Abstract-Broadband Terahertz Light–Matter Interaction Enhancement for Precise Spectroscopy of Thin Films and Micro-Samples

Romain Peretti. Flavie Braud, Emilien Peytavit, Emmanuel Dubois,  Jean-François Lampin,

http://www.mdpi.com/2304-6732/5/2/11

In biology, molecules and macromolecules such as sugars, proteins, DNA, RNA, etc., are of utmost importance. Detecting their presence as well as getting information on their actual structure is still a challenge in many cases. The vibrational states of such molecules correspond to a spectral range extending from infrared to terahertz. Spectroscopy is used for the detection and the identification of such compounds and their structure. Terahertz spectroscopy of a biosample is challenging for two main reasons: the high terahertz absorption by water molecules in the sample; and the small size of the sample—its volume is usually smaller than the cube of the terahertz wavelength, thus the light–matter interaction is extremely reduced. In this paper, we present the design, fabrication, characterization, and first typical use of a biophotonic device that aims to increase the light–matter interaction to enable terahertz spectroscopy of very small samples over a broad band (0.2–2 THz). Finally, we demonstrate the validity of our approach by time-domain spectroscopy of samples of a few µL.

Abstract-Broadband Terahertz Light-Matter Interaction Enhancement for Precise Spectroscopy of Thin Films and Micro-Samples

Romain Peretti, Flavie Braud, Emilien Peytavit,  Emmanuel Dubois, Jean-François Lampin

https://www.preprints.org/manuscript/201802.0157/v1


In biology molecules and macromolecules like sugars, proteins, DNA, and RNA are of utter importance. Detecting their presence as well as their conformation is still a challenge in many cases. It is well known that the vibrational states of such molecules lie from the infrared to the TeraHertz range. Spectroscopy can be used to detect such compounds and probe their conformation. Still, terahertz spectroscopy on biosample is a challenge for two main reasons: water absorption; and the small size of the samples. The sample volume is smaller than the cube of the TeraHertz wavelength; the light matter interactions are thus extremely reduced. In this paper, we present the design, fabrication, characterization and the first typical uses of a biophotonic device aiming at increasing light matter interaction to enable terahertz spectroscopy of minute samples on a broad band (0.2–2 THz). We demonstrate time domain spectroscopy experiments on few µl samples showing the validity of our approach.

Abstract-Optically-pumped continuous-wave terahertz sources

Philipp Latzel ; Fabio Pavanello ; Emilien Peytavit ; Mohammed Zaknoune ;Guillaume Ducournau ; Xavier Wallart ; Jean-François Lampin

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2110839

Philipp Latzel, Fabio Pavanello, Emilien Peytavit, Mohammed Zaknoune, Guillaume Ducournau, Xavier Wallart, Jean-François Lampin

Institut d'Electronique de Microélectronique et de Nanotechnologie (France)

Proc. SPIE 9370, Quantum Sensing and Nanophotonic Devices XII, 937008 (February 8, 2015); doi:10.1117/12.2080756

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Recently we have improved the efficiency and the output power of our optically pumped continuous-wave THz sources. These sources are based on the beating of two laser lines in a wide bandwidth photodetector. Its intrinsic nonlinear behaviour is used to produce a beatnote at the frequency difference between the two laser lines (photomixing). These photomixers are continuously tunable THz sources working at room temperature. We have developed two kinds of photomixers: GaAs-based for 0.8 μm pumping and InP-based for 1.5 μm pumping. On GaAs the best results has been obtained thanks to low-temperature-grown GaAs (LTG-GaAs) photoconductors (PC). Efficiency and power were optimized by designing a new type of thin PC placed in a Fabry-Pérot resonator. The high impedance of the PC is a wellknown limitation of this device but with our approach it was possible to reduce its impedance by a factor 100. Moreover by designing an impedance matching network it was possible to obtain 1.8 mW at 252 GHz with a total efficiency of 0.5 %. On InP the best results are obtained with uni-travelling-carrier photodiodes (UTC-PD). The device was improved by designing a new heterostructure and new semi-transparent contacts with sub-wavelength apertures. The active layer was also bonded to a silicon substrate thanks to metal thermocompression. It is demonstrated that with this approach it is possible to obtain a power of 0.7 mW at 300 GHz with a total efficiency of 0.7 %. More generally the efficiency of optically pumped terahertz sources will be discussed. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.