Patent ID: 8144323

Claim:
A system comprising: a cavity ring-down spectrometer comprising: a transmitter configured to transmit a continuous-wave electromagnetic signal at each of one or more selectable, transmission frequencies in the Terahertz region of the electromagnetic spectrum; a modulator configured to modulate the electromagnetic signal at a modulation frequency; a cavity resonator configured to receive the modulated electromagnetic signal and pass at least a portion of the modulated electromagnetic signal, wherein the transmitter and cavity resonator are configured so as to excite a single resonant mode of the cavity resonator; and a receiver configured to receive the portion of the modulated electromagnetic signal passing the cavity resonator; and a processor configured to receive a measurement of the portion of the modulated electromagnetic signal received by the receiver, and determine a phase shift of the modulated electromagnetic signal at the modulation frequency based upon the measurement, and wherein the processor is configured to calculate a ring-down time of the cavity resonator as a function of the phase shift.