A. Mysyrowicz

CONICAL EMISSION FROM SELF-GUIDED FEMTOSECOND PULSES IN AIR

Conical emission in the forward direction is observed from intense femtosecond light pulses propagating through air over long distances. The conical emission is attributed to Cerenkov radiation from a dynamic self-guiding structure consisting of a weakly ionized core surrounded by Kerr cladding.

Writing of permanent birefringent microlayers in bulk fused silica with femtosecond laser pulses

Permanent birefringent structures with controllable microscopic dimensions are inscribed in pure fused silica platelets. The birefringence properties of transmission gratings and of a quasi-uniform layer have been established.

Triggering and guiding megavolt discharges by use of laser-induced ionized filaments

We have demonstrated the ability to trigger and guide high-voltage discharges with ionized filaments generated by femtosecond terawatt laser pulses. The plasma filaments extended over the whole gap, providing a direct ohmic connection between the electrodes. Laser-guided straight discharges have been observed for gaps of as much as 3.8 m at a high voltage reduced to 68% of the natural breakdown voltage. The triggering efficiency was found to depend critically on the spatial connection of the laser filaments to the electrode as well as on the temporal coincidence of the laser with the peak of the high voltage.

Infrared extension of the supercontinuum generated by femtosecond terawatt laser pulses propagating in the atmosphere

We investigated the spectral behavior of a white-light continuum generated in air by 2-TW femtosecond laser pulses at 800 nm. The spectrum extends at least from 300 nm to 4.5 mum. From 1 to 1.6 mum the continuums intensity increases strongly with the laser energy and depends on the initial chirp.

Time-evolution of the plasma channel at the trail of a self-guided IR femtosecond laser pulse in air

The density and decay kinetics of a plasma channel created in air by a self-guided intense ultra-short laser pulse is determined by a new electric cross-conductivity method and by diffraction interferometry. A fast decay is measured, due to the dominant intrinsic recombination process at high plasma density.

Study of damage in fused silica induced by ultra-short IR laser pulses

We report on a new type of permanent damage obtained in bulk fused silica by focusing IR femtosecond laser pulses with microjoule energy. It consists of an uniaxial birefringence zone over a lateral size of a few microns and a depth of a few tens of microns. The birefringence zone is followed by sub-micrometer filamentary cracks extending up to 80 μm. Nonlinear pulse propagation plays a crucial role in the onset of this type of damage.

Frequency-domain interferometer for measuring the phase and amplitude of a femtosecond pulse probing a laser-produced plasma

A frequency-domain interferometer for probing the variations of the dielectric constant of a plasma with sub-100- fs temporal resolution and lambda/2000 phase resolution is described. Imaging the plasma on the entrance slit of a spectrograph provides spatial resolution along a diameter of the focal spot. The technique is used to map out the expansion of the critical density surface of a femtosecond laser-produced plasma with subnanometer spatial resolution along the laser axis.

Pulse self-compression to the single-cycle limit by filamentation in a gas with a pressure gradient

We calculate pulse self-compression of a 30 fs laser pulse traversing gas with different pressure gradients. We show that an appropriate density profile brings significant improvement to the self-compression by filamentation. Under an optimal pressure gradient, the pulse duration is reduced to the single optical cycle limit over a long distance, allowing easy extraction into an interaction chamber.

Coherent subterahertz radiation from femtosecond infrared filaments in air

We report on what is believed to be the first observation of coherent subterahertz (sub-THz) emission from a 1-m string in the atmosphere. The sub-THz pulse emitted by the filamentary structure from an intense IR femtosecond laser pulse is detected perpendicularly to the laser propagation axis by use of two heterodyne detectors at 94+/-1 and 118+/-1GHz . We describe the characteristics of this emission and show evidence of constructive interference between two separate strings.

Self-compression of ultra-short laser pulses down to one optical cycle by filamentation

Theoretical studies of filamentation of ultra-short near-IR laser pulses propagating in a noble gas predict near single-cycle pulses with the intensity being clamped to the field ionization threshold. Experimental results show that this method is carrier envelope offset phase preserving and provides a very simple source for generating few-cycle intense laser pulses. This suggests a very simple design for the generation of ultra-short, sub-femtosecond XUV optical pulses.