Abstract

Pulse compression through filamentation to the two-optical-cycle regime has been demonstrated, including its capability of maintaining the carrier-envelope-offset (CEO) phase. Simulations reproduce these results well but also indicate significant spatial structure in the output beam calling for spatio-temporal characterization of these pulses [1, 2]. We used 30-fs pulses centered at 795 nm with energies of up to 1 mJ, to generate ultra-short pulses by filamentation in two subsequent cells filled with Argon at an absolute pressure of 900 mbar and 820 mbar, respectively. Each stage was designed as following: focusing of the input beam into the cell, collimation of the output beam and temporal recompression with specially designed chirped mirrors. The full system produces pulses with a considerably broadened spectrum, blue shifted due to ionization and pulse durations measured by SPIDER, down to 4.9 fs with 70 uJ energy contained in the central beam core. We investigated the spatial dependence of the temporal profile and phase of these output pulses by spatially selecting a part of the output beam (Figure 1). Fig. 1: Spatial dependence of the temporal profile from the inner part centered at 0 mm in the transverse beam profile (up left) to the outer part (down right) centered at (i-0.5) mm off-axis (i={l,9}). Each subfigure presented in Fig.l, shows the time profile of a 1 mm large spatial selection of the output beam. When the inner part of the beam was selected (up left), a single 4.9 fs pulse was measured. The outer parts of the beam exhibit temporal structures which feature a double pulse when the distance from axis of the selected part of the beam is larger than x mm. It is clear that without any spatial selection of the short pulse component, throughput is maximized at the expense of pulse contrast. On the other hand our shortest pulse (with 70-uJ energy extracted from the central part of the beam) was successfully used to generate high-order harmonics in Argon.

© 2007 IEEE