Phase modulation and second-harmonic nulling to eliminate interference fringes from the spectrum of a coherent frequency-domain THz spectrometer

We report on the continued progress of a portable, battery-operated frequency domain terahertz spectrometer with an integrated, fiber-coupled, lithium-niobate optical phase-modulator. We discuss the progress on shifting the THz phase 90 degrees between consecutive data samples to remove the interference pattern and on developing a method of employing second harmonic nulling to actively adjust the THz phase and continuously maintain a maximum detected THz signal.