High-precision phase determination in a continuous-wave terahertz spectrometer by heterodyning of three lasers

In a continuous-wave terahertz spectrometer, we employ photomixing of three lasers, allowing us to measure at three terahertz frequencies simultaneously. Whilst two of the terahertz frequencies can be tuned to obtain terahertz spectra, one terahertz frequency remains fixed. The data recorded at the fixed frequency is used to normalize the spectra of the two other frequencies. As a result, the accuracy of the terahertz phase measurement can be greatly enhanced.