Terahertz wave spectrometer

• US 6,747,736 B2
• Filed: 12/19/2001
• Issued: 06/08/2004
• Est. Priority Date: 06/21/1999
• Status: Expired due to Fees

• Current Assignee: Hamamatsu Photonics KK
• Original Assignee: Hamamatsu Photonics KK
• Inventors: Takahashi, Hironori
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): LAUCHMAN, LAYLA G
• Application Number:
  US10/020,982
• Publication Number:
  US 20020067480A1
• Time in Patent Office: 902 Days
• Field of Search: 356/317, 356/318, 356/319, 356/320, 356/326, 250/338.1
• US Class Current: 356/319
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation
• CPC Class Codes: G01N 21/49 within a body or fluid
• CPC Class Codes: G01N 22/00 Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more G01N3/00 - G01N17/00, G01N24/00 take precedence

Abstract

A terahertz wave detector is for detecting a terahertz wave which is emitted from a terahertz wave generator and which is transmitted through a sample. The timing, at which a probe light is irradiated on an optical switching device in the terahertz wave detector, is vibratingly varied by driving a movable reflector in a variable optical delay device at a predetermined vibration frequency. The resultant detection signal generated thereby and changing periodically and vibratingly is subjected to frequency analysis by a spectrum analyzer in a spectroscopic processor. The detection signal has the same temporal waveform as that of the terahertz wave and subjected to scale conversion. Therefore, the frequency analysis of the detection signal enables frequency measurement of a terahertz wave in real time. As a result, real-time spectroscopy is possible, and the device configuration is simplified.

Claims

1. A terahertz wave spectrometer for performing spectroscopic measurement by using terahertz wave, comprising:

a predetermined excitation light optical system guiding an excitation light;

a terahertz wave generator generating terahertz wave by using the excitation light guided by the predetermined excitation light optical system;

a terahertz wave optical system guiding the terahertz wave generated by the terahertz wave generator to a sample for spectroscopic measurement, and further guiding the terahertz wave which has been affected by the sample;

a predetermined probe light optical system guiding a probe light that is in synchronization with the excitation light;

a terahertz wave detector detecting, using the probe light guided by the predetermined probe light optical system, the terahertz wave that is affected by the sample and that is guided by the terahertz wave optical system, and outputting a detection signal;

optical delay vibrating means provided in either one of the excitation light optical system and the probe light optical system, the optical delay vibrating means vibrating, at a predetermined vibration frequency, the length of the optical path of the corresponding one of the excitation light and the probe light, thereby periodically vibrating the irradiation timing of the corresponding one of the excitation light and the probe light onto a corresponding one of the terahertz wave generator and the terahertz wave detector; and

spectroscopic processing means performing spectroscopic measurement on the sample based on the detection signal obtained by the terahertz wave detector, the spectroscopic processing means including frequency analyzing means performing frequency analysis on the detection signal that periodically changes in accordance with the vibration frequency, the frequency analyzing means performing the frequency analysis of the detection signal by performing a frequency domain measurement, the frequency-analysis result obtained by the frequency analyzing means indicating frequency-analysis information on the terahertz wave that has been affected by the sample, thereby indicating the spectroscopic information of the sample.

2. A terahertz wave spectrometer as claimed in claim 1, wherein the frequency analyzing means includes a spectrum analyzer producing a frequency spectrum by performing a frequency analysis on the detection signal.

3. A terahertz wave spectrometer as claimed in claim 1, wherein the frequency analyzing means includes a band pass filter selecting a predetermined frequency component from the detection signal.

4. A terahertz wave spectrometer as claimed in claim 3, wherein the band pass filter includes a plurality of band pass filters for selecting frequency components different from one another, the spectroscopic processing means further including correlation analyzing means determining a correlation between the plurality of frequency components selected by the plurality of band pass filters.

5. A terahertz wave spectrometer as claimed in claim 1, wherein the spectroscopic processing means further includes frequency setting/changing means controlling the optical delay vibrating means and changing or setting the value of the vibration frequency, at which the optical delay vibrating means vibrates the length of the optical path for the corresponding one of the excitation light and the probe light, the frequency analyzing means performing the frequency analysis based on the thus changed or set vibration frequency.

6. A terahertz wave spectrometer as claimed in claim 1, wherein at least one of the terahertz wave generator and the terahertz wave detector is constructed from an optical switching device.

7. A terahertz wave spectrometer as claimed in claim 1, wherein at least one of the terahertz wave generator and the terahertz wave detector is constructed from an electro-optic crystal.

8. A terahertz wave spectrometer as claimed in claim 1, further comprising sample moving means moving the sample two-dimensionally, thereby causing the spectroscopic processing means to perform two-dimensional spectroscopic measurement on the sample.

9. A terahertz wave spectrometer as claimed in claim 1, wherein the terahertz wave detector is constructed from a two-dimensional detector, in which a plurality of terahertz wave detecting portions are arranged two-dimensionally, the spectroscopic processing means including a plurality of frequency analyzing means, the plural terahertz wave detecting portions being connected to the plural frequency analyzing means, respectively, each frequency analyzing means performing frequency analysis on a detection signal obtained by the corresponding terahertz wave detecting portion, thereby attaining two-dimensional spectroscopic measurement on the sample.

10. A terahertz wave spectrometer as claimed in claim 1, wherein the excitation light optical system includes an optical chopper controlling on and off of the excitation light.

11. A terahertz wave spectrometer as claimed in claim 1, wherein the spectroscopic processing means further includes analyzing means determining frequency analysis of the terahertz wave, which is affected by the sample and which indicates the spectroscopic information of the sample, based on the frequency-analysis result of the detection signal obtained by the frequency analyzing means.

12. A terahertz wave spectrometer as claimed in claim 1, wherein the frequency analyzing means detects a desired frequency component of the detection signal by performing the frequency-domain measurement.

13. A terahertz wave spectrometer as claimed in claim 12, wherein the frequency analyzing means is constructed from a spectrum analyzer.

14. A terahertz wave spectrometer as claimed in claim 13, wherein the spectrum analyzer is set to a zero span mode.

15. A terahertz wave spectrometer as claimed in claim 12, wherein the frequency analyzing means includes a band pass filter selecting the desired frequency component,

wherein the spectroscopic processing means further includes frequency setting/changing means controlling the optical delay vibrating means and changing or setting the value of the vibrating frequency, at which the optical delay vibrating means vibrates the length of the optical path of the corresponding one of the excitation light and the probe light, to a value that corresponds to a frequency value of the desired frequency component to be selected by the band pass filter.

16. A terahertz wave spectrometer as claimed in claim 12, wherein the terahertz wave detector is constructed from a two-dimensional detector, in which a plurality of terahertz wave detecting portions are arranged two-dimensionally, the spectroscopic processing means including a plurality of band pass filters, the plural terahertz wave detecting portions being connected to the plural band pass filters, respectively, each band pass filter performing frequency-domain measurement on a detection signal obtained by the corresponding terahertz wave detecting portion to select the desired frequency component, thereby attaining two-dimensional spectroscopic measurement on the sample.

17. A terahertz wave spectrometer as claimed in claim 12, wherein the excitation light optical system includes an optical chopper controlling on and off of the excitation light at a predetermined driving frequency, the frequency analyzing means detecting, by performing frequency-domain measurement, a frequency component of the detection signal that is determined with respect to the predetermined driving frequency.

18. A terahertz wave spectrometer as claimed in claim 17, wherein the frequency analyzing means includes a spectrum analyzer.

19. A terahertz wave spectrometer as claimed in claim 16, wherein the frequency analyzing means includes a band pass filter.