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Sambit Kumar Ghosh

Bio: Sambit Kumar Ghosh is an academic researcher from Indian Institute of Technology (BHU) Varanasi. The author has contributed to research in topics: Terahertz radiation & Polarization (waves). The author has an hindex of 6, co-authored 26 publications receiving 151 citations. Previous affiliations of Sambit Kumar Ghosh include Saha Institute of Nuclear Physics & Indian Institutes of Technology.

Papers
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TL;DR: A graphene-based metasurface structure comprises periodical ϕ-shaped graphene on the top surface of a noble-metal-backed dielectric silicon dioxide (SiO2) that converts the incident linearly polarized wave into cross-polarized components with a peak polarization conversion ratio of more than 0.9 over a large band.
Abstract: In this paper, using a graphene-based metasurface, we demonstrate a unique design to develop a highly efficient, broadband, mid-infrared cross-polarization converter. The proposed graphene-based metasurface structure comprises periodical ϕ-shaped graphene on the top surface of a noble-metal-backed dielectric silicon dioxide (SiO2). The reported structure converts the incident linearly polarized wave into cross-polarized components with a peak polarization conversion ratio of more than 0.9 over a large band. Furthermore, the metasurface structure exhibits the full width at half-maximum bandwidth of 41.98% with respect to its center frequency of 5.98 THz. The physical insights behind electromagnetic polarization conversion are supported by field distributions and retrieved electromagnetic parameters. The structure works as a broadband cross-polarization converter up to 40° incident angle for both TE and TM polarizations. In addition, the structure is found to be as thin as ∼λ/6 with respect to lowermost frequency of the polarization conversion. The period of the unit cell is ∼λ/24 to support the fact that the structure can be treated as a metasurface.

69 citations

Journal ArticleDOI
TL;DR: In this article, a tunable graphene-based wideband metasurface for high absorption in the lower mid-infrared frequency region was proposed, where the unit cell of the proposed structure consists of slot generated out of modified fractal-shaped graphene layer deposited on top of amorphous silicon dioxide.
Abstract: This paper proposes a tunable graphene-based wideband metasurface for high absorption in the lower mid-infrared frequency region. The unit cell of the proposed structure consists of slot generated out of modified fractal-shaped graphene layer deposited on top of amorphous silicon dioxide (SiO2) grown over 0.1-μm-thick gold layer. The structure exhibits distinctive high absorption greater than 90% absorptivity over the range of 3.69–9.77 THz covering a wideband of 6.08 THz. Incorporation of graphene in the metastructure can tune the absorption bandwidth owing to conductivity modulation of graphene by the control of impurity doping and mechanical stretching. Besides, the absorber is polarization independent under normal incidence because of the fourfold symmetry of the deposited graphene pattern. The designed prototype has been studied under oblique incidences for both transverse electric and transverse magnetic polarizations where wideband absorption has been experienced up to 40° incident angles for both cases. The prototype is found to be as thin as ∼ λ /11 with respect to the lowermost frequency of the absorption. The period of the unit cell is ∼ λ /13 supporting the effective homogeneity condition in subwavelength region. The structure can have applications toward sensing, spectroscopy, etc.

51 citations

Journal ArticleDOI
TL;DR: In this article, a monolayer graphene-based metasurface was designed and proposed for broadband polarisation conversion over a wide angle of incidence, which can be maintained up to 40° incident angles under both transverse electric and transverse magnetic polarisations.
Abstract: In this study, the authors have designed and proposed a monolayer graphene-based metasurface, performing as a broadband polarisation converter over a wide angle of incidence. The unit cell of the metasurface consists of split ring generated over a perforated single layer of graphene grown over metal-backed silicon dioxide. The structure converts incident linearly polarised wave into its cross-polarised component over a wide bandwidth with peak polarisation conversion exhibits value to unity. The plane of polarisation of the incident electromagnetic wave is rotated orthogonally on reflection from the proposed metasurface over full width at half maxima bandwidth around 72.83% compared with centre frequency of 2.16 THz, which can be maintained up to 40° incident angles under both transverse electric and transverse magnetic polarisations. The proposed structure is as thin as ~ λ /7.3 with respect to lowermost frequency and the period of the structure is about λ /10.7. The frequency band of polarisation conversion can be tuned by altering chemical doping as well as the electrostatic grating of the graphene sheet. The structure can find applications toward sensing, spectroscopy etc.

32 citations

Journal ArticleDOI
TL;DR: In this article, a graphene-based transmittive-type triple-band linear to circular polarization converter (TTLCPC) was proposed for the lower mid infrared (MIR) region, covering the terahertz gap.

28 citations


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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

01 Jan 2016
TL;DR: The computational methods for electromagnetics is universally compatible with any devices to read, and is available in the digital library an online access to it is set as public so you can download it instantly.
Abstract: Thank you very much for downloading computational methods for electromagnetics. Maybe you have knowledge that, people have search numerous times for their favorite readings like this computational methods for electromagnetics, but end up in malicious downloads. Rather than enjoying a good book with a cup of tea in the afternoon, instead they juggled with some malicious bugs inside their laptop. computational methods for electromagnetics is available in our digital library an online access to it is set as public so you can download it instantly. Our books collection hosts in multiple countries, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the computational methods for electromagnetics is universally compatible with any devices to read.

146 citations

Journal ArticleDOI
TL;DR: In this article, a simple graphene metasurface was proposed to achieve obvious graphene plasmon-induced transparency (PIT) phenomenon, which can find that PIT, reflectivity and absorbance can be effectively tuned by the Fermi level.
Abstract: Ultra-high sensitivity sensor has significant application for micro-nano optical devices in terahertz. Here, we propose a simple graphene metasurface, which can achieve obvious graphene plasmon-induced transparency (PIT) phenomenon. We can find that PIT, reflectivity, and absorbance can be effectively tuned by the Fermi level. Moreover, the finite-different time-domain (FDTD) numerical results are well agreement with the coupled mode theory (CMT) results. Interestingly, an ultra-high sensitivity sensor performance based on tunable PIT in terahertz bands can be realized in our proposed metasurface, the sensitivity and Figure of merit (FOM) can reach up to 1.7745 THz/RIU and 23.61, respectively. Hence, these results can provide theoretical guidance for terahertz dynamic integrated photonic devices.

75 citations

Journal ArticleDOI
TL;DR: This work presents an efficient polarization conversion device via using a hollow graphene metasurface that can simultaneously realize a series of excellent performances, including the broadband x-to-y cross polarization conversion (CPC) function with near unity polarization conversion ratio (PCR), dual-frequency linear- to-circular polarization Conversion (LTC) function, and highly sensitive polarization conversion function manipulation under wide oblique incidence angle range.
Abstract: In this work, we present an efficient polarization conversion device via using a hollow graphene metasurface. The platform can simultaneously realize a series of excellent performances, including the broadband x-to-y cross polarization conversion (CPC) function with near unity polarization conversion ratio (PCR), dual-frequency linear-to-circular polarization conversion (LTC-PC) function, and highly sensitive polarization conversion function manipulation under wide oblique incidence angle range. For instance, the proposed device obtains an x-to-y CPC function with the bandwidth up to 1.83 THz (χPCR ≥98.8%). Moreover, the x-to-y CPC function can be switched to LTC-PC function via artificially tuning the Fermi energy of graphene. The maximal frequency shift sensitivity (S) of polarization conversion function reaches 23.09 THz/eV, suggesting a frequency shift of 2.309 THz for the LTC-PC function when the chemical potential is changed by 0.1 eV. Based on these superior performances, the polarization converter can hold potential applications in integrated and compact devices, such as polarization sensor, switches and other optical polarization control components.

55 citations