# US 12,181,842 B2 · Ramsey spectrometer, optical lattice clock, and Ramsey spectroscopic method

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- Number: US 12,181,842 B2
- Document ID: US12181842B2
- Status: Granted
- Kind: B2
- Application number: 17/868,099
- Filed: 2022-07-19
- Published: 2023-01-26
- Granted: 2024-12-31
- Earliest claimed: 2021-07-21
- Assignees: Shimadzu Corporation; Hidetoshi Katori; Masao Takamoto
- Applicants: Hidetoshi Katori; Masao Takamoto; Shimadzu Corporation
- Inventors: Hidetoshi Katori; Masao Takamoto
- Web page: https://patentgrep.com/patent/US12181842B2

## CPC

- G04F 5/14: using atomic clocks
- G04F 5/145: {using Coherent Population Trapping}
- G01J 3/44: Raman spectrometry; Scattering spectrometry {; Fluorescence spectrometry}
- G01N 21/1702: {with opto-acoustic detection, e.g. for gases or analysing solids}
- G01N 29/2418: {using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics (photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046)}
- G04F: TIME-INTERVAL MEASURING (measuring pulse characteristics G01R, e.g. G01R29/02; in radar or like systems G01S)
- 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

A Ramsey spectrometer is provided with an optical path, an optical path length stabilization circuit configured to stabilize a length of the optical path, a modulator optically connected to the optical path, the modulator being configured to generate resonant laser light of a first frequency f1 that causes a resonance of an atom, a molecule, or an ion as a spectroscopic target in pulses a plurality of times and generates non-resonant laser light of a second frequency f2 that does not cause the resonance, and a spectroscopic unit configured to spectroscope the spectroscopic target. The spectroscopic unit detects a state change of the spectroscopic target corresponding to the first frequency f1, the state change being caused by irradiating the resonant laser light to the spectroscopic target.

## Claims

### Claim 1

A Ramsey spectrometer comprising:
an optical path;
an optical path length stabilization circuit configured to stabilize a length of the optical path;
a modulator optically connected to the optical path, the modulator being configured to generate resonant laser light of a first frequency f1 that causes a resonance of an atom, a molecule, or an ion as a spectroscopic target in pulses a plurality of times and to generate non-resonant laser light of a second frequency f2 that does not cause the resonance at times between the pulses of the resonant laser light to separate the pulses of the resonant laser light; and
a spectroscopic unit configured to spectroscope the spectroscopic target,
wherein the spectroscopic unit is configured to detect a state change of the spectroscopic target corresponding to the first frequency f1, the state change being caused by irradiating the spectroscopic target with the resonant laser light.

### Claim 2 (depends on 1)

The Ramsey spectrometer as recited in claim 1,
wherein when n is an arbitrary natural number, an oscillation interval of the resonant laser light is T, and a time T1 and a time T2 are defined as times that satisfy |f1−f2|=n/T1, and |f1−f2|=(n+1)/T2, respectively,
the oscillation interval T is set to satisfy
T1−0.25·(T2−T1)≤T≤T1+0.25·(T2−T1).

### Claim 3 (depends on 1)

The Ramsey spectrometer as recited in claim 1,
wherein the modulator generates the resonant laser light and the non-resonant laser light in such a manner that their phases are temporally continuous.

### Claim 4 (depends on 1)

The Ramsey spectrometer as recited in claim 1,
wherein the modulator includes a switching element that generates the resonant laser light and the non-resonant laser light by switching therebetween.

### Claim 5 (depends on 2)

The Ramsey spectrometer as recited in claim 2,
wherein a difference |f1−f2| between the first frequency f1 and the second frequency f2 is set to satisfy |f1−f2|=n/T.

### Claim 6 (depends on 1)

The Ramsey spectrometer as recited in claim 1,
wherein the optical path includes an optical fiber.

### Claim 7 (depends on 1)

The Ramsey spectrometer as recited in claim 1,
wherein the optical path includes a free space.

### Claim 8 (depends on 1)

The Ramsey spectrometer as recited in claim 1,
wherein the modulator and the optical path length stabilization circuit are integral.

### Claim 9 (depends on 8)

The Ramsey spectrometer as recited in claim 8,
wherein the optical path length stabilization circuit is provided with a PC controlled oscillator, a voltage-controlled oscillator, and a multiplication circuit.

### Claim 10 (depends on 1)

The Ramsey spectrometer as recited in claim 1,
wherein the modulator and the optical path length stabilization circuit are independent.

### Claim 11 (depends on 10)

The Ramsey spectrometer as recited in claim 10,
wherein the optical path length stabilization circuit is provided with a PLL circuit.

### Claim 12 (depends on 1)

The Ramsey spectrometer as recited in claim 1, further comprising:
a laser light source connected to one end of the optical path.

### Claim 13 (depends on 12)

The Ramsey spectrometer as recited in claim 12, further comprising:
a laser light modulator connected to the modulator, the laser light modulator being configured to modulate laser light emitted by the laser light source.

### Claim 14 (depends on 13)

The Ramsey spectrometer as recited in claim 13,
wherein the laser light modulator is an acousto-optic modulator.

### Claim 15 (depends on 1)

An optical lattice clock comprising:
the Ramsey spectrometer as recited in claim 1.

### Claim 16

A spectroscopic method using a Ramsey spectrometer,
wherein the Ramsey spectrometer comprises:
an optical path;
an optical path length stabilization circuit; and
a modulator optically connected to the optical path, and
a spectroscopic unit, and
wherein the spectroscopic method comprises the steps of:
stabilizing a length of the optical path using the optical path length stabilization circuit;
generating resonant laser light of a first frequency f1 that causes a resonance of an atom, a molecule, or an ion as a spectroscopic target in pulses a plurality of times and generating non-resonant laser light of a second frequency f2 that does not cause the resonance at times between the pulses of the resonant laser light to separate the pulses of the resonant laser light; and
spectroscopying the spectroscopic target using the spectroscopic unit.

### Claim 17 (depends on 16)

The spectroscopic method as recited in claim 16,
wherein when n is an arbitrary natural number, an oscillation interval of the resonant laser light is T, and a time T1 and a time T2 are defined as times that satisfy |f1−f2|=n/T1, and |f1−f2|=(n+1)/T2, respectively,
the oscillation interval T is set to satisfy
T1−0.25·(T2−T1)≤T≤T1+0.25·(T2−T1).

### Claim 18 (depends on 17)

The spectroscopic method as recited in claim 17,
wherein a difference |f1−f2| between the first frequency f1 and the second frequency f2 is set to satisfy |f1−f2|=n/T.