Anirban Sarkar

Gain-separated non-distributed feedback-based optofluidic random lasers (RLs) are realized using disordered microfluidic devices. Due to spatial separation of the scatterers from the gain medium, these RLs provide unique advantages compared to distributed feedback type optofluidic random lasers. The threshold characteristics, nature of the emission, and statistical distribution of the intensity of random lasing are investigated. The emissions from these devices are observed to be highly coherent in nature, which increases with the density of the scatterers. The coherent part of the emission follows a power-law distribution, signifying Lévy statistics, whereas the incoherent component exhibits an exponential profile with close resemblance to that of amplified spontaneous emission.

Efficient and green exfoliation of bulk MoS ₂ into few-layer nanosheets remains challenging due to its intrinsic hydrophobicity and van der Waals interlayer forces. Although pure water is an ideal solvent for sustainable processing, solubility theory and experiments show that MoS ₂ nanostructures rapidly aggregate in aqueous dispersions. To address this issue, surfactants are commonly used during liquid-phase exfoliation (LPE) to stabilize nanosheets, prevent restacking, and improve colloidal stability. However, many conventional surfactants are toxic and environmentally harmful, limiting their sustainable application. Plant extract-based surfactants provide greener alternatives, but their use in LPE is still limited. In this study, MoS ₂ nanosheets are exfoliated using sodium cholate (SC) and green tea (GT) extract, and their morphological and optical properties are compared to evaluate their potential for Förster resonance energy transfer (FRET) applications. Morphological analysis shows that SC-assisted exfoliation produces thinner and smaller nanosheets than those obtained using GT extract. Optical spectra reveal the characteristic A- and B-excitonic peaks, with a slight blue shift of the A-exciton in SC exfoliated nanosheets. FRET studies with Rhodamine 6G (R6G), Rhodamine B (RhB), and 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dyes demonstrate efficient energy transfer, with the highest efficiency observed for Rhodamine B due to greater spectral overlap. Time-resolved fluorescence measurements (TRFS) further confirm the FRET process through a significant reduction in the fluorescence lifetime of the donor MoS ₂ in the presence of RhB. These results highlight the potential of both SC- and GT-exfoliated MoS ₂ nanosheets for sustainable FRET-based photonic and optoelectronic applications.

Manipulation of the electric field confinement of Tamm plasmon polaritons (TPPs) holds immense importance in the development of plasmonic-based nanophotonic devices. Most of the excitation schemes of TPPs employed till date are single-sided launching of the excitation wave. However, simultaneous bidirectional excitation of TPPs can be an efficient and effective modality to control their electric field confinement. In this work, we investigate the effect of simultaneous bidirectional excitation of TPPs on their electric field confinement using a deep neural network (DNN) model. The results of single-side and simultaneous bidirectional excitations of TPPs in a fixed metal-DBR structure are analyzed and compared to demonstrate that bidirectional excitation can be effective to manipulate and enhance the electric field confinement of TPP modes in comparison to that for single-side excitations. In addition, it is shown that the well-optimized DNN could predict the expected electric field distribution with more than 99% accuracy under the bidirectional excitation scheme.

Light confinement in a disordered medium by multiple scattering processes plays a crucial role in the development of a random laser (RL). Modes of an RL are complex and emit in all directions due to the absence of a well-defined cavity. In a non-distributed feedback random laser (NDFRL), cavity formation has a close similarity with the Fabry-Pérot cavity (FPC) of a conventional laser. Hence, the investigation of an NDFRL is advantageous to understand the RL modes. In this regard, a detailed analysis of its passive cavity resonance modes is essential. However, these resonance modes are fundamentally different from the spectral intensity distribution, namely the Airy distribution of the cavity. The Airy distribution has periodic peaks due to constructive interference of light and its peaks appear similar to the resonance modes. For a cavity with a high quality factor (Q-factor), the Airy distribution and the resonance modes are exactly the same and indistinguishable, but they differ significantly when the cavity becomes lossy (i.e., low Q). The random passive cavity of an NDFRL has a low Q-factor as the system is inherently open and lossy. We investigate the mode profiles and the Airy distribution of a passive cavity of NDFRL and observe that their relation is similar to that of a conventional passive FPC.

Rare-earth-doped solid-state lasers utilize distributed-feedback (DFB) resonators to generate ultra-narrow-linewidth emission down to a few kHz. The longitudinal modes of a single Fabry-Pérot and a DFB resonator are influenced by the structure, the optical excitation configuration, and external feedback, as has been observed experimentally. Here we investigate the influence of bi-directional launching of light and external feedback on the longitudinal modes of single Fabry-Pérot, double Fabry-Pérot, and DFB resonators. These results can be exploited for the technological advancement of DFB lasers.

Improving Grindability of Inconel-600

Grinding Performance Using a Compound Nozzle Characterised by Small Discharge of Fluid

We have designed an optofluidic laser based on a dye-filled microfluidic channel. Random laser emission attributed to the inherent randomness of the structure reveals fundamental aspects as well as potential applications of this system.