arXiv subjects

G. Vijaya Prakash

Publications and source records attributed to G. Vijaya Prakash.

10 recordsLinked to original sources

arXiv2021

Photonic and electronic state interactions in BaTiO3 based Optical Microcavity

The photonic modes mediated absorption dynamics at femtosecond time scales along with the control of spontaneous emission tunability are investigated all-dielectric optical microcavity having BaTiO3 (BTO) as defect layer. The cavity-enhanced transient absorption reveals the dominant excited state absorption (ESA) of both photonic and electronic modes due to strong third-order optical nonlinearity influence. Photoluminescence of BTO is found to be guided and tuned by the photonic cavity mode. Such active photonic structures can be envisaged as a potential candidate in nonlinear optics and photonic device applications.

physics.optics↗

arXiv2021

Ultrafast nonlinear pulse propagation dynamics in metal-dielectric periodic photonic architectures

One-dimensional (1D) metal-dielectric (MD) periodic structures take advantage of large refractive index contrast between metal and dielectrics to invoke extremely high nonlinear ultrafast responses of metal. These structures are also special due to their extremely high laser damage threshold. The Bragg like 1D MD structure (Ag/SiO2)4 enables strong optical field confinement with much enhanced nonlinear features as compared to simple metal or single (Ag/SiO2)1 structure. In the present work, the ultrafast nonlinear optical responses of the above structures are investigated via femtosecond broadband optical pump-probe technique. The enhanced nonlinear optical absorption is of reverse saturation of absorption (RSA) nature, resulted due to free-carrier absorption (FCA) and excited-state absorption (ESA) processes. The spectral nonlinearities are closely related to the pump-induced modification of the metal's dielectric functions, which are qualitatively visualized by transfer matrix and two-temperature models. The ultrafast temporal evolution of nonlinear absorption clearly demonstrated enhanced optical nonlinearity, disentangled by the electron-electron and electron-phonon dynamic interactions at picosecond time scales. A phenomenological pulse propagation model is employed that incorporates the experimentally obtained nonlinear absorption coefficients and different nonlinear effects exhibited by the system. Nonlinearity plays a crucial role in controlling the ultrafast pulse propagation and could open a new window for many nonlinear device applications. The findings of these new optical materials could possibly pave the way for promising applications in ultrafast photonics.

physics.optics↗

arXiv2018

Angle dependent localized surface plasmon resonance from silver nanoparticles embedded in SiO2 thin film

Near surface silver nanoparticles embedded in silicon oxide were obtained by 40 keV silver negative ion implantation without the requirement of an annealing step. Ion beam induced local heating within the film leads to an exo-diffusion of the silver ions towards the film surface resulting in the protrusion of larger nanoparticles. Cross-sectional transmission electron microscopy (XTEM) reveals the presence of poly-disperse nanoparticles (NPs), ranging between 2 nm-20 nm, at different depths of the SiO2 film. The normal incidence reflectance spectrum shows a double kink feature in the vicinity of 400nm, indicating a strong localized surface plasmon resonance (LSPR) from the embedded NPs. However, due to overlap of the bilayer interference and LSPR, the related features are difficult to separate. The ambiguity in associating the correct kink with the LSPR related absorption is cleared with the use of transfer matrix simulations in combination with an effective medium approximation. The simulations are further verified with angle dependent reflectance measurements. Additionally, transfer matrix simulation is also used to calculate the electric field intensity profile through the depth of the film, wherein an enhanced electric field intensity is predicted at the surface of the implanted films.

physics.app-ph↗

arXiv2016

Investigating resonance energy transfer from protein molecules to van der Waals nanosheets

The resonance energy transfer (RET) from tryptophan present in bovine serum albumin (BSA) to two dimensional (2D) nanomaterials has been reported. In these bio-nano systems, BSA molecules act as efficient donors while 2D van der Waals nanosheets of graphene, molybdenum disulfide (Mo$S_2$) and tungsten disulfide (W$S_2$) act as acceptors. The fluorescence emission from tryptophan arises at 350 nm, in presence of 2D nanosheets, the fluorescence intensity of BSA decreases. The time resolved fluorescence study shows that there is decrease in the fluorescence lifetime of BSA molecules in presence of 2D nanosheets. The decrease in fluorescence lifetime of BSA confirms the energy transfer phenomenon in bio-nano interactions. This study is important for finding the bio-compatibility of 2D nanomaterials in biological applications.

cond-mat.mtrl-sci↗

arXiv2016

Gold nanoflowers as efficient hot-spots for surface enhanced Raman scattering

Gold nanoflowers are known for their use as efficient host for surface enhanced Raman scattering of organic dye molecules. In this article, gold nanoflowers have been synthesised and rhodamine 6 G (R6G) molecules have been used as probe molecules. It is found that the gold nanoflowers can detect the presence of R6G molecules upto 10^{-10} M. The petals of these nanoflowers play an important role for the enhancement of Raman signals, and the intensity of Raman signals is enhanced many folds in presence of gold nanoflowers - the enhancement factor is of the order of 10^6. This is explained in terms of electromagnetic mechanism.

cond-mat.mtrl-sci↗

arXiv2016

Resonance Raman scattering and ab initio calculation of electron energy loss spectra of MoS2 nanosheets

The presence of electron energy loss (EELS) peak is proposed theoretically in molybdenum disulfide (MoS2) nanosheets. Using density functional theory simulations and calculations, one EELS peak is identified in the visible energy range, for MoS2 nanosheets with molybdenum vacancy. Experimentally, four different laser sources are used for the Raman scattering study of MoS2 nanosheets, which show two distinct Raman peaks, one at 385 cm-1 (E12g) and the other at 408 cm-1 (A1g). In the cases of three laser sources with wavelengths 405 nm (3.06 eV), 632 nm (1.96 eV) and 785 nm (1.58 eV), respectively, the intensity of E12g Raman peak is more than the A1g Raman peak, while in the case of excitation source of 532 nm (2.33 eV), the intensity profile is reversed and A1g peak is the most intense. Thus a resonance Raman scattering phenomenon is observed for 532 nm laser source.

cond-mat.mtrl-sci↗

arXiv2007

Optical properties of Er3+ doped alkali-chloro phosphate glasses for optical amplifiers

A new class of Erbium doped glasses with compositions xNa2O - (60-x)PbCl2 - 40P2O5 (x=0, 10, 20 and 30) were fabricated and characterized for optical properties. Absorption spectra were analyzed for important Judd-Ofelt parameters from the integrated intensities of various Er3+ glass absorption bands. Photoluminescence (PL) and its decay behavior studies were carried out for the transition 4I13/2 -> 4I15/2. A systematic correlation between the Judd-Ofelt parameter {omega}2 and the covalent nature of the glass matrix was observed, due to increased role of bridging oxygens in the glass network. The PL broadness and life times of 4I13/2_> 4I15/2 transition were typically in the range of 40-60nm and 2.13-2.5ms respectively. These glasses broadly showed high transparency, high refractive index, shorter life times and, most importantly, these glasses were found to be capable of being doped with larger concentrations of Er3+ (up to 4 wt%). Increase of Er3+ concentration resulted in the increase in PL line-widths with no significant effect of concentration quenching, indicating that these glasses are suitable for optical fibre/waveguide amplifiers.

cond-mat.mtrl-sci↗

arXiv2005

Fabrication and characterisation of CdSe photonic structures from self-assembly

We demonstrate here a method to fabricate CdSe photonic crystal from a very cheap fabrication route of templated self-assembly. The hexagonal close-packed photonic crystals are formed by the electrochemical growth of CdSe through the interstitial spaces between polymer nano/micro sphere templates. The confocal voids containing photonic crystals can be made either interconnected or well separated, with high uniformity. Structural and optical characterization confirms the good quality of electrochemically grown CdSe. These cheaply fabricated 2D photonic crystals provide a wide range of opportunities for optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2005

Pyramidal micro-mirrors for microsystems and atom chips

Concave pyramids are created in the (100) surface of a silicon wafer by anisotropic etching in potassium hydroxide. High quality micro-mirrors are then formed by sputtering gold onto the smooth silicon (111) faces of the pyramids. These mirrors show great promise as high quality optical devices suitable for integration into MOEMS and atom chips. We have shown that structures of this shape can be used to laser-cool and hold atoms in a magneto-optical trap.

physics.atom-ph↗

arXiv2004

Fabrication of micro-mirrors with pyramidal shape using anisotropic etching of silicon

Gold micro-mirrors have been formed in silicon in an inverted pyramidal shape. The pyramidal structures are created in the (100) surface of a silicon wafer by anisotropic etching in potassium hydroxide. High quality micro-mirrors are then formed by sputtering gold onto the smooth silicon (111) faces of the pyramids. These mirrors show great promise as high quality optical devices suitable for integration into MOEMS systems.

physics.optics↗