Post Compression of Intense Ultra Short Pulses and Spatial Shaping for Generation of Intense Attosecond Pulses

Dr Antoine Dubrouil

Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology

3:30 pm Friday, 10 August 2012, EN103 Lecture Theatre (EN Building), Hawthorn.

High order harmonic generation is a well-known phenomenon to produce broadband spectra spanning form ultraviolet to soft X-rays (XUV domain). Attosecond pulses via high order harmonics generation in a gaseous medium are an ideal tool to probe the electronic structure of atoms or molecules. However, the intensity of the XUV radiation is usually not sufficient to induce non-linear processes (two-photon transitions). In the frame of this work, we have developed a harmonic source capable of producing an intense XUV radiation to access non-linear physics in this wavelength range. To achieve these results, significant work on the infrared driving pulses was necessary, both in the spatial and temporal domain. This work therefore relies on three stages:

- The development of an high energy harmonic source and related diagnostics using a Ti : sapphire laser system which delivers 40-fs pulses up to an energy of 150 mJ at 10 Hz repetition rate.

- The development of a spatial shaping technique suited for intense ultrashort lasers. It allows one to produce, in the focal region, beams with a radially constant intensity over a large volume (flat top beams) and thus provide additional control of the harmonics generating process.

- The development of a post compression technique in guided geometry based on the ionization induced spectral broadening. This technique is suitable for intense pulses (3.5 TW) and produces pulses above the Terawatt level in the 10-fs range.

Those two approaches have been tested and validated on the high energy harmonic source, and the results open interesting perspectives such as the generation of isolated attosecond pulses of high energy.

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