JP2009229310A - Device and method for measuring spectrum phase of discrete spectrum - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the spectral phase of a discrete spectrum at a high speed and high sensitivity. <P>SOLUTION: A measuring device measures the spectral phase of the discrete spectrum observes a state, where each spectral ray mutually interferences with an observation device 16 by regarding one light to be measured L1a, L1a separated with a beam splitter 11 from laser lights L1, L2 as the exciting light; generates a wide-band discrete spectrum with a cell 12 for generating wide-band discrete spectrum including a non-linear medium 12A; gives a delay amount with a light delay unit 13 to the other lights to be measured L1b, L2b separated with the beam splitter 11; mixes a spectrum generated with the cell 12 for generating the wide-band discrete spectrum and the other lights to be measured L1b, L2b delayed by the light delay unit 13 to generate a sum frequency spectrum, by passing a non-linear optical crystal 14B of a sum frequency spectrum generator 14; and variably controls the delay amount given to the other lights to be measured L1b, L2b with the light delay unit 13 by a control part 15. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a spectrum phase measurement of a discrete spectrum in a broadband discrete spectrum generator that generates a broadband discrete spectrum by inducing a coherent refractive index change of a frequency corresponding to the difference frequency in the nonlinear medium of the two-wavelength excitation laser light. The present invention relates to an apparatus, a spectral phase measurement method of a discrete spectrum, and a frequency control method thereof.

  In recent years, it has become possible to amplify the vibration and rotation states of gas molecules adiabatically and to generate molecules with high coherence approaching the maximum value between two specific levels at high density. A group of molecules having high coherence behaves as a medium that periodically changes the refractive index at the transition frequency between corresponding quantum states, and can modulate light passing therethrough with high efficiency. As a result, a broadband discrete spectrum called Raman sideband light is generated.

  For the generation of Raman coherence, two types of laser beams having a frequency difference corresponding to the Raman transition are simultaneously incident. By slightly detuning the frequency difference from the resonance frequency of the Raman transition, a superposition state between the two levels can be generated adiabatically. Optical modulation by a group of molecules having high coherence has a characteristic that all Raman sideband light is generated coaxially with the excitation light because of high frequency conversion efficiency. This works favorably for the generation of ultrashort pulses by Fourier synthesis, and is attracting attention as a realistic new technique for generating ultrashort pulses.

  In addition, femtosecond ultra-short pulse light can be used not only for non-destructive and non-invasive substance measurement using nonlinear optical response, ultra-fine processing of glass, metal and semiconductor, cell cutting and manipulation, etc. Expected to be applied to OCT (Optical Coherence Tomography) that images the inside of an object using coherence, a light source of a multiphoton microscope, a terahertz wave generator with a wavelength of 30 μm to 3 nm, which becomes an electromagnetic wave for inspection instead of X-rays, etc. Yes.

JP-A-2005-251810

  By the way, when a high-intensity laser beam having two wavelengths slightly detuned from Raman resonance is irradiated with a molecule, a high coherence can be generated in the molecule. As a result, a broadband discrete light called Raman sideband light is generated. The spectrum can be generated simultaneously and coaxially. If appropriate phase compensation is performed on the sideband light, it is possible to generate ultrafast pulses with ultrafast repetition due to spectral discreteness. This is essentially different from conventional ultrashort pulse generation, and a high repetition frequency exceeding the response limit of the electrical element can be achieved. Generating ultrashort pulses from a broadband spectrum requires pulse compression, ie, spectral phase compensation. However, so far, no phase measurement method for such a discrete spectrum has been established, so that advanced dispersion compensation has not been possible. Until now, it was mostly evaluated by the method of performing autocorrelation measurement after generating appropriate pulses, but there were problems such as that it could not be evaluated without a certain degree of pulsing, and phase information could not be evaluated correctly .

  Accordingly, an object of the present invention is to provide a discrete spectrum spectrum phase measuring apparatus and a discrete spectrum spectrum phase measuring method capable of measuring the spectrum phase of a discrete spectrum at high speed and with high sensitivity in view of the conventional situation as described above. There is to do.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the embodiments described below with reference to the drawings.

  In the present invention, the phase of a discrete spectrum derived from two frequency components is evaluated from interference between two types of sum frequency spectra. For example, a sum frequency spectrum of a Raman sideband and a fundamental wave of two wavelengths used for the generation is generated, and the spectrum phase is measured using interference between the two sum frequency spectra. By controlling the delay of the fundamental wave, the interference condition between each component of the discrete spectrum can be continuously swept, and the spectrum phase can be estimated from the state of the interference.

  That is, the present invention is a discrete spectrum spectral phase measuring device, which is a beam splitter for separating laser light of two wavelengths for generating a discrete spectrum, which is measured light, into one measured light and the other measured light. The one measured light separated by the beam splitter is incident as excitation light, includes a nonlinear medium, and the nonlinear medium of the two-wavelength laser light that is the one measured light incident as the excitation light A broadband discrete spectrum generating cell for generating a broadband discrete spectrum by inducing a coherent refractive index change of a frequency corresponding to a difference frequency in the optical delay, and an optical delay in which the other measured light separated by the beam splitter is incident And a broadband generated by the broadband discrete spectrum generating cell using the one measured light as excitation light. A sum frequency spectrum generator for generating a sum frequency spectrum by passing a non-linear optical crystal in which the diffuse spectrum and the other measured light delayed by the optical delay device are mixed and incident; and the optical delay device A control unit that variably controls the amount of delay given to the other measured light by the above and an observation device that spectrally observes the sum frequency spectrum generated by the sum frequency spectrum generator, By controlling the delay amount of the delay device and observing with the observation device how the spectral lines of the sum frequency spectrum generated by the sum frequency spectrum generator interfere with each other, the phase difference between the spectral lines can be determined. The phase of the light to be measured is estimated.

  The discrete spectrum spectral phase measurement apparatus according to the present invention, for example, controls the delay amount of the optical delay device by the control unit and sweeps the delay amount to be given to the other measured light. The optical frequency corresponding to the reciprocal of the frequency interval is set to one period, the interference condition of all the sum frequency components is changed, and the sum frequency spectrum generated by the sum frequency spectrum generator is spectrally observed by the observation device.

  In the discrete spectrum spectral phase measuring apparatus according to the present invention, for example, the broadband discrete spectrum generating cell includes a Raman medium as a nonlinear medium.

  The present invention is a method for measuring a spectrum phase of a discrete spectrum, wherein a laser beam having two wavelengths for generating a discrete spectrum, which is a measured light, is separated into one measured light and the other measured light by a beam splitter, One of the measured light beams separated by the beam splitter is incident on a broadband discrete spectrum generating cell including a nonlinear medium as excitation light, and the difference in the two-wavelength laser light, which is the one measured light beam, in the nonlinear medium. A coherent refractive index change corresponding to the frequency is induced to generate a wideband discrete spectrum, and the other measured light separated by the beam splitter is incident on an optical delay device, so that the other measured A delay amount is given to the two-wavelength laser light that is light, and the broadband discrete spectrum is obtained using the one measured light as excitation light. A wideband discrete spectrum generated by the cell and the other measured light delayed by the optical delay device are mixed and passed through the nonlinear optical crystal of the sum frequency spectrum generator to generate a sum frequency spectrum. The delay amount given to the other measured light is variably controlled by the optical delay device, and the observation device observes how the spectral lines of the sum frequency spectrum generated by the sum frequency spectrum generator interfere with each other. Thus, the phase of the light to be measured is estimated from the phase difference between the spectral lines.

  According to the present invention, the spectrum phase of a discrete spectrum can be measured at high speed and with high sensitivity.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  The present invention is applied to, for example, a spectral phase measurement apparatus 10 for a discrete spectrum configured as shown in FIG.

  This spectral phase measuring apparatus 10 is a beam splitter 11 that separates laser light L1 and L2 having two wavelengths for generating a discrete spectrum, which is measured light, into one measured light L1a and L2a and the other measured light L1b and L2b. A broadband discrete spectrum generating cell 12 on which one of the measured light beams L1a and L2a separated by the beam splitter 11 is incident as excitation light, and the other measured light beams L1b and L2b separated by the beam splitter 11 , The broadband discrete spectrum generated by the broadband discrete spectrum generating cell 12 using the one of the measured light beams L1a and L2a as pumping light, and the optical delayer 13 delayed by the optical delayer 13 A sum frequency spectrum for generating a sum frequency spectrum by combining the other measured light beams L1b and L2b The generator 14, the control unit 15 that variably controls the amount of delay given to the other measured light L1b, L2b by the optical delay device 13, and the sum frequency spectrum generated by the sum frequency spectrum generator 14 are spectrally separated. And an observation device 16 for observation.

  The laser light source 20 that enters the laser light L1 and L2 having two wavelengths for generating a discrete spectrum, which is the measurement light, includes, for example, the first laser light source 20A that generates the laser light L1 having the first frequency f1, and the first laser light source 20A. A second laser light source 20B that generates laser light L2 having a frequency f2 of 2, a first laser light L1 generated by the first laser light source 20A, and a second laser light source 20B generated by the second laser light source 20B. And an optical system 20C for emitting two-wavelength excitation laser light.

  The broadband discrete spectrum generating cell 12 includes a nonlinear medium 12A, and the difference between the two laser light beams L1a and L2a of the two wavelengths in the nonlinear medium 12A using the one measured light L1a and L2a as excitation light. A broadband discrete spectrum is generated by inducing a coherent refractive index change of the corresponding frequency. As the nonlinear medium 12A, for example, a Raman medium (parahydrogen) is used, and when the two-wavelength laser beams L1a and L2a are incident, a high-order sideband is generated through a Raman process, and a broadband discrete spectrum is obtained. Is generated.

  The optical delay device 13 varies the optical path length through which the other measured light L1b, L2b passes in accordance with a control signal from the control unit 15, thereby providing a delay to the other measured light L1b, L2b. The amount can be varied.

  The sum frequency spectrum generator 14 is delayed by the broadband discrete spectrum generated by the broadband discrete spectrum generating cell 12 using the one measured light L1a and L2a as excitation light and the optical delay device 13. An optical system 14A for mixing the other measured light L1b and L2b, and a nonlinear optical crystal 14B on which the broadband discrete spectrum mixed by the optical system 14A and the other measured light L1b and L2b delayed are incident. It consists of.

  The sum frequency spectrum generator 14 generates the sum frequency spectrum by mixing the broadband discrete spectrum and the delayed other measured light L1b, L2b by the optical system 14A and passing through the nonlinear optical crystal 14B. Let At this time, two different sum frequency spectra derived from the two excitation lights are simultaneously generated. When this is observed with a spectroscope in the observation device 16, it can be observed that the spectral lines of the sum frequency overlap in the frequency space and interfere with each other. The condition for strengthening or weakening the interference corresponds to the phase difference between the spectral lines, and from this, the phase of the light under measurement can be estimated.

  That is, for example, as shown in FIG. 2, the intensity of interference appears at different phases, and the spectrum phase can be known from this information. Analyzing the direction in which the delay is applied and the direction of the change in the interference spectrum, it is possible to extract information about the front-rear direction of the ultrashort pulse, although it is a second-order nonlinear effect.

  Therefore, in the spectral phase measuring apparatus 10, when the delay amount of the optical delay device 13 is controlled by the control unit 15 and the delay amount given to the other measured light L1b, L2b is swept, the frequency interval of the discrete spectrum is obtained. The interference condition of all sum frequency components changes with an optical delay corresponding to the reciprocal of 1 as one period.

  That is, in the spectrum phase measuring apparatus 10, the laser light L1 and L2 having two wavelengths for generating a discrete spectrum, which is the light to be measured, is separated by the beam splitter 11, and one of the light to be measured L1a separated by the beam splitter 11 is used. , L2a is incident on the broadband discrete spectrum generating cell 12 including the nonlinear medium 12A as excitation light, and corresponds to the difference frequency in the nonlinear medium 12A of the two-wavelength laser lights L1a and L2a, which is the one measured light. Inducing a coherent refractive index change of the frequency to generate a broadband discrete spectrum, and the other measured light L1b, L2b separated by the beam splitter 11 is incident on the optical delay device 13, and the other A delay amount is given to the laser light L1b and L2b of the above-mentioned two wavelengths, which are light to be measured A broadband discrete spectrum generated by the broadband discrete spectrum generating cell 12 using one of the measured light beams L1a and L2a as excitation light and the other measured light delayed by the optical delay device 13 are mixed to obtain a sum frequency. A sum frequency spectrum is generated by passing through the nonlinear optical crystal 14A of the spectrum generator 14, and the control unit 15 variably controls the delay amount given to the other measured light L1b, L2b by the optical delay device 13. The observation device 16 observes how the spectrum lines of the sum frequency spectrum generated by the sum frequency spectrum generator 14 interfere with each other, thereby estimating the phase of the light under measurement from the phase difference between the spectrum lines.

  Here, the spectrum phase can be identified from the frequency interference spectrum by the first measurement executed according to the procedure shown in the flowchart of FIG. 3 and the second and subsequent measurements executed according to the procedure shown in the flowchart of FIG.

  In the first measurement, first, the sum frequency interference spectrum is measured by sweeping the delay time of the fundamental wave (step S1).

  Next, the delay time at which each sum frequency spectrum becomes stronger, that is, interferes and strengthens is recorded (step S2).

  Since the delay time in step S2 represents a phase difference between two adjacent spectral lines of the original discrete spectrum, each delay time t and the frequency interval df (eg, 10.6 THz) of the discrete spectrum are The phase difference is uniquely derived as 2 pi dft (step S3).

  In the second and subsequent measurements, the sum frequency interference spectrum is measured with an appropriate delay time (step S11).

  Using the maximum and minimum values of the interference spectrum already known in the first measurement, the intensity of the measured spectral line is set in the range of −1 to 1 (step S12).

  When the arc cosine of the standardized interference spectrum intensity is taken, the phase is obtained without code (step S13).

  Further, the interference spectrum is measured again with a delay time different from the previous one (the best efficiency is obtained by shifting by (1 / 4f)), and the phase code is identified by seeing the change from the previous time (step S14).

  The spectrum measurement time is very short (milliseconds), and from the second time onward, near real-time high-speed measurement can be performed.

  Therefore, the spectral phase measuring apparatus 10 can measure the spectral phase of the discrete spectrum at high speed and with high sensitivity.

  According to the present invention, since the spectrum phase of a discrete spectrum can be measured at high speed and with high sensitivity, an ultrashort pulse can be compensated from the discrete spectrum in consideration of the influence of high-order dispersion. Due to the discrete nature of the spectrum, a pulse train having a high repetition frequency can aggregate the single-shot effects of conventional ultrashort pulses in a short time. If this is applied to control the selectivity of a chemical reaction, an arbitrary reactive product can be efficiently produced in a short time.

  In addition, by compensating high-order dispersion using phase information, an ultrashort pulse with a Fourier transform limit can be generated.

  It can also be applied to arbitrarily control the time waveform of ultrashort pulses, and can be applied to synthesizers in the optical domain.

  Furthermore, new knowledge can be obtained regarding the elucidation of physicochemical processes, such as the phase added in the process of generating discrete spectra.

  In addition, this invention is not limited only to the above embodiment, Of course, a various change is possible in the range which does not deviate from the summary of this invention.

It is a block diagram which shows the whole structure of the spectrum phase measurement apparatus of the discrete spectrum to which this invention is applied. It is a figure which shows the example of the spectrum observed with the said spectrum phase measurement apparatus. It is a flowchart which shows the process sequence in the first measurement for specifying a spectrum phase from a frequency interference spectrum in the said spectrum phase measurement apparatus. In the said spectrum phase measuring device, it is a flowchart which shows the process sequence in the measurement after the 2nd for specifying a spectrum phase from a frequency interference spectrum.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Spectral phase measuring device, 11 Beam splitter, 12 Broadband discrete spectrum generating cell, 12A nonlinear medium, 13 optical delay device, 14 sum frequency spectrum generator, 14A optical system 14B nonlinear optical crystal, 15 control unit, 16 observation device

Claims (4)

A beam splitter that separates laser light of two wavelengths for generating a discrete spectrum, which is measured light, into one measured light and the other measured light;
One of the measured light beams separated by the beam splitter is incident as excitation light, includes a nonlinear medium, and the one of the measured light beams that is incident as the excitation light in the nonlinear medium. A broadband discrete spectrum generating cell that generates a broadband discrete spectrum by inducing a coherent refractive index change in a frequency corresponding to the difference frequency;
An optical delay device on which the other measured light separated by the beam splitter is incident;
A nonlinear optical crystal in which a broadband discrete spectrum generated by the broadband discrete spectrum generating cell using the one measured light as excitation light and the other measured light delayed by the optical delay device are mixed and incident A sum frequency spectrum generator that generates a sum frequency spectrum by passing
A control unit that variably controls a delay amount given to the other measured light by the optical delay device;
An observation device for spectroscopically observing the sum frequency spectrum generated by the sum frequency spectrum generator,
By controlling the delay amount of the optical delay unit by the control unit and observing with the observation device how the spectral lines of the sum frequency spectrum generated by the sum frequency spectrum generator interfere with each other. A spectral phase measurement device for a discrete spectrum characterized in that the phase of the light to be measured is estimated from the phase difference between the lines.   By controlling the delay amount of the optical delay device by the control unit and sweeping the delay amount given to the other measured light, the optical delay corresponding to the reciprocal of the frequency interval of the discrete spectrum is set as one period, and 2. The spectral phase measurement of a discrete spectrum according to claim 1, wherein the interference condition of the sum frequency component is changed and the sum frequency spectrum generated by the sum frequency spectrum generator is spectroscopically observed by the observation device. apparatus.   2. The spectral phase measuring apparatus according to claim 1, wherein the broadband discrete spectrum generating cell includes a Raman medium as a nonlinear medium. A laser beam having two wavelengths for generating a discrete spectrum, which is a measured light, is separated into one measured light and the other measured light by a beam splitter,
The one measured light separated by the beam splitter is incident as excitation light on a broadband discrete spectrum generating cell including a nonlinear medium, and the two-wavelength laser light as the one measured light in the nonlinear medium Inducing a coherent refractive index change of the frequency corresponding to the difference frequency to generate a broadband discrete spectrum,
The other measured light separated by the beam splitter is incident on an optical delay device, and a delay amount is given to the two-wavelength laser light that is the other measured light.
A broadband frequency spectrum generated by the broadband discrete spectrum generating cell using the one measured light as excitation light and the other measured light delayed by the optical delay unit are mixed to generate a sum frequency spectrum generator. Generate a sum frequency spectrum by passing through a nonlinear optical crystal,
The delay amount given to the other measured light by the optical delay device is variably controlled, and the observation device observes how the spectral lines of the sum frequency spectrum generated by the sum frequency spectrum generator interfere with each other. A method for measuring a spectral phase of a discrete spectrum, wherein the phase of the light to be measured is estimated from the phase difference between the spectral lines.

Images