Alexander Rebane

Second-harmonic generation of amplified femtosecond Ti:sapphire laser pulses

We study theoretically and experimentally second-harmonic generation (SHG) of 150-fs-duration amplified Ti:sapphire laser pulses at a wavelength of 780 nm in the nonlinear crystal KDP of different lengths and at different power densities as high as 150 GW cm(-2). The experimentally observed SHG conversion efficiency does not exceed 50%. It is shown theoretically that one possible process limiting the SHG efficiency at low as well as at high intensities is the modulation of the phase of the fundamental wave. In addition, continuum generation is observed at high intensities and can decrease the SHG efficiency.

Holography in frequency selective media: hologram phase and causality

Abstract Diffraction properties of holograms stored in persistent spectral hole burning media are shown to be directly related to the causality principle and are studied experimentally by using a frequency-tunable arrow band laser. Amplification (erasing) of certain diffraction orders that are allowed (forbidden) by the causality principle is done by manipulating the spectral and phase properties of the holograms. The possibility to minimize cross-talk between holograms stored at different frequencies is also demonstrated.

Noncollinear parametric generation in LiIO 3 and β-barium borate by frequency-doubled femtosecond Ti:sapphire laser pulses

In LiIO(3) and BBO crystals the wave-matching conditions for femtosecond noncollinear parametric light generation at lambda = 390 nm pumping wavelength are investigated. In the LiIO(3) crystal simultaneous phase- and group-velocity-matching angles are determined. Parametric generation occurred at 0.45-2.9-mu;m wavelengths by pumping with the second harmonic of 150-fs Ti:sapphire laser pulses and is in qualitative agreement with calculated directions in both crystals.

Stimulated Raman amplification of femtosecond pulses in hydrogen gas.

We report efficient amplification of weak femtosecond supercontinuum pulses by a stimulated Raman scattering process in pressurized H(2) gas excited with 350-fs-duration frequency-doubled pulses from a regenerativeamplified Ti:sapphire laser. An amplification factor of 10(9) is obtained at the wavelength of 465 nm for seed pulses produced by supercontinuum generation in glass.

Holography in frequency-selective media. III. Spectral synthesis of arbitrary time-domain pulse shapes

We study theoretically and experimentally the synthesis of arbitrary time-domain pulse shapes, using short laser pulses scattered by holograms stored in a spectrally selective hole-burning material. In general, writing holograms in spectrally selective materials results in cross talk and interference between different frequencies because of Kramers–Kronig dispersion relations. We discuss different ways to exclude the cross talk that disturbs faithful reproduction of the desired time-domain pulse shapes. In particular, we show that one can exclude the cross talk by writing holograms in a way that simulates a time-domain offset of the object pulse. To confirm our theoretical considerations we carry out experiments by writing persistent spectral hole-burning holograms with a tunable dye laser in an organic dye–polymer system at low temperature. By reading out the time-domain response with subpicosecond white-light pulses we demonstrate the feasibility of spectral synthesis of light pulses with complicated amplitude and phase properties on the time scale of hundreds of picoseconds with a subpicosecond time resolution.

Subpicosecond pulse shaping via spectral hole-burning

Abstract A new method of Fourier synthesis of arbitrary pulse amplitudes on ultrafast time scale is demonstrated. Spectral hole structures are burnt in the 150 cm −1 broad inhomogeneous absorption band of a standard hole burning material as holographic gratings. The desired pulse shapes are then produced via diffraction of spectrally very broad 200 fs pulses by these spectrally and spatially prepared samples. The shaping of both, periodic and predefined aperiodic fs pulse trains as well as single fs pulses with predefined time delay are demonstrated.

Spectral hole burning and holography. V. Asymmetric diffraction from thin holograms

Thin holograms with novel diffraction properties were created in spectral hole-burning materials. Simultaneously sweeping the frequency of the recording light and the phase of the holograms results in an asymmetric distribution of diffraction efficiency between positive and negative orders. Experiments were performed that demonstrate amplified or attenuated diffraction efficiency with respect to holograms recorded at a single frequency. The observed diffraction is well described by a simple model in which small grating amplitudes and weak burning are assumed.

Total fluorescence spectra of free base chlorin and its photo-product in polyvinylbutyral at liquid helium temperatures

Abstract The total fluorescence spectra of free base chlorin and its photoproduct in polyvinylbutyral at liquid helium temperatures were investigated. Five electronic origins (ππ ∗ ) of chlorin were identified. For the photoproduct, the S 1 ← S 0 (ππ ∗ ) origin and three possible Soret bands were found. The energy selection phenomenon upon S 1 ← S 0 excitation was observed for both tautomers. In the case of free base chlorin, energy selection for the S 3 ← S 0 excitation was also observed. The broad spectral features corresponding to the S 1 ← S 0 transition of the photoproduct suggest that there is strong interaction between its electronic transition and the matrix, and its large Stokes shift supports the contention that there is a substantial change in geometry in its first excited state.

Femtosecond time-and-space-domain holography

Publisher Summary This chapter discusses femtosecond time-and-space-domain holography. Time-and-space-domain holography is a new method in coherent optics that allows one to manipulate both the spatial waveforms and the temporal characteristics of optical wave amplitude. The holographic recording in time-and-space domain uses the frequency selectivity of certain light sensitive materials, which allows one to capture the frequency-and-space-domain interference of the object with the reference wave pulse amplitude, instead of the conventional spatial interference. The experiments performed so far have been designed to investigate the principal new ways of recording, manipulating, and synthesizing broad-band time-and-space-domain optical signals. The fact that frequency selectivity is an intrinsic property of the PSHB material is of principal importance, especially for multidimensional coherent optics. Finally, it may be easier to achieve this goal if one allows the homogeneous line width to be on the order of 1 cm -1 by increasing, correspondingly, the value of τ inh. It would be interesting to observe whether the holograms recorded in such ultrabroad bandwidth materials can reach higher resolution in the time domain than presently achieved in organic materials and what the diffraction properties of such holograms can be.

Stark effect in dye-doped polymers studied by photochemically accumulated photon echo

We study theoretically and experimentally the influence of a homogeneous static electric field on a photochemically accumulated stimulated photon echo in dye-doped polymers. The dependence of the time profile of the echo signal on the strength of the electric field is evaluated in the case of a linear Stark effect. Experiments using polymers doped with organic dye molecules are carried out at low temperature, and our new technique is applied to determine the difference of the permanent dipole moment in the ground and the first excited singlet electronic state of the impurity molecules.