Ultrafast dynamics of a near-solid-density layer in an intense femtosecond laser-excited plasma

Abstract

We report on the picosecond dynamics of a near-solid-density plasma generated by an intense, infrared (λ = 800 nm) femtosecond laser using time-resolved pump-probe Doppler spectrometry. An initial red-shift is observed in the reflected third harmonic (λ = 266 nm) probe pulse, which gets blue-shifted at longer probe-delays. A combination of particle-in-cell and radiation-hydrodynamics modelling is performed to model the pump laser interaction with the solid target. The results are post-processed to predict the Doppler shift. An excellent agreement is found between the results of such modelling and the experiment. The modelling suggests that the initial inward motion of the critical surface observed in the experiment is due to the passage of a shock-wave-like disturbance, launched by the pump interaction, propagating into the target. Furthermore, in order to achieve the best possible fit to the experimental data, it was necessary to incorporate the effects of bulk ion-acceleration resulting from the electrostatic field set up by the expulsion of electrons from the laser envelope. We also present results of time-resolved pump-probe reflectometry, which are corroborated with the spectrometry results using a 1-D reflectivity model.

Controlling femtosecond-laser-driven shock-waves in hot, dense plasma

“…Figure 2(b) shows the comparison of the experimental observations (velocity of the probe-critical surface) from the low-contrast laser-plasma interaction in Ref. 12 to the results of the serial hydro-PIC-hydro calculations. Similarly Fig.…”

“…The time-resolved Doppler shifts with the high-contrast laser, are shown in Fig. 1(b) by blue circles (the pump pulse energy of 90 mJ) and those measured in the earlier study 12 are multiplied by 10 (black square). An order higher wavelength shifts for the high-contrast laser imply that the plasma dynamics in this case are more rapid i.e.…”

“…To compare the physical mechanism producing the shock waves observed in both the experiments with low (Adak et al 12 ) and high-contrast lasers, numerical simulations for both situations are compared. In both cases, HYADES 26 , a 1-D Lagrangian radiation-hydrodynamics simulation code incorporating multi-group radiation diffusion and a flux-limited diffusion model of electron conduction, is used to model the interaction of the pump laser pre-pulse with the initially solid BK7 glass target.…”

“…On the other hand, creation of high energy density plasmas in the laboratory is possible by virtue of intense laser-solid interactions 1,3 which can lead to the realization of dynamic compression of the material achieving much higher pressures than those in diamond anvil cells 2 . The technique of chirped pulse amplification 4 produces intense ultrashort laser pulses on a table top and has spurred controllable exploration of 'extreme conditions' of matter [5][6][7][8][9][10][11][12][13][14][15][16][17] . The temporal dynamics of ultrashort laser-plasma interactions have just begun to be explored in overdense and near solid density plasma [10][11][12] .…”

Terahertz Acoustics in Hot Dense Laser Plasmas

“…The velocity of the critical surface was determined by the relation, V cr ¼ −0.5cðδλ=λÞ where, c and λ are the speed of light in free space and the central wavelength of the probe pulse, respectively. The details of this technique are explained elsewhere [10,11].…”