Saikat Ghosh

Resonant optical interactions with molecules confined in photonic band-gap fibers

We investigate resonant nonlinear optical interactions and demonstrate induced transparency in acetylene molecules in a hollow-core photonic-band-gap fiber at 1.5 mum. The induced spectral transmission window is used to demonstrate slow-light effects, and we show that the observed broadening of the spectral features is due to collisions of the molecules with the inner walls of the fiber core. Our results illustrate that such fibers can be used to facilitate strong coherent light-matter interactions even when the optical response of the individual molecules is weak.

Low-light-level optical interactions with rubidium vapor in a photonic band-gap fiber

We show that rubidium vapor can be produced within the core of a photonic band-gap fiber yielding an optical depth in excess of 2000. Our technique for producing the vapor is based on coating the inner walls of the fiber core with organosilane and using light-induced atomic desorption to release Rb atoms into the core. As an initial demonstration of the potential of this system for supporting ultralow-level nonlinear optical interactions, we perform electromagnetically induced transparency with control-field powers in the nanowatt regime, which represents more than a 1000-fold reduction from the power required for bulk, focused geometries.

Self-Focusing Dynamics of Coupled Optical Beams

In this Letter, we investigate both theoretically and experimentally the spatial collapse dynamics of two coherently coupled beams in Kerr media. We observe repulsion and attraction between the collapsing beams, and a sharp transition to fusion of the beams, which is dependent on their initial power, spatial separation and relative phase. We further show that this transition, accompanied by a peak in the collapse distance, can be exploited to control and manipulate the collapse dynamics of two coupled beams. Our results shed light on the basic nonlinear interaction between self-focused collapsing beams and are applicable in different scenarios, including that of multiple filamentation and collapse of complex multilobe beams such as necklace beams [25]. To investigate the propagation and collapse of two spatially separated beams in Kerr media, we numerically +� ] + +�

Nonlinear optical interactions with Rubidium atoms confined in a hollow-core photonic crystal fiber

We use light-induced atomic desorption to produce an appreciable density of Rubidium atoms in a hollow-core photonic bandgap fiber and demonstrate electromagnetically induced transparency at very low light levels.

Novel nonlinear processes in hollow-core photonic bandgap fibers

We present the results of several experiments in which nonlinear-optical processes are enhanced by introducing gases into the hollow core of a photonic bandgap fiber. Such fibers offer the potential of greatly enhancing nonlinear interactions

Motion transduction with thermo-mechanically squeezed graphene resonator modes

There is a recent surge of interest in amplification and detection of tiny motion in the growing field of opto- and electromechanics. Here, we demonstrate widely tunable, broad bandwidth, and high gain all-mechanical motion amplifiers based on graphene/silicon nitride (SiNx) hybrids. In these devices, a tiny motion of a large-area SiNx membrane is transduced to a much larger motion in a graphene drum resonator coupled to SiNx. Furthermore, the thermal noise of graphene is reduced (squeezed) through parametric tension modulation. The parameters of the amplifier are measured by photothermally actuating SiNx and interferometrically detecting graphene displacement. We obtain a displacement power gain of 38 dB and demonstrate 4.7 dB of squeezing, resulting in a detection sensitivity of 3.8 [Formula: see text], close to the thermal noise limit of SiNx.

Coherent resonant interactions with molecules in photonic band-gap fibers

We show that through use of an acetylene-filled hollow-core photonic band-gap fiber, coherent three-level spectroscopy can be performed and electromagnetically induced transparency can be observed using a molecular system with a weak optical response.

Optically Tunable "Slow" Light in Waveguides

We demonstrate a technique for generating tunable all-optical delays as long as 20 ns in single-mode fibers at telecommunication wavelengths using stimulated Brillouin scattering. This process represents a step towards implementing slow-light in telecommunication systems.