WO2022009436A1 - Light source for multimodal nonlinear optical microscope - Google Patents

Abstract

Provided is a light source for use in a multimodal nonlinear optical microscope 2. The present invention comprises a mode-locked laser (1) configured so as to output a femtosecond pulse train (5) having a central wavelength λ_s, a steady-state oscillation solid-state laser (4) configured so as to output continuous light (6) having a wavelength λ_p, a secondary nonlinear optical element (7) for outputting a difference frequency generation converted optical pulse train (8) having a frequency λ_c comprising picosecond pulses by difference frequency generation between the continuous light (6) and a portion of the femtosecond pulse train (5), and a glass fiber amplifier (9) for amplifying the difference frequency generation converted optical pulse train (8). The steady-state oscillation solid-state laser (4) is configured so as to output continuous light (6) having a wavelength λ_p that satisfies the expression 1/λ_c=1/λ_p–1/λ_s.

Description

Light source for multimodal nonlinear optical microscope

The disclosure of the present application detects Second Harmonic Generation (SHG), Third Harmonic Generation (THG), Coherent Anti-Stokes Raman Scattering (CARS), and the like. It relates to a light source used in a nonlinear spectroscopy and a nonlinear optical microscope.

Raman scattering spectroscopy is widely used in many academic fields such as chemistry, biology, medicine, pharmacy, agriculture, and physics as a means of obtaining vibration information such as molecules, crystals, and amorphous structures. It is also widely used in medicine and industry. Spontaneous Raman scattering is a phenomenon in which scattered light having a frequency shifted by the frequency of molecular vibration or lattice vibration with respect to incident light is generated. Since this scattered light has a very weak power with respect to the original incident light power, it is necessary to use a light source having a high power as the incident light in order to obtain the scattered light that can be measured by the detector. However, most measurement samples have an upper limit on the power per unit area that can be irradiated, and if it exceeds that, it will be altered or destroyed. In many cases, the scattered light is weak even when a light source having a power corresponding to the upper limit is used, and a significantly longer measurement time is required than the CARS measurement in order to acquire a signal having a high SN ratio. On the other hand, since CARS is a nonlinear optical process using a light source with high instantaneous power, the power of Raman scattered light is much stronger and shorter as a result when a light source with the same level of power is used as compared with spontaneous Raman scattering. It is possible to measure in time.

With the development of the pulsed laser used as a light source, the development of CARS measurement is remarkable, and the effect is remarkable especially when acquiring a microscope image. When a pulsed laser with high instantaneous power is used as a light source, not only CARS but also SHG and THG can be detected at the same time, so such an experimental configuration is called a multimodal nonlinear optical microscope. Many uses of the multimodal nonlinear optical microscope have been proposed in life science, medicine and pharmacy, and further development is desired (see Non-Patent Document 1).

There are two important wavenumber region when the measured Raman scattering spectroscopy of biological, The first region is a region of 1800 cm ^-1 wave number 500 cm ^-1 called fingerprint region, second region, carbon hydrogen (C-H) bonds, nitrogen-hydrogen (N-H) bond, or a region of 3100 cm ^-1 wave number 2800 cm ^-1 due to oxygen-hydrogen (O-H) bond (see non-Patent Document 1). When measuring CARS spectroscopy, light with two wavelengths having a wavenumber difference corresponding to the wavenumber in the above region (the difference between the wavelengths of the two lights is the wavenumber corresponding to the wavenumber in the above region). Is incident on the object to be measured.

FIG. 1 is a diagram showing a configuration of a light source of a conventional multimodal nonlinear optical microscope described in Non-Patent Document 1. The conventional light source shown in FIG. 1 includes a composite light source 101 and a photonic crystal fiber 104. Compound light source 101, Nd: YVO ₄ is constituted by a laser and Yb-doped glass fiber amplifiers, wavelength 1.06 .mu.m, the pulse width is 85 ps, pulse energy 1 .mu.J, repetition frequency to generate picosecond pulses of 0.82MHz .. The generated picosecond pulse is divided into two systems for energy and output from the composite light source 101. One system of bifurcated picosecond pulses is input to the microscope 102. The other system of bifurcated picosecond pulses is input to the photonic crystal fiber 104. The photonic crystal fiber 104 includes wideband light having a wavelength of 1.1 μm to 1.7 μm, and generates and outputs supercontinuum light 105 having a pulse energy of 2 μJ. A multimodal nonlinear optical microscope image is obtained by inputting two systems of light of the picosecond pulse train 103 and the supercontinuum light 105 into the microscope 102 at the same timing and irradiating the sample to be measured. CARS is generated by irradiating a sample with two systems of light, a picosecond pulse train 103 and a supercontinuum light 105. SHG and THG are generated by irradiating a sample with a picosecond pulse train 103 having a wavelength of 1.06 μm, respectively.

FIG. 2 is a diagram showing an energy diagram of a molecule of a sample to be measured when measuring CARS spectroscopy. As shown in FIG. 2, when measuring CARS spectroscopy, the measurement target is measured by incident _{pump light 106 (angular frequency ω 1} ), Stokes light 107 (angular frequency ω ₂ ), and probe light 108 (angular frequency ω _{3). CARS light 109 (angular frequency ω CARS} ) corresponding to the angular frequency Ω of the vibration mode 110 of the molecule is generated. In the conventional example shown in FIG. 1, since the picosecond pulse train 103 is used as the pump light 106 and the probe light 108 (ω ₁ = ω ₃ ) and the wideband super continuation light 105 is used as the Stokes light 107, a large number of vibration modes 110 are used. Is excited, and the wideband CARS light 109 can be measured (see Non-Patent Document 2).

However, the total average power of the light of the two systems of the picosecond pulse train 103 and the super-continue light 105 output from the light source shown in FIG. 1 becomes 2.5 W, and these lights are input to the microscope 102 without being attenuated. In some cases, the sample to be measured was damaged. Therefore, it is necessary to improve the measurement so that the measurement by the multimodal nonlinear optical microscope can be performed with high sensitivity even when the sample is irradiated with the light of low average power.

An object of the disclosure of the present application is to improve the conversion efficiency of SHG and THG by reducing the duty ratio, which is the product of the repetition frequency and the pulse width, as a light source of a multimodal nonlinear optical microscope for detecting SHG, THG and CARS, for example. It is an object of the present invention to provide a light source capable of reducing the average power of light input to a nonlinear optical microscope.

In order to achieve such an object, one embodiment of the present invention is a light source used for spectroscopic measurement or spectroscopic microscopic image acquisition. Spectroscopic measurements or spectroscopic microscopic image acquisition may include signal measurements by coherent traman scattering and signal measurements by at least one or both of the second and third harmonic generations. The light sources are a mode-synchronized laser configured to output a femtosecond pulse train with a center wavelength of λ _s , a stationary oscillating solid-state laser configured to output continuous light _{with a wavelength of λ p, and continuous light and femtoseconds.} Difference frequency generation conversion of the _{center wavelength λ c} consisting of picosecond pulses in one of the two systems in which the femtosecond pulse train is divided in terms of power by generating the difference frequency with one of the two systems in which the pulse train is divided in terms of power. It includes a second-order nonlinear optical element that converts to an optical pulse train and outputs it, and a glass fiber amplifier that amplifies the differential frequency generation conversion optical pulse train. This light source is configured to output the amplified differential frequency generation conversion light pulse train and the remaining one of the femtosecond pulse trains. The steady-state oscillating solid-state laser of this light source is configured to output continuous light having a _{wavelength of λ p that satisfies Equation 3 described later.}

The configuration of the light source of one embodiment reduces the duty ratio, which is the product of the repetition frequency and the pulse width, resulting in higher conversion efficiency of SHG and THG and reduction of the average power of light input to the nonlinear optical microscope. Can provide a light source.

FIG. 1 is a schematic diagram showing a light source for a conventional multimodal nonlinear optical microscope. FIG. 2 is a diagram showing an energy diagram of a molecule to be measured in coherent anti-Stokes Raman scattering. FIG. 3 is a schematic diagram showing a light source for a multimodal nonlinear optical microscope according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The numerical values and materials used in the following description are examples, and the present invention can be carried out using other numerical values and materials without departing from the gist of the present invention.

FIG. 3 is a schematic diagram showing a light source for a multimodal nonlinear optical microscope according to an embodiment of the present invention. The light sources shown in FIG. 3 are _{a mode-synchronized laser 1 configured to output a femtosecond pulse train 5 having a center wavelength of λ s} , a beam splitter 10 that divides the femtosecond pulse train 5 into two systems with respect to power, and an equation described later. _{A stationary oscillating solid-state laser 4 configured to output continuous light 6 having a wavelength λ p} that satisfies 3 and a continuous light 6 are transmitted and reflected by one of the bifurcated femtosecond pulse trains 5. And the center wavelength λ consisting of a picosecond pulse on one of the femtosecond pulse trains 5 due to the generation of a difference frequency between the mirror 11 that outputs one of the femtosecond pulse trains 5 on the same axis and one of the continuous light 6 and the femtosecond pulse train 5. A second-order nonlinear optical element 7 that converts and outputs the difference frequency generation conversion optical pulse train 8 of _{c, and a glass fiber amplifier 9 that amplifies the difference frequency generation conversion light pulse train 8 are provided.} FIG. 3 also shows a multimodal nonlinear optical microscope 2.

The picosecond pulse train 3, which is the differential frequency generation conversion optical pulse train 8 amplified by the glass fiber amplifier 9, is configured to output together with the other of the femtosecond pulse train 5 bifurcated by the beam splitter 10. The other of the picosecond pulse train 3 and the bifurcated femtosecond pulse train 5 output from the light source according to the present embodiment is input to the multimodal nonlinear optical microscope 2. With the above configuration, as a result of reducing the duty ratio, which is the product of the repetition frequency and the pulse width, the conversion efficiency of SHG and THG is increased, and it is possible to reduce the average power of the light input to the nonlinear optical microscope. can.

In one embodiment, the mode-synchronized laser 1 provides ^{one crystal or ceramic selected from Cr 4+} : YAG, Cr forsterite, Ti sapphire, Cr: LiSAF, Cr: LiCAF, Cr: ZnSe, Cr: ZnS, and the like. It can be configured using a mode-synchronized laser as a laser medium. In another embodiment, the mode-synchronized laser 1 uses a mode-synchronized laser using a YAG crystal or ceramics supplemented with one rare earth ion selected from Yb, Er, Nd, Tm, Ho, etc. as a laser medium. It may be configured. In still another embodiment, the mode-synchronized laser 1 is a mode-synchronized laser using a crystal or ceramics of _{YVO 4} supplemented with one rare earth ion selected from Yb, Er, Nd, Tm, Ho and the like as a laser medium. It may be configured using. In yet another embodiment, the mode-synchronized laser 1 is a mode-synchronized laser using a glass (bulk and fiber) supplemented with one rare earth ion selected from Yb, Er, Nd, Tm, Ho and the like as a laser medium. May be configured using. Further, in another mounting embodiment, a mode-synchronized laser using a semiconductor crystal as a laser medium may be used.

In one embodiment, the shape of the gain medium constituting the mode-synchronized laser 1 can be a rod, a disk, or a fiber.

In one embodiment, the beam splitter 10 can be configured with a half mirror or beam splitter cube that splits the power of the input light into two, reflects one and transmits the other.

In one embodiment, the stationary oscillating solid-state laser 4 uses a glass fiber laser, a bulk-shaped single crystal laser, a bulk-shaped ceramics laser, a waveguide-type single crystal laser, a waveguide-type ceramics laser, or a semiconductor laser. Can be configured.

In one embodiment, the mirror 11 can be configured using a dichroic mirror that reflects light of a predetermined wavelength and transmits light of another wavelength.

In one embodiment, the second-order nonlinear optical element 7 can be configured by using periodic polarization inversion lithium niobate, periodic polarization inversion lithium tantalate, or periodic polarization inversion KTP, which satisfies the formula 4 described below.

In one embodiment, the glass fiber amplifier 9 can be configured by using a glass fiber amplifier to which one rare earth ion selected from Yb, Er, Nd, Tm, Ho and the like is added.

Light source of the present embodiment can be used as a light source at the time of observing the region of 3100 cm ^-1 wave number 2800 cm ^-1 in CARS spectroscopy of multimodal nonlinear optical microscope.

^{The light source of the present embodiment uses a mode-synchronized laser using a Cr 4+} : YAG laser as a laser medium as the mode-synchronized laser 1, and a periodic polarization inversion lithium niobate (PPLN) as the second-order nonlinear optical element 7. It is configured by using a Yb-added glass fiber amplifier (YbFA) as 9, and using a CW solid-state laser that oscillates at a single wavelength of 0.612 μm as a constant wave (CW) solid-state laser 4.

^{The Cr 4+} : YAG laser as the mode-synchronized laser 1 oscillates in mode-synchronization and outputs a femtosecond pulse train 5 having a center wavelength of 1.5 μm, a pulse width of 40 fs, and a repetition frequency of 80 MHz (see Non-Patent Document 3). The femtosecond pulse train 5 is split into two by the beam splitter 10. One of the bifurcated femtosecond pulse trains is reflected by the mirror 11 and input to the PPLN 7 to generate the picosecond pulse train 3 at a different frequency. The other of the bifurcated femtosecond pulse trains 5 is input to the nonlinear optical microscope 2. The bifurcated femtosecond pulse trains 5 each have a pulse energy of about 1 nJ.

The CW solid-state laser 4 outputs continuous (CW) light 6 having a single wavelength of 0.612 μm. The CW light 6 passes through the mirror 11 and is input to the PPLN 7 in order to generate a picosecond pulse train 3 at a different frequency.

The CW light 6 is input to the PPLN 7 coaxially from the same direction as the excitation light for generating the difference frequency and the femtosecond pulse train 5 as the signal light. The pulse energy of the conversion light (difference frequency generation conversion light pulse train 8) generated from the CW light 6 and the femtosecond pulse train 5 in the PPLN 7 can be calculated as follows.

First, the abnormal optical refractive index of the PPLN used is calculated by the following equation 1 with the wavelength as λ (μm) (see Non-Patent Document 4).

When the picosecond pulse train is generated by taking the difference frequency between the CW light 6 and the femtosecond pulse train 5, the length of the PPLN that can be used is limited by the difference in the group velocity caused by the difference in the wavelengths of both pulses in the PPLN7. .. Non-Patent Document 5 describes the usable length (Pulse-width-preservation length: L _τ ) in the case of SHG. Since the excitation light is the CW light 6 in the differential frequency generation in the PPLN 7 in the present embodiment, the same calculation formula, that is, the formula 2 can be used _{for L τ.}

Here, τ _c is the pulse width (half-value full width) of the converted light (difference frequency generation converted light pulse train 8), v _gt is the group velocity of the converted light, and v _gs is the signal light (femto second pulse train 5). Group velocity. Calculated from Equation 1, the wavelength of the signal light (femtosecond pulse train 5) is 1.50 μm, the wavelength of the converted light (difference frequency generation converted light pulse train 8) is 1.04 μm, and the group speed of the two lights in PPLN7. _{L τ} is calculated to be 0.012 m for a pulse width of 1 ps of the converted light generated by the difference between the two.

Here, λ _c , λ _s , and λ _p are wavelengths of the conversion light (difference frequency generation conversion light pulse train 8), the signal light (femtosecond pulse train 5), and the excitation light (CW light 6), respectively, and are as follows. Equation 3 is satisfied.

In order to maximize the conversion efficiency of the periodic polarization inversion lithium niobate (PPRN) 7, it is required that the inversion period Λ satisfy the phase matching condition represented by the following equation 4 (see Non-Patent Document 6). ).

Efficiency of difference frequency generation eta (% / W) is the converted light (difference frequency generation converted optical pulse train 8), the signal light (femtosecond pulse train 5), and each P _c the power of the excitation light (CW light _6), P _{If s} and P _p (W) are set, the equation 5 is obtained.

When Equation 4 is satisfied, the efficiency η (% / W) of differential frequency generation can be expressed as Equation 6.

Here, C _LN is a constant with respect to PPLN 7, L is the length (m) of PPLN 7, and A _eff is the beam cross-sectional area (femtosecond pulse train 5) of excitation light (CW light 6) and signal light (femtosecond pulse train 5) in PPLN 7. μm ² ). In Non-Patent Document 6, it is 100% / W with _{respect to λ c} = 2.3 _{μm, λ s} = 1.58 μm, λ _p = 0.937 μm, L = 0.05 m, and A _eff = 8.6 × 13 μm ^2. since it has been reported, _C LN = 2.28 × 10 ⁸ is calculated from this.

In this embodiment, PPLN7 having L = 0.010 m, _{which is less than L τ = 0.012 m, is used.} The minimum average beam radius in PPLN7 for λ _s = 1.50 μm and L = 0.010 m can be calculated as 36 μm. From Equation 6, η = 0.52% / W is calculated for _{λ c} = 1.04 μm, λ _s = 1.50 μm, and λ _{p = 0.612 μm.} The signal light (femtosecond pulse train 5) input to the PPLN 7 has a pulse width of 40 fs and a pulse energy of 1 nJ as described above. In the generation of the difference frequency in the PPLN 7, a pulse of 1 ps is generated due to the difference in the group velocity between the signal light (femtosecond pulse train 5) and the conversion light (difference frequency generation conversion light pulse train 8) described above. Therefore, the signal light needs to be calculated as a pulse of 1 ps, and the pulse energy is equivalent to 0.04 nJ. Since the output of the CW light 6 is 0.1 W, the pulse energy of the converted light (difference frequency generation converted light pulse train 8) is 10 fJ when calculated from the equation 5.

The wavelength of 1.04 μm of the converted light (difference frequency generation converted light pulse train 8) is included in the gain band of the Yb-added glass fiber amplifier (YbFA) constituting the glass fiber amplifier 9. By combining a plurality of glass fiber amplifiers 9 (for example, two or three) of YbFA, a gain of about 60 dB can be obtained, so that the YbFA is synchronized with the ^{Cr 4+: YAG laser constituting the mode-synchronized laser 1.} A picosecond pulse train 3 having a maximum pulse energy of about 10 nJ and a pulse width of 1 ps is output. Cr ^4+: wave number by the input pulse width 40fs femtosecond pulse train 5 from YAG laser becomes 300 cm ^-1 in terms of wavenumber, the nonlinear optical microscope 2 is synchronized with the picosecond pulse train 3 and the femtosecond pulse train 5 2800 cm ^- It is possible to obtain a CARS image which is the same as the conventional example described with reference to FIG. 1 for the region of ¹ to 3100 cm ^-1. SHG and THG are generated by irradiating the sample with a femtosecond pulse from a ^{Cr 4+: YAG laser, respectively.} In order to synchronize the picosecond pulse train 3 and the femtosecond pulse train 5, the other optical path length of the bifurcated femtosecond pulse train 5 between the beam splitter 10 and the nonlinear optical microscope 2 or the picosecond pulse train 3 ( The optical path length of the bifurcated femtosecond pulse train 5) between the beam splitter 10 and the nonlinear optical microscope 2 may be adjusted.

Here, the relationship between the input average power of the light source and the signal intensities of THG and SHG will be compared between the conventional example and the present embodiment.

_{Let I ω} (t, x _i ) (W / m ² ) be _{the light intensity per unit area at the time t and position x i} (i = 1, 2, 3) of the light pulse having an angular frequency ω. Peak intensity I _{ω ・ 0} (W / m ² ), pulse width τ (s), repetition frequency _rep (Hz), average power P _{ω ・ av} (W), and oscillation wavelength λ (μm) (λ = 2πcω ^-1 , c: light speed). The duty ratio D is defined by the following equation 7.

If the beam focal area A is set to the minimum possible value, it will be proportional to the square of the oscillation wavelength λ, and can be expressed by the following equation 8.

As a result, the proportional relationship of the following equation 9 is established for the average power.

Since the signal power P _{3ω · av} of THG is proportional to the product of the cube of the peak intensity, the beam focal area, and the duty ratio, the following equation 10 holds.

Further, since the signal power P _{2ω · av} of SHG is proportional to the product of the square of the peak intensity, the beam focal area, and the duty ratio, the following equation 11 holds.

Therefore, in order to compare the signal intensities due to the difference in the light source when the same average power is input, λ ^-4 D ^-2 may be examined in ^{THG, and λ -2} D ^-1 may be examined in SHG.

As shown in Table 1, in the present embodiment, compared to the conventional example, when the same average power is input, a signal strength of 100 times or more can be obtained in THG, and a signal strength of 10 times or more can be obtained in SHG. Therefore, the superiority of the light source in this embodiment is clear. Even if the average power of the optical pulse input to the nonlinear optical microscope is the same, the instantaneous power of the optical pulse increases by reducing the duty ratio, which is the product of the repetition frequency and the pulse width. Therefore, wavelength conversion of SHG and THG. Higher efficiency. Therefore, it is possible to reduce the average power of the input light pulse required to obtain the same SHG and THG signal power.

In this embodiment, ^{a light source having a configuration in which a mode-synchronized laser 1 using a Cr 4+} : YAG laser and a glass fiber amplifier 9 using a Yb-added glass fiber amplifier (YbFA) are combined is shown as an example.

As the mode-synchronized laser 1 that outputs the femtosecond pulse train 5, any of the above-mentioned mode-synchronized lasers using various crystals, ceramics, glass, or semiconductor crystals as a laser medium can be used, if necessary. As the laser medium of the mode-synchronized laser 1, any of bulk shape, disk shape, and fiber shape may be used.

Similarly, for the glass fiber amplifier 9, any of the above-mentioned glass fiber amplifiers to which various rare earth ions are added can be used, if necessary.

Further, the wavelengths of the CW solid-state laser 4 and the second-order nonlinear optical element 7 are selected according to the equation 3, and as a result, the difference frequency generation conversion optical pulse train 8 generated by the difference frequency generation from the femtosecond pulse train 5 from the mode-synchronized laser 1 is generated. The wavelength is converted within the gain band of the glass fiber amplifier 9. The CW solid-state laser 4 and the second-order nonlinear optical element 7 can be configured by using any of the various lasers and nonlinear optics described above, if necessary.

Further, although the example of using the periodic polarization inversion lithium niobate satisfying the equation 4 has been described for the second-order nonlinear optical element 7, the second-order nonlinear optical element 7 shall be configured by using other materials such as the periodic polarization inversion lithium tantalate and the periodic polarization inversion KTP. Can be done. Further, the inversion period Λ can be adjusted by using a second-order nonlinear optical element 7 having a fan-out type periodic polarization inversion structure so as to cope with the wavelength fluctuation of the CW solid-state laser 4.

The light source of this embodiment can also be used for spectroscopic measurement and spectroscopic microscopic image acquisition by coherent Raman scattering other than CARS (for example, induced Raman gain and induced Raman loss).

Claims (7)

1. A light source used for spectroscopic measurement or spectroscopic microscopic image acquisition, wherein the spectroscopic measurement or spectroscopic microscopic image acquisition is signal measurement by coherent traman scattering, and at least one or both of second harmonic generation and third harmonic generation. The light source includes a signal measurement by
   A mode-synchronized laser configured to output a femtosecond pulse train with a center wavelength of λ _s,
   A steady-state oscillating solid-state laser configured to output continuous light with a wavelength of λ _p,
   The center consisting of picosecond pulses in one of the two systems in which the femtosecond pulse train is divided in terms of power due to the generation of a difference frequency between the continuous light and one of the two systems in which the femtosecond pulse train is divided in terms of power. A second-order nonlinear optical element that converts and outputs a differential frequency generation conversion optical pulse train with a wavelength of λ _{c, and}
   A glass fiber amplifier that amplifies the differential frequency generation conversion optical pulse train,
   Is configured to output the amplified differential frequency generation conversion optical pulse train and the remaining one of the femtosecond pulse trains.
   The steady oscillation solid-state laser is configured to output continuous light of the wavelength lambda _p that satisfies the expression A, a light source.
   

   
2. A beam splitter that splits the femtosecond pulse train into two systems with respect to power, which is placed between the mode-synchronized laser and the second-order nonlinear optical element.
   A part of the continuous light and the femtosecond pulse train arranged between the stationary oscillating solid-state laser and the second-order nonlinear optical element, transmitting the continuous light and reflecting a part of the femtosecond pulse train. With a mirror that outputs on the same axis,
   The light source according to claim 1, further comprising.
3. The mode-synchronized laser is
   One crystal or ceramic selected from Cr ⁴⁺ : YAG, Cr forsterite, Ti sapphire, Cr: LiSAF, Cr: LiCAF, Cr: ZnSe, and Cr: ZnS,
   Crystals or ceramics of YAG supplemented with one rare earth ion selected from Yb, Er, Nd, Tm, and Ho.
   _{Crystals of YVO 4} supplemented with one rare earth ion selected from Yb, Er, Nd, Tm, and Ho or ceramics Glass supplemented with one rare earth ion selected from Yb, Er, Nd, Tm, and Ho. The light source according to claim 1 or 2, which is configured by using a mode-synchronized laser using one selected from semiconductor crystals as a laser medium.
4. The light source according to claim 3, wherein the shape of the gain medium constituting the mode-synchronized laser is a rod, a disk, or a fiber.
5. The invention according to any one of claims 1 to 4, wherein the glass fiber amplifier is configured by using a glass fiber amplifier to which one rare earth ion selected from Yb, Er, Nd, Tm, and Ho is added. light source.
6. The steady-state oscillating solid-state laser is composed of a glass fiber laser, a bulk-shaped single crystal laser, a bulk-shaped ceramics laser, a waveguide-type single crystal laser, a waveguide-type ceramics laser, or a semiconductor laser. Item 5. The light source according to any one of Items 1 to 5.
7. The light source according to any one of claims 1 to 6, wherein the second-order nonlinear optical element is configured by using periodic polarization inversion lithium niobate, periodic polarization inversion lithium tantalate, or periodic polarization inversion KTP.

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