A. G. Shmelev

Optical control of the anisotropy of the orientation of molecules in a liquid

The control of the anisotropy of the orientation of molecules in pure 1,2-dichlorobenzene, C6H4Cl2 at room temperature is demonstrated experimentally. To accomplish the optical control, the medium is exposed to non-resonant excitation with two successive linearly polarized laser pulses with a duration of 60 fs. The state of transient anisotropy is probed with the third pulse by detecting the ultrafast optical Kerr effect via optical heterodyne detection and synchronous demodulation. It is shown that variations in the two parameters, the delay time between two pump pulses, and the angle between the polarization directions of the pump pulses ensure the control of the anisotropy of the orientation of molecules in the subpicosecond region.

Femtosecond non-resonance double-pulse spectroscopy of molecular librations in ortho-dichlorobenzene

The first experimental results on selective detection of the collective (libration) response in a liquid using a scheme of non-resonance double-pulse spectroscopy based on detecting the ultrafast optical Kerr effect (OKE) in ortho-dichlorobenzene at room temperature are presented. Nonrelevant vibrational and rotational responses are dumped and the relevant libration molecular responses are amplified by varying the duration, delay, and relative intensities of linearly polarized pump pulses.

Femtosecond multipulse polarization spectroscopy of molecular vibrations and rotations in liquids

Simultaneous control over the vibrational and rotational molecular responses in ultrafast optical Kerr-effect signals in acetonitrile, toluene, and chloroform at room temperature is achieved by means of non-resonance excitation with two 30-fs orthogonal linearly polarized laser pulses. It is shown that the orientational response of the molecules can be suppressed and their vibrational response isolated by enhanced the delay between the exciting pulses and their relative intensity.

Femtosecond laser control of intramolecular vibrations in a liquid

Optical control of coherent intramolecular oscillations in chloroform CHCl3 and dimethyl sulfoxide (CH3)2SO is attained experimentally under normal conditions by means of femtosecond polarization spectroscopy. Nonresonant excitation of the medium is accomplished by a sequence of two linearly polarized laser pulses. The state of the medium is probed by the third pulse via the optical Kerr effect. We show that control over the vibrational dynamics of molecules on a sub-picosecond scale can be achieved by varying the delay between the excitation pulses and their relative intensity.

Femtosecond selective optical Kerr-effect spectroscopy: Molecular dynamics study of chloroform

The femtosecond selective spectroscopy of vibrational-rotational dynamics of molecules in a liquid was realized using optical Kerr effect registration under two-pulse nonresonant excitation. The object chosen for the study was the chloroform at room temperature. It was shown that control of the separate molecular motions by creating the constructive or destructive interference of corresponding wave packets allows one to determine directly from the experiment such constants of molecular dynamics as the relaxation times of the coherent vibrations (≈1.5 ps) and those of orientational anisotropy (≈1.2 ps).

Ultrafast spectroscopy of CdS/CdSe quantum dots

Results from the nonresonance spectroscopy of CdS/CdSe quantum dots (composites of CdSe–CdS nanoparticles (core–shell)) are presented. The nonlinear optical properties of CdS/CdSe QDs in PMMA are studied with fs pulses at 1053 nm using the transient lens technique. QDs generate rapidly oscillating signals with amplitude rise times of around 200 fs and decay times of around 500 fs, while pure PMMA polymer only generates an oscillating signal whose envelope coincides with its autocorrelation function.

Polarization two-pulse method for analysis of sensing femtosecond signals based on the ultrafast optical Kerr effect

A novel molecular polarization spectroscopy method of processing the strengthened femtosecond signals, based on the ultrafast optical Kerr effect, is proposed. The processing of the reference chloroform signal by the novel method at a room temperature is demonstrated. It is shown that due to the manipulation by individual molecular motions through the constructive or destructive interference of corresponding wave packets it is possible to determine directly from the experiment such constants of molecular dynamics as the relaxation times of the coherent vibrations (≈1.5 ps) and orientation anisotropy (≈1.2 ps).