Terahertz spectrometer operation by laser repetition frequency tuning

We present a fully fiber-coupled terahertz time domain spectrometer based on a single ultrafast laser with an adjustable pulse repetition frequency that does not employ an external delay line. Our approach represents a major improvement over other schemes that either employ external movable delay lines or alternatively asynchronous optical sampling schemes that also do not need an external delay stage, but employ two lasers instead. The scanning range of our spectrometer covers the full temporal delay between two adjacent pulses of 4 ns. This allows for a fully fiber-coupled system, enabling unprecedented robustness and ease of use.