystals, a beam position shift amount due to an arrangement error in the movable part in the positioning is smaller than a change in the beam position shift amount. .   The optical parametric oscillator according to claim 1, wherein the movable unit includes a slide mechanism that realizes parallel movement along the movable axis, or a rotation mechanism that realizes rotation around the movable axis. A nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of the incident pump light into different wavelengths by the angle phase matching method are disposed;
At least two resonator mirrors forming a light collection state;
Have
The nonlinear optical crystal unit is:
Each of the plurality of nonlinear optical crystals is disposed with respect to a movable portion that operates based on a predetermined movable axis,
With at least two crystal planes of each of the nonlinear optical crystals as reference planes, the reference planes are positioned with respect to the movable shaft,
A phase matching angle measured from the reference plane of each of the nonlinear optical crystals is different between at least two of the plurality of nonlinear optical crystals;
An optical parametric oscillator in which one of the plurality of nonlinear optical crystals is disposed within the Rayleigh length of the waist portion in the condensed state by moving the movable portion;
A laser light source for emitting pump light of a predetermined wavelength to the optical parametric oscillator;
A light source unit.   The laser light source includes a master oscillator composed of a semiconductor laser and a resonator, and an optical amplifier that amplifies the laser light from the master oscillator, and a master oscillator power amplifier (MOPA). The light source unit according to claim 8 which is a light source. A nonlinear optical crystal unit in which a plurality of nonlinear optical crystals that convert the wavelength of the incident pump light into different wavelengths by the angle phase matching method are disposed;
At least two resonator mirrors forming a light collection state;
Have
The nonlinear optical crystal unit is:
Each of the plurality of nonlinear optical crystals is disposed with respect to a movable portion that operates based on a predetermined movable axis,
With at least two crystal planes of each of the nonlinear optical crystals as reference planes, the reference planes are positioned with respect to the movable shaft,
A phase matching angle measured from the reference plane of each of the nonlinear optical crystals is different between at least two of the plurality of nonlinear optical crystals;
An optical parametric oscillator in which one of the plurality of nonlinear optical crystals is disposed within the Rayleigh length of the waist portion in the condensed state by moving the movable portion;
A laser light source for emitting pump light of a predetermined wavelength to the optical parametric oscillator;
A light source unit having
A microscope optical system that guides the illumination light emitted from the light source unit to the observation object, and guides the light from the observation object to the light detection unit,
A microscope.

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