Visualization of superluminal pulses inside a white light cavity using plane wave spatio temporal transfer functions.

In a white light cavity (WLC), the group velocity is superluminal over a finite bandwidth. For a WLC-based data buffering system we recently proposed, it is important to visualize the behavior of pulses inside such a cavity. The conventional plane wave transfer functions, valid only over space that is translationally invariant, cannot be used for the space inside WLC or any cavity, which is translationally variant. Here, we develop the plane wave spatio temporal transfer function (PWSTTF) method to solve this problem, and produce visual representations of a Gaussian input pulse incident on a WLC, for all times and positions.

Distortion free pulse delay system using a pair of tunable white light cavities.

Recently, a tunable bandwidth white light cavity (WLC) was demonstrated by using an anomalously dispersive intra-cavity medium to adjust a cavity linewidth without reducing the cavity buildup factor [G.S. Pati et al., Phys. Rev. Lett. 99, 133601 (2007)]. In this paper, we show theoretically how such a WLC can be used to realize a distortion-free delay system for a data pulse. The system consists of two WLCs placed in series. Once the pulse has passed through them, the fast-light media in both WLCs are deactivated, so that each of these now acts as a very high reflectivity mirror. The data pulse bounces around between these mirrors, undergoing negligible attenuation per pass. The trapped pulse can be released by activating the fast-light medium in either WLC. Numerical simulations show that such a system can far exceed the delay-bandwidth constraint encountered in a typical data buffer employing slow light. We also show that the pulse remains virtually undistorted during the process.

Superluminal ring laser for hypersensitive sensing.

The group velocity of light becomes superluminal in a medium with a tuned negative dispersion, using two gain peaks, for example. Inside a laser, however, the gain is constant, equaling the loss. We show here that the effective dispersion experienced by the lasing frequency is still sensitive to the spectral profile of the unsaturated gain. In particular, a dip in the gain profile leads to a superluminal group velocity for the lasing mode. The displacement sensitivity of the lasing frequency is enhanced by nearly five orders of magnitude, leading to a versatile sensor of hyper sensitivity.

Fast-light in a photorefractive crystal for gravitational wave detection.

We demonstrate superluminal light propagation using two frequency multiplexed pump beams to produce a gain doublet in a photorefractive crystal of Ce:BaTiO(3). The two gain lines are obtained by two-wave mixing between a probe field and two individual pump fields. The angular frequencies of the pumps are symmetrically tuned from the frequency of the probe. The frequency difference between the pumps corresponds to the separation of the two gain lines; as it increases, the crystal gradually converts from normal dispersion without detuning to an anomalously dispersive medium. The time advance is measured as 0.28 sec for a pulse propagating through a medium with a 2 Hz gain separation, compared to the same pulse propagating through empty space. We also demonstrate directly anomalous dispersion profile using a modified experimental configuration. Finally, we discuss how anomalous dispersion produced this way in a faster photorefractive crystal (such as SPS: Sn(2)P(2)S(6)) could be employed to enhance the sensitivity-bandwidth product of a LIGO type gravitational wave detector augmented by a White Light Cavity.

Time-resolved magnetic sensing with electronic spins in diamond.

Quantum probes can measure time-varying fields with high sensitivity and spatial resolution, enabling the study of biological, material and physical phenomena at the nanometre scale. In particular, nitrogen-vacancy centres in diamond have recently emerged as promising sensors of magnetic and electric fields. Although coherent control techniques have measured the amplitude of constant or oscillating fields, these techniques are not suitable for measuring time-varying fields with unknown dynamics. Here we introduce a coherent acquisition method to accurately reconstruct the temporal profile of time-varying fields using Walsh sequences. These decoupling sequences act as digital filters that efficiently extract spectral coefficients while suppressing decoherence, thus providing improved sensitivity over existing strategies. We experimentally reconstruct the magnetic field radiated by a physical model of a neuron using a single electronic spin in diamond and discuss practical applications. These results will be useful to implement time-resolved magnetic sensing with quantum probes at the nanometre scale.

Demonstration of a multiwave coherent holographic beam combiner in a polymeric substrate.

We demonstrate an efficient coherent holographic beam combiner (CHBC) that uses angle multiplexing of gratings in a thick polymeric substrate. Our experimental results compare well with the theoretical model based on the coupled-wave theory of multiwave mixing in a passive medium. A CHBC of this type may prove useful in producing a high-power laser by combining amplified beams produced by splitting a master oscillator. Furthermore, the ability to angle multiplex a large number of beams enables a CHBC to be used in multiple-beam interferometry applications as a high-precision surface sensor.

Demonstration of a simple technique for determining the M/# of a holographic substrate by use of a single exposure.

We propose and demonstrate a simple technique for determining the M/# parameter of a holographic recording material. In this method, divergent object and reference beams are used to produce a spatially varying index modulation. One can analyze the resultant diffraction pattern to find M/# by using only a single grating; existing techniques require many gratings.