2010, Klatt, Gregor, Gebs, Raphael, Schäfer, Hanjo, Nagel, Michael, Janke, Christof, Bartels, Albrecht, Dekorsy, Thomas

Terahertz time-domain spectroscopy (THz-TDS) based on high-speed asynchronous optical sampling (ASOPS) with two offset-locked GHz femtosecond lasers requires no mechanical time-delay scanner. Consequently, measurements with 1-GHz frequency resolution are performed at intrinsically high scan rates in the multikilohertz range. This is at least one order, in most cases several orders of magnitude faster than conventional approaches employing mechanical time-delay scanners. We report a system offering a unique combination of high-frequency resolution (1 GHz) and high scan rate (2 kHz) with a spectral coverage of more than 6 THz. Its capabilities for high-precision spectroscopy are demonstrated by measuring the absorption spectrum of a mixture of $hbox{H}_{2}hbox{O}$, D$_2$O, and hydrogen deuterium oxide (HDO) vapor. $hbox{H}_{2}hbox{O}$ and HDO vapor absorption spectra are accurately tabulated in databases. However, D$_2$ O absorption data are rare, because of residual $hbox{H}_{2}hbox{O}$ and HDO often present when measuring pure D$_2$O. Here, we present a high-resolution absorption spectrum of D$_2$O vapor numerically extracted from the absorption spectrum of the three-component mixture. In addition, we show that the high spectral resolution of the ASOPS THz-TDS system provides benefits in the analysis of frequency-selective surface sensors, which are promising candidates for biosensing applications in the THz regime.

2007, Först, Michael, Nagel, Michael, Awad, Mohammad, Wächter, Markus, Dekorsy, Thomas, Kurz, Heinrich

III-V compound semiconductors offer a fascinating multitude of phenomena which have become accessible via ultrafast time-resolved spectroscopy. Coherent vibronic and electronic dynamics are prepared by excitation with taylored femtosecond laser pulses. The analysis of their temporal dephasing or decay provides deep insights into the interaction between electronic and vibronic degrees of freedem and the surrounding bath in high purity quantum structures. In contrast to coherent electronic or vibronic states, deliberately introduced growth defects can be used to drastically shorten the lifetime of optically excited carriers. Sub-picosecond carrier lifetimes open the possibility to realize ultrafast saturable absorbers and optoelectronic transducer elements. They are particularly important as key elements in THz technology, such as efficient THz emitters, detectors, and for on-chip THz technology. This paper summarizes the most distinguished results relevant in the context of ultrafast optoelectronics and THz technology obtained in close collaboration with the Paul-Drude-Institute Berlin over the past decade.

2009, Nagel, Michael, Klatt, Gregor, Awad, Mohammad, Kurz, Heinrich, Bartels, Albrecht, Dekorsy, Thomas

Using high-speed asynchronous optical sampling, read-out of novel terahertz surface sensors directed at bio-sensing applications is presented. The surface sensor is based on periodically arranged metallic THz split ring resonators on a 27-ìm-thin polymer membrane.

2005, Janke, Christof, Först, Michael, Nagel, Michael, Kurz, Heinrich, Bartels, Albrecht

Two femtosecond Ti:sapphire lasers with slightly different repetition rates near 1 GHz are coupled to implement high-speed asynchronous optical sampling. The application of this technique is successfully demonstrated in the field of terahertz time-domain spectroscopy (TDS). A time delay of 1 ns is scanned at a frequency of 5 kHz without moving mechanical parts. Compared with that of conventional TDS schemes based on lock-m detection and moving mirrors, the readout time of integrated resonant THz sensors is reduced by a factor of 20, opening the way for high-throughput THz sensing in marker-free DNA analysis.

2009, Klatt, Gregor, Nagel, Michael, Dekorsy, Thomas, Bartels, Albrecht

High-speed asynchronous optical sampling is used for the rapid and precise determination of transmission resonances of terahertz surface sensors based on asymmetric double split ring resonator arrays. The sensor response represented by a characteristic resonant frequency is determined to 0.66113 THz with an accuracy of +325 MHz within 2 seconds of read-out time.

1998, Nagel, Michael, Meyer, Christoph, Heiliger, Hanns-Michael, Dekorsy, Thomas, Kurz, Heinrich, Hey, Rudolf, Ploog, Klaus

We report the application of electric field-induced second-harmonic (EFISH) generation for time-resolved measurement of ultra-fast electrical pulses propagating on thin-film microstrip lines fabricated with a polymer based on benzocyclobutene as a dielectric layer on a silicon substrate. This contactless field detection enables the characterization of electric pulses on the transmission line up to 1.95 THz. In comparison to external electro-optic sampling the EFISH technique provides a better characterization tool concerning time-resolution and noninvasiveness.