Patent ID: 9429473
Filing Date: 2016-08-30
CPC Classification: G01J

Claim Text:
1. A method for determining terahertz frequency spectral information of a material in a sampling area, comprising: generating a first light at a first frequency; generating a second light at a second frequency such that the first frequency and second frequency are different from one another by a difference frequency; modulating the phase of a portion of the first light relative to the second light by passing the portion of the first light through a phase modulator to produce a phase modulated light at a phase modulation frequency; photo-mixing an phase modulated light and the second light and generating a difference frequency signal at the difference frequency based at least in part on the photo-mixing; transmitting the difference frequency signal through the sampling area wherein the difference frequency signal is modified to include the terahertz frequency spectral information by the material; receiving the modified difference frequency signal from the sampling area and generating a received signal in response; photo-mixing an unmodulated portion of the first light and the second light to generate a detection oscillation; mixing the received signal and the detection oscillation to generate a detector signal, the detector signal including an interference pattern resulting from photo-mixing and the terahertz frequency spectral information; detecting a first harmonic component of the detector signal using a first harmonic of the modulation frequency; detecting a second harmonic component of the detector signal using a second harmonic of the modulation frequency; and combining the first harmonic component and the second harmonic component to produce a power curve of the terahertz frequency spectral information in which the interference pattern is at least partially eliminated.