Terahertz Frequency Domain Spectrometer with Controllable Phase Shift

• US 20090283680A1
• Filed: 05/13/2009
• Published: 11/19/2009
• Est. Priority Date: 05/19/2008
• Status: Active Grant

• Current Assignee: Joseph R. Demers
• Original Assignee: Emcore Corporation
• Inventors: Demers, Joseph R., Logan, Ronald T. JR.
• Granted Patent: US 7,781,736 B2
• Time in Patent Office: Days
• US Class Current: 250/339.70
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01J 3/4531 Devices without moving parts
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation

Abstract

An apparatus for analyzing, identifying or imaging an target including an integrated dual laser module coupled to a pair of photoconductive switches to produce cw signals in the range of frequencies from 100 GHz to over 2 THz focused on and transmitted through or reflected from the target; and a detector for acquiring spectral information from signals received from the target and using a multi-spectral homodyne process to generate an electrical signal representative of some characteristics of the target with resolution less than 250 MHz. The photoconductive switches are activated by laser beams from the dual laser module. The lasers in the module are tuned to different frequencies and a phase shifter in the path of one beam allows the beams to have an adjustable phase difference.

Claims

1. An apparatus for analyzing, identifying or imaging a target comprising

first and second lasers having tunable frequencies for producing a first composite output beam;

a source of CW signals in the range of frequencies from 100 GHz to over 2 THz including a first photoconductive switch activated by said first composite optical beam;

a radiative element for causing said signals to be substantially simultaneously focused on or through said target; and

a detector for acquiring spectral information reflected from said target and coupled to a second composite optical beam having an adjustable phase or frequency difference from said first composite beam for generating an electrical signal representative of some characteristic of the target.

2. An apparatus as in claim 1, wherein said detector includes a second photoconductive switch activated by said second composite optical beam.

3. An apparatus as defined in claim 1, further comprising a processor coupled to said detector for analyzing said electrical signal and determining a characteristic of said target based upon the absorption characteristics of said target in the 100 GHz to over 2 THz frequency band.

4. An apparatus as defined in claim 1, wherein said lasers are DFB or DBR lasers with different frequencies.

5. An apparatus as defined in claim 1, wherein said photoconductive switch is a low temperature grown ErAs, GaAs photomixer.

6. An apparatus for analyzing, identifying or imaging a target comprising

a first THz signal source including a first laser having a tunable frequency for producing a first composite output beam;

a first source of CW signals in the range of frequencies from 100 GHz to over 2 THz including a first photoconductive switch activated by said first composite optical beam;

a first radiative element for causing said signals to be substantially simultaneously focused on or through said target;

a second THz signal source including a second laser having a tunable frequency for producing a second composite output beam;

a second source of CW signals in the range of frequencies from 100 GHz to over 2 THz including a second photoconductive switch activated by said second composite optical beam;

a second radiative element for causing said signals to be substantially simultaneously focused on or through said target

a detector for acquiring spectral information reflected from said target and coupled to a third composite optical beam having an adjustable phase or frequency difference from said first and said second composite beam for generating an electrical signal representative of some characteristic of the target.

7. A method for analyzing, identifying or imaging a target comprising

providing first and second lasers having tunable frequencies for producing a first composite output beam;

generating CW signals in the range of frequencies from 100 GHz to over 2 THz including a first photoconductive switch activated by said first composite optical beam;

causing said signals to be substantially simultaneously focused on or through said target; and

acquiring a spectral information signal from said target, said signal being coupled to a second composite optical beam having an adjustable phase or frequency difference from said first composite beam for generating an electrical signal representative of some characteristic of the target.

8. An apparatus for analyzing, identifying or imaging a target comprising

first and second lasers having tunable frequencies for producing a first composite output beam;

a source of CW signals in the range of frequencies from 100 GHz to over 2 THz including a first photoconductive switch activated by said first composite optical beam;

a radiative element for causing said signals to be substantially simultaneously focused on or through said target; and

a detector for acquiring spectral information reflected from said target and coupled to a second composite optical beam having an adjustable phase or frequency difference from said first composite beam for generating an electrical signal representative of some characteristic of the target.