Rapid thickness measurement with a SLAPCOPS-based terahertz TDS system

Terahertz time-domain spectroscopy traditionally requires either one mode-locked laser and an external delay line or two mode-locked lasers with a controllable repetition rate difference. Here we demonstrate a polarization-multiplexed single-laser system, which combines the benefits of both approaches without any external delay line. The fiber laser emits two pulse trains with independently adjustable repetition rates, utilizing only one laser-active section and one pump diode. With a standard fiber-coupled terahertz setup, we are able to measure transients with a spectral bandwidth of 2.5 THz and a dynamic range of 50 dB in a measurement time of 1 s. An additional benefit of the underlying concept is the possibility for the rapid measurement of very thick samples usually not possible with traditional single-laser systems.