Dual electro-optic frequency comb photonic thermometry.

We report a precision realization of photonic thermometry using dual-comb spectroscopy to interrogate a π-phase-shifted fiber Bragg grating. We achieve readout stability of 7.5 mK at 1 s and resolve temperature changes of similar magnitude-sufficient for most industrial applications. Our dual-comb approach enables rapid sensing of dynamic temperature, and our scalable and reconfigurable electro-optic generation scheme enables a broad sensing range without laser tuning. Reproducibility on the International Temperature Scale of 1990 is tested, and ultimately limited by the frequency reference and check-thermometer stability. Our demonstration opens the door for a universal interrogator deployable to multiple photonic devices in parallel to potentially unravel complex multi-physical quantity measurements.

High power light emitting diode based setup for photobleaching fluorescent impurities.

Single molecule fluorescence experiments, with their associated low signals, require very low background fluorescence in the sample. Even high purity liquids will often possess large numbers of fluorescent impurities that are difficult to completely remove through standard purification techniques such as distillation and recrystallization. We have constructed a simple setup in which such impurities can be photobleached before final sample preparation. The instrument consists of high power light emitting diodes, and it delivers almost 10 W of light to the sample without the heating associated with more conventional light sources or the cost and safety concerns associated with a high power laser.

Spatial and temporal heterogeneity in supercooled glycerol: evidence from wide field single molecule imaging.

We quantify spatial and temporal heterogeneity in supercooled glycerol at T=T(g)+14 K employing a widefield detection scheme and using rubrene as the probe molecule. We describe how microscopy configuration affects measured intensity, linear dichroism, and the resulting autocorrelation function. Rotational relaxation times tau(c) of 241 probe molecules are measured, and we find spatial heterogeneity over almost three orders of magnitude present at this temperature. An approach for detecting temporally heterogeneous molecules and quantifying exchange times is introduced. Of molecules that can be assessed, approximately 15% display evidence of temporal heterogeneity-changes of tau(c) during the measurement-that are detected with the analysis technique employed. Exchanges between dynamically disparate environments occur rarely but in the proportion expected given the rarity of very slowly rotating molecules present. Heterogeneous molecules are characterized by persistence and exchange times. Median exchange and persistence times of the molecules identified as heterogeneous relative to glycerol's structural relaxation time tau(alpha) are found to be tau(ex)/tau(alpha)=202 and tau(pers)/tau(alpha)=405, respectively. These results are discussed in the context of values of exchange times that have been determined in other experiments.

Freezing and pressure-driven flow of solid helium in Vycor.

The recent torsional oscillator results of Kim and Chan suggest a supersolid phase transition in solid 4He confined in Vycor. We have used a capacitive technique to directly monitor density changes for helium confined in Vycor at low temperature and have used a piezoelectrically driven diaphragm to study the pressure-induced flow of solid helium into the Vycor pores. Our measurements showed no indication of a mass redistribution in the Vycor that could mimic supersolid decoupling and put an upper limit of about 0.003 microm/s on any pressure-induced supersolid flow in the pores of Vycor.