Abstract-Terahertz detection by upconversion to the near-infrared using picosecond pulses

 

 Schematic of the experimental setup. A pulsed laser at about 1550 nm (orange) is used to pump the terahertz source and a frequency-doubling crystal to generate the NIR pump beam (red). Reflective bandpass filters are used to narrow the spectrum before the pump enters the nonlinear medium together with the terahertz radiation (green). SHG: second harmonics generation, PPLN: periodically poled lithium niobate crystal, RBP: reflective bandpass, M: mirror, ITO: indium-tin-oxide coated glass, PCA: photoconductive antenna, f1,f2${\mathrm{f}}_1,{\mathrm{f}}_2$: lenses (focal lengths of f1${\mathrm{f}}_1$: 125 mm, f2${\mathrm{f}}_2$: 400 mm).

Tobias Pfeiffer, Daniel Molter, and Georg von Freymann

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-20-29419

The detection of terahertz photons by using silicon-based devices enabled by visible photons is one of the fundamental ideas of quantum optics. Here, we present a classical detection principle using optical upconversion of terahertz photons to the near-infrared spectral range in the picosecond pulse regime, which finally enables the detection with a conventional sCMOS camera. By superimposing terahertz and optical pump pulses in a periodically poled lithium-niobate crystal, terahertz photons at 0.87 THz are converted to optical photons with wavelengths close to the central pump wavelength of 776 nm. A tunable delay between the pulses helps overlap the pulses and enables time-of-flight measurements. Using a sCMOS camera, we achieve a dynamic range of 47.8 dB with a signal to noise ratio of 23.5 dB at a measurement time of one second, in our current setup.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz thickness determination with interferometric vibration correction for industrial applications

Tobias Pfeiffer, Stefan Weber, Jens Klier, Sebastian Bachtler, Daniel Molter, Joachim Jonuscheit, and Georg Von Freymann

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-10-12558

In many industrial fields, like automotive and painting industry, the thickness of thin layers is a crucial parameter for quality control. Hence, the demand for thickness measurement techniques continuously grows. In particular, non-destructive and contact-free terahertz techniques access a wide range of thickness determination applications. However, terahertz time-domain spectroscopy based systems perform the measurement in a sampling manner, requiring fixed distances between measurement head and sample. In harsh industrial environments vibrations of sample and measurement head distort the time-base and decrease measurement accuracy. We present an interferometer-based vibration correction for terahertz time-domain measurements, able to reduce thickness distortion by one order of magnitude for vibrations with frequencies up to 100 Hz and amplitudes up to 100 µm. We further verify the experimental results by numerical calculations and find very good agreement.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement