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Projects

Multipass Enhanced Raman Scattering within Multimode ECDL

Due to its inherent simplicity and versatility, spontaneous Raman scattering is ideally suited for chemical gas analysis. However, with a small scattering cross-section, the process typically requires an enhancement method, of which the most famous example is probably surface enhanced Raman scattering. In recent years, many other approaches have been developed, such as cavity, capillary, hollow core fiber, and Purcell-enhanced Raman scattering, some of which have demonstrated gas sensing capabilities in the parts-per-million range. The primary goal of this project is to develop a novel method expected to offer dramatic improvements, in particular, detection limits in the parts-per-billion range, while employing a low-cost compact design. The novel approach is based on a multipass cavity integrated as part of an external cavity diode laser. These efforts could pave the way for versatile 鈥渁rtificial noses鈥� that could be widely deployed in industrial process control, medical diagnostics, and environmental sensing.

Slow-Fast Dynamics in High-Finesse Microcavities

The resonant buildup of photons inside a high-finesse optical microcavity can routinely produce circulating intensities of order Icirc 鈭� 100 MW鈭昪m2 even when the laser input power is only a few milliwatts. At such intensities, the circulating photons may deform the cavity boundaries to such an extent as to affect the cavity resonance condition, and thus the circulating photon flux. An interesting situation arises when two or more light- induced processes act oppositely and on different time scales, such that the system dynamics are governed by a set of coupled differential equations that resemble those found in the physics of chemical reactions, neural networks, and other natural systems. We are interested in these dynamics in the context of cavity optomechanics which is concerned with the back-action of mechanical deformations onto the optical fields that generate them. In particular, we study thermomechanical mirror deformations in high finesse Fabry-Perot cavities which act on picometer length scales and give rise to 鈥渟low-fast鈥� nonlinear oscillations.

Multiphoton Spectral Characterization of Light

Photon correlations are the primary tool for characterizing light-matter interactions at the few or single quantum level. In principle, if photon correlation functions to all orders were known, all measurable properties of a given light source would be known. A fascinating development in the understanding of photon statistics has been the generalization by del Valle et al. of frequency-resolved photon correlations into a 鈥淣-photon spectrum鈥�, a quantity g(N) (蟿1,蠅1;...;蟿N,蠅N) proportional to the joint probability of detecting a photon in channel 1 at time 蟿1 filtered at frequency 蠅1, a photon in channel 2 at time 蟿2 filtered at frequency 蠅2,..., and a photon in channel N at time 蟿N filtered at frequency 蠅N. We are now able to record this quantity experimentally which can be visualized by a 2 dimensional map at second order, and by a cube at third order.

Resonance fluorescence from a single semiconductor quantum dot is an ideal test source for characterizing the two (left) or three (right) photon spectrum. A rich landscape of transitions is uniquely revealed. The underlying correlations can be used for example as generators of Franson interference and time-energy entanglement.

Microcavity Purcell-Enhanced Raman Scattering

Purcell first observed that the presence of reflectors in the vicinity of an emitter can significantly alter its spontaneous emission rate. This effect is now well-known for the case of two-level fluorescence from atoms. It is also the subject of intensive research in single quantum emitter solid-state cavity quantumelectrodynamics in the context of single-photon generation for quantum communication applications. Its ubiquity in fluorescence measurements notwithstanding, the Purcell effect has been studied much less for the case of Raman scattering. Enhancement of spontaneous Raman scattering is however highly desirable, particularly in gases that have notoriously weak scattering cross-sections. We have observed Purcell enhanced spontaneous Raman scattering in three-dimensionally-confining optical microresonators. It involves creating a pump/Stokes double resonance which critically depends on the frequency-dependent dielectric mirror phase shifts. Highlights include the detection of spontaneous Raman scattering from only order 105 molecules in a microscopic volume.

Development of High-Quality Micromirrors and Waveguides Using Focused Laser Template Fabrication

In order to obtain strong interactions between light and single quantum emitters, we are developing micromirror-based Fabry-Perot microcavities. A microcavity recirculates light at a resonant frequency within a small volume (typically on the order of less than 10 cubic microns) giving rise to a light matter coupling that is enhanced compared to free-space. In order to obtain the smallest possible mirrors yet with the highest possible reflectivity (>9