Suneel Singh

Effect of collisions with surface on nonlinear optical properties and nonlinear selective reflection

Abstract Nonlinear optical properties of an atomic system are calculated by taking into account the collisions with the walls of the cell. The nonlocality of such optical properties is discussed. Using these, the characteristics of the nonlinear selective reflection are calculated. The nonlinear selective reflection can lead to considerable improvement in the resolution of the spectral lines produced by a Doppler broadened system.

Electromagnetically induced transparency and steady-state propagation characteristics in Doppler broadened diamond systems

We explore the feasibility of attaining simultaneous electromagnetically induced transparency (EIT) and efficient nonlinear generation in different configurations of Doppler broadened diamond (double-cascade) systems such as, the frequency up-conversion, nearly degenerate and degenerate scheme. We show that EIT and nonlinear generation efficiency depend critically on the type of residual Doppler broadening present in each of the two cascade subsystems constituting the diamond system. Furthermore, it is observed that nonlinear generation with perfect EIT simultaneously in both subsystems is not possible as the process of nonlinear generation actually tends to oppose EIT. Yet in an extended medium, on resonance field propagation under matched conditions for probe and generated signal can occur when a balance (equilibrium) is established between these two competing processes.

Enhanced coherent emission aided by an incoherent process.

Enhanced emission of a coherent signal generated by the nonlinear process omega(f)+omega(b)-omega(p) has been found in an incoherently pumped four-level system. It is shown that finite (large) atomic coherence can be generated by (incoherent) pumping of the intermediate states, which removes the destructive interference effects that otherwise inhibit coherent emission of signals.

Subluminal and superluminal light propagation via electromagnetically induced transparency in radiatively and inhomogeneously broadened media

Abstract Contrary to popular belief, we demonstrate the feasibility of generating superluminal (and subluminal) probe (and signal) light via electromagnetically induced transparency in a medium comprising coupled double-ladder systems. This scheme can be realized in both homogeneously (radiative) as well as in inhomogeneously (Doppler) broadened atomic systems. Unlike more intricate earlier schemes, our scheme is based simply on steady-state propagation dynamics resulting from compensation of the inevitable absorption losses by large nonlinear gain generated through appropriate choice of the pump and coupling fields. We show how easily in this scheme the speed of weak probe (and signal) fields can be switched from subluminal to superluminal by simply varying the strengths of the coherent pump and coupling fields. Furthermore, it is shown that under these conditions both the signal and probe fields are intensity matched and both propagate with the same subluminal (or superluminal) group velocity without suffering loss or gain for long distance in the medium.

Coherent perfect absorption in multi-elements composite medium

We demonstrate tunable anti lasing (or coherent perfect absorption) in a three component (Au + Ag + SiO2) composite medium has absorption in longer wavelength than comparatively two component (Au + SiO2 or Ag + SiO2) composite medium.

Effect of different packaging films on shelf-life and quality of Daisy mandarin under ambient conditions

The fruits of Daisy mandarin were harvested at dark orange colour satge and packed in paper moulded trays followed by wrapping with different packaging films, viz., heat shrinkable film (15 μ), cling (15 μ) and low density polyethylene (25 μ LDPE) film. After packaging, the fruits were stored under ambient conditions (1820°C; 90–95% RH). The fruits were then evaluated for various quality attributes periodically. The in-package gaseous composition (O2 and CO2) in shrink film packed fruits was found to be at desired level, which resulted in maintenance of pleasant flavour of the fruits. On the other hand, LDPE film accumulated very high level of CO2, which led to formation of fermenting odour and decay of fruits in the package. After 15 days of storage, shrink film helped in reducing the loss in weight (1.12%), firmness (7 lb force), decay incidence (0%) and maintained various qualities attributes like total soluble solids (11.8%), sugars (7.75%), acidity (0.46%) and ascorbic acid content (12.3 mg/100 g) of the fruits during shelf-life better than unwrapped control fruits where PLW (10.71%), firmness (4 lb force) and decay (5%) was recorded. The data revealed that shrink film proved quite effective in prolonging the shelf-life and maintaining the quality of Daisy mandarin fruits for 15 days compared to only 5 days in case of unpacked control.

Coherent perfect absorption with Gaussian beams

We study coherent perfect absorption in a metal-dielectric composite slab with bi-directional illumination using Gaussian beams. We show that CPA is possible with broader Gaussian beams, while tightly focused beams lead to incomplete absorption.

Electromagnetically Induced Transparency in a V‐Type Atomic System: Homogeneous Vs. Inhomogeneous Broadening

We investigate the possibility of electromagnetically induced transparency (EIT) phenomenon in a three level V‐type atomic system considering both homogenous and inhomogeneously (Doppler) broadened media. Although reduction (dips) in the absorption lines have been experimentally reported in various three‐level systems, a certain ambiguity remains as to whether these results are consequences of EIT or a similar phenomenon known as Autler‐Townes (AT) splitting. The latter phenomenon has a signature that looks very similar to that of EIT. Both phenomena display a reduction in absorption where a maximum is expected in the absence of the coupling field. We present results to demonstrate that EIT occurs in an inhomogeneous Doppler broadened medium, whereas it is not possible to observe EIT in a homogenous medium. The reduced absorption of probe in a homogenous medium is due to Autler‐Towns effect (AT).

Four wave mixing at air-dielectric interfaces with a femtosecond laser excitation

In this article we report our experimental results on non collinear four-wave mixing (FWM) at air-dielectric interfaces. We generated FWM signal from the two interfaces of a 1mm thick fused silica slide with air using two 800 nm, 100 fs pump pulses in non-collinear pump-probe type geometry. We observe that there is a maximum peak shift of approximately 1.5 nm in FWM signals corresponding to the two interfaces of the same silica slide. Further, we find that the intensity of FWM signal observed at air to silica interface is less than that from silica to air interface. We briefly elaborate on this observation with systematic study of FWM in fused silica.