Andrei G. Stepanov

Generation of 30 μJ single-cycle terahertz pulses at 100 Hz repetition rate by optical rectification

We report the generation of 30 microJ single-cycle terahertz pulses at 100 Hz repetition rate by phase-matched optical rectification in lithium niobate using 28 mJ femtosecond laser pulses. The phase-matching condition is achieved by tilting the laser pulse intensity front. Temporal, spectral, and propagation properties of the generated terahertz pulses are presented. In addition, we discuss possibilities for further increasing the energy of single-cycle terahertz pulses obtained by optical rectification.

Two-photon absorption of powerful femtosecond pulses in C60 film

Abstract Irradiance-dependent transmission measurements were conducted for thin C60 film irradiated by 300 fs laser pulse at 612 nm in the intensity range from 108 W/cm2 to the values ≈ 1012 W/cm2 corresponding to the film damage. The upper limit for the two-photon absorption coefficient was derived from these measurements as (3 ± 1.5) × 10−8 cm/W, which corresponds to an Im χ(3) values of (2.6 ± 1.3) × 10−11 esu.

Geometric-optical reconstruction of a wavefront

A new method of achromatic wavefront reconstruction by geometric-optical reflection of the reconstructing radiation from surfaces with constant phase difference between the object and reference waves is theoretically described and experimentally realized. Methods distinction from holographic one is discussed. Femtosecond laser pulses are used for recording in the experiment.

Geometric-optical reconstruction of a wavefront experimental realization with femtosecond laser pulses

Abstract The mechanism of wavefront reconstruction by geometric-optical reflection of reconstruction radiation from surfaces with constant phase differences between the object and reference waves has been investigated. The main difference between this mechanism and a holographic one is the absence of diffraction of the reconstructing radiation by the periodic structure and as a consequence the achromatism of the reconstruction process. Incoherent continuous radiation and ultrashort laser pulses were used in the experiments. The effect of achromatic reconstruction has been obtained after recording the interference of counterpropagating 30–40 fs pulses from an Al 2 O 3 :Ti 3+ laser in bulk media.

Ultrahigh-spatial-resolution photoelectron projection microscopy using femtosecond lasers

Ultrahigh spatial resolution of two-photon photoelectron images (as high as 3 nm, which is the best value that has been achieved to date in photoelectron microscopy with spatial resolution) is obtained when silicon nanotips are irradiated by the second harmonic of a pulsed femtosecond Ti: sapphire laser. In addition, the absolute value of the two-photon external photoeffect coefficient is measured.

Spectral modifications of femtosecond laser pulses induced by phase-matched optical rectification in LiNbO 3

In this paper, we report experimental observations of the spectral modifications of ultrashort laser pulses caused by high-efficiency optical rectification. Moreover, we assert that the observed spectral modifications can be used to evaluate the absolute energy of generated THz pulses without calibrated THz detector. Abilities to obtain more than 100% optical-to-THz quantum conversion efficiency by phase-matched optical rectification are discussed. THz radiation in our experiment was generated in a LiNbO3 crystal using a tilted pulse front phase-matching.

Phototransformation and photoinduced oxygen uptake in C60 films irradiated by femtosecond laser pulses

Photopolymerization and photoinduced diffusion of the molecular oxygen in oxygen bearing C60 films by (lambda) equals 459, 514 nm continuous laser radiation and by 100-fs, (lambda) equals 395, 410 nm pulses were compared by visual observation of photodarkening spots and by recording the Raman spectra, in the range 200 - 1700 cm-1, of the irradiated regions. It was found out that in the case of femtosecond pulses, the efficiencies of both photoinduced processes are significantly lower than those in the case of continuous radiation.