Laser frequency locking by direct measurement of detuning.

We present a new method of laser frequency locking in which the feedback signal is directly proportional to the detuning from an atomic transition, even at detunings many times the natural linewidth of the transition. Our method is a form of sub-Doppler polarization spectroscopy, based on measuring two Stokes parameters (I2 and I3) of light transmitted through a vapor cell. It extends the linear capture range of the lock loop by as much as an order of magnitude and provides frequency discrimination equivalent to or better than those of other commonly used locking techniques.

Measuring entangled qutrits and their use for quantum bit commitment.

We produce and holographically measure entangled qudits encoded in transverse spatial modes of single photons. With the novel use of a quantum state tomography method that only requires two-state superpositions, we achieve the most complete characterization of entangled qutrits to date. Ideally, entangled qutrits provide better security than qubits in quantum bit commitment: we model the sensitivity of this to mixture and show experimentally and theoretically that qutrits with even a small amount of decoherence cannot offer increased security over qubits.

Absorption and fluorescence spectroscopy of rhodamine 6G in titanium dioxide nanocomposites.

A comparison has been made between the spectroscopic properties of the laser dye rhodamine 6G (R6G) in mesostructured titanium dioxide (TiO(2)) and in ethanol. Steady-state excitation and emission techniques have been used to probe the dye-matrix interactions. We show that the TiO(2)-nanocomposite studied is a good host for R6G, as it allows high dye concentrations, while keeping dye molecules isolated, and preventing aggregation. Our findings have important implications in the context of solid state dye-lasers and microphotonic device applications.

Utilization of the non-covalent fluorescent dye, NanoOrange, as a potential clinical diagnostic tool. Nanomolar human serum albumin quantitation.

The commercially available dye, NanoOrange, has been investigated as a potential tool for clinical diagnostics due to its low cost, ease of use, and ability to detect nanomolar concentrations of protein. Virtually non-fluorescent in dilute aqueous solutions, NanoOrange fluorescence is enhanced by at least an order of magnitude upon non-covalent interaction with proteins. These features, coupled with the requirement for high throughput assays in the clinical laboratory has prompted the development of two orthogonal NanoOrange approaches. Human serum albumin (HSA) was used as a model protein for the development of both 96-well microplate and capillary electrophoresis laser-induced fluorescence (CE-LIF) assay formats. Dye performance in five commonly used buffers of various concentrations and pH indicated considerable flexibility in assay buffer selection, with optimal performance at pH 9.0. A salt concentration study indicated that increasing NaCl concentration generally decreases fluorescence emission and can be minimized by pre-diluting biological samples to a final salt concentration of 20-80 mM. Titration of protein with NanoOrange resulted in optimal HSA-NanoOrange complex formation utilizing 1 x and 2 x NanoOrange in the 96-well microplate and CE-LIF approaches, respectively. A NanoOrange binding model based on rapid signal enhancement and zero order fluorescence emission kinetics is proposed. The utilization of NanoOrange in CE-LIF based human serum analysis results in a signal-to-background ratio improvement of up to two orders of magnitude.

Subnanomolar detection limit for sodium dodecyl sulfate-capillary gel electrophoresis using a fluorogenic, noncovalent dye.

Picomolar limits of detection are obtained using the noncovalent, fluorogenic dye, Sypro Red. The size separation of four commonly used sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) molecular weight markers with 8% linear polyacrylamide (PAA) as the sieving matrix is used to construct a calibration curve for molecular weight determinations. SDS-CGE purity and molecular weight determination of purified chorismate mutase-prephenate dehydrogenase (CMPD) from Escherichia coli is shown to be comparable in accuracy with slab gel SDS-polyacrylamide gel electrophoresis (SDS-PAGE). A migration time precision study indicates excellent reproducibility. Sypro red labeling of SDS-bovine serum albumin (SDS-BSA) complexes at nanomolar protein concentrations suggests assay detection limits surpassing those of silver staining. This detectability exceeds that achieved in previous SDS-CGE laser-induced fluorescence studies. This approach is expected to be easily adapted for use with commercial polymer formulations and automated instrumentation.