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2024-11-23 18:26

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Conference: Bucharest University Faculty of Physics 2009 Meeting

Section: Optics, Spectroscopy, Plasma and Lasers

Title:

THz Time Domain Spectroscopy System for Biomolecular Systems

Authors:

1)Aurel LECA, 2)Mihai P. DINCA, 1)Traian DASCALU

Affiliation:

1)National Institute for Laser, Plasma and Radiation Physics

2)University of Bucharest Faculty of Physics

E-mail

aurel.leca@inflpr.ro

Keywords:

THz Spectroscopy

Abstract:

Time-domain spectroscopy (TDS) becomes a promising technology in studies of biological tissues, cancer diagnosis and low-frequency collective modes in large biomolecules. THz-TDS is based on the optoelectronic generation and reception of a beam of subpicosecond terahertz pulses. Since many protein and DNA molecules have distinct signatures in the terahertz spectral region, various types of proteins can be identified. This paper aims to present the setup calibration, various noise and etalon effects which often interfere with THz-TDS technique. In the present experimental setup, the generation and detection of terahertz electromagnetic pulses employ photoconductive switching transmitter and receiver. Femtoseconds, 780nm wavelength, optical pulses generated from a self mode locked fiber laser are split and used to irradiate photoconductive antenna and to gate the photoconductive receiver. The delay line allows a temporal scan of THz pulses from time gate measurements. By scanning optical delay line in 10-20 fs steps, the waveform of electric field of THz radiation is built. The Fourier transform of waveform gives the spectral content of THz radiation. We made various measurements on bovine serum albumin (BSA) 0.5 mm thick, lyophilized and humid forms. THz TDS spectra were obtained in the range 0.2-2.8THz. The noise level was decreased by averaging the data over ten acquisitions. In order to improve the accuracy one has to look for the origin of the noise and find out methods to suppress it. There are several noise sources: laser peak power fluctuation, the emitter noise, the detector noise, 50 Hz noise, etc. Moreover, because the water has rotational spectra in the region 0.2-3THz, the water vapor contents in the atmosphere can affect dramatically the accuracy of the measurements. We present the preliminary results which show how the useful frequency range of the THz –TDS setup is increased.