Absorption spectra of sixteen polymers have been examined using terahertz (THz) time-domain spectroscopy system in
THz frequency range (0.1 - 3 THz). All the experimental data showed a characteristic wide absorption peak at the
frequencies around 2.5 THz accompanied by smoothly decreasing of refraction (except "transparent" polymers). Such
behavior could be described by a modified Debye model. We also tried to clarify the impact of flexibility,
polymerization, crystalline degree and number of monomer end groups on polymer dielectric properties. We suggest that
the absorption mechanism in spectral range lower than 3 THz is related with relaxation and amorphous state of polymers.
In the present paper the results of the study of semiconductor and optical properties of GaSe crystals important for their
applications in nonlinear optics of terahertz and mid-IR ranges are reported as well as influence of doping with isovalent
chemical elements on them. The performed first-principles calculations of charge neutrality level (CNL) in GaSe have
shown its position at 0.8 eV above the top of the valence band. The location of CNL in the lower part of the band gap
can explain GaSe intrinsic p-type of conductivity. In this case it is necessary to radically improve the growth technology
to obtain GaSe crystals with low free carrier concentrations. Extraordinarily large birefringence of GaSe B~0.8 in
terahertz range has been measured directly. In order to study the potential efficiency of application of doped GaSe
crystals for terahertz generation and detection their study using terahertz time domain spectroscopy (THz-TDS) setup has
been performed. According to the obtained results doped GaSe crystals are slightly less efficient for terahertz detection
and generation in the frequency range 0.2-3.2 THz via optical rectification of laser pulses with λ=790 nm and τ=80 fs.
On the other hand doping of GaSe with In, Al, S, Te leads to 2-3 times increase of the microhardness and the doped
crystals become suitable for the mechanical treatment.
The terahertz time-domain and Raman spectra of corticosteroid hormones in the region of low-frequency infrared
vibrations have been measured. On the ground of quantum chemical calculations of the frequencies and normal modes
the assignments of vibrational bands in the THz-spectra are performed.
Experimental absorption and refraction spectra measured for different tooth structures in THz frequency range from 0.1
to 3 THz (3-100 cm-1) are presented. Characteristic features of refraction spectrum were found for different areas of
tooth enamel and dentin.
Broadband THz pulse generation via optical rectification of femtosecond laser pulse is
studied. We optimize the phase-matching conditions by taking into account the material dispersion
properties of ZnTe and GaP crystals, with are measured and modeled. Laser pulse duration influence
Experimental absorption spectrum in THz frequency range of fat, sugar, hemoglobin and water are presented.
Characteristic features for some of those substances where found in absorption and refraction spectrum. Changing laser
wavelength and nonlinear crystal thickness THz generation and detection was optimized for certain frequency, allowing
one to increase spectrometer sensitivity for biological samples.
Propagation of terahertz waves in segmented waveguides (1 -D photonic crystal) is experimentally demonstrated. Data are well fitted using a modified FDTD method. Dispersion curves of the first guided modes are determined.
We report here on experiments with surface plasmon excitation and propagation along corrugated and smooth aluminum surface in the terahertz frequency range. Plasmon excitation by a picosecond terahertz pulse is shown to be a transient process and plasmon propagation sufficiently changes its measured time profile. Plasmon duration and life-time were defined and plasmon propagation lengths on smooth and corrugated surface were measured. Plasmon propagation length on flat surface turned out to be much smaller than the Drude model predicts.
We present the Raman spectra of sulfur-containing biomolecules and the spectra measured in far-infrared region with
the use of terahertz (THz) time-domain spectroscopic technique. The spectral features in THz and Raman spectra are
different among sulfur-containing di- and tetrapeptides in powder. We are discussing the possibility to observe and to
assign the low-frequency THz and Raman lines to the disulfide bridges.
A new surface-sensitive method of time-resolved optical studies is proposed. The method consists in the independent excitation of several surface electromagnetic waves (SEW) by two laser femtosecond pulse beams with varied time delay Δτ and distance Δr between corresponding excitation regions on surface. To fulfill phase matching condition for plasmon-photon coupling metal grating is used. Due to nonlinear plasmon interaction, the optical radiation with ω1 + ω2 and 2ω1 - ω2, (where ω1, ω2 are correspondent laser beam frequency) is generated. The intensity of this nonlinear response versus Δτ and Δr are studied. The direct measurements of the SEW temporal properties are presented. Experiments of this type are important for the development of the femtosecond surface plasmon optics for study of ultrafast phenomena in nanostructures.
Frequency mixing is demonstrated in degenerate three-wave mixing with two noncollinear beams of femtosecond laser pulses on a metal grating. The observed enhancement of the nonlinear optical response is connected with the synchronized excitation of two surface plasmon-polaritons waves, their nonlinear interaction and photon generation with the sum frequency. The dependencies of this process versus the temporal delay between laser pulses and the mutual spatial overlapping of the beams on the grating surface are studied. Experiments of this type opens a possibility of development of femtosecond time- resolved surface SPP optics and spectroscopy.