title: Terahertz acoustics in hot dense laser plasmas.
abstract: We present a hitherto unobserved facet of hydrodynamics, namely the generation of an ultrahigh frequency acoustic disturbance in the terahertz 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 (∼5×10(16)  W/cm(2)). The picosecond scale observations enable us to capture these high frequency oscillations (1.9±0.6  THz) 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 terahertz acoustic disturbance. Hydrodynamic simulations well reproduce the observations, offering insight into this process.
authors.affiliation: Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai-400005, India.
authors.forename: Amitava
authors.initials: A
authors.lastname: Adak
authors.affiliation: Central Laser Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX10 0QX, United Kingdom.
authors.forename: A P L
authors.initials: AP
authors.lastname: Robinson
authors.affiliation: Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai-400005, India.
authors.forename: Prashant Kumar
authors.initials: PK
authors.lastname: Singh
authors.affiliation: Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai-400005, India.
authors.forename: Gourab
authors.initials: G
authors.lastname: Chatterjee
authors.affiliation: Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai-400005, India.
authors.forename: Amit D
authors.initials: AD
authors.lastname: Lad
authors.affiliation: Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai-400005, India.|Central Laser Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX10 0QX, United Kingdom.|York Plasma Institute, University of York, Heslington, York YO10 5DQ, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Pasley
authors.affiliation: Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai-400005, India.
authors.forename: G Ravindra
authors.initials: GR
authors.lastname: Kumar