Start
May 30, 2017 - 16:00
End
May 30, 2017 - 17:00
Venue
Room No. 235 1-st floor Chem. Engg. dept
Event Type
Speaker
Prof. Debabrata Goswami Dept of Chemistry IIT Kanpur
Title
Microrheology of Newtonian and non-Newtonian fluids and Suspensions using Femtosecond Optical Tweezers
Abstract: Absolute temperature and viscosity measurement and control at microscale dimensions is very important for microrheological measurements. Present off-line techniques cannot provide absolute values and have very low spatial resolution. Power spectral density analyses of optical tweezers have been used earlier for ‘on the fly’ calibration from Brownian fluctuation of optically trapped bead in frequency domain. However such techniques are computationally intensive and only works for Newtonian fluids where the trapping exists for a sufficiently long time. On the other hand we have developed a novel ‘on the fly’ calibration of optical tweezers that does not have any such restrictions and can in turn provide control and measurement of absolute temperature and viscosity at microscales. We apply such time domain calibration methods to probe microscopic structural changes in complex fluids. We present results that show microrheological aging dynamics of laponite suspension using femtosecond optical tweezers. Bio: Debabrata Goswami (DG) works at the frontiers of interdisciplinary research embodying theoretical and experimental developments in the fundamental aspects of femtosecond laser-matter interactions. In past two decades DG has been independently carrying out research in his self-made laboratories where he constructed several versions of tunable and programmable femtosecond pulse shapers. DG utilizes Fourier Optics and interferometers to circumvent ultrashort timescales in coherent control superresolution microscopy etc. and he was the first to propose how the phase of a laser pulse can be critical in Quantum Computing. He was also the first to propose how thermal lens introduced by high repetition rate femtosecond lasers lead to the additional convection channel usage resulting in molecular structure distinction. DG developed self-calibrated femtosecond optical tweezers that can directly detect colloidal assembly and their structure and orientation. DG used this novel method of self-calibrated femtosecond optical tweezers to provide a direct measure and control of 'in situ' temperature and viscosity at microscale volumes. He has managed to show how to distinguish between overlapping fluorophores in multi-photon imaging microscopy by exploiting repeated excitation and de-excitation processes with high repetitive rate femtosecond lasers. His research contributions have resulted in over 125 peer-reviewed publications and numerous conference proceedings.