scispace - formally typeset
Search or ask a question
Author

Ajay Ghosh

Bio: Ajay Ghosh is an academic researcher from Jadavpur University. The author has contributed to research in topics: Polarizer & Lens (optics). The author has an hindex of 16, co-authored 124 publications receiving 910 citations. Previous affiliations of Ajay Ghosh include University of Tokyo & University of Calcutta.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, a novel synthesis method, characterization and application of a new class of ferromagnetic cubic cobalt ferrite magnetic nanoparticles (MNPs) for hyperthermia therapy and temperature triggered drug release was reported.

105 citations

Journal ArticleDOI
TL;DR: The Sparrow criterion is employed for designing an imaging system with high depth of focus and it is shown that, when the two foci are separated by the Sparrow limit of resolution, the focal depth is maximum and the intensity point-spread function remains almost identical within this limit.
Abstract: The Strehl definition along the axis of a birefringent lens sandwiched between two polarizers is studied analytically. The optic axis of the birefringent lens made of a uniaxial crystal is perpendicular to the lens axis, and the system behaves like a bifocus lens for proper orientation of the polarizers. The Sparrow criterion is employed for designing an imaging system with high depth of focus. It is shown that, when the two foci are separated by the Sparrow limit of resolution, the focal depth is maximum and the intensity point-spread function remains almost identical within this limit. The resolution according to the Rayleigh criterion in this zone is more than that of an ideal lens.

60 citations

Journal ArticleDOI
TL;DR: In this paper, a TAP-LPG with similar to 3dB attenuation at resonance was used to attain a sensitivity of similar to 1850 nm/RIU with similar 3 dB attenuation.
Abstract: Long period grating (LPG) at turn-around-point (TAP) has been studied with a view to enumerate the dependence of sensitivity of a particular resonant mode at the TAP to surrounding refractive index on the initial coupling strength. It has been shown theoretically and also validated experimentally that sensitivity can be enhanced significantly by tailoring the coupling strength of the cladding mode at the resonant wavelength near the TAP. Sensitivity characteristics have been studied for surrounding refractive index in the range 1.335-1.360, which is of interest in the field of biosensors, where the sensitivity of conventional LPGs is relatively small. We could attain a sensitivity of similar to 1850 nm/RIU using a TAP-LPG with similar to 3-dB attenuation at resonance.

54 citations

Journal ArticleDOI
TL;DR: It was confirmed that CFMNPs are nontoxic and biocompatible in nature, which assures that the synthesized particles can be successfully used in localized cancer treatment by stimuli responsive drug delivery technique.
Abstract: This work reports the application possibilities of cobalt ferrite (CoFe2 O4 ) magnetic nanoparticles (CFMNPs) for stimuli responsive drug delivery by magnetic field induced hyperthermia technique. The CFMNPs were characterized by X-ray diffraction (XRD) with Rietveld analysis, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), fourier transform infrared spectroscopy (FTIR), thermogravimetry and differential thermal analysis (TG-DTA), vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) magnetometry. Particles were functionalized with folic acid (FA) by EDC-NHS coupling method and loaded with anticancer drug (DOX) by activated folate ions. The drug release was studied as a function of time at two different temperatures (37 and 44 °C) under pH∼5.5 and 7. It was observed that the drug release rate is higher at elevated temperature (44 °C) and acidic pH∼5.5 as compared to our normal body temperature and pH∼7 using the CFMNPs. This way, we have developed a pH and temperature sensitive drug delivery system, which can release the anticancer drug selectively by applying ac magnetic field as under ac field particles are heated up. We have calculated the amount of heat generation by the particles around 1.67 °C per second at ∼600 Hz frequency. By MTT assay on cancer cell and normal cell, it was confirmed that CFMNPs are nontoxic and biocompatible in nature, which assures that our synthesized particles can be successfully used in localized cancer treatment by stimuli responsive drug delivery technique.

38 citations

Journal ArticleDOI
TL;DR: In this article, the anisotropic upper critical field in CaAlSi with an AlB structure has been investigated by magnetic, transport, and specific heat measurements, and it has been found that the angular dependence is consistent with Tinkham's formula for thin film superconductors.
Abstract: The anisotropic upper critical field in CaAlSi with an ${\mathrm{AlB}}_{2}$ structure has been investigated by magnetic, transport, and specific heat measurements. The variation of ${H}_{c2}$ with $\ensuremath{\theta},$ the angle between the $\mathrm{ab}$ plane and the applied field, determined from the transport measurements at various temperatures, show a cusplike behavior near $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$ unlike the prediction of the Ginzburg-Landau anisotropic mass model. Rather, the angular dependence is consistent with Tinkham's formula for thin film superconductors. We have found an increase in the anisotropy parameter with temperature. The negligible in-plane anisotropy of ${H}_{c2}$ is consistent with the small mean free path in this compound.

36 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: The results show that, when compared with conventional imaging, PDI yields a factor of 2-3 increase in the distance at which certain target features can be detected.
Abstract: Polarization-difference imaging (PDI) was recently presented by us as a method of imaging through scattering media [Opt. Lett. 20, 608 (1995)]. Here, PDI is compared with conventional, polarizationblind imaging systems under a variety of conditions not previously studied. Through visual and numerical comparison of polarization-difference and polarization-sum images of metallic targets suspended in scattering media, target features initially visible in both types of images are shown to disappear in polarization-sum images as the scatterer concentration is increased, whereas these features remain visible in polarization-difference images. Target features producing an observed degree of linear polarization of less than 1% are visible in polarization-difference images. The ability of PDI to suppress partially polarized background variations selectively is demonstrated, and discrimination of target features on the basis of polarization information is discussed. Our results show that, when compared with conventional imaging, PDI yields a factor of 2-3 increase in the distance at which certain target features can be detected.

294 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarized various features of magnetic penetration depth in unconventional superconductors and discussed how field-dependent measurements can be used to study surface Andreev bound states, nonlinear Meissner effects, magnetic impurities, magnetic ordering, proximity effects and vortex motion.
Abstract: This topical review summarizes various features of magnetic penetration depth in unconventional superconductors. Precise measurements of the penetration depth as a function of temperature, magnetic field and crystal orientation can provide detailed information about the pairing state. Examples are given of unconventional pairing in hole- and electron-doped cuprates, organic and heavy fermion superconductors. The ability to apply an external magnetic field adds a new dimension to measurements of penetration depth. We discuss how field-dependent measurements can be used to study surface Andreev bound states, nonlinear Meissner effects, magnetic impurities, magnetic ordering, proximity effects and vortex motion. We also discuss how measurements of penetration depth as a function of orientation can be used to explore superconductors with more than one gap and with anisotropic gaps. Details relevant to the analysis of penetration depth data in anisotropic samples are also discussed.

219 citations

Journal ArticleDOI
TL;DR: In this paper, a topical review summarizes various features of magnetic penetration depth in unconventional superconductors and discusses how field dependent measurements can be used to study surface Andreev bound states, nonlinear Meissner effects, magnetic impurities, magnetic ordering, proximity effects and vortex motion.
Abstract: This topical review summarizes various features of magnetic penetration depth in unconventional superconductors. Precise measurements of the penetration depth as a function of temperature, magnetic field and crystal orientation can provide detailed information about the pairing state. Examples are given of unconventional pairing in hole- and electron-doped cuprates, organic and heavy fermion superconductors. The ability to apply an external magnetic field adds a new dimension to penetration depth measurements. We discuss how field dependent measurements can be used to study surface Andreev bound states, nonlinear Meissner effects, magnetic impurities, magnetic ordering, proximity effects and vortex motion. We also discuss how penetration depth measurements as a function of orientation can be used to explore superconductors with more than one gap and with anisotropic gaps. Details relevant to the analysis of penetration depth data in anisotropic samples are also discussed.

218 citations

Journal ArticleDOI
TL;DR: It is shown how to two dimensionally encode the polarization state of an incident light beam using a parallel-aligned liquid-crystal spatial light modulator (LCSLM), which might be useful in image processing applications.
Abstract: We show how to two dimensionally encode the polarization state of an incident light beam using a parallel-aligned liquid-crystal spatial light modulator (LCSLM). Each pixel of the LCSLM acts as a voltage-controlled wave plate and can be programmed over a 2pi phase range at a wavelength of 514.5 nm. Techniques are reviewed for either rotating the major axis of elliptically polarized light or for converting an input linearly polarized beam into an arbitrary elliptically polarized beam. Experimental results are demonstrated in which we generate various two-dimensional spatial patterns of polarized light. Several potential applications are suggested. We also report an unexpected edge-enhancement effect that might be useful in image processing applications.

211 citations

Proceedings ArticleDOI
TL;DR: In this article, the sensitivity of long-period fiber gratings as a function of processed parameters by high-frequency CO 2 laser pulses has been investigated and a theoretical and experimental investigation has been conducted.
Abstract: Full characterization of the sensitivity of the LPFG is a precursor to practical device design, and knowledge of the sensitivity of the Long-period fiber gratings to the parameters of its physical environment processed is clearly important. We present a theoretical and experimental investigation into the sensitivity of long-period fiber gratings as a function of processed parameters by high-frequency CO 2 laser pulses.

199 citations