arXiv subjects

Harish Sasikumar

Publications and source records attributed to Harish Sasikumar.

5 recordsLinked to original sources

arXiv2026

3D scanning microscopy through scattering surfaces using the optical memory effect

Wavefront shaping allows light to be focused through scattering objects. However, the wavefront correction found is only valid in a small region called the isoplanatic patch. Here we present a simple approach to extend this isoplanatic patch by shifting and scaling the corrected wavefront appropriately, demonstrating an 8.6-fold increase in the lateral scanning range and a 1.5-fold increase in the axial range through a scattering layer without the need to perform additional wavefront shaping measurements. Our findings agree well with a simple geometrical model that also allows us to extract the effective position of the scattering layer from the measurements.

physics.optics↗

arXiv2025

Inline calibration of spatial light modulators in nonlinear microscopy

We present a method for calibrating the response of a phase-only spatial light modulator in nonlinear microscopy. Our method uses the microscope image itself as calibration measurement and requires no additional hardware components. Our method is adapted to the nonlinear signals encountered in multi-photon excitation fluorescence microscopes, and works well even under low light conditions and with strong photobleaching.

physics.optics↗

arXiv2021

Quality-Quantity Trade-offs in Tests for Management of COVID-19-like Epidemics

There are multiple testing methods to ascertain an infection in an individual and they vary in their performances, cost and delay. Unfortunately, better performing tests are sometimes costlier and time consuming and can only be done for a small fraction of the population. On the other hand, greater number of individuals can be tested using a cheaper, rapid test, but may only provide less reliable results. In this work, we studied the interplay between cost and delay of the tests as well the additional advantages offered by partial and complete lockdowns. To understand the influence of different test strategies, we implemented them on realistic random social networks with a COVID-19-like epidemic in progression. Specifically, we compared the performance of two tests mimicking the characteristics of popular tests implemented for COVID-19 detection. We present procedures and intuitive understanding to ascertain the optimum combination of the tests to minimize the peak infection as well as total quarantine days when the number of tests is constrained by a fixed total budget.

cs.SI↗

arXiv2019

Tracking-free Determination of Microparticle Motion from Image Variance

In this work, we use the standard deviation of image pixel intensity to analyse the speed, direction and surface-interaction of microparticles in fluid. First, we present an analytical model for estimating the total variance in the image space for directed or diffusive motion of microparticles and show that this measure is correlated to the density and speed of the particles. The analytical model was found to have good agreement with numerical simulations for low particle density. Then, using only the local image variance we obtain the magnitude and direction of the particle velocity in a rectangular microfluidic channel, closely matching the theoretical profile. Further, we also demonstrate the application of this method as a probe for particle-surface interactions by extracting the differences in distribution and time-evolution of image variance from mobile microparticles adhering to different surfaces. We believe that the image variance based method described here presents an addition to the suite of tracking-free techniques such as Differential Dynamic Microscopy (DDM) to extract motility parameters from video data.

physics.app-ph↗

arXiv2017

Detection Limit for Optically Sensing Specific Protein Interactions in Free-solution

Optical molecular sensing techniques are often limited by the refractive index change associated with the probed interactions. In this work, we present a closed form analytical model to estimate the magnitude of optical refractive index change arising from protein-protein interactions. The model, based on the Maxwell Garnett effective medium theory and first order chemical kinetics serves as a general framework for estimating the detection limits of optical sensing of molecular interactions. The model is applicable to situations where one interacting species is immobilized to a surface, as commonly done, or to emerging techniques such as Back-Scattering Interferometry (BSI) where both interacting species are un-tethered. Our findings from this model point to the strong role of as yet unidentified factors in the origin of the BSI signal resulting in significant deviation from linear optical response.

physics.app-ph↗