Biomedical subjects

Filip Kadlec

Publications and source records attributed to Filip Kadlec.

4 recordsLinked to original sources

PubMed2005

Nonresonant ionization of oxygen molecules by femtosecond pulses: plasma dynamics studied by time-resolved terahertz spectroscopy.

We show that optical pump-terahertz probe spectroscopy is a direct experimental tool for exploring laser-induced ionization and plasma formation in gases. Plasma was produced in gaseous oxygen by focused amplified femtosecond pulses. The ionization mechanisms at 400- and 800-nm excitation wavelengths differ significantly being primarily of a multiphoton character in the former case and a strong-field process in the latter case. The generation of the plasma in the focal volume of the laser and its expansion on subnanosecond time scale is directly monitored through its density-dependent susceptibility. A Drude model used to evaluate the plasma densities and electron-scattering rates successfully captures the observations for a wide range of pump intensities. In addition, rotational fingerprints of molecular and ionic species were also observed in the spectra.

Journal Article↗

PubMed2005

Study of terahertz radiation generated by optical rectification on thin gold films.

Emission of terahertz (THz) radiation as a result of optical rectification of intense femtosecond laser pulses on thin gold films has been studied by time-domain THz spectroscopy. The THz amplitude was measured as a function of film thickness and incidence angle. The experiments reveal that the emitted THz field is suppressed for a thickness below 100 nm, which gives evidence of the nonlocal character of the response. The variation of incidence angle allows us to estimate the components of susceptibility tensor chi2ijk. For thicker films and near grazing incidence, the emitted THz field attains a peak value of 4 kV/cm.

Journal Article↗

PubMed2004

Optical rectification at metal surfaces.

The emission of freely propagating terahertz (THz) radiation coming from optical rectification at metallic surfaces has been detected and characterized for the first time to the authors' knowledge. The observed THz transients are induced through nonlinear electronic processes at gold and silver surfaces on intense pulsed optical photoexcitation and exhibit a peak electric field of as much as 200 V/cm. This finding opens a qualitatively new way to investigate nonlinear phenomena at metal surfaces and also can be exploited for the development of new THz emitters.

Journal Article↗

PubMed2004

Optical pump-terahertz probe spectroscopy of dyes in solutions: probing the dynamics of liquid solvent or solid precipitate?

The optical pump-terahertz probe spectroscopy was used together with ab initio calculations and molecular dynamics simulations to investigate ultrafast dynamics following electronic excitation of Coumarin 153 and TBNC (2,11,20,29-tetra-tert-butyl-2,3-naphtalocyanine) dyes in polar solvents. By scanning the terahertz waveform for different pump-probe delays this experimental technique allows us to obtain two dimensional spectra directly reflecting the temporal response of the system. A distinct signal was obtained for TBNC in chloroform, 2-propanol, and n-butanol, while no signal was recorded for Coumarin 153 in either of these solvents. We explain the nonequilibrium signal detected in TBNC solutions by the presence of a solid, polycrystalline phase of the dye resulting from irradiating the solution by intense optical pulses.

Journal Article↗