JP2021181909A - Difference detection conjugate compensation cars measurement apparatus - Google Patents

Abstract

To provide CARS measurement capable of solving the problems to be solved of CARS that are stabilization of a CARS signal and improvement of resonance signal/non-resonance signal ratio; and capable of implementing measurement quantitatively.SOLUTION: A CARS measurement apparatus in which a pump light pulse is delayed with respect to a stokes light pulse in the pump light pulse and the stokes light pulse of CARS excitation, includes: a CARS excitation detection system of a sample to be measured and a non-resonance CARS excitation detection system of a reference sample that have a same optical system. The CARS measurement apparatus, in the non-resonance CARS excitation detection system of the reference sample, splits a non-resonant CARS light into two, and has a compensation signal detection system for detecting one of the non-resonant CARS lights; includes a difference detector 21 which outputs a difference between a photocurrent from a CARS light of the sample to be measured and a photocurrent from the other of the non-resonant CARS lights; has a signal processing system of a difference signal/non-resonance CARS signal; and thereby achieves stabilization of the CARS signal and improvement of the resonance signal/non-resonance signal ratio.SELECTED DRAWING: Figure 12

Description

The present invention relates to a differential detection conjugated compensation CARS (coherent anti-Stoke Raman scattering, hereinafter simply referred to as "CARS") measuring device.

Infrared vibration absorption spectroscopy is a technique for molecular identification. This measures the absorption of infrared light at the molecular frequency of the fingerprint region of each molecule. However, it is difficult to apply the measurement of molecules in the living body because the main component of the living tissue is water and infrared light absorbs a large amount of infrared light. On the other hand, Raman scattering measurement measures Raman scattered light whose frequency is shifted by the molecular vibration frequency with respect to the incident light. , Applicable. However, Raman scattered light is extremely weak, and increasing the sensitivity is an issue.

CARS (coherent anti-Stoke Raman scattering) technology solves this sensitivity problem. As shown in FIG. 1 (a), when CARS is simultaneously irradiated with a pump light pulse and a Stokes light pulse having a frequency difference Δω corresponding to the vibration absorption band of the molecule, the molecule is subjected to the ground level by the pump light pulse. As it rises from V = 0 to the upper level, it is guided to the excitation level V = 1 by the Stokes optical pulse. Further, after rising to the upper level by the pump light pulse, anti-Stokes light is generated in the process of relaxing to the base level V = 0. Due to the energy level, the frequencies of Stokes light and anti-Stokes light are the frequencies folded back by Δω around the _{pump light ω p , and ω s} = ω _{p −} Δω, ω _as = 2 _{ω p} −ω _s . Become. Since ω _p and ω _s can be roughly set, if this is set in the near infrared region, the information of Δω of infrared vibration absorption can be measured by anti-Stokes light by pump light and Stokes light of two wavelengths in the near infrared region. ..

CARS signal intensity I _CARS (Ω) is proportional to the product of the _{square of the pump light intensity P pump} and the Stokes light intensity P _stokes , reflecting the excitation process, and has the characteristic of [Equation 1]. Due to this characteristic, Raman scattered light measurement (Equation 1)
I _CARS (Ω) ∝ P _pump ²・ P _stokes
On the other hand, a large signal strength can be secured. The pulse energy stability of a normal pulse laser is about ± 3%. Then, the CARS signal stability is (0.97) ³ = 0.91, which is approximately ± 10%. This poor stability of the CARS signal is that CARS is suitable for substance identification, but unsuitable for substance quantification. This is a major issue when applying CARS to quantitative measurement.

Stabilization of the CARS signal has problems other than the above-mentioned stabilization of pulse energy. In CARS, the pump optical pulse and the Stokes optical pulse must match in six elements: time (t), polarized light (p), frequency difference (ω), and three spatial axes (x, y, z). It is disclosed that the coincidence between the pump optical pulse and the Stokes pulse on the time axis can be solved by using the two wavelengths of OPO oscillation for CARS excitation. Further, the frequency difference between the pump light and the Stokes light corresponding to the molecular vibration level is allowed to fluctuate within the molecular vibration spectrum width range. On the other hand, fluctuations in the polarization axes of pump light and Stokes light greatly affect the CARS excitation efficiency. In addition, the laser light source usually has a pointing fluctuation of the laser light, which leads to a fluctuation of the focusing position of the pump light and the Stokes light, which becomes a fluctuation factor of the CARS signal. Stabilization of the CARS signal, which suppresses the fluctuation factors of the CARS signal, is a major issue when applying CARS to quantitative measurement.

Another issue of CARS is the non-resonant signal. The CARS signal does not go through the resonance process (Fig. 1 (a)), which is relaxation to the V = 0 level by anti-Stokes light generation via the V = 1 level of molecular vibration, and not through the V = 1 level (Fig. 1 (a)). There are two types based on the non-resonant process (FIG. 1 (b)), which is relaxation to the V = 0 level by anti-Stokes light generation (via virtual level). The S / N ratio of the CARS signal is determined by the real resonance signal / non-resonance signal ratio. Therefore, various methods for securing the resonance signal / non-resonance signal ratio are being studied.

The frequency modulation CARS technique is known to realize the improvement of the resonance signal / non-resonance signal ratio. CARS is a kind of third-order nonlinear optical effect. The optical electric field of CARS light ^{is proportional to the third-order nonlinear susceptibility χ (3),} _{and the difference frequency characteristic I CARS} (Ω) of CARS signal intensity is calculated by the following equation 2. It is already known that it will be decided.
(Number 2)
I _CARS (Ω) ∝ ∣ χ ⁽³⁾ _R (Ω) ＋ χ ⁽³⁾ _NR ∣ ²
= ∣ χ ⁽³⁾ _R (Ω) ∣ ² + (χ ⁽³⁾ _NR ) ² + 2Re {χ ⁽³⁾ _R (Ω)} χ ⁽³⁾ _NR
Will be. Here, χ ⁽³⁾ _R (Ω) is the third-order nonlinear susceptibility of the resonance signal, and χ ⁽³⁾ _NR is the third-order nonlinear susceptibility of the non-resonant signal. FIG. 2A shows the characteristics of the three terms of [Equation 1] in the vicinity of the resonance frequency. _{FIG. 2 (b) shows I CARS} (Ω) and (χ ⁽³⁾ _NR ) ² as the sum of the three terms of [Equation 1]. Now, when the difference frequency δ = ωp−ωs between pump light and Stokes light is changed over time (frequency modulation), I _CARS (Ω) becomes a signal in which the resonance signal of the AC component is superimposed on the non-resonance signal of the DC component. .. That is, since _{the DC component of I CARS} (Ω) is a non-resonant signal and the AC component is a resonance signal, it is possible to selectively detect only the resonance signal by measuring the amplitude level of the AC component. However, if the stability of the non-resonant signal, which should be a DC component, is poor, the non-resonant signal is mixed with the AC component of the resonance signal, which does not lead to an improvement in the resonance signal / non-resonance signal ratio. In order to utilize the original characteristics of frequency modulation CARS, it is essential to stabilize the CARS signal.

Another thing that realizes the improvement of the resonance signal / non-resonance signal ratio is the polarization difference CARS. Focusing on the fact that the resonance signal has a real component and an imaginary component, the imaginary component is directly related to the spontaneous Raman spectrum, and the non-resonant signal has only the real component, two CARS in orthogonal polarization. By simultaneously generating signals and subtracting the two signals, the real component is canceled, while the imaginary component is enhanced and only the resonance signal is selected. Again, the CARS signal needs to be stabilized for the subtraction process of the two signals to function steadily.

Further, there is an interference difference CARS that realizes an improvement in the resonance signal / non-resonance signal ratio. The pump light with the extended pulse width and the idler light from the optical parametric amplifier (OPA) with the original pump light as the excitation light are CARS excited as Stokes light, and the resonance CARS generated in the pump light pulse single region. Light is detected by interfering with OPA signal light, and resonance CARS light is selected and detected. Since this also detects the interference component (AC component), the stability of the CARS signal is required.

When applying CARS to quantitative measurement in this way, stabilizing the CARS signal and securing the resonance signal / non-resonance signal ratio are major issues.

Patent 4618341 Patent 5901346 Patent 6606803 Special table 2013-536415

Optics Letters. 2006 Vol.31 (12): 1872-1874 Applied Physics Letters. 2004 Vol.85 (23): 5787-5789

It stabilizes the CARS signal and realizes selective measurement of the resonant CARS signal.

It is characterized by having a CARS excitation detection system for the sample to be measured having the same optical system and a non-resonant CARS excitation detection system for the reference sample, and having a signal processing system of {(CARS signal to be measured / non-resonant CARS signal) -1}. CARS measuring device

A CARS excitation detection system for the sample under test and a non-resonant CARS excitation detection system for the reference sample, which have the same optical system, are provided. It has a compensation signal detection system that detects light, and is equipped with a difference detector that outputs the difference between the CARS light of the sample to be measured and the optical current from the other non-resonant CARS light (difference signal / non-resonant CARS signal). CARS measuring device characterized by having a signal processing system of.

The CARS measuring device according to the above description, wherein the pump optical pulse is delayed with respect to the Stokes optical pulse in the CARS-excited pump optical pulse and the Stokes optical pulse.

In the CARS-excited pump light pulse and Stokes light pulse, the delay time Dt of the pump light pulse with respect to the Stokes light pulse is 0.83T ≤ Dt ≤ 1 when the pulse width of both light pulses is T at half-value full width (FWHM). The CARS measuring device according to the above description, which is characterized by being .03T.

It is equipped with a CARS excitation detection system for the sample under test and a non-resonant CARS excitation detection system for the reference sample, which have the same optical system, and is stable by performing signal processing of {(CARS signal under test / non-resonant CARS signal) -1}. Realizes the measurement of the resonance signal component.

Table 1 adjusts the OPO2 wavelength to the pump light wavelength of 1003 nm and the Stokes light wavelength of 1133 nm corresponding to the CO expansion and contraction vibration band of glucose, 1130 cm ^-1 , and stabilizes the CARS signal when 1 mol glucose aqueous solution and distilled water are CARS excited respectively. It is the result of comparing the stability of degree and (glucose CARS signal / distilled water CARS signal). Since the repetition frequency of OPO is 45Hz, the mean, standard deviation (SD), and standard deviation / mean of 45 pulses are compared. Comparing the fluctuations of 45 pulses with the standard deviation / average, the glucose CARS signal and the distilled water CARS signal each have a large fluctuation of about 20% due to the influence of various fluctuation factors of CARS excitation. On the other hand, (glucose CARS signal / distilled water CARS signal) is suppressed to 3.8% by compensation processing (conjugate compensation processing) using signals obtained in the same optical system.

Next, for glucose concentration (glucose CARS signal-distilled water CARS signal) / distilled water CARS signal = (glucose CARS signal / distilled water CARS signal) -1
The result of the measurement is shown in FIG. Since the glucose CARS signal includes a glucose CARS resonance signal and a non-resonance signal, and the distilled water CARS signal is only a non-resonance signal, the vertical axis in FIG. 3 is a glucose CRAS resonance signal. From FIG. 3, it can be seen that the linearity is obtained in the range of glucose concentration of 1 mol to 0.1 mol, and the quantitative measurement of glucose is possible. The low concentration side is suppressed at 0.1 mol because the dynamic range of the photodetector is taken by the non-resonant component in the glucose CARS signal.

Therefore, the CARS excitation detection system of the sample to be measured and the non-resonant CARS excitation detection system of the reference sample having the same optical system are provided. It has a compensation signal detection system that detects resonant CARS light, and is equipped with a differential detector that outputs the difference between the CARS light of the sample under test and the optical current from the other non-resonant CARS light (difference signal / non-resonant CARS). By having a signal processing system (signal), the measurement dynamic range can be expanded.

FIG. 4 is a plot of the signal obtained by performing conjugate compensation processing on the difference signal from the difference detector with respect to the glucose concentration. The lower limit of glucose concentration has expanded from 0.1 mol to 0.01 mol.

In order to further expand the dynamic range, the resonance signal component is enhanced by delaying the pump optical pulse with respect to the Stokes optical pulse in the CARS-excited pump optical pulse and the Stokes optical pulse.

In the resonance process shown in FIG. 1, the molecule under test exists at V = 1 at the excited level. Therefore, if the pump light for the probe (pump light in the subsequent stage) is irradiated within the excitation level lifetime, the simultaneous generation of the pump light for the probe and the Stokes light is not necessarily required to generate the resonance CARS light. On the other hand, in the non-resonant process, non-resonant CARS light is generated via the virtual level, so the simultaneity of the pump light and the Stokes light is indispensable. Focusing on this difference in characteristics, it is possible to enhance the resonance signal by delaying the pump optical pulse with respect to the Stokes optical pulse and performing CARS excitation. The situation is shown in FIG. When the pump light pulse and the Stokes light pulse in (1) in the figure are simultaneously irradiated to the sample to be measured, CARS excitation of the resonance process and the non-resonance process occurs in the time domain where both pulses overlap. Resonant CARS light and non-resonant CARS light are generated in an aqueous glucose solution, and the ratio of non-resonant CARS light is larger. Only non-resonant CARS light is generated from distilled water. On the other hand, in the case of (2) where the pump light pulse is delayed by half the pulse width (FWHM) with respect to the Stokes light pulse, the resonant CARS light and the non-resonant CARS light are in the time region (gray hatch part) where both pulses overlap in the glucose aqueous solution. Is generated, and only resonance CARS light is generated in the time region (diagonal line hatch portion) of the pump light pulse that does not overlap with the Stokes light pulse. In distilled water, non-resonant CARS light is generated in the time domain where both pulsed lights overlap. Therefore, the CARS resonance signal remaining by the signal processing of (glucose CARS signal-distilled water CARS signal) is enhanced in (2) rather than (1).

FIG. 6 shows the result of measuring the relationship between the time delay amount of the pump light pulse and the ratio of the resonance signal / non-resonance signal with respect to the Stokes light pulse. When the pulse width of both pulsed lights was 6 ns, the delay amount Dt became resonance signal / non-resonance signal ≧ 1 in the range of 5 ns <Dt <6.2 ns, and the resonance signal was enhanced.

FIG. 7 shows the result of plotting the differential conjugate compensation signal against the glucose concentration by the differential signal conjugate compensation in which the pump optical pulse is passed through the optical delay path and delayed by 5.6 ns with respect to the Stokes optical pulse. By enhancing the resonance signal by the pump optical pulse delay, the linearity of the differential conjugate compensation signal can be ensured in the range of glucose concentration of 1 mol to 0.002 mol. This indicates that the glucose concentration of 0.002 mol = 36 mg / dl can be measured.

As described above, quantitative measurement up to 36 mg / dl can be realized by differential conjugated compensation consisting of the same optical system of pump optical pulse delayed excitation.

The figure which shows the relationship between the molecular vibrational bands of the resonance process and the non-resonance process of CARS. The figure which shows the non-linear susceptibility and the frequency characteristic of a CARS signal. The figure which shows the characteristic of the difference value of a glucose concentration vs. a conjugate compensation signal Figure showing the characteristics of glucose concentration vs. direct difference detection conjugated compensation signal The figure which shows the relationship between the resonance signal and the non-resonance signal of simultaneous timing excitation of pump light and Stokes light and pump light delay excitation. Diagram showing the characteristics of the delay time of the pump optical pulse vs. the resonance signal / non-resonance signal. Glucose Concentration vs. Delay Pump Optical Pulse Excitation Direct Difference Detection Conjugated Compensation Signal Characteristics The block diagram which shows the 1st Embodiment of this invention. The block diagram which shows the 2nd Embodiment of this invention. The block diagram which shows the 3rd Embodiment of this invention. The block diagram which shows the 4th Embodiment of this invention. The block diagram which shows the 5th Embodiment of this invention.

Example 1 is shown in FIG. 8, Example 2 is shown in FIG. 9, Example 3 is shown in FIG. 10, Example 4 is shown in FIG. 11, and Example 5 is shown in FIG. The difference between Example 1 and Example 2 is that OPO 2-wavelength light with polarized light is used for CARS excitation via a polarizing element with an optical axis of 45 degrees, or OPO 2-wavelength light with polarized light is once separated by a polarizing beam splitter. The difference is whether one is rotated 90 degrees in the polarization direction with a λ / 2 plate, and then the dichroic mirror is used to re-wavelength coaxially and use it for CARS excitation. The same applies to the difference between Example 3 and Example 4. Further, the difference between Example 1 and Example 2 and Example 3 and Example 4 is that the difference processing between the signals obtained by photoelectric conversion and amplification in the light detection is performed and the signal processing of the compensation processing is performed, or the difference detection in the light detection. It is the difference between taking out the signal that is differentiated and amplified in the state of the optical current by the device and performing the signal processing of the compensation processing. In the fifth embodiment, an optical delay path for imparting a time delay of the pump optical pulse is provided in the fourth embodiment.

FIG. 8 shows Example 1. The 101 optical parametric oscillator (OPO) is excited by an excitation laser (not shown in the figure), and the signal light and idler light oscillate coaxially. When the excitation laser light is P-polarized, the signal light is S-polarized and the idler light is P-polarized. When CARS excitation is performed with the oscillation two-wavelength light of 101OPO, the signal light becomes the pump light and the idler light becomes the Stokes light.

Coaxial 1-pump light (S-polarized light) and 2-Stokes light (P-polarized light) from 101OPO are split into two by a 4-half beam splitter via a 3-reflector. One is for measurement and the other is for reference.

Coaxial 1-pump light and 2-Stokes light for measurement are focused on a 7a sample cell for measurement by a 6a condenser lens as light with a 45-degree polarization axis aligned by a 5-polarizer with an optical axis of 45 degrees. NS. The CARS light generated in the condensing region is collected by an 8a collimated lens to become parallel light, and is measured by an 11a photodetector via a 9-variable ND filter and a 10a filter that cuts pump light and Stokes light. The 102 optical path length adjusting unit equalizes the measurement side optical path length from the 4 half beam splitter to the 6a condenser lens and the optical path length from the 4 half beam splitter to the 6b condenser lens. As a result, a conjugated optical system on the measurement side and the reference side is established. The 9-variable ND filter is for arranging distilled water cells on the measurement side and the reference side before measurement and calibrating the measurement side CARS signal strength to the same level as the reference CARS signal strength described later.

The coaxial 1-pump light and 2 Stokes light for reference are focused on the 7b sample cell for reference via a 5b polarizing element and a 6b condenser lens as in the case of measurement. Hereinafter, the CARS light is measured by the 11b photodetector in the same manner as for the measurement.

Assuming that the sample on the measurement side is an aqueous glucose solution and the sample on the reference side is distilled water, the 12G signal from the 11a photodetector consists of a CARS resonance signal of glucose and a CARS non-resonance signal of water. On the other hand, the 13W signal is only the CARS non-resonant signal of water. The 103 signal processing unit outputs a 14-difference conjugate compensation signal {(glucose CARS resonance signal / CARS non-resonance signal) -1} by subtracting the 12G signal and the 13W signal, and further performing division processing with the 13W signal. .. By performing this difference-conjugated compensation processing, various variable factors associated with CARS excitation can be collectively compensated, and a stable CARS resonance signal of the molecule to be measured can be measured.

FIG. 9 shows Example 2. Coaxial 1-pump light (S-polarized light) and 2-Stokes light (P-polarized light) from OPO are separated by a 15-polarized beam splitter, and 1-pump light (S-polarized light) is converted to 1-pump light (P-polarized light) by a 16λ / 2 plate. , 1 pump light (P polarized light) and 2 Stokes light (P polarized light) are coaxially combined on a 17-dycroic mirror. Subsequent operations are the same as in the first embodiment. However, since the 1-pump light and the 2-Stokes light have the same polarization in the embodiment, the 5-polarizer arranged in the first embodiment is unnecessary on both the measurement side and the reference side. The transducer aligns the polarization of orthogonally polarized light in the 45 degree direction, but the optical power is reduced to 1 / √2. On the other hand, in the second embodiment, since the polarizing element is not required, there is an effect that the optical power can be effectively used.

In the first and second embodiments, the difference processing of the CARS signals on the measurement side and the reference side is performed by taking the difference between the output signals from the respective photodetectors. The signal on the measurement side is the sum of the CARS resonance signal and the non-resonance signal of the molecule to be measured, and the resonance signal / non-resonance signal = about 1/5, and most of the output signals are non-resonance signal components. Therefore, the dynamic range of the photodetector is occupied by the non-resonant signal, and the dynamic range of the resonance signal cannot be sufficiently secured. Example 3 is an improvement in this respect. FIG. 9 shows Example 3. A 21 difference detector is used that can make a difference in the photocurrent itself of the photoelectric conversion element by CARS light on the measurement side and the reference side. As a result, the CARS non-resonant component is canceled at the time of the photocurrent, and only the CARS resonance component remains as the photocurrent. Therefore, the entire dynamic range of the detector can be allocated to the CARS resonance signal. The 19 condenser lenses and 20 optical fibers on the measurement side and the reference side are for optical guidance to the 21 difference detector. Another difference from Example 1 is that the 23 CARS non-resonant signal for conjugate compensation of the 22 direct difference signals from the difference detector is taken out, so that the 10b filter and 11b are passed through an 18 half mirror after the 8b collimating lens on the reference side. A photodetector is provided. The 22 direct difference signal and the 23 CARS non-resonant signal from the 21 difference detector are formed into a 24 direct difference conjugate compensation signal by the division process of (22 direct difference signal / 23 CARS non-resonant signal) in the 103 signal processing unit. This allocates the entire dynamic range of the photodetector to the difference signal.

FIG. 11 shows Example 4. In the fourth embodiment, the configuration shown in the third embodiment is added so that the differential conjugated compensation signal can be directly acquired in the second embodiment.

FIG. 12 shows Example 5. The fifth embodiment has a function of further expanding the dynamic range of the fourth embodiment. In the CARS-excited pump light pulse and Stokes light pulse, the resonance signal component is enhanced by delaying the pump light pulse with respect to the Stokes light pulse. 1 pump light (S polarized light) and 2 Stokes light (P polarized light) of orthogonal polarization from 101OPO are separated by a 15 polarized beam splitter, and 1 pump light (S polarized light) is separated by 1 pump light (P polarized light) with a 16λ / 2 plate. Then, after adjusting the optical path length difference between the pump light and the Stokes light between the 15 polarization beam splitter and the 17 dichroic mirror at the 104 light delay part that generates a time delay for the 2 Stokes light, it is coaxially on the 17 dichroic mirror again. To meet the waves. The 25-beam reducer in the 1-pump light (P-polarized) optical path corrects the inconsistency with the beam diameter of the 2-Stokes light on the 17-dichroic mirror caused by the long-optical path length propagation of the 1-pump light (P-polarized). Is. The functions after the 17 dichroic mirror are the same as those in the fourth embodiment. As a result, the CARS resonance signal of the molecule to be measured on the measurement side is enhanced by the effect of the delay pump optical pulse, the dynamic range of CARS resonance signal detection is further expanded as compared with Example 4, and the minimum detection sensitivity is improved.

These bring great practicality to CARS, which has been extremely poor in practicality, and have the effect of generalizing the characteristics of in-vivo molecular measurement originally possessed by CARS technology.

1 Pump light 2 Stokes light 3 Reflector 4 Half beam splitter 5 Splitter 6 Condensing lens 7 Sample cell 8 Collimated lens 9 Variable ND filter 10 Filter 11 Light detector 12 G signal 13 W signal 14 Difference conjugate compensation signal 15 Polarized beam Splitter 16 λ / 2 Plate 17 Dycroic Mirror 18 Half Mirror 19 Condensing Lens 20 Optical Fiber 21 Difference Detector 22 Direct Difference Signal 23 CARS Non-Resonance Signal 24 Direct Difference Coupling Compensation Signal 25 Beam Shrinker 101 Optical Parametric Oscillator (OPO)
102 Optical path length adjustment unit 103 Signal processing unit 104 Optical delay unit a in the same number indicates the measurement side, and b indicates the reference side.

Claims (4)

It is characterized by having a CARS excitation detection system for the sample to be measured having the same optical system and a non-resonant CARS excitation detection system for the reference sample, and having a signal processing system of {(CARS signal to be measured / non-resonant CARS signal) -1}. CARS measuring device A CARS excitation detection system for the sample under test and a non-resonant CARS excitation detection system for the reference sample, which have the same optical system, are provided. It has a compensation signal detection system that detects light, and is equipped with a difference detector that outputs the difference between the CARS light of the sample to be measured and the optical current from the other non-resonant CARS light (difference signal / non-resonant CARS signal). CARS measuring device characterized by having a signal processing system of. The CARS measuring device according to claim 2, wherein the pump optical pulse is delayed with respect to the Stokes optical pulse in the CARS-excited pump optical pulse and the Stokes optical pulse. In the CARS-excited pump light pulse and Stokes light pulse, the delay time Dt of the pump light pulse with respect to the Stokes light pulse is 0.83T ≤ Dt ≤ 1 when the pulse width of both light pulses is T at half-value full width (FWHM). The CARS measuring device according to claim 3, characterized in that it is .03T.

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