Developing methods for observing processes induced by femtosecond laser pulses with high spatiotemporal resolution

A combination of femtosecond laser techniques and nanomicroscopy creates promising new possibilities for studying both matter and a whole number of ultrafast physical processes. The results obtained at the Institute for Spectroscopy as a result of developing a new area of femtosecond nanomicroscopy are presented.     

Formation of ultrashort electron pulses on scattering of an electron beam by a standing laser wave of ultrashort duration

The scattering of a well collimated electron beam by a strong standing laser wave of ultrashort duration, giving rise to a great number of scattered photons, is considered. This type of scattering is found to cause an electron beam to divide effectively into two parts. Ultrashort laser pulses are shown to be capable of forming ultrashort electron bunches whose length is governed by the laser beam diameter.     

Dynamics of cold atoms in a quadrupole magnetic trap with an orbiting potential

We study the dynamics of atoms confined to a quadrupole magnetic trap with an orbiting potential. For typical values of the experimental parameters of the trap, the rotating magnetic field is shown to produce high-frequency modulation of atomic momenta with an amplitude comparable to the widths of the momentum distributions for the lowest oscillation states of atoms in the time-averaged potential. We find the quantum-statistical momentum and position distributions of atoms and show that at temperatures much higher than the effective vibrational temperature of the atoms in the trap the quantum-statistical momentum and position distributions are Gaussian. We also establish that at temperatures comparable to the effective vibrational temperature of the atoms the quantum-statistical momentum distribution has an annular structure in the trap’s symmetry plane, which is due to the deep modulation of the atomic momenta caused by the rotating magnetic field. Zh. éksp. Teor. Fiz. 114, 23–36 (July 1998)     

Deceleration and monochromatization of atomic beams by laser radiation pressure

Deceleration and velocity distribution narrowing of an atomic beam irradiated by a counter-running resonant light wave is discussed. Velocity distribution evolution under the action of light pressure force and diffusion is found. The results of a numerical solution of the kinetic equation for the atomic velocity distribution function are presented. These results show the efficiency of using the light pressure to decelerate atomic beams and narrow their velocity distribution.     

Resonant light pressure due to a strong standing wave

This paper calculates the light pressure force due to a standing wave, including the lowest order modification of the populations. The result is compared with that of the rate-equation approximation.     

Visualization of the spatio-temporal structure of a pulsed photoelectron beam formed by femtosecond laser radiation

A method based on an original electron microscope created for investigating photoelectron beams is presented. It ensures a nanometer spatial resolution and picosecond time resolution. Electrons appearing when a metal needle is irradiated by femtosecond laser pulses are transmitted through a dielectric microcapillary and are subjected to a ponderomotive potential created by femtosecond laser radiation focused near the capillary tip. The position-sensitive detection scheme allows for the detection of the spatial profile of a photo-electron beam with a magnification of K ≅ 4 × 10⁴. The time structure of the photoelectron beam is visualized by scanning the delay time between laser pulses irradiating the needle and a laser pulse focused near the capillary tip.     

Identities for the electron forms 2 and their 3D representation

New type of identities for products of the electron forms 2 (Fs2) and the bilinear forms (BFs) are derived. The identities are found for both temporal Fs2 describing the electron energy and quasi energy densities and spatial Fs2 describing the linear momentum and quasi linear momentum densities. The identities allow one to transform the quasi energy densities into the energy densities as well as the quasi linear momentum densities into the linear momentum densities. It is shown that by choosing any one of the 16 electron temporal or spatial Fs2 one can represent the remaining 15 temporal or spatial Fs2 as combinations of a chosen form 2 (F2) and the derivatives of a number of BFs. Any one of such 16 sets of identities can be considered as a specific form of an irreducible representation for the temporal or spatial Fs2. Similar to the bilinear identities for BFs the derived identities can be used for reduction different physical quantities describing the electron to the forms defined by the basic physical observables. As an example we consider transformation of the electron energy density to a new fundamental form that presents the energy density through the linear momentum density.     

Collimation of atomic beams by resonant laser radiation pressure

The application of the resonant light pressure created by an axially symmetrical light field for collimating atomic beams has been considered. As an example, consideration is given to the possibility of collimating an atomic beam by the light field produced by the reflection of a plane wave from the internal surface of a metal cone. It has been shown that the radiation pressure can reduce the atomic-beam transverse velocities to the value of the order of 100 cm/s which corresponds to effective temperature of about 10^–3 K. A method for producing collimated beams of cold atoms based on simultaneous deceleration and collimation of atomic beams by resonant laser radiation pressure is proposed.     

Quantum motions of ultracooled atoms in resonant laser field

The analysis has been made of quantum motions of cooled atoms in a resonant light field. The existence of the band structure of energetic levels is predicted of quantum atom motions in a standing light wave field. Cooling and trapping of atoms has been described from the quantum point of view. The possibility of detection r.f. photons on the transitions of ultracooled atoms and molecules in a standing light wave field is proposed.