Chirped pulse shadowgraphy for single shot time resolved plasma expansion measurements

Abstract

The dynamics of ultrashort laser plasmas demand single shot temporal measurements on fast time scales. We describe a method to record the plasma expansion on picosecond (ps) timescales continuously over hundreds of ps, in single shot. The method uses the chirp of a Ti:sapphire laser as a time-resolved optical diagnostic tool. Using this technique, the evolution of the plasma expansion had been recorded with ps time resolutions, by probing with a chirped laser pulse of 200 ps duration. A peak expansion velocity of 1.8×107 cm/s is observed and its evolution in time is obtained for ∼300 ps.

High-speed two-frame shadowgraphy for velocity measurements of laser-induced plasma and shock-wave evolution

“…A great interest in instantaneous-velocity measurements of plasma and shock waves produced by highintensity, nanosecond laser pulses arises from many laser-assisted applications, where the shock-wave peak pressure, which is related to the shock-wave propagation speed [10,20], is a crucial parameter. Since these expansion velocities exceed 100 km=s [21,22], successive 2D images of a single event should be captured in a time interval shorter than 1 ns. In addition, to get insight into the development of plasma within the few-nanosecondexcitation-laser pulse, time delays below 1 ns are also mandatory.…”

Ultra-Fast Opacity in Transparent Dielectrics Induced by Picosecond Bursts of Laser-Driven Ions

“…The temporal evolution of TO was then encoded as variation of the signal in the probe spectrum (bandwidth ~ 4nm) with respect to depth in the target. Figure 1c) shows a typical streaked image 18,19 , as detected using an optical Andor CCD. Here we define the onset of TO for a reduction in transmission > 5% due to fluctuations of ± 3% on the spatial intensity profile probe beam.…”

“…To permit a more accurate measurement of the TO, the full temporal evolution was instead recorded on a single shot basis. This was achieved by optically streaking 18,19 (Figure 1c In this arrangement the original ultrafast probe is stretched in time (or chirped) to create a long pulse (> 200 ps) with an approximately linear frequency sweep 18 . This pulse in turn permits direct mapping of the temporal evolution of the TO onto the spectrum of the probe pulse as it passes through the interaction region i.e.…”

“…To permit a more accurate measurement of the TO, the full temporal evolution was instead recorded on a single shot basis. This was achieved by optically streaking 18,19 (Figure 1c) the region outlined by the red dashed boxes in Figure 1b).…”

“…each successive frequency encodes a different level of opacity in the target. The optical streak is then achieved by passing the pulse over a diffraction grating to separate the frequency components spatially and imaging the interaction region onto a CCD 19 . In essence this allows the ultrafast dynamics of transient ion induced opacity to be observed along 1-dimension.…”