Measuring the transport mean free path using a reference random medium

We report on the performance of a new, multiharmonic frequency-domain instrument that uses the high harmonic content of a passively mode-locked, pulse-picked femto-second Ti-sapphire laser as the excitation source for the determination of one-, two-, or three-photon excited time-resolved fluorescence anisotropy and intensity decay kinetics. In operation, the new instrument can provide a complete frequency-domain data set at 100 modulation frequencies in less than 1 min. The new instrument exhibits 5-10-ps measurement precision and it can rapidly and accurately recover complex excited-state fluorescence anisotropy and intensity decay kinetics under one-, two-, or three-photon excitation for dilute or optically dense samples that exhibit single or multiexponential decay kinetics. This latter aspect of the instrument is demonstrated by successfully determining the excited-state intensity decay kinetics for a dilute aqueous solution of rhodamine 6G dissolved in a high concentration of bromocresol green. This approach is extended by determining the excited-state fluorescence intensity decay kinetics of dilute fluorescein directly in undiluted, whole blood as a function of pH under two-photon excitation conditions. The high-speed capabilities of the new instrument are exploited by performing two-photon excited fluorescence anisotropy decay experiments on the fly for site-selectively labeled bovine serum albumin as it undergoes enzymatic digestion by trypsin.

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Electromagnetic Resonances in Low Density Collections of Dielectric Spheres

Stoytchev

Garcı́a

Genack

1996

Advances in Optical Imaging and Photon Migration

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The diffusion coefficient D and the transport mean free path ℓ of microwave radiation have been measured in random collections of 0.95 cm diameter alumina spheres at a volume filling fraction of 0.06. Both parameters show sharp resonances as the frequency is tuned. From the measured values of D and ℓ the transport velocity v E has been calculated. Values of v E as small as 1/5 of the speed of light in vacuum are observed.

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Measuring the transport mean free path using a reference random medium

Cited by 3 publications

References 6 publications

On light propagation through glass bead packings

On light propagation through glass bead packings

A Parallel Multiharmonic Frequency-Domain Fluorometer for Measuring Excited-State Decay Kinetics Following One-, Two-, or Three-Photon Excitation

Electromagnetic Resonances in Low Density Collections of Dielectric Spheres

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