Research during the period April 2018 – March 2019

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[1] The optical response of a material scales linearly with respect to incident radiation. However, when the intensity of the incoming radiation is sufficiently high the material can respond nonlinearly. The study of the interaction of intense light with matter is known as nonlinear optics. One part of the research in this period has been the study of nanostructured and other materials capable of nonlinearly transmitting light through them. Such materials have variety of applications including optical limiting and saturable absorption. Optical limiters, for example, are materials that can attenuate intense laser pulses by limiting the output fluence to a safe range so that delicate optical instruments, optical sensors and human eyes can be saved from accidental or hostile laser exposure.  Reji Philip and colleagues (Nithin Joy and Agnes George) tested diverse materials for their optical limiting characteristics, including discotic liquid crystals (with A. Gowda and Sandeep Kumar, RRI) and nanostructured perovskites (with V.S. Muthukumar, SSSIHL and K.B.R. Varma, IISc). 

[2] Irradiation of a solid surface by intense laser pulses results in the generation of a plasma (Laser-produced plasma, LPP). Reji Philip and colleagues (Pranitha Sankar, Nancy Verma) carried out a number of studies in LPPs including time-resolved optical emission spectroscopy of a picosecond laser produced Cr plasma (with K.H. Rao and R.T. Sang, Griffith University) and the effect of laser beam size on the dynamics of a femtosecond laser-produced aluminium plasma. The role of ambient gas pressure on nanosecond LPP from Ni thin films in a forward ablation geometry was studied (with J. Thomas, IPR, Ahmedabad). In addition, ultrashort pulses from a Ti:sapphire laser were used to fabricate large area nanoscale order laser-induced periodic surface structures (LIPSSs) on a silicon (100) surface [with K.K. Anoop (CUSAT, Cochin)]. Sample characterization led to the observation that the LIPSS patterns are strongly dependent on the laser pulse energy, state of polarization, number of shots delivered on the target and ambient pressure.

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