Pulsed THz radiation under ultrafast optical discharge of vacuum photodiode.

In this paper, we first present an experimental demonstration of terahertz radiation pulse generation with energy up to 5 pJ under the electron emission during ultrafast optical discharge of a vacuum photodiode. We use a femtosecond optical excitation of metallic copper photocathode for the generation of ultrashort electron bunch and up to 45 kV/cm external electric field for the photo-emitted electron acceleration. Measurements of terahertz pulses energy as a function of emitted charge density, incidence angle of optical radiation and applied electric field have been provided.

Analysis of intra-specific variations in the venom of individual snakes based on Raman spectroscopy.

The knowledge of variations in the composition of venoms from different snakes is important from both theoretical and practical points of view, in particular, at developing and selecting an antivenom. Many studies on this topic are conducted with pooled venoms, while the existence and significance of variations in the composition of venoms between individual snakes of the same species are emphasized by many authors. It is important to study both inter- and intra-specific, including intra-population, venom variations, because intra-specific variations in the venom composition may affect the effectiveness of antivenoms as strongly as inter-specific.

Optical Pump-Terahertz Probe Diagnostics of the Carrier Dynamics in Diamonds.

Diamond is a promising material for terahertz applications. In this work, we use a non-invasive optical pump-terahertz probe method to experimentally study the photoinduced carrier dynamics in doped diamond monocrystals and a new diamond-silicon composite. The chemical vapor deposited diamond substrate with embedded silicon microparticles showed two photoinduced carrier lifetimes (short lifetime on the order of 4 ps and long lifetime on the order of 200 ps).

Narrow intensity range optical anisotropy in air induced by a femtosecond laser breakdown.

In this paper, we study the optical anisotropy induced by femtosecond laser radiation in air during an optical breakdown. Using a transverse pump-probe technique, we demonstrate that this anisotropy appears in a narrow range of pump intensities, which are close to the optical breakdown threshold in air and lead to a phase shift of probe radiation, polarized collinear to the pump. The intensity range where an induced intense anisotropy occurs makes it possible to estimate the magnitude of the 5th-order Kerr nonlinear refractive index component in air.

Differentiation of snake venom using Raman spectroscopic analysis.

Snake venoms are complex mixtures of different substances, proteins being their predominant components. To study the composition of venoms, methods based on chromatographic separation and mass spectrometric analysis are currently used, requiring the application of a number of sophisticated instruments. To assess the composition of snake venoms, we propose an alternative method based on Raman spectroscopy, which is an express method to study the structural features of different substances, including proteins.

Toxins' classification through Raman spectroscopy with principal component analysis.

The method based on the combination of Raman spectroscopy and principal component analysis (PCA) was applied to the set of peptide and protein toxins from animal venoms and to synthetic analogues of peptides. The study demonstrated the possibility of toxin classification according to their primary and secondary structures based on Raman spectroscopy. The method described here allows discrimination of snake venom three-finger toxins from predatory marine mollusks α-conotoxins.

Photoconductive terahertz generation in nitrogen-doped single-crystal diamond.

The generation of terahertz radiation in a photoconductive emitter based on nitrogen-doped single-crystal diamond was realized for the first time. Under 400 nm femtosecond laser pumping, the performance of diamond antennas with different dopant levels was investigated and compared with a reference ZnSe antenna. Terahertz waveforms and corresponding spectra were measured.

"Terhune-like" transformation of the terahertz polarization ellipse "mutually induced" by three-wave joint propagation in liquid.

In this Letter, we show experimentally for the first time, to the best of our knowledge, the possibility to observe the effect of polarization mutual action of three elliptically polarized waves, with one of them at terahertz frequency, when they propagate in the isotropic nonlinear medium. When three light pulses are propagated at frequencies , 2, and through liquid nitrogen, we observed the rotation of the ellipse main axis and the ellipticity change. We have shown that this effect is very well described theoretically in the framework of a physical approach analogous to the self-rotation of the polarization ellipse first described in 1964 by Maker et al.

All-optical control of ultrafast photocurrents in unbiased graphene.

Graphene has recently become a unique playground for studying light-matter interaction effects in low-dimensional electronic systems. Being of strong fundamental importance, these effects also open a wide range of opportunities in photonics and optoelectronics. In particular, strong and broadband light absorption in graphene allows one to achieve high carrier densities essential for observation of nonlinear optical phenomena.

Plasma filament investigation by transverse optical interferometry and terahertz scattering.

Transverse plasma distribution with 10(17) cm(-3) maximum electron density and 150 μm transverse size in a plasma filament formed in air by an intense femtosecond laser pulse was measured by means of optical interferometry. Two orders of magnitude decay of the electron density within 2 ns was obtained by combined use of the interferometry and newly proposed terahertz scattering techniques. Excellent agreement was obtained between the measured plasma density evolution and theoretical calculation.

Broadband light-induced absorbance change in multilayer graphene.

We report the ultrafast light-induced absorbance change in CVD-grown multilayer graphene. Using femtosecond pump-probe measurements in 1100-1800 nm spectral range, we revealed broadband absorbance change when the probe photon energy was higher than that of the pump photon. The observed phenomenon is interpreted in terms of the Auger recombination and impact ionization playing a significant role in the dynamics of photoexcited carriers in graphene.