Electric field vector detection method and electric field vector detection device

• US 9,612,153 B2
• Filed: 11/24/2015
• Issued: 04/04/2017
• Est. Priority Date: 11/26/2014
• Status: Active Grant

• Current Assignee: Hamamatsu Photonics KK
• Original Assignee: Hamamatsu Photonics KK
• Inventors: Kawada, Yoichi, Yasuda, Takashi, Takahashi, Hironori
• Primary Examiner(s): Makiya, David J
• Assistant Examiner(s): Jo, Taeho
• Application Number:
  US14/950,617
• Publication Number:
  US 20160146666A1
• Time in Patent Office: 497 Days
• Field of Search: 2503413
• CPC Class Codes: G01J 1/0429 using polarisation elements
• CPC Class Codes: G01J 1/4228 arrangements with two or more detectors, e.g. for sensitivity compensation
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 2001/4242 Modulated light, e.g. for synchronizing source and detector circuit
• CPC Class Codes: G01J 3/0224 using polarising or depolarising elements
• CPC Class Codes: G01J 3/0262 Constructional arrangements for removing stray light
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01J 3/433 Modulation spectrometry; Derivative spectrometry
• CPC Class Codes: G01J 3/4338 Frequency modulated spectrometry
• CPC Class Codes: G01J 4/04 Polarimeters using electric detection means G01J4/02 takes precedence
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation
• CPC Class Codes: G01R 15/241 using electro-optical modulators, e.g. electro-absorption probes containing electro-optic elements G01R1/071
• CPC Class Codes: G01R 29/0871 Complete apparatus or systems; circuits, e.g. receivers or amplifiers G01R29/0878, G01R29/0892 take precedence; dosimeters, warning devices G01R29/0857

Abstract

In this electric field vector detection method, an electro-optic crystal, where a (111) surface of an optical isotropic medium is cut out, is used as a terahertz wave detection element. The method includes: causing polarization of probe light of ultrashort pulsed light to be circular polarization; allowing the probe light having circular polarization to enter the terahertz wave detection element and probing the terahertz wave; modulating the probe light, having probed the terahertz wave, by a rotating analyzer and detecting the modulated probe light by a photodetector; performing lock-in detection of a detection signal from the photodetector by a lock-in detector using a frequency based on a rotational frequency of the rotating analyzer as a reference signal; and detecting an electric field vector of the terahertz wave based on a detection signal from the lock-in detector.

Claims

1. An electric field vector detection method for detecting an electric field vector of a terahertz wave,

wherein ultrashort pulsed light is used as probe light and an electro-optic crystal, where a (111) surface of an optical isotropic medium is cut out, is used as a terahertz wave detection element for detecting the terahertz wave, the method comprising:

causing polarization of the probe light to be circular polarization;

allowing the probe light having circular polarization to enter the terahertz wave detection element and probing the terahertz wave;

modulating the probe light, having probed the terahertz wave, by a rotating analyzer and detecting the modulated probe light by a photodetector;

performing lock-in detection of a detection signal from the photodetector by a lock-in detector using a frequency based on a rotational frequency of the rotating analyzer as a reference signal; and

detecting an electric field vector of the terahertz wave based on a detection signal from the lock-in detector.

2. The electric field vector detection method according to claim 1,

wherein amplitude of an electric field vector of the terahertz wave is detected based on amplitude of the detection signal from the lock-in detector, and, a direction of an electric field vector of the terahertz wave is detected based on a phase of the detection signal from the lock-in detector.

3. The electric field vector detection method according to claim 1,

wherein a dual phase lock-in detector is used as the lock-in detector.

4. The electric field vector detection method according to claim 1,

wherein a terahertz wave generating element configured to generate the terahertz wave by incidence of pump light is used,

the method further comprising:

branching the ultrashort pulsed light into the probe light and the pump light; and

modulating, in a cyclic manner, the pump light incident on the terahertz wave generating element by an optical modulator.

5. The electric field vector detection method according to claim 4,

wherein, when a rotational frequency of the rotating analyzer is defined as f₁ and a modulation frequency of the pump light is defined as f₂, lock-in detection is performed while a frequency of the reference signal in the lock-in detector is defined as f₂±

2f₁.

6. An electric field vector detection device for detecting an electric field vector of a terahertz wave, the device comprising:

a polarization adjusting unit configured to cause polarization of probe light of ultrashort pulsed light to be circular polarization;

a terahertz wave detection element including an electro-optic crystal, where a (111) surface of an optical isotropic medium is cut out;

a rotating analyzer configured to modulate the probe light having probed the terahertz wave;

a photodetector configured to detect the probe light having been modulated by the rotating analyzer;

a lock-in detector configured to perform lock-in detection of a detection signal from the photodetector using a frequency based on a rotational frequency of the rotating analyzer as a reference signal; and

an electric field vector detection unit configured to detect an electric field vector of the terahertz wave based on a detection signal from the lock-in detector.

7. The electric field vector detection device according to claim 6,

wherein the electric field vector detection unit detects amplitude of an electric field, vector of the terahertz wave based on amplitude of the detection signal from the lock-in detector and a direction of an electric field vector of the terahertz wave based on a phase of the detection signal from the lock-in detector.

8. The electric field vector detection device according to claim 6,

wherein the lock-in detector is a dual phase lock-in detector.

9. The electric field vector detection device according to claims 6, further comprising:

a terahertz wave generating element configured to generate the terahertz wave by incidence of pump light;

a branching unit configured to branch the ultrashort pulsed light into the probe light and the pump light; and

an optical modulator configured to modulate the pump light in a cyclic manner.

10. The electric field vector detection device according to claim 9,

wherein, when a rotational frequency of the rotating analyzer is defined as f₁ and a modulation frequency of the pump light is defined as f₂, the lock-in detector performs lock-in detection while defining a frequency of the reference signal as f₂±

2f₁.