Laboratory of Cold Atoms Near Surfaces

Start research nanofibers
Experiment with nanofibers

The main idea of the experiment is to rotate a flat domain of parallel-oriented needles (p-6p) over an angle of 2π and to excite the domain with polarized UV (325 nm) EW radiation while detecting simultaneously the emitted fluorescence (max. 430 nm) intensity (Fig. 1). Two specific properties of the nanofiber samples are used. Firstly, owing to their special growth mechanism, all the nanofibers are oriented strictly parallel to each other. Secondly, the height distribution function of the nanofibers for given growth conditions is very narrow, i.e., they all have roughly the same height.

During sample rotation we observed fluorescence maxima corresponding to a superposition of the EW’s electric vector with the molecular transition dipole moments (Fig. 2). We performed a series of measurements for both the TE and the TM cases with the same beam intensity 500 mW/cm2 for different incident angles in the range below and above the critical angle. For each measurement we fitted a sinus square function to the data and took the amplitude as a quantity proportional to the appropriate mean-square value of the electric vector component.

To obtain EW excitation we have used a half-sphere and samples on mica in two configurations: 2-phase (mica, air) and 3–phase (quartz, air, mica):

Fig. 1 MO- microscope objective, F-filter, L- lens, PMT- photomultiplier, Ph-pinhole, P- polarizer, HWP- half-wave plate.

Fig. 2

Experimental and theoretical results for “two-phase” TIR configuration (mica, air). We emphasize very good quantitative agreement of experimental and theoretical curves after multiplying theoretical curves by a factor of 5 (Fig. 3).

Fig. 3

Results for “three-phase” configuration (quartz — air — mica)(Fig. 4):

Fig. 4