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Rapid thickness measurement with a SLAPCOPS-based terahertz TDS system

: Kolano, Michael; Boidol, Oliver; Molter, Daniel; Freymann, Georg von


Institute of Electrical and Electronics Engineers -IEEE-:
44th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2019 : 1-6 September 2019, Paris, France
Piscataway, NJ: IEEE, 2019
ISBN: 978-1-5386-8285-2
ISBN: 978-1-5386-8286-9
International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) <44, 2019, Paris>
Fraunhofer ITWM ()
mode-locked laser; external delay line; controllable repetition rate difference; polarization-multiplexed single-laser system; fiber laser; independently adjustable repetition rates; laser-active section; standard fiber-coupled terahertz setup; measurement time; rapid measurement; traditional single-laser systems; rapid thickness measurement; SLAPCOPS-based terahertz TDS system; terahertz time-domain spectroscopy; frequency 2.5 THz; noise figure 50.0 dB; time 1.0 s

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.