Patent ID: 9086374
Filing Date: 2015-07-21
Classification: G01N

Abstract:
1. A method for identifying a terahertz frequency spectral characteristic of a material in a sampling region, the method comprising: generating a first terahertz signal and a second terahertz signal; modulating the phase of at least one of the first terahertz signal and second terahertz signal relative to a phase offset in a periodic manner at a modulating frequency; transmitting a terahertz electromagnetic radiation beam, based on the first terahertz signal, to the sampling region such that a characterized terahertz radiation is produced by an interaction of the terahertz electromagnetic radiation beam with the material in the sampling region, the characterized terahertz radiation including the terahertz frequency spectral characteristic related to the material; receiving the characterized terahertz electromagnetic radiation from the sampling region and producing a characterized terahertz signal responsive to the received radiation; mixing the characterized terahertz signal and the second terahertz signal to produce a detector signal that includes a characterized signal component related to the characteristic of the material, and a first harmonic signal component at a first harmonic of the modulating frequency resulting from the phase modulation, and a second harmonic signal component at a second harmonic of the modulating frequency resulting, at least in part, from the phase offset which is a difference between the phases of the characterized terahertz signal and the second terahertz signal; extracting the characterized signal component from the detector signal to identify the terahertz frequency spectral characteristic of the material in the sampling region, the extracted characterized signal component defining a characterized power curve that includes nulls which are reduced power levels at certain frequencies related to the second harmonic signal component of the detector signal; and controlling the phase offset using the second harmonic signal component such that the nulls are, at least in part, removed from the characterized power curve.