Complete Stokes vector analysis with a compact, portable rotating waveplate polarimeter.

Accurate calibration of polarization-dependent optical elements is often necessary in optics experiments. A versatile polarimeter device to measure the polarization state of light is a valuable tool in these experiments. Here, we report a rotating waveplate-based polarimeter capable of complete Stokes vector analysis of collimated light. Calibration of the device allows accurate measurements over a range of wavelengths, with a bandwidth of >30 nm in this implementation. A photo-interrupter trigger system supplies the phase information necessary for full determination of the Stokes vector. An Arduino microcontroller performs rapid analysis and displays the results on a liquid crystal display. The Arduino can also be interfaced with a computer to store time series of Stokes vectors. The optical measurement apparatus of the polarimeter is compact and can be placed anywhere on an optical table on a single standard post. The components to construct the device are only a fraction of the cost of commercially available devices, while the accuracy and precision of the measurements are of the same order of magnitude.

Salmonella rarely detected in Mississippi coastal waters and sediment.

AIMS: Standards for the rapid detection of individual pathogens from environmental samples have not been developed, but in their absence, the use of molecular-based detection methods coupled with traditional microbiology techniques allows for rapid and accurate pathogen detection from environmental waters and sediment. The aim of this research was to combine the use of enrichment with PCR for detection of Salmonella in Mississippi coastal waters and sediment and observe if that presence correlated with levels of enterococci and climatological variables. METHODS AND RESULTS: Salmonella were primarily found in samples that underwent nutrient enrichment and were present more frequently in freshwater than marine waters. Salmonella were detected infrequently in marine and freshwater sediments. There was a significant positive correlation between the presence of detectable Salmonella and the average enterococcal count. An inverse relationship, however, was observed between the frequency of detection and the levels of salinity, turbidity and sunlight exposure. CONCLUSIONS: Results from this study indicated the presence of Salmonella in Mississippi coastal waters, and sediments are very low with significant differences between freshwater and marine environments. SIGNIFICANCE AND IMPACT OF THE STUDY: Using pathogenic and novel nonpathogenic molecular markers, Salmonella do not appear to be a significant pathogenic genus along the Mississippi Coast.

Observation of mode locking in a synchronously pumped Nd:YAG laser.

We report on the mode-locking behavior of a 1.06-microm Nd:YAG ring oscillator synchronously pumped by a 76-MHz, 20-psec dye laser at 0.59 microm with an average power of 600 mW. Gain modulation is based on relaxation from the pump band to the upper laser level with a time constant (minimum gain modulation time) of 470 psec; stable modelocked operation is achieved with a gain modulation of only 10(-4). Preliminary results give a minimum pulse width of 140 psec and suggest a novel way of mode locking rare-earth waveguide lasers.

Preferential operation of an end-pumped Nd:YAG laser in high-order Laguerre-Gauss modes.

A small Nd:YAG laser with plano-concave resonator end pumped by a dye laser is observed to possess single Laguerre-Gauss transverse modes as the lowest-loss modes. This anomalous behavior occurs when the transverse dimension of the gain spot is much smaller than the fundamental TEM(00)-mode spot size of the resonator; the Laguerre-Gauss transverse-mode order varies with resonator length.

Efficient continuous-wave TEM(00) operation of a transversely diode-pumped Nd:YAG laser.

A new, highly efficient, scalable technique for cw high-power diode-array side pumping of gain media has been eveloped. The use of simple all-reflective optics permits diode emission collection efficiencies of >95%. We have achieved a cw TEM(00) mode output (M(2) < 1.1) of 13.1 W at 1.06 microm from a Nd:YAG rod pumped with 60 W of laser-diode output (808 nm), representing 22% conversion efficiency (29% conversion of absorbed pump power). Numerical simulations and experimental results indicate that good thermal management results in thermally induced aberrations of

Effect of spatial hole burning in a mode-locked diode end-pumped Nd:YAG laser.

We have controlled the amount of spatial hole burning in a diode end-pumped Nd:YAG laser to quantitatively analyze its role in active mode locking. We demonstrate inhomogeneous broadening of the lasing bandwidth to >60 GHz, accompanied by a pulse-width reduction from 40 to 15 ps and an ~30% increase in the time-bandwidth product. Both homogeneous and inhomogeneous broadening have been included in a successful calculation of the steady-state pulse width.

Kilohertz allsolid-state picosecond lithium triborate optical parametric generator.

An all-solid-state picosecond optical parametric generation system that uses a single-pass noncritically phase-matched lithium triborate crystal is demonstrated. We have achieved > 20% total conversion from lambda = 532 nm (pump) to lambda = 800 nm (signal) and 1.6 microm (idler) with a pulse width of ~15 ps and average power of 200 mW at a repetition rate of 3 kHz (~50 microJ/signal pulse). Frequency tuning from <750 nm to >1.8 microm is achieved by temperature tuning of the lithium triborate.