This book presents the separation-of-variables and T-matrix methods of calculating the scattering of electromagnetic waves by particles. Analytical details and computer programs are provided for determining the scattering and absorption characteristics of the finite-thickness slab, infinite circular cylinder (normal incidence), general axisymmetric particle, and sphere.The computer programs are designed to generate data that is easy to graph and visualize, and test cases in the book illustrate the capabilities of the programs. The connection between the theory and the computer programs is reinforced by references in the computer programs to equations in the text. This cross-referencing will help the reader understand the computer programs, and, if necessary, modify them for other purposes.

Light scattering by particles: Computational methods

The optical properties of transition metal dichalcogenide monolayers are widely dominated by excitons, Coulomb-bound electron-hole pairs. These quasi-particles exhibit giant oscillator strength and give rise to narrow-band, well-pronounced optical transitions, which can be brought into resonance with electromagnetic fields in microcavities and plasmonic nanostructures. Due to the atomic thinness and robustness of the monolayers, their integration in van der Waals heterostructures provides unique opportunities for engineering strong light-matter coupling. We review first results in this emerging field and outline future opportunities and challenges.

Two-dimensional semiconductors in the regime of strong light-matter coupling

Lasers are the pillars of modern optics and sensing. Microlasers based on whispering-gallery modes (WGMs) are miniature in size and have excellent lasing characteristics suitable for biosensing. WGM lasers have been used for label-free detection of single virus particles, detection of molecular electrostatic changes at biointerfaces, and barcode-type live-cell tagging and tracking. The most recent advances in biosensing with WGM microlasers are described in this review. We cover the basic concepts of WGM resonators, the integration of gain media into various active WGM sensors and devices, and the cutting-edge advances in photonic devices for micro- and nanoprobing of biological samples that can be integrated with WGM lasers.

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Review of biosensing with whispering-gallery mode lasers

Recently emerging large-area single-layer MoS2 grown by chemical vapor deposition has triggered great interest due to its exciting potential for applications in advanced electronic and optoelectronic devices. Unlike gapless graphene, MoS2 has an intrinsic band gap in the visible which crosses over from an indirect to a direct gap when reduced to a single atomic layer. In this paper, we report a comprehensive study of fundamental optical properties of MoS2 revealed by optical spectroscopy of Raman, photoluminescence, and vacuum ultraviolet spectroscopic ellipsometry. A band gap of 1.42 eV is determined by the absorption threshold of bulk MoS2 that shifts to 1.83 eV in monolayer MoS2. We extracted the high precision dielectric function up to 9.0 eV, which leads to the identification of many unique interband transitions at high symmetry points in the MoS2 momentum space. The positions of the so-called A and B excitons in single layers are found to shift upwards in energy compared with those of the bulk form and have smaller separation because of the decreased interactions between the layers. A very strong optical critical point predicted to correspond to a quasiparticle gap is observed at

Broadband optical properties of large-area monolayer CVD molybdenum disulfide

Assembly of MoS2 nanosheet-TiO2 nanorod heterostructure as sensor scaffold for photoelectrochemical biosensing

The charge transfer (CT) interaction between the blue emitting graphene quantum dots (GQDs) and an organic dye (fluorescein 27, F27) has been first studied by steady-state and time-resolved spectroscopy as a function of the pH. F27 exists in the form of different inherent fluorescent species depending on the pH of the solvent. At pH 7, the CT interaction of GQDs with F27 results in a small red shift in the absorption and fluorescence spectra of the dye. The results indicate formation of a weak van der Waals (vdW) complex in the ground state. The photoluminescence decay rate of the GQDs is generally unaffected in the mixture indicating the absence of dynamic quenching. The fluorescence intensity of F27-GQD system shows a 3-fold increase. Numerical simulations reveal that apart from the CT interaction, hotspots in the nearfield of the GQDs contribute to the fluorescence enhancement.

Photoluminescence enhancement of organic dye by graphene quantum dots

Temperature dependence of whispering gallery modes of quantum dot-doped microbottle resonators

We demonstrate self-assembly of microbottle resonators (MBRs) that support high-quality-factor (high- $Q$ ) whispering gallery modes (WGMs). Polymethyl methacrylate (PMMA), a transparent organic polymer, has been used for the self-assembly. Active MBRs have been created by doping PMMA with laser dye rhodamine 6G. WGM-modulated photoluminescence has been observed from the active MBRs. The self-assembled passive MBRs show $Q$ -factors of the order of $10^{6}$ . Fano- and electromagnetically induced transparency-type resonances have been observed in the transmission spectra.

Fano Resonances and Photoluminescence in Self-Assembled High-Quality-Factor Microbottle Resonators

Control over the charge transfer in dye-nanoparticle decorated graphene

Identification of Whispering Gallery Mode (WGM) coupled photoluminescence and Raman modes in complex spectra of MoS 2 in Polymethyl methacrylate (PMMA) microspheres

Aneesh V. Veluthandath

Papers

Photoluminescence enhancement of organic dye by graphene quantum dots

Temperature dependence of whispering gallery modes of quantum dot-doped microbottle resonators

Fano Resonances and Photoluminescence in Self-Assembled High-Quality-Factor Microbottle Resonators

Control over the charge transfer in dye-nanoparticle decorated graphene

Identification of Whispering Gallery Mode (WGM) coupled photoluminescence and Raman modes in complex spectra of MoS 2 in Polymethyl methacrylate (PMMA) microspheres