Aleksander A. Dreischuh

Vortices in femtosecond laser fields

We experimentally generate optical vortices in the output beam of Ti:Sapphire laser emitting 20-fs pulses. Screw phase dislocations are imposed in each spectral component of the short pulses by aligning computer-generated hologram within a 4f-setup.

Odd and even two-dimensional dark spatial solitons

The formation of two-Dimensional (2D) odd dark spatial solutions is analyzed numerically at an initial helical dark-beam phase distribution. Experimental results are presented for the first time confirming the existence of two-dimensional optical even dark solitons (ring dark solitons). Several aspects of the evolution of input 1D and 2D odd/even dark beams are compared qualitatively.

Femtosecond interferometric autocorrelations in the presence of pulse-front distortions

The tilt of the pulse front caused by misalignment in stretcher-compressor devices which are used in chirped pulse amplification should be carefully considered in the design of femtosecond laser systems. We present a convenient procedure for online measurement and minimization of the tilt in a grating stretcher/compressor setup. In addition, we present a theoretical model for the autocorrelation signal in the presence of pulse front distortion. The influence of the pulse front tilt to the autocorrelation function is numerically simulated and compared with the case for pulses with fourth order chirp.

Phase measurements of ring dark solitons

A four-frame technique for interferogram analysis is used to measure the transverse phase distribution of nonlinearly split 2D dark beams. Pairs of diametrical phase shifts within each ring are retrieved from the experiment. This result is one of the tests required to denote the formations observed as ring dark solitons.

Linear optics of dark beams with mixed phase dislocations

In this work we present extended numerical simulation on the evolution and interaction of one-dimensional dark beams of finite length carrying mixed phase dislocations. In the linear regime of propagation two possible ways to control their transverse velocities are investigated and compared.

Simultaneous shaping and shortening of nanosecond pulses

Pump-induced probe beam deflection in an off-axis geometry is used to achieve simultaneous shaping and shortening of probe pulses. The first and the second harmonic of a Q-switched Nd:YAG laser served as a pump and probe wave respectively. Each pulse generated (super- Gaussian, sequences of two and three pulses) was of a reduced duration as compared to that of the incoming probe pulse.

Phase dislocations in femtosecond laser fields

We experimentally generate optical vortices in the output beam of a Ti:sapphire laser emitting 20-fs pulses. Screw phase dislocations are imposed in each spectral component of the short pulses by aligning computer generated hologram within a 4f-setup. The analysis shows that phase dislocations can be generated also at the stage of femtosecond pluse compression.

Variational analysis of SPM- and IPM-based interactions in cubic non-local nonlinear media

We analytically show the non-locality of cubic nonlinear media causes an increase of the critical power for self- and induced focusing and influences the condition for signal beam attraction/repulsion in an off-axis geometry.

Dispersion control in a 100-kHz repetition rate 35-fs laser system

We present a 100 kHz femtosecond amplifier system delivering pulses with a duration of 35 fs and an energy of 7 μJ at 800 nm. The system does not include a stretcher, since the large amount of dispersion accumulated during the amplification process is sufficient to prevent self-focusing. Compensation in all orders is achieved through a combination of a special prism compressor, chirped mirrors, and a liquid-crystal modulator.

Generation of lattices of optical vortices

Square and hexagonal lattices of optical vortices are generated in a saturable nonlinear medium. If the topological charges of the vortices are of the same sign the lattice exhibit rotation, while if alternative, stable propagation of the structures is observed. In a nonlinear medium vortex lattices induce periodic modulation of the refractive index. Diffraction of a probe beam by this optically-induced phase grating is observed.