Publications by authors named "Gopal Verma"

We resolve the main bottleneck of achieving optimal fringe contrast on highly reflective surfaces through the innovative application of rear surface mirrors, unveiling a pioneering approach to precision measurements exemplified by the modified liquid drop interferometry (LDI) technique. By utilizing a liquid drop on a highly reflective surface, the need for a reference lens with a specific coating is eliminated, showcasing the technique's versatility. Furthermore, we first validate a novel, to our knowledge, expression for p-polarization-dependent radiation pressure, addressing a century-old problem reported in the literature.

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We investigated photomolecular-induced evaporation, wherein photons cleave off water clusters near water-vapor interfaces, bypassing the typical thermal evaporation process. However, thermal-induced evaporation is the main bottleneck to precisely identify photon-induced evaporation. Liquid drop interferometry (LDI) resolved this bottleneck, utilizing evaporating water drops as an active element.

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The detection of uranium in drinking water has ignited concerns among the public, regulators, and policymakers, particularly as around 1% of the 55,554 water samples in India have shown uranium levels surpassing the 60 µg/l guideline established by the Atomic Energy Regulatory Board (AERB) based on radiological toxicity. Further, the Bureau of Indian Standard (BIS), has given a limit of 30 µg/l, which is derived from World Health Organization (WHO) guidelines. Besides the chemical and radiological aspects associated with uranium, factors such as technological constraints in water purification, waste management, environmental factors, and socio-economic conditions significantly influence these guideline values, which are often overlooked.

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Background As the aging population increases, osteoporotic neck of femur fracture cases will continue to rise. Although hemiarthroplasty or half hip replacement is the treatment of choice in a majority of patients, a small but definite cohort of patients would need a total hip replacement. In these elderly patients who often have comorbidities, the use of cement to fix the prosthesis is often quoted as beneficial in view of perceived lower blood loss compared to uncemented fixation of the prosthesis.

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Eco-friendly, efficient, and durable electrocatalysts from earth-abundant materials are crucial for water splitting through hydrogen and oxygen generation. However, available methods to fabricate electrocatalysts are either hazardous and time-consuming or require expensive equipment, hindering the large-scale, eco-friendly production of artificial fuels. Here, we present a rapid, single-step method for producing MoS/NiF electrocatalysts with controlled sulfur-vacancies via electric-field-assisted pulsed laser ablation (EF-PLA) in liquid and deposition on nickel foam, enabling efficient water splitting.

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A systematic mapping of natural absorbed dose rate was carried out to assess the existing exposure situation in India. The mammoth nationwide survey covered the entire terrestrial region of the country comprising of 45127 sampling grids (grid size 36 km) with more than 100,000 data points. The data was processed using Geographic Information System.

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We quantitatively measure the nanomechanical dynamics of a water surface excited by the radiation pressure of a Gaussian/annular laser beam of incidence near total internal reflection (TIR). Notably, the radiation pressure near TIR allowed us to induce a pushing force (Abraham's momentum of light) for a wide annular Gaussian beam excitation of the thin-film regime of water, which, to the best of our knowledge, has never been observed with nanometric precision previously. Our finding suggests that the observation of either/both Abraham's and Minkowski's theories can be witnessed by the interplay between optics and fluid mechanics.

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Laser-induced thermocapillary deformation of liquid surfaces has emerged as a promising tool to precisely characterize the thermophysical properties of pure fluids. However, challenges arise for nanofluid (NF) and soft bio-fluid systems where the direct interaction of the laser generates an intriguing interplay between heating, momentum, and scattering forces which can even damage soft biofluids. Here, we report a versatile, pump-probe-based, rapid, and non-contact interferometric technique that resolves interface dynamics of complex fluids with the precision of ~1 nm in thick-film and 150 pm in thin-film regimes below the thermal limit without the use of lock-in or modulated beams.

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We introduce a phase change material (PCM) based metal-dielectric-metal (MDM) cavity of gold (Au)-antimony trisulfide (Sb2S3)-Au as a hot electron photodetector (HEPD). Sb2S3 shows significant contrast in the bandgap (Eg) upon phase transition from the crystalline (Cry) (Eg = 2.01 eV) to the amorphous (Amp) (Eg = 1.

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Structural phase transition induced by temperature or voltage in phase change materials has been used for many tunable photonic applications. Exploiting reversible and sub-ns fast switching in antimony trisulfide (SbS) from amorphous (Amp) to crystalline (Cry), we introduced a reflection modulator based on metal-dielectric-metal structure. The proposed design exhibits tunable, perfect, and multi-band absorption from visible to the near-infrared region.

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One of the classical limitations for the investigation of the local rheology of small scale soft objects and/or confined fluids is related to the difficulty to control mechanical contact and its consequences. In order to overcome these issues, we implement a new local, active, fast and contactless optical strategy, called optorheology, which is based on both the optical radiation pressure of a laser wave to dynamically deform a fluid interface and interferometry to probe this deformation with nanometric resolution. This optical approach is first validated by measuring the surface tension and the viscosity of transparent Newtonian liquids.

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We propose a simple compact interferometer using twisted light to detect picometer displacement on a solid or liquid surface. The heart of the interferometer lies in producing a daisy petal pattern formed by interference between two oppositely charged twisted beams. The sample being probed is an active component of the interferometer.

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Precision measurement on momentum transfer between light and fluid interface has many implications including resolving the intriguing nature of photons momentum in a medium. For example, the existence of Abraham pressure of light under specific experimental configuration and the predictions of Chau-Amperian formalism of optical momentum for TE and TM polarizations remain untested. Here, we quantitatively and cleanly measure nanomehanical dynamics of water surface excited by radiation pressure of a laser beam.

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Resolving mechanical effects of light on fluids has fundamental importance with wide applications. Most experiments to date on optofluidic interface deformation exploited radiation forces exerted by normally incident lasers. However, the intriguing effects of photon momentum for any configuration, including the unique total internal reflection regime, where an evanescent wave leaks above the interface, remain largely unexplored.

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