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Schematic representation of the experimental apparatus. Near single-cycle THz pulses are generated from a biased GaAs photoconductive (PC) emitter. The electric field of the transmitted THz pulse is then detected as a function of time using a thick ⟨110⟩ ZnTe crystal via broadband electro-optic (EO) sampling. Inset: Schematic representation of the THz radiation before (left) and after (right) transmission through a sample. In the frequency domain, the absorption simply causes a spectral dip (bottom-right) at the resonance frequency of the sample. In the time domain, absorption is followed by subsequent radiation of a decaying electric field (solid curve, top right), in addition to the transmitted THz pulse (dashed curve, top right).
THz pulse measured in the absence of a sample (curve 1) and after transmission through a polycrystalline cytosine sample at (curve 2). Fast oscillations are observed (in curve 2) immediately after the main peak (see inset). Curve 3 shows an amplified portion of curve 2 between 3 and (dotted line) weighted by a Gaussian window centred at . All signals are vertically offset for clarity. Inset shows the measured (point) and calculated (line) THz signal between 3.5 and .
(a) The time-partitioned Fourier transform spectra of the measured THz signals for cytosine at . The time interval between two adjacent curves is , with the time on the left-hand side of the graph being the center of the wide Gaussian window. The top curve is the transmission spectrum of cytosine. (b) The time-partitioned Fourier transform of the simulated THz data for a Lorenz oscillator . The time on the left-hand side of the graph is the center of the wide Gaussian window. The top curve shows the simulated transmission spectrum.
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