B. L. Yu

Torsional Vibrational Modes of Tryptophan Studied by Terahertz Time-Domain Spectroscopy

The low-frequency torsional modes, index of refraction, and absorption of a tryptophan film and pressed powders from 0.2 to 2.0 THz (6.6-66 cm(-1)) were measured by terahertz time-domain spectroscopy at room temperature. It was found that there were two dominated torsional vibrational modes at around 1.435 and 1.842 THz. The associated relaxation lifetimes ( approximately 1 ps) for these modes of the tryptophan molecule were measured. Using a density-functional calculation, the origins of the observed torsional vibrations were assigned to the chain and ring of the tryptophan molecule.

Terahertz studies of the dielectric response and second-order phonons in a GaSe crystal

The dielectric function and momentum relaxation time of carriers for a single-crystal GaSe were investigated using terahertz time-domain spectroscopy over the frequency range from 0.4to2.4THz. The key parameters determined from THz data using the Drude model are: the plasma frequency ωp=2.6±0.2THz, the average momentum relaxation time ⟨τ⟩=56±2fs, and the mobility μ=89cm2∕Vs for electrons. The THz absorption spectrum showed resonance structures attributed to the difference frequency combinations associated with acoustical and optical phonons.

Femtosecond optical Kerr shutter using lead-bismuth-gallium oxide glass

Abstract A femtosecond Kerr shutter was demonstrated using a lead–bismuth–gallate oxide glass. The optical gating time was measured to be less than 350 fs and the peak Kerr transmittance was found to be 2.3 times larger than that of the standard Kerr CS 2 liquid medium, giving nonlinear Kerr coefficient n 2 =4.4×10 −11 esu.

Reorientation of the H2O cage studied by terahertz time-domain spectroscopy

The terahertz absorption spectrum of a thin film of liquid H2O of ∼14μm thickness showed a clear absorption mode at 1.56THz(∼53cm−1). This mode is attributed to the bending motion of the intermolecular hydrogen-bond coordinate in a water cage. The dielectric relaxation times of a slow τ1∼9ps and a fast τ2∼0.2ps component (0.4–2.0THz) were determined using a double Debye dielectric model.The terahertz absorption spectrum of a thin film of liquid H2O of ∼14μm thickness showed a clear absorption mode at 1.56THz(∼53cm−1). This mode is attributed to the bending motion of the intermolecular hydrogen-bond coordinate in a water cage. The dielectric relaxation times of a slow τ1∼9ps and a fast τ2∼0.2ps component (0.4–2.0THz) were determined using a double Debye dielectric model.

Probing dielectric relaxation properties of liquid CS2 with terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy is used to investigate the dielectric relaxation properties of liquid CS2. The frequency-dependent absorption coefficient and index of refraction were measured in the frequency range 0.2–2.0 THz. The ultrafast dielectric relaxation time of liquid CS2 was determined to be 630±30 fs by fitting the dielectric function to the Debye model which is attributed to average time for rocking and rotational response of the CS2 molecules possessing an anisotropic polarizability.

Direct observation of coherent rotational excitation, dephasing and depopulation of methanol and its isotopes using THz pulse radiation

Coherent transients are directly observed in the time-domain as a sequence of decreasing commensurate pulses in methanol (CH3OH) and its isotopes (CH3OD and CD3OD) gases to yield fundamental information on its dephasing and depopulation. The delay times between coherent pulses of ∼21, 22, and 26ps are measured for the CH3OH, CH3OD, and CD3OD corresponding to the inverse of rotational energy spacing for ΔJ=±1 transitions, respectively. The dephasing time T2=23±0.5ps and depopulation time T1=48±0.5ps were measured for CH3OH at room temperature.

Room Temperature Terahertz (THz) Spectroscopy of CCl3F (CFC-11)

The rotational spectrum for the lowest vibrational mode for CCl3F has been measured in the 0.1 to 1.5THz frequency range. The observed absorption profile was well modeled with rotational and vapor pressure parameters.

Terahertz time-domain spectroscopy of torsional vibrational modes of tryptophan

The low-frequency torsional modes of tryptophan were measured by terahertz time-domain spectroscopy (THz-TDS). It was found that there are two dominated torsional vibrational modes at around 1.435 and 1.842 THz. The origin of the observed torsional vibrations are assigned to the chain and ring of the tryptophan molecule.