Prof. Sharath Ananthamurthy Profile

Prof. Sharath Ananthamurthy

University Professor at Univ of Hyderabad

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Publications (8)

Proceedings Article | 20 September 2023 Paper

Hydrodynamics mediated interactions between live active rotors in dual optical tweezers

Ashwini Bhat, Naveena S., Sharath Ananthamurthy

Proceedings Volume 12606, 126061F (2023) https://doi.org/10.1117/12.3008383

KEYWORDS: Bacteria, Optical tweezers, Dichroic mirrors, Video microscopy, Scattered light, Time metrology, Systems modeling, Polarization, Physics, Objectives

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Proceedings Article | 20 August 2020 Presentation + Paper

Dynamics of Bacillus subtilis bacterium in an optical trap

Ashwini Bhat, Sharath Ananthamurthy

Proceedings Volume 11463, 114630G (2020) https://doi.org/10.1117/12.2569149

KEYWORDS: Optical tweezers, Bacteria, Objectives, Light scattering, Visualization, Mirrors, Ions, Environmental sensing, Scattering

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We monitor the rotation of a flagellated bacterium in a single laser beam optical trap. Bacillus subtilis, a rod shaped bacterium shows both run and tumble sequences as a free swimmer, the swimming aided by flagellar rotations. We detect and characterize the changes in flagellar and cell body rotations of the bacterium through detection of the forward scattered signal using a quadrant photo-detector(QPD). Simultaneously, the rotations in trap are visualized in time via video microscopy and the rotational frequency is measured through power spectral analysis . While the body rotation results in the appearance of a peak at lower frequencies (approx. 3 Hz) against the background Lorentzian spectrum, flagella rotations result in a broad higher frequency peak (approx. 88 Hz) in the power spectrum. The resultant peaks are modeled by a solution to the Langevin equation that takes into account the drag forces acting on the system. By monitoring the flagellar rotation speed’s variation with time, through continuous frequency measurement, we are able to determine the extent of photodamage to the cell and thereby, the time it takes to completely stop the rotations. We observe periodic fluctuations in the rotation frequency of the flagella that varies between a relatively higher and a lower value, with each of them gradually decreasing with time, until no further rotations are seen. In further, measurements, look for effects on the rotating bacterium in a fluid environment with altered pH. We observe a significant increase in time before the rotation of the flagella completely stops when the pH of the suspension media is lowered. Thus, direct monitoring of the optically trapped bacterium and onset of photodamage, is enabled through sequential power spectrum recording and this can clearly reveal the response of the bacterium to environmental changes. The experimental setup offers a simple and convenient way to confining and studying a single bacterium’s response to different fluid environments in real time.

Proceedings Article | 16 September 2016 Paper

Probing the interaction between two microspheres in a single Gaussian beam optical trap

Praveen Parthasarathi, Shruthi Subhash Iyengar, Yogesha Lakkegowda, Sarbari Bhattacharya, Sharath Ananthamurthy

Proceedings Volume 9922, 99222M (2016) https://doi.org/10.1117/12.2237600

KEYWORDS: Gaussian beams, Optical tweezers, Laser beam propagation, Laser scattering, Scattering, Backscatter, Sensors, Objectives, Light scattering, Optical filters

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Proceedings Article | 21 April 2016 Paper

Autocorrelation and relaxation time measurements on metal oxide core: dielectric shell beads in an optical trap

Shruthi Iyengar, Praveen Parthasarathi, Rekha Selvan, Sarbari Bhattacharya, Sharath Ananthamurthy

Proceedings Volume 9884, 98842P (2016) https://doi.org/10.1117/12.2227406

KEYWORDS: Dielectrics, Particles, Optical tweezers, Metals, Oxides, Polarizability, Reflectivity, Transmittance, Laser scattering, Scattering, Time metrology, Silica, Objectives, Magnetism

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Optical Tweezers are capable of trapping individual particles of sizes that range from micrometers to sub micrometers. One can compute the trap strength experienced by a particle by analyzing the fluctuations in the position of the trapped particle with time. It is reported that the trap strength of a dielectric bead increases linearly with increase in the power of the trapping laser. The situation with metallic particles, however, is strongly dependent on the particle size. Available literature shows that metallic Rayleigh particles experience enhanced trap strengths when compared to dielectric particles of similar sizes due to a larger polarizability. On the contrary, micrometer sized metallic particles are poor candidates for trapping due to high reflectivity. We report here that commercially available micrometer sized metal oxide core - dielectric shell (core – shell) beads are trapped in a single beam optical tweezer in a manner similar to dielectric beads. However as the laser power is increased these core – shell beads are trapped with a reduced corner frequency, which represents a lowered trap strength, in contrast to the situation with ordinary dielectric beads. We attribute this anomaly to an increase in the temperature of the medium in the vicinity of the core – shell bead due to an enhanced dissipation of the laser power as heat. We have computed autocorrelation functions for both types of beads at various trapping laser powers and observe that the variation in the relaxation times with laser power for core - shell beads is opposite in trend to that of ordinary dielectric beads. This supports our claim of an enhanced medium temperature about the trapped core – shell bead. Since an increase in temperature should lead to a change in the local viscosity of the medium, we have estimated the ratio of viscosity to temperature for core – shell and dielectric beads of the same size. We observe that while for ordinary dielectric beads this ratio remains a constant with increasing laser power, there is a decrease for core – shell beads. We plan to extend this work towards studying the hydrodynamic correlations between a pair of trapped beads where one of the beads acts as a heat source.

Proceedings Article | 15 June 2015 Paper

Conical Fresnel zone lens for optical trapping

A. Vijayakumar, Praveen Parthasarathi, Shruthi Iyengar, Rekha Selvan, Sharath Ananthamurthy, Shanti Bhattacharya, Sarbari Bhattacharya

Proceedings Volume 9654, 965426 (2015) https://doi.org/10.1117/12.2180850

KEYWORDS: Etching, Optical tweezers, Axicons, Optical components, Borosilicate glass, Confocal microscopy, Microscopes, Particles, Chemical elements, Optical lithography

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SPIE Journal Paper | 14 November 2014 Open Access

Birefringence of a normal human red blood cell and related optomechanics in an optical trap

Belavadi Venkatakrishnaiah Nagesh, . Yogesha, Ramarao Pratibha, Praveen Parthasarathi, Shruthi Subhash Iyengar, Sarbari Bhattacharya, Sharath Ananthamurthy

JBO, Vol. 19, Issue 11, 115004, (November 2014) https://doi.org/10.1117/12.10.1117/1.JBO.19.11.115004

KEYWORDS: Birefringence, Molecules, Blood, Optical tweezers, Polarizers, Microscopes, Optomechanical design, Polarization, Polarizability, Wave plates

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Proceedings Article | 4 March 2014 Paper

Optical properties of red blood cells: an optical tweezer based analysis

B. Nagesh, Yogesha Lakkegowda, R. Pratibha, P. Praveen, Sarbari Bhattacharya, Sharath Ananthamurthy

Proceedings Volume 8947, 89471P (2014) https://doi.org/10.1117/12.2039222

KEYWORDS: Birefringence, Optical tweezers, Molecules, Polarization, Polarizers, Blood, Wave plates, Microscopes, Optical properties, Physics

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SPIE Journal Paper | 4 February 2013 Open Access

Orientational dynamics of human red blood cells in an optical trap

Praveen Parthasarathi, Belavadi Nagesh, Yogesha Lakkegowda, Shruthi Lyengar, Sharath Ananthamurthy, Sarbari Bhattacharya

JBO, Vol. 18, Issue 02, 025001, (February 2013) https://doi.org/10.1117/12.10.1117/1.JBO.18.2.025001

KEYWORDS: Optical tweezers, Blood, Solids, Laser beam propagation, Time metrology, Video, Microscopes, Beam propagation method, Image processing, Eye

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