Polarization-selective Excitation of Dye Luminescence on a Gold Film by Structured Ultrashort Laser Pulses

Donut-shaped visible (515 nm) femtosecond laser pulses with linear, radial and azimuthal polarizations after tight focusing (numerical aperture NA = 0.65) have been used for spectrally adjusted excitation of plasmonenhanced rhodamine 6G dye luminescence on the surface of a nanocrystalline 45-nm thick gold film with its plasmon resonance near the laser line. Significant luminescence output increments-1.7-fold for radial polarization compared to the azimuthal one, and almost 3-fold-compared to the linear one, have been observed. This effect is related to significant transformation of the transverse electrical field component into longitudinal one for radial polarization (up to 33% in intensity, according to our calculations), and corresponding increase in excitation efficiency of plasmons in the smaller nanocrystallites throughout the film.