Most Recent Publications

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Improving resolution in two orthogonal orientations from a single-shot digital holographic microscopy


K Samanta, A Tiwari, PT Samsheerali, J Joseph
Results in Optics, Volume 14, February 2024, 100586


We demonstrate a single-shot digital holographic microscopy technique to improve the diffraction-limited resolution in two orthogonal orientations simultaneously by dual-channel orthogonal polarization multiplexing approach. Orthogonally polarized two oblique beams are employed to illuminate the sample and two reference beams with mutually orthogonal polarization are interfered with the object beams in a custom-designed Mach–Zehnder configuration. This technique is potentially beneficial to encode high frequency sample information from two orthogonal directions simultaneously in a single recorded hologram where the high frequency spectra is synthesized by the selective spectral stitching. Thus, the resolution is enhanced along two orientations from a single-shot hologram in this work. Both the simulation and experimental results are shown for the proposed technique with around 2-fold resolution enhancement over the diffraction limit.

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Dielectric Metasurface Enabled Compact, Single-Shot Digital Holography for Quantitative Phase Imaging


Jyoti Sardana, Shital Devinder, Wenqi Zhu, Amit Agrawal, Joby Joseph
Nano Lett. 2023, 23, 23, 11112–11119, IF (12.5)


Quantitative phase imaging (QPI) enables nondestructive, real-time, label-free imaging of transparent specimens and can reveal information about their fundamental properties such as cell size and morphology, mass density, particle dynamics, and cellular fluctuations. Development of high-performance and low-cost quantitative phase imaging systems is thus required in many fields, including on-site biomedical imaging and industrial inspection. Here, we propose an ultracompact, highly stable interferometer based on a single-layer dielectric metasurface for common path off-axis digital holography and experimentally demonstrate quantitative phase imaging. The interferometric imaging system leveraging an ultrathin multifunctional metasurface captures image plane holograms in a single shot and provides quantitative phase information on the test samples for extraction of its physical properties. With the benefits of planar engineering and high integrability, the proposed metasurface-based method establishes a stable miniaturized QPI system for reliable and cost-effective point-of-care devices, live cell imaging, 3D topography, and edge detection for optical computing.

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Low-cost, interdigitated capacitive sensor using laser-written graphene foam for touch, proximity, and liquid level detection


Shital Devinder, Shereena Joseph, Saurabh Pandey, and Joby Joseph
Appl.Phys.Lett.123,164101(2023)


Flexible capacitive sensors are gaining popularity in place of sophisticated optical sensing or bulky mechanical designs for specific applications such as proximity/gesture detection and liquid level sensing. So, here, we propose Laser Induced Graphene Foam (LIGF) based planar capacitive sensors, which are flexible, highly sensitive, energy-efficient, and cost-effective, making them accessible for various applications. The working of these sensors involves the interdigitated planar electrode configuration and the fringing effect, influencing capacitance when the permittivity or the electric charge of the surrounding medium changes. LIGF planar capacitive elements were produced on a commercially availed polymer polyimide by using direct laser writing technique employing a low-cost diode laser. The developed LIGF-based planar capacitive touch sensor showed an average touch response (|ΔC/Co|) of more than 49%; moreover, when used for proximity sensing, this sensor could detect the presence of human hand up to a maximum distance of 170 mm from the sensor surface. An extended design of the sensor has demonstrated liquid level sensing with an accuracy of 0.97 mm. As a result of its ability to sense dielectric materials, contactless operation, long-range sensing, cost-effectiveness, low-power consumption, and environmental friendliness, the LIGF electrode-based capacitive sensor can be incorporated into a variety of modern technology and devices.

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Guided mode resonance immunosensor for label-free detection of pathogenic bacteria Pseudomonas aeruginosa


Shereena Joseph, Soumya Rajpal, Debashree Kar, Shital Devinder, Saurabh Pandey, Prashant Mishra, Joby Joseph
Biosensors and Bioelectronics, 2023/9/23


Photonic biosensors are promising platforms for the rapid detection of pathogens with the potential to replace conventional diagnostics based on microbiological culturing methods. Intricately designed sensing elements with robust architectures can offer highly sensitive detection at minimal development cost enabling rapid adoption in low-resource settings. In this work, an optical detection scheme is developed by structuring guided mode resonance (GMR) on a highly stable, transparent silicon nitride (SiN) substrate and further biofunctionalized to identify a specific bacteria Pseudomonas aeruginosa. The resonance condition of the GMR chip is optimized to have relatively high bulk sensitivity with a good quality factor. The biofunctionalization aims at oriented immobilization of specific antibodies to allow maximum bacteria attachment and improved specificity. The sensitivity of the assays is evaluated for clinically relevant concentrations ranging from 102 to 108 CFU/mL. From the calibration curves, the sensitivity of the chip is extracted as 0.134nm/Log10 [concentration], and the detection modality possesses a favorably good limit of detection (LOD) 89 CFU/mL. The use of antibodies as a biorecognition element complemented with a good figure of merit of GMR sensing element allows selective bacteria identification compared to other non-specific pathogenic bacteria that are relevant for testing physiological samples. Our developed GMR biosensor is low-cost, easy to handle, and readily transformable into a portable handheld detection modality for remote usage.

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UV-LIG-Based Perfect Broadband Absorber for Solar Thermoelectric Generation


Shital Devinder, Manoj Kumar Vishwakarma, Shereena Joseph, Saurabh Pandey, and Joby Joseph
ACS Appl. Energy Mater. May 10, 2023.


Thermoelectric technology is gaining paramount importance for solar energy conversion and electricity production to increase green energy resources with high efficiency. An enormous amount of research is being carried out for engineering various solar absorbers using tailored materials and structures for solar energy harvesting. However, the methods to achieve cost-effective light absorbers are still challenging. Here we present a perfect broadband solar absorber for efficient photothermal conversion of sunlight employing a low-cost ultraviolet laser-induced graphene (UV-LIG) prepared on a polymer material using the conventional direct laser writing method. Recently the LIG generation employing the direct laser writing method has been recognized as a straightforward and low-cost technique to generate graphene foam. We have patterned the UV-LIG to produce a two-dimensional grid pattern to limit the reflection losses. The resulting UV-LIG surface exhibits very high absorption (>99%) for the entire spectral range of sunlight. Significantly, the absorber attains a temperature of 90.4 °C under 1 sun irradiation within a response time of less than 60 s. Further, we have exploited the extraordinary photothermal property of the patterned UV-LIG together with a commercially available thermoelectric generator (TEG) to make a solar thermoelectric generator (STEG) device with excellent output performance. Our investigation perceived that the structured UV-LIG absorber-based STEG has excellent power generation capability compared to the STEGs with other absorbing materials. Remarkably, we could achieve an output voltage of 273.9 mV under 1 sun irradiation, one of the highest among the recent STEGs, primarily due to the enhanced absorption of absorbing material. These results suggest that the proposed versatile and robust solar energy harvesting technology can be employed for solar–thermoelectric conversion systems.

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Hybrid Photonic-Plasmonic Photoelectrode for enhanced photoelectrochemical current generation


Saurabh Pandey, Shereena Joseph, Shital Devinder, Aditya Singh, Suddhasatwa Basu & Joby Joseph
Nano Energy, 27 February 2023, 108307


Abstract: Photoelectrochemical (PEC) reactions realized through the nonradiative decay of plasmonic process in metallic nanostructure earned tremendous potential to harvest solar irradiance. In conventional metal-semiconductor photoelectrodes, the electric field confinement using optical resonating modes is crucial to instigate plasmonic charge for enhanced photocurrent generation. However, the effect of such resonant states in a semiconductor-free plasmonic photoelectrode is limitedly explored. In this essence, we have experimentally realized a Schottky junction-free plasmonic-photonic hybrid photoelectrode consisting of one-dimensional porous grating of gold nanoparticles (GNPs) on top of a ITO waveguide. This designed photoelectrode exhibits PEC photocurrent generation solely from plasmonic hole transfer to the molecules/ions at the metal-adsorbed water interface. Spectral overlapping of plasmonic activities with photonic modes and porosity-induced large metal-electrolyte interface surface area further enhance the charge generation and transfer. In the results, the GNPs photoelectrode recorded 3.4 and 12.6-fold increases in the incident photon to electron conversion efficiency (IPCE) in contrast to conventional gold bar grating photonic crystal and random GNPs photoelectrodes, respectively. Further, modal coupling of resonant states witnesses a substantial rise in the photocurrent generation than the uncoupled resonant states. The present report delivers a facile strategy for tailoring the plasmonic photocurrent generation in futuristic solar energy harvesting applications.