# US 11,909,164 B2 · Optical pulse pair generator, light detection device, and light detection method

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- Number: US 11,909,164 B2
- Document ID: US11909164B2
- Status: Granted
- Kind: B2
- Application number: 17/054,849
- Filed: 2019-04-19
- Published: 2021-07-15
- Granted: 2024-02-20
- Earliest claimed: 2018-05-14
- Assignees: National University Corporation Tokyo University of Agriculture and Technology
- Applicants: National University Corporation Tokyo University of Agriculture & Technology
- Inventors: Kazuhiko Misawa; Terumasa Ito
- Web page: https://patentgrep.com/patent/US11909164B2

## CPC

- G02B 21/0076: {arrangements using fluorescence or luminescence}
- H01S 3/0057: {Temporal shaping, e.g. pulse compression, frequency chirping (soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108)}
- G01J 11/00: Measuring the characteristics of individual optical pulses or of optical pulse trains
- G01N 21/65: Raman scattering
- G02B 21/0084: {time-scale detection, e.g. strobed, ultra-fast, heterodyne detection}
- G02B 21/06: Means for illuminating specimens
- G02B 27/1006: {for splitting or combining different wavelengths (G02B27/1086, G02B27/141 take precedence)}
- H01S 3/0078: {Frequency filtering}
- H01S 3/30: using scattering effects, e.g. stimulated Brillouin or Raman effects
- G01N 2021/655: {Stimulated Raman}
- H01S 3/0085: {Modulating the output, i.e. the laser beam is modulated outside the laser cavity}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- 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
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

An optical pulse pair generator is configured to generate an optical pulse pair including a first pulse beam and a second pulse beam having respective central wavelengths that are separated by a predetermined wavelength difference from each other and having target time waveforms that are substantially the same as each other. The optical pulse pair generator provided includes a splitter section configured to split an incident pulse beam into two, a first shaping section configured to shape one of the pulse beams split by the splitter section by shaping into the target time waveform and setting a central frequency so as to configure the first pulse beam, and a second shaping section configured to shape the other of the pulse beams split by the splitter section by shaping into the target time waveform so as to configure the second pulse beam.

## Claims

### Claim 1

An optical pulse pair generator configured to generate an optical pulse pair including a first pulse beam and a second pulse beam having respective central wavelengths that are separated by a predetermined wavelength difference from each other and having target time waveforms that are substantially the same as each other, the optical pulse pair generator comprising:
a splitter section configured to split an incident pulse beam into two;
a first shaping section configured to shape one of the pulse beams split by the splitter section by shaping into the target time waveform and setting a central frequency so as to configure the first pulse beam; and
a second shaping section configured to shape the other of the pulse beams split by the splitter section by shaping into the target time waveform so as to configure the second pulse beam,
wherein the first pulse beam and the second pulse beam both have an asymmetric waveform with a fall time that is longer than a rise time, and are temporally superimposed on each other.

### Claim 2 (depends on 1)

The optical pulse pair generator of claim 1, wherein:
the first shaping section includes a first bandpass filter having a bandwidth corresponding to the target time waveform of the one pulse beam and rotatable in a direction intersecting a propagation direction of the one pulse beam, and further includes a delay member configured to impart a variable time delay to the one pulse beam; and
the second shaping section includes a second bandpass filter having a bandwidth corresponding to the target time waveform of the other pulse beam.

### Claim 3 (depends on 2)

The optical pulse pair generator of claim 2, wherein:
a wavelength scanning section for scanning the wavelength difference is configured by the first bandpass filter and the delay member;
the first pulse beam and the second pulse beam are temporally superimposed on each other; and
the wavelength scanning section sets the wavelength difference by using a rotation angle of the first bandpass filter, and compensates a time difference between the first pulse beam and the second pulse beam accompanying rotation of the first bandpass filter by using the time delay of the delay member.

### Claim 4 (depends on 2)

The optical pulse pair generator of claim 2, wherein the splitter section is configured by the second bandpass filter.

### Claim 5 (depends on 1)

A light detection device comprising the optical pulse pair generator of claim 1 and configured to perform light detection using an excitation pulse beam, a first probe pulse beam, and a second probe pulse beam, wherein the first pulse beam configures the first probe pulse beam, the light detection device further comprising:
a laser light source configured to generate a light source pulse beam;
a light source splitter section configured to split the light source pulse beam in two by splitting into the excitation pulse beam and the incident pulse beam;
a modulation section configured to phase modulate the second pulse beam so as to configure the second probe pulse beam;
a multiplexing section configured to multiplex the excitation pulse beam, the first probe pulse beam, and the second probe pulse beam so as to generate a multiplexed beam;
an illumination section configured to illuminate a sample with the multiplexed beam; and
a detection section configured to employ heterodyne interference due to the first probe pulse beam and the second probe pulse beam to detect a molecular vibration excited by the excitation pulse beam when the multiplexed beam is illuminating the sample.

### Claim 6 (depends on 5)

The light detection device of claim 5, wherein the first probe pulse beam and the second probe pulse beam both have an asymmetric waveform with a fall time that is longer than a rise time, are temporally superimposed on each other, and are delayed by a predetermined delay time relative to the excitation pulse beam.

### Claim 7 (depends on 5)

The light detection device of claim 5, wherein:
the excitation pulse beam is polarized in advance;
a wavelength of the first probe pulse beam and a wavelength of the second probe pulse beam are different from each other;
the illumination section includes a microscope; and
the detection section includes a polarizer configured to remove the excitation pulse beam from the multiplexed beam after the sample has been illuminated, an optical filter configured to remove the second probe pulse beam from the multiplexed beam after the sample has been illuminated, and a light reception section configured to receive the first probe pulse beam.

### Claim 8 (depends on 7)

The light detection device of claim 7, wherein:
the first shaping section includes a wavelength scanning section configured to scan the wavelength difference, the wavelength scanning section including a first bandpass filter having a bandwidth corresponding to the target time waveform of the one pulse beam and rotatable in a direction intersecting a propagation direction of the first pulse beam, and further including a delay member configured to impart a variable time delay to the one pulse beam; and
the light detection device further comprises a control section configured to control the wavelength scanning section so as to set the wavelength difference by using a rotation angle of the first bandpass filter and to compensate a time difference between the first probe pulse beam and the second probe pulse beam accompanying rotation of the first bandpass filter by using the time delay of the delay member, and further configured to control the modulation section so as to perform phase modulation with a modulation signal having a saw-tooth waveform including regions of linear change in phase for the second probe pulse beam transmitted through a second bandpass filter having a bandwidth corresponding to the target time waveform and including connection regions at which there is a steep change of phase difference 2π.

### Claim 9 (depends on 8)

The light detection device of claim 8, wherein the control section is configured to accept a received light signal output from the light reception section, to configure a lock-in amplifier using the received light signal and the modulation signal, and to detect an amplitude-modulated signal from modulating the first probe pulse beam resulting from heterodyne interference due to the lock-in amplifier as a signal corresponding to a stimulated Raman scattering signal.

### Claim 10 (depends on 9)

The light detection device of claim 9, wherein:
the first bandpass filter applies a predetermined odd-number high order dispersion to the first probe pulse beam; and
the second bandpass filter applies the predetermined odd-number high order dispersion to the second probe pulse beam.

### Claim 11

A method of detecting light of a molecular vibration using a light detection device including a laser light source configured to generate a light source pulse beam, a splitter section configured to split the light source pulse beam into three by splitting into an excitation pulse beam, and a first probe pulse beam and a second probe pulse beam that both have a predetermined waveform, a first shaping section configured to shape the first probe pulse beam by shaping into the predetermined waveform and setting a central frequency, a second shaping section configured to shape the second probe pulse beam by shaping into the predetermined waveform, a modulation section configured to phase modulate the second probe pulse beam, a multiplexing section configured to multiplex the excitation pulse beam, the first probe pulse beam, and the second probe pulse beam so as to generate a multiplexed beam, and an illumination section configured to illuminate a sample with the multiplexed beam, the light detection method comprising:
setting a difference between a central wavelength of the first probe pulse beam and a central wavelength of the second probe pulse beam so as to be separated by a wavelength difference corresponding to a frequency of the molecular vibration;
setting the predetermined waveforms so as to be substantially the same asymmetric waveforms having a fall time that is longer than a rise time;
temporally superimposing the first probe pulse beam and the second probe pulse beam and delaying the first probe pulse beam and the second probe pulse beam relative to the excitation pulse beam by a predetermined delay time; and
by a detection section, detecting a molecular vibration excited by the excitation pulse beam when the multiplexed beam is illuminating the sample by employing heterodyne interference due to the first probe pulse beam and the second probe pulse beam.