Abstract-Terahertz acoustics in hot dense laser-plasmas

Amitava Adak, A. P. L. Robinson, Prashant Kumar Singh, Gourab Chatterjee, Amit D. Lad, John Pasley, and G. Ravindra Kumar

https://journals.aps.org/prl/accepted/d9075Y04L871e53088d84d9333e97437df827daf8

We present a hitherto unobserved facet of hydrodynamics, namely the generation of an ultrahigh frequency acoustic disturbance in the terahertz (THz) frequency range, whose origins are purely hydrodynamic in nature. The disturbance is caused by differential flow velocities down a density gradient in a plasma created by a 30 fs, 800 nm high-intensity laser (\sim 5\times1016 W/cm2). The picosecond scale observations enable us to capture these high frequency oscillations (1.9\pm0.6THz) which are generated as a consequence of the rapid heating of the medium by the laser. Adoption of two complementary techniques, namely pump-probe reflectometry and pump-probe Doppler spectrometry provides unambiguous identification of this THz acoustic disturbance. Hydrodynamic simulations well reproduce the observations, offering insight into this process.