E. A. Vinogradov

Parametric excitation of vacuum by use of femtosecond laser pulses

We discuss the method of parametric excitation of electromagnetic waves in a cavity by creating a dense plasma layer (which represents the mobile wall of the cavity) due to irradiation of a semiconductor film with femtosecond laser pulses. The effect is analysed for various initial states including an initial vacuum state. The state of the field produced by this method from an initial vacuum state is different from an electromagnetic field of another origin because only even quantum levels are populated (similar to Schrodinger cat states) and specific distributions of wave packets in phase space takes place. Besides, the parametrically excited field has a specific angle distribution and appears in shorter time scales than the ones required for appearance of radiation of other origin. The instantaneous and adiabatic slow excitation of eigenmodes of the cavity are described. Estimations for experimental detection of the effect are made.

Resonances of thermally stimulated electromagnetic excitations of thin films on a substrate in a near field

The spectral features of thermally stimulated electromagnetic excitations generated by films of wide band gap semiconductors on metals in vacuum at different distances from a sample surface were investigated. Special attention was given to the interaction of characteristic resonances in the excitation spectrum of these fields with local vibrations of Cd impurity atoms inside ZnTe films on metal substrates.

Femtosecond dynamics of semiconductor microcavity polaritons

Dynamics of semiconductor microcavity modes in ZnS-Ni structure was investigated by femtosecond pump-supercontinuum probe spectroscopy in wide spectral region 1.6 - 3.2 eV. The change of reflectivity of the ZnS thin films (of 0.29 micrometer, 1.08 micrometer and 1.17 micrometer) on thick Ni film on quartz substrate was monitored. Two different pumping photon energies

Ultrafast transient phenomena in semiconductor microcavities

HBAR(omega) pul equals 2.75 eV and

Ultrafast Spectroscopy of Optical Microcavity Modes on the Unique Femtosecond Spectrometric Complex at the Institute of Spectroscopy RAS

HBAR(omega) pu2 equals 5.5 eV were used for the excitation of the microcavity and produced different photoresponse spectra. The first pumping energy (2.75 eV) is lower than the energy gap of ZnS (3.7 eV) and the powerful laser pulse excites mainly electrons of metal (i.e. boundary of the microcavity) and of ZnS layer (by two-photon absorption). Nonequilibrium carriers of metal penetrate through Schottky electron barrier into the semiconductor. For the second pumping energy (5.5 eV) the pumping pulse is practically totally absorbed in thin surface ZnS layer of 40 nm in thickness and creates nonhomogeneous hot carriers distribution semiconductor. The differences in the processes of carrier excitation are responsible for the differences in the changes of dielectric function of ZnS and Ni and for the differences in the change of cavity modes.

Femtosecond evolution of semiconductor microcavity modes

The excitation of semiconductor microcavity modes (ZnSe films on Cr and Cu surfaces) were investigated by femtosecond pump- supercontinuum probe spectroscopy in wide spectral region 300 - 800 nm. Photoinduced red shift of cavity modes due to parametric pump of ZnSe film and film-metal interface and the generation of coherent phonon oscillations in ZnSe were observed.

Femtosecond photoresponse of structures with the Schottky Barrier

The relaxation of nonequilibrium charge carriers in ZnSe films on metal substrates has been investigated by the femtosecond spectroscopic pump-supercontinuum probe method. Upon subgap and overgap excitations of ZnSe, red and blue photoinduced frequency shifts for the interference cavity modes in ZnSe films on chromium have been revealed. Such shifts and features of the relaxation times are explained by photoinduced changes in the boundary conditions and optical thickness of the microcavity.

Electron injection dynamics through the Schottky barrier

Dynamics of semiconductor microcavity modes in ZnSe- metal structure was investigated by femtosecond pump- supercontinuum probe spectroscopy in wide spectral region 300 - 800 nm. The powerful laser pump pulse excites electrons of metal (i.e. boundary of the microcavity) and of ZnSe layer (by two-photon absorption and absorption of second-harmonics generated photon). Photoinduced changes of dielectric function of metal transform the boundary condition. It leads to shift of frequencies of cavity modes to red region of spectrum. Another contribution to change of boundary condition is connected with tunneling of excited electrons through Schottky electron barrier into ZnSe layer. The generation of coherent phonon oscillations (LO-phonon mode 250 cm-1 and TO-phonon mode 200 cm-1) in ZnSe was detected.