WO2015136939A1 - Appareil de mesure de diffusion de raman et procédé de mesure de diffusion de raman - Google Patents

Appareil de mesure de diffusion de raman et procédé de mesure de diffusion de raman Download PDF

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Publication number
WO2015136939A1
WO2015136939A1 PCT/JP2015/001360 JP2015001360W WO2015136939A1 WO 2015136939 A1 WO2015136939 A1 WO 2015136939A1 JP 2015001360 W JP2015001360 W JP 2015001360W WO 2015136939 A1 WO2015136939 A1 WO 2015136939A1
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pulse
optical
raman scattering
optical pulse
scattering measurement
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PCT/JP2015/001360
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English (en)
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Yuki Yonetani
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Canon Kabushiki Kaisha
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/06—Means for illuminating specimens
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H01S5/4087—Array arrangements, e.g. constituted by discrete laser diodes or laser bar emitting more than one wavelength
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0057—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for temporal shaping, e.g. pulse compression, frequency chirping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0085—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for modulating the output, i.e. the laser beam is modulated outside the laser cavity

Definitions

  • the present invention relates to a Raman scattering measurement apparatus such as a microscope utilizing Raman scattering.
  • microscopes capable of observing a three-dimensional distribution of molecules in a biological object and a body composition ones utilizing CARS (Coherent Anti-Stokes Raman scattering) or SRS (stimulated Raman scattering) are proposed.
  • CARS Coherent Anti-Stokes Raman scattering
  • SRS stimulated Raman scattering
  • Patent Document 1 discloses a method of generating an optical pulse from a continuous light at a repetition frequency of a signal serving as a trigger and thereby generating two synchronized optical pulses whose wavelengths are mutually different.
  • This method which uses a solid laser in a wide wavelength band as a light source, controls an oscillation wavelength of the solid laser to perform wavelength sweep of the optical pulse.
  • Patent Document 2 discloses a method of generating an optical pulse from a continuous light by using a signal sent from an external signal generator and thereby generating two synchronized optical pulses and of controlling a repetition frequency of the external signal to perform synchronization control of the optical pulses.
  • Patent Document 2 does not disclose methods of wavelength selection and wavelength sweep of the optical pulse.
  • Arbitrary wavelength selection and wavelength sweep in a wide wavelength band require, similarly to the method disclosed in Patent Document 1, using a solid laser which has a large size and whose maintainability is not good.
  • the use of the solid laser requires controlling an inside of a resonator such as a laser crystal angle, which makes it impossible to perform wavelength sweep at high speed.
  • the present invention provides a compact light source apparatus capable of arbitrarily selecting wavelengths of two synchronized optical pulses having mutually different wavelengths and of sweeping the wavelengths thereof at high speed.
  • the present invention provides as an aspect thereof a Raman scattering measurement apparatus including a light generator configured to generate a first continuous light and a second continuous light whose wavelengths are mutually different, a pulse generator configured to generate a first optical pulse and a second optical pulse respectively from the first continuous light and the second continuous light, and a light detector configured to detect light whose intensity is modulated by Raman scattering generated by focusing the first and second optical pulses onto a sample.
  • the pulse generator is configured to generate the first and second optical pulses such that a repetition frequency of the second optical pulse coincides with an integral multiple of a repetition frequency of the first optical pulse.
  • the present invention provides as another aspect thereof a Raman scattering measurement method including a light generating step of generating a first continuous light and a second continuous light whose wavelengths are mutually different, a pulse generating step of generating a first optical pulse and a second optical pulse respectively from the first continuous light and the second continuous light, and a light detecting step of detecting light whose intensity is modulated by Raman scattering generated by focusing the first and second optical pulses onto a sample.
  • the first and second optical pulses are generated such that a repetition frequency of the second optical pulse coincides with an integral multiple of a repetition frequency of the first optical pulse.
  • the present invention achieves a compact and simple configuration capable of generating, from two continuous lights, two optical pulses that are to be focused onto a sample for generating Raman scattering and one of which has a repetition frequency coinciding with an integral multiple of that of the other and capable of arbitrarily selecting a wavelength band of at least one of the optical pulses.
  • the present invention thereby enables realizing a compact measurement apparatus capable of performing good measurement using the Raman scattering.
  • the present invention enables efficiently measuring the Raman scattering with a simple configuration even when the wavelength sweep is not performed. That is, an expander, a compressor and a selector are not essential constituent elements for the present invention and may be provided as needed when the wavelength sweep is performed.
  • FIG. 1 is a block diagram illustrating a configuration of a light source apparatus to be used for an SRS measurement apparatus that is Example 1 of the present invention.
  • FIG. 2 illustrates an example configuration of a pulse width compressor used for the light source apparatus in Example 1.
  • FIGS. 3A to 3D illustrate a calculation result in Example 1.
  • FIGS. 4A to 4C illustrate the calculation result in Example 1.
  • FIG. 5 is a block diagram illustrating a configuration of a light source apparatus to be used for an SRS measurement apparatus that is Example 2 of the present invention.
  • FIG. 6 is a block diagram illustrating a variation of the light source apparatus in Example 2.
  • FIG. 7 is a block diagram illustrating a configuration of a light source apparatus to be used for an SRS measurement apparatus that is Example 3 of the present invention.
  • FIG. 8 is a block diagram illustrating a modified example of the light source apparatus in Example 3.
  • FIG. 9 is a block diagram illustrating a configuration of an SRS microscope that is Example 4 of the present invention.
  • FIG. 1 illustrates a configuration of a light source apparatus to be used for an SRS measurement apparatus as a reference example (hereinafter referred to as "Example 1") of the present invention.
  • reference numeral 101 denotes an external signal generator (SG).
  • Reference numeral 102 denotes a first semiconductor laser (L1) whose oscillation wavelength is a first wavelength, and 112 a second semiconductor laser (L2) whose oscillation wavelength is a second wavelength.
  • the first and second semiconductor lasers 102 and 112 constitute a light generator.
  • Reference numerals 103 and 113 denote pulse generators (IM), and 104, 109 and 114 optical amplifiers (AMP).
  • IM pulse generators
  • AMP optical amplifiers
  • Reference numerals 105 and 115 denote spectrum expanders (SE) serving as an expander, and 106 and 116 pulse width compressors (PWC) serving as a compressor.
  • Reference numeral 107 denotes a tunable band-pass filter (hereinafter referred to as "a TBPF") serving as a selector, and 108 a band-pass-filter controller (C) that controls the TBPF 107, which serves as a controller.
  • Reference numeral 110 denotes a wave combiner (WC), and 111 an electrical delay line (DL).
  • the first semiconductor laser 102 generates a first laser light as a first continuous light with the first wavelength
  • the second semiconductor laser 112 generates a second laser light as a second continuous light with the second wavelength.
  • the first and second laser lights are respectively introduced to the pulse generators 103 and 113.
  • the pulse generators 103 and 113 respectively generate a first optical pulse and a second optical pulse from the first laser light and the second laser light at a timing corresponding to a timing signal output from the external signal generator 101.
  • the first and second optical pulses are respectively amplified by the optical amplifiers 104 and 114 and respectively enter the spectrum expanders 105 and 115.
  • the spectrum expanders 105 and 115 respectively expand spectrum widths of the first and second optical pulses to predetermined wide wavelength bands.
  • the first and second optical pulses with the expanded spectrum widths respectively enter the pulse width compressors 106 and 116.
  • the pulse width compressors 106 and 116 respectively compress the pulse widths of the first and second optical pulses with the expanded spectrum widths.
  • the first optical pulse with the expanded spectrum width and the compressed pulse width is compressed enters the TBPF 107.
  • the TBPF 107 extracts, from the entering first optical pulse, an optical pulse component in a specific wavelength band that is selected as an extraction wavelength band to emit the optical pulse component.
  • the specific wavelength band can be selected (changed) through the band-pass-filter controller 108.
  • the optical pulse component in the specific wavelength band is introduced to the optical amplifier 109.
  • the optical amplifier 109 amplifies an intensity of the optical pulse component attenuated by the wavelength extraction (wavelength selection) at the TBPF 107.
  • the optical pulse component in the specific wavelength band (hereinafter, the component is also referred to as "a first optical pulse") after passing through the pulse width compressor 106, the TBPF 107 and the optical amplifier 109 and the second optical pulse after passing through the pulse width compressor 116 are coaxially combined (coaxially introduced) by the wave combiner 110 and then emitted from the light source apparatus.
  • Optical paths from the first and second semiconductor lasers 102 and 112 to the wave combiner 110 are entirely formed by optical fibers.
  • other optical fibers than the polarization-maintaining fiber may alternatively be used, or the polarization-maintaining fiber may be used together with a polarization controller.
  • the first and second semiconductor lasers 102 and 112 respectively emit monochromatic continuous lights respectively corresponding to the first and second wavelengths. For instance, when the light source apparatus of this example is used for a CARS microscope or an SRS microscope, it is desirable to select the first and second wavelengths such that a difference therebetween approximately coincides with a vibrational level of a molecule to be observed.
  • a common laser diode, quantum dot laser, quantum cascade laser or the like may be used as the first and second semiconductor lasers 102 and 112 .
  • the pulse generators 103 and 113 are selected depending on the first and second wavelengths. Using a common intensity modulator as each of the pulse generators 103 and 113 enables converting a continuous light into an optical pulse having a pulse width of up to several tens of picoseconds (ps).
  • the timing signals to be used to control the repetition frequencies at which the pulse generators 103 and 113 generate the first and second pulses from the first and second continuous lights are provided from the external signal generator 101.
  • the external signal generator 101 changes a repetition frequency of the timing signal, which controls the repetition frequencies of the first and second optical pulses respectively emitted from the pulse generators 103 and 113.
  • an LN (Lithium Niobate) modulator, an electroabsorption light modulator or the like may be used as the pulse generators 103 and 113.
  • the optical amplifiers 104 and 114 respectively compensate insertion losses generated at the pulse generators (intensity modulator) 103 and 113 and respectively amplify intensities of the first and second optical pulses to a level required by the subsequent spectrum expanders 105 and 115.
  • optical amplifiers 104 and 114 optical fiber amplifiers each using, as a gain medium, an optical fiber doped with a rare earth such as ytterbium (Yb) or erbium (Er) may be used.
  • the optical amplifiers 104 and 114 are desirable to be ones each constituted by a polarization-maintaining optical fiber.
  • the optical amplifiers 104 and 114 may, as needed, be configured as multistage amplifiers.
  • the spectrum expander 105 that the first optical pulse amplified by the optical amplifier 104 enters is a high nonlinearity fiber (hereinafter referred to as "an HNLF").
  • the spectrum expander 105 expands a spectrum width of the first optical pulse to a wide wavelength band by utilizing a nonlinear optical effect.
  • An upper limit of the spectrum width expansion corresponds approximately to a gain band of the optical amplifier 104 to be used.
  • the spectrum expander 105 expanding the spectrum to a wide wavelength band as just described above may alternatively be a long-distance single-mode fiber (the single-mode fiber is hereinafter referred to as "an SMF”), a photonic crystal fiber, a liquid core fiber or the like. Since a fiber with a higher nonlinearity has a shorter length, use of such a fiber enables constituting a more compact and stable system.
  • the spectrum expander 115 that the second optical pulse amplified by the optical amplifier 114 enters is an SMF which expands the spectrum width of the second optical pulse as well as the spectrum expander 105 by utilizing the nonlinear optical effect.
  • the spectrum extension by the SMF does not aim to expand the spectrum width to a wide wavelength bandwidth, but to compress the pulse width.
  • the pulse width of the second optical pulse when being output from the intensity modulator (pulse generator 113) is required to be further compressed.
  • compressing the pulse width requires expanding the spectrum width. Since a width to be expanded by the spectrum expansion is approximately 0.1 to 1nm, the spectrum expander 115 is not required to be a high-nonlinearity fiber.
  • the pulse width compressors 106 and 116 are each constituted by a combination of a circulator and a chirped fiber bragg grating (hereinafter referred to as "a CFBG").
  • the CFBG is a fiber diffraction grating that reflects an entering optical pulse at positions different depending on a wavelength of the entering optical pulse and that is capable of compressing a pulse width of the entering light by providing a chirp inverse to that of the entering optical pulse.
  • FIG. 2 illustrates an example configuration of each of the pulse width compressors 106 and 116.
  • Reference numeral 201 denotes the circulator, and 202 the CFBG.
  • the optical pulse entering the circulator 201 is introduced to the CFBG 202, and then its pulse width is compressed by the CFBG 202.
  • the optical pulse with the compressed pulse width returns to the circulator 201 and exits from the pulse width compressor.
  • the pulse width compressor 106 compresses the pulse width of the first optical pulse, in order to reduce a timing difference generated in the wavelength selection depending on wavelengths, to a pulse width from several hundreds of femtoseconds (fs) to several picoseconds (ps).
  • the pulse width compressor 116 compresses the pulse width of the second optical pulse to approximately several to 10ps.
  • this example uses the CFBG as the pulse width compressor, a dispersion compensation optical fiber, paired prisms, paired diffraction gratings or the like may alternatively be used.
  • the TBPF 107 transmits only an optical pulse component in the specific wavelength band selected from the first optical pulse with the spectrum width expanded to a wide wavelength bandwidth (in this example, and with the compressed pulse width) to extract the optical pulse component.
  • a commonly used device such as a combination of a diffraction grating and a slit, an acoustic optic tunable filter, a waveguide diffraction grating or a fiber Bragg grading (FBG) can be used.
  • FBG fiber Bragg grading
  • a wavelength width of the specific wavelength band to be selected is desirable to be approximately 0.5 to 1nm.
  • the pulse width compressor 106 and the TBPF 107 function linearly, they can be arranged in reverse order. That is, a configuration may be employed in which the TBPF 107 extracts the optical pulse component in the specific wavelength band from the first optical pulse before its pulse width is compressed by the pulse width compressor 106.
  • the pulse width compressor 106 functions as a delay compensator that compensates for a relative time delay for each wavelength.
  • the band-pass-filter controller 108 is constituted by a computer and controls the specific wavelength band extracted by the TBPF 107. For instance, when the combination of the diffraction grating and the slit is used as the TBPF 107, the band-pass-filter controller 108 drives a movable stage supporting the slit to control a position and a sweep speed of the slit with respect to the diffraction grating. Sequentially changing the specific wavelength band enables performing wavelength sweep of the first optical pulse extracted by the TBPF 107.
  • the optical amplifier 109 amplifies, as mentioned above, the intensity of the first optical pulse attenuated by the wavelength extraction at the TBPF 107 to a predetermined light intensity.
  • the optical amplifier 109 may be configured as a multistage amplifier as needed.
  • the electrical delay line 111 provides a time delay amount to the timing signal output from the external signal generator 101 and input to the pulse generator 113, thereby electrically controlling a difference between generation timings of the first and second optical pulses.
  • the generation timing of each optical pulse is hereinafter referred to as "a pulse timing”. If the difference of the pulse timings (hereinafter referred to as “a pulse timing difference") is large, an electrical delay line having a fixed time delay amount may be additionally provided.
  • the pulse timing difference may be detected by directly detecting output of the light source apparatus of this example with a detector such as an oscilloscope or a high-speed streak camera.
  • the pulse timing difference may be indirectly detected by using a method such as a cross-correlation method (which, for example, collects two wavelength optical pulses on a semiconductor sensor capable of detecting two-photon absorption to detect a pulse timing difference between the two wavelength optical pulses). Controlling the time delay amount of the electrical delay line 111 according to the detected pulse timing difference enables synchronizing the first and second optical pulses with each other.
  • a cross-correlation method which, for example, collects two wavelength optical pulses on a semiconductor sensor capable of detecting two-photon absorption to detect a pulse timing difference between the two wavelength optical pulses.
  • the wave combiner 110 is constituted by a wavelength-multiplexing coupler and coaxially combines the first and second optical pulses.
  • the wave combiner 110 is not required to be a fiber coupler. That is, the first and second optical pulses may be output in the space through fiber collimators provided to fiber exit ends and then coaxially combined by a dichroic mirror or the like.
  • a device to coaxially combine them may be omitted.
  • A represents an envelope function of the optical pulse
  • z represents an optical-axis-directional coordinate
  • a propagation loss represents a group velocity dispersion
  • a third-order dispersion represents a third-order dispersion
  • T represents a period of time
  • a nonlinearity coefficient represents a frequency
  • T R represents a delayed Raman response.
  • the pulse generator 103 performs pulse generation at a repetition frequency of 40MHz. Since, on a basis of the following Document A, it is possible to generate an optical pulse with a pulse width of 55ps, which is a pulse width in full width of half maximum (FWHM), by using an intensity modulator, the pulse width of the generated optical pulse (first pulse) is 55ps.
  • FWHM full width of half maximum
  • the optical amplifier 104 amplifies the generated first optical pulse to a peak output power of 460W.
  • This amplification can be achieved by configuring the optical amplifier 104 as a two-stage optical amplifier such that the two stages respectively amplify the first optical pulse by approximately 20dB.
  • FIG. 3A illustrates a pulse waveform (time waveform) and a spectrum (power spectrum density) of the amplified first optical pulse.
  • the pulse waveform and the spectrum were each assumed to have a Sech shape. A chirp at a point of time after the amplification was disregarded.
  • FIG. 3B illustrates the calculation result of the pulse waveform and the spectrum corresponding to when the amplified first optical pulse is transmitted through the spectrum expander 105.
  • the spectrum width of the amplified first optical pulse was expanded to approximately 50nm (approximately 207cm -1 ).
  • FIG. 3C illustrates a pulse waveform of the first optical pulse with a compressed pulse width corresponding to when the dispersion parameter at the CFBG 202 of the pulse width compressor 106 is 0.39ps/nm.
  • the pulse width of the first optical pulse became approximately 2.7ps in FWHM.
  • a nonlinear effect in the circulator 201 and the CFBG 202 was disregarded.
  • FIG. 3D illustrates a pulse waveform and a spectrum of the first optical pulse corresponding to when the specific wavelength band at the TBPF 107 is approximately 1559.5 to 1560.5nm.
  • the pulse width was calculated using a Fourier transform of the spectrum.
  • the pulse waveform illustrated in FIG. 3D is double pulses.
  • the light source apparatus of this example is used for the CARS microscope or the SRS microscope, only the synchronized two wavelength optical pulses contribute to the scattering. Therefore, an earlier pulse of the double pulses that is generated several tens of ps earlier than a later pulse of thereof can be disregarded.
  • the specific wavelength band illustrated in FIG. 3D is merely an example. Even when other specific wavelength band is selected, a pulse waveform and a spectrum similar to those illustrated in the drawing are observed. Moreover, sequentially changing the specific wavelength band makes it possible to perform wavelength sweep in an entire wavelength band of the first optical pulse entering the TBPF 107.
  • the above-described configuration enables providing the first optical pulse having, in FWHM, a spectrum selection (sweep) width of approximately 50nm and a pulse width of approximately 7ps.
  • a wavelength and a mean output power of the second semiconductor laser 112 are 1064nm and 30mW, respectively.
  • the pulse generator 113 performs pulse generation at a repetition frequency of 40MHz, and the generated optical pulse (second optical pulse) has a pulse width of 55ps.
  • the optical amplifier 114 amplifies the generated second optical pulse to a peak output power of 460W.
  • FIG. 4A illustrates a pulse waveform (time waveform) and a spectrum (power spectrum density) of the amplified second optical pulse.
  • FIG. 4B illustrates the calculation result of the pulse waveform and the spectrum corresponding to when the amplified second optical pulse is transmitted through the spectrum expander 115.
  • the spectrum width was expanded to approximately 0.5nm.
  • FIG. 4C illustrates a pulse waveform of the second optical pulse with a compressed pulse width corresponding to when the dispersion parameter at the CFBG202 of the pulse width compressor 116 is 70ps/nm.
  • the above-described configuration enables providing the second optical pulse having a pulse width of approximately 4.6ps in FWHM.
  • the above-described pulse generation in the two lines can achieve a wave number resolution of 8cm -1 and a wavelength sweep width of approximately 207cm -1 .
  • Providing wide wavelength bands to both the two lines or adding another wavelength band line enables wave number selection and wavelength sweep in a wider wavelength band.
  • a pulse generator may be alternatively used which directory modulates a semiconductor laser by gain switching or the like.
  • a single semiconductor laser whose output is separated into two lines may be used.
  • the single semiconductor laser and the two separated lines constitute a light generator, a continuous light emitted from one of the two separated lines is used as a first laser light, and a continuous light emitted from the other of the two separated lines is used as a second laser light.
  • This example can realize a compact light source apparatus capable of stably generating two wavelength optical pulses allowing wavelength sweep.
  • Use of this light source apparatus for the CARS and SRS microscope (measurement apparatus) enables good detection of a molecular vibration spectrum (Raman spectrum) in a wide wavelength band.
  • Example 2 a light source apparatus to be used for an SRS measurement apparatus that is a first example (hereinafter referred to as "Example 2") of the present invention.
  • Example 2 the repetition frequency of one optical pulse of the first and second optical pulses is multiplied with respect to that of the other.
  • the light source apparatus of this example has a configuration in which a multiplying unit (multiplier) 1011 is added to the configuration of the light source apparatus of Example 1 (FIG. 1).
  • a multiplying unit (multiplier) 1011 is added to the configuration of the light source apparatus of Example 1 (FIG. 1).
  • constituent elements common to those of Example 1 are denoted by the same reference numerals as those of Example 1, and description thereof is omitted.
  • the multiplying unit 1011 is constituted by a frequency multiplying device such as a frequency doubler, a frequency tripler or a frequency multiplier.
  • the multiplying unit 1011 multiplies the repetition frequency of the timing signal input to the pulse generator 113. Thereby, the repetition frequency of the second optical pulse that is the above one optical pulse is multiplied with respect to that of the first optical pulse that is the other optical pulse.
  • doubling a repetition frequency of one of optical pulses enables improving an SNR (Signal to Ratio) in an SRS microscope. This is because a lock-in detection frequency can be maximized when the SRS microscope performs lock-in detection of an SRS signal from a sample.
  • an optical delay line using an optical fiber and a coupler as a multiplying unit 1011' may be inserted, as illustrated in FIG. 6, between the pulse generator 113 and the optical amplifier 114.
  • This example can realize a compact light source apparatus which is used for a measurement apparatus such as a biological microscope and capable of, with a simple configuration, emitting two wavelength optical pulses allowing wavelength sweep and having a repetition frequency ratio advantageous for lock-in detection.
  • this example multiplies the timing signal (second timing signal) output from the signal generator 101 and supplied to the pulse generator 113 to generate the second optical pulse at the repetition frequency corresponding to the integral multiple of the repetition frequency of the first optical pulse
  • the example of the present invention is not limited thereto.
  • a frequency divider may be employed which divides the repetition frequency of the timing signal (first timing signal) supplied to the pulse generator 103 such that the repetition frequency of the second optical pulse corresponds to the integral multiple of the repetition frequency of the first optical pulse.
  • the signal generator may be configured to output first and second timing signals that cause the repetition frequency of the second optical pulse to correspond to an integral multiple of the repetition frequency of the first optical pulse.
  • the signal generator may be configured to generate only one timing signal, to divide the timing signal into two and to output the two timing signals as the first and second timing signals.
  • the signal generator may be configured to output only the first timing signal to one of the pulse generators and to generate, in response to a signal from the one pulse generator to which the first timing signal is input, the second timing signal to be input to the other pulse generator.
  • Example 3 a light source apparatus to be used for an SRS measurement apparatus that is a second example (hereinafter referred to as "Example 3") of the present invention.
  • This example detects a pulse timing difference (relative time difference) between the first and second optical pulses and controls the first and second optical pulses (hereinafter collectively referred to as "two wavelength optical pulses”) by adjusting a time delay amount therebetween so as to synchronize them with each other.
  • FIG. 7 illustrates a configuration of the light source apparatus of Example 3.
  • a pulse timing detector (PTD) 1203 serving as a time difference detector and a synchronization controller (SC) 1204 are added to the configuration of the light source apparatus of Example 2 illustrated in FIG. 5.
  • constituent elements common to those of Examples 1 and 2 are denoted by the same reference numerals as those in Example 2, and description thereof is omitted.
  • Reference numeral 1201 denotes a fiber collimator that collimates an output light from an optical fiber to output a collimated light to a space.
  • Reference numeral 1202 denotes an objective lens that collects the two wavelength optical pulses to the pulse timing detector 1203 which detects the pulse timing difference between the two wavelength optical pulses.
  • the pulse timing difference can be detected by using a cross-correlation waveform showing a cross-correlation, such as two-photon absorption, between the two wavelength optical pulses. Since the cross-correlation waveform has a higher peak as the two wavelength pulses have wavelengths whose overlapping wavelength range increases, the cross-correlation waveform can be used as an index for evaluating the pulse timing difference between the two wavelength optical pulses.
  • a photodiode can be used which is composed of a semiconductor made by Si, InGaAs or the like and which has a low sensitivity in a wavelength band of two-photon absorption generated for only one of the two wavelength optical pulses but has a high sensitivity in a wavelength band of two-photon absorption between the two wavelength optical pulses.
  • the synchronization controller 1204 controls a delay amount of the electrical delay line 111 such that an electrical signal output from the pulse timing detector 1203 has a constant value, that is, such that the pulse timing difference is reduced. This configuration enables reducing the pulse timing difference between the two wavelength optical pulses.
  • FIG. 8 illustrates a configuration of a light source apparatus as a modified Example 3.
  • the modified example performs synchronization control of the two wavelength optical pulses, not by electrical delay adjustment, but by optical delay adjustment by using an optical delay line (OD) 1301.
  • OD optical delay line
  • the optical delay line 1301 is configured by providing a piezostage in an air-gap type variable delay line and coarsely adjusts a time delay amount given to the second optical pulse in a broad range at low speed.
  • a phase modulator (PM) 1302 performs phase modulation on the second optical pulse to finely adjust the time delay amount given to the second optical pulse at high speed.
  • the optical delay line 1301 and the phase modulator 1302 perform the synchronization control in a complementary manner in response to a feedback signal from the synchronization controller 1204.
  • the synchronization control may be performed only by using the optical delay line 1301 or by using the delay line 111 together.
  • This example can realize a compact light source apparatus capable of stably generating optical pulses whose wavelengths are mutually different and of performing wavelength sweep.
  • the spectrum expander and the pulse width compressor may be provided for at least one of the first and second optical pulses (the optical pulse whose wavelength is selected by the TBPF 107).
  • the TBPF 107 is provided only for the first optical pulse
  • the TBPF may be provided for each of the first and second optical pulses.
  • Example 4 will describe an SRS microscope as a measurement apparatus using, as a light source unit, any one of the light source apparatuses described in Examples 2 and 3. Simultaneously focusing, on to a sample, two wavelength optical pulses with a frequency difference (wavelength difference) that resonates with vibration of a molecule to be observed in the sample and thereby forcibly vibrating the molecule generates a phenomenon in which energy of a shorter wavelength-side optical pulse of the two wavelength optical pulses decreases and that of a longer wavelength-side optical pulse increases. This phenomenon is stimulated Raman scattering (SRS).
  • SRS microscope stimulated Raman scattering
  • the SRS microscope performs lock-in detection of the increase or decrease of the energy of the optical pulses to perform high-contrast and high-sensitivity molecular vibration imaging.
  • the SRS microscope is capable of acquiring Raman spectra by sweeping the wavelength difference between the two wavelength optical pulses and also of identifying a tissue structure and a composition of the sample.
  • FIG. 9 illustrates a configuration of the SRS microscope. The SRS microscope detects the decrease of the energy of the shorter wavelength-side optical pulse.
  • reference numeral 1401 denotes any one of the light source apparatuses described in Examples 2 and 3.
  • Reference numeral 1402 denotes a fiber collimator, and 1403 a scanning apparatus serving as a scanner that two-dimensionally scans the sample with the two wavelength optical pulses.
  • Reference numeral 1404 denotes an objective lens (objective optical system), and 1405 a sample stage that adjusts a position of the sample mounted thereon.
  • Reference numeral 1406 denotes a condenser lens, 1407 a mirror, and 1408 a wavelength filter.
  • Reference numeral 1409 denotes a sensor, and 1410 a lock-in detection apparatus that performs the lock-in detection of an output signal of the sensor 1409.
  • the sensor 1409 and the lock-in detection apparatus 1410 constitute a light detector.
  • Reference numeral 1411 denotes an image processing apparatus serving as a processor that processes the output signal of the lock-in detection apparatus 1410 and displays a resultant image.
  • the light source apparatus 1401 emits two wavelength optical pulses (first and second optical pulses) whose ratio of the repetition frequencies is 1:2.
  • An energy (wavelength) difference between the two wavelength optical pulses is set such that it approximately coincides with a vibrational level of the molecule to be observed which is contained in the sample.
  • the fiber collimator 1402 is attached. The two wavelength optical pulses output from the fiber collimator 1402 to a space are introduced to the scanning apparatus 1403.
  • the scanning apparatus 1403 is constituted by a dual-axis galvanometer mirror and two-dimensionally scans the sample with a light-focusing point of the two wavelength optical pulses.
  • a resonant mirror may be used instead of the galvanometer mirror.
  • the objective lens 1404 focuses the two wavelength optical pulses toward the sample.
  • the condenser lens 1406 collects light transmitted through the sample.
  • paired relay lenses may be provided which make a mirror surface of the scanning apparatus 1403 conjugate with an exit pupil plane of the objective lens 1404 to uniform a light quantity distribution on the sample during the scanning.
  • the condenser lens 1406 have a numerical aperture (NA) larger than that of the objective lens 1404.
  • the sample stage 1405 can be coarsely and minutely moved in two horizontal axis directions and a vertical direction. After the sample sandwiched by a slide glass and a cover glass is mounted on the sample stage 1405, the sample stage 1405 is driven to move the sample into a two-dimensionally scanning area scanned by the scanner 1403.
  • the mirror 1407 reflects the light from the condenser lens 1406 to introduce the light to the sensor 1409.
  • the wavelength filter 1408 transmits only the wavelength band of one of the two wavelength optical pulses which has a higher repetition frequency.
  • the sensor 1409 is constituted by a photodetector and converts the received optical pulse into an electrical signal. In order to efficiently collect the optical pulse on the light-receiving portion of the sensor 1409, another condenser lens may be placed at a position preceding the sensor 1409.
  • the lock-in detection apparatus 1410 is constituted by a so-called lock-in amplifier and performs lock-in detection of the output signal from the sensor 1409 at a frequency half of the repetition frequency of the optical pulse transmitted through the wavelength filter 1408.
  • a band-pass filter that removes frequency components other than the repetition frequency to be detected may be placed at a position preceding the lock-in detection apparatus 1410.
  • the image processing apparatus 1411 is constituted by a personal computer and analyzes the signal detected by the lock-in detection to convert the signal into a two-dimensional image and displays the image on a display.
  • the image processing apparatus 1411 may be used alternatively as a control apparatus for the scanning apparatus 1403 and the sample stage 1405.
  • any one of the light source apparatuses of Examples 2 and 3 can realize an entirely downsized SRS microscope capable of stably performing the molecular vibration imaging. Moreover, performing the wavelength sweep of the two wavelength optical pulses in the light source apparatus enables acquiring spectral information of the sample in a broader wavelength band.
  • the light source apparatus can be used also in other measurement apparatuses using two wavelength optical pulses such as a CARS microscope and an endoscope.
  • the present invention provides a Raman scattering measurement apparatus capable of efficiently measuring Raman scattering with a compact and simple configuration.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Optics & Photonics (AREA)
  • Health & Medical Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Immunology (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Pathology (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • Biochemistry (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Microscoopes, Condenser (AREA)
  • Lasers (AREA)

Abstract

L'invention concerne un appareil de mesure de diffusion de Raman qui comprend un générateur de lumière configuré pour générer une première lumière continue et une seconde lumière continue, dont les longueurs d'onde sont différentes les unes des autres, un générateur d'impulsion configuré pour générer une première impulsion optique et une seconde impulsion optique respectivement à partir de la première lumière continue et de la seconde lumière continue, et un détecteur de lumière configuré pour détecter la lumière dont l'intensité est modulée par une diffusion de Raman générée par la focalisation des première et seconde impulsions optiques sur un échantillon. Le générateur d'impulsion est configuré pour générer les première et seconde impulsions optiques de telle sorte qu'une fréquence de répétition de la seconde impulsion optique coïncide avec un multiple entier d'une fréquence de répétition de la première impulsion optique.
PCT/JP2015/001360 2014-03-14 2015-03-12 Appareil de mesure de diffusion de raman et procédé de mesure de diffusion de raman WO2015136939A1 (fr)

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Cited By (2)

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US10876894B2 (en) 2015-03-09 2020-12-29 Renishaw Plc Transmission Raman spectroscopy
DE102021103899A1 (de) 2021-02-18 2022-08-18 Toptica Photonics Ag Beleuchtungsvorrichtung für ein Konfokalmikroskop

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US9774161B2 (en) * 2015-02-18 2017-09-26 Toptica Photonics Ag Fiber delivery of short laser pulses
WO2019176115A1 (fr) * 2018-03-16 2019-09-19 光トライオード株式会社 Dispositif d'analyse de l'absorbance lumineuse
WO2023243052A1 (fr) * 2022-06-16 2023-12-21 日本電信電話株式会社 Source de lumière

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10876894B2 (en) 2015-03-09 2020-12-29 Renishaw Plc Transmission Raman spectroscopy
EP3268726B1 (fr) * 2015-03-09 2024-07-17 Renishaw Plc. Spectroscopie raman à transmission
DE102021103899A1 (de) 2021-02-18 2022-08-18 Toptica Photonics Ag Beleuchtungsvorrichtung für ein Konfokalmikroskop

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