ABSTRACT
Surface-relief gratings with submicrometer modulation periods were ablated by F2-laser radiation in thin metal-oxide films to produce resonant grating waveguide structures. For 150 nm films of Nb2O5, grating amplitudes in the range of 5-50 nm could be reproducibly excised with a controlled exposure of a laser energy density and a number of pulses within a narrow processing window. Resonant coupling of 800 nm ultrashort pulsed laser light into the resulting grating waveguide structure is verified with reflection and transmission spectra and satisfactorily modeled by coupled-mode theory. The laser-fabricated grating waveguides are attractive for high damage threshold reflectors and biosensor applications.
ABSTRACT
We report enhancement of two-photon fluorescence (TPF) excitation in fluorescent dyes and fluorescently labeled biomolecules by exploiting the optical properties of double grating waveguide structures (DGWSs). Picosecond laser pulses generate a large evanescent field based on the guided mode phenomenon in the resonant DGWSs, which induces strong TPF signals from fluorescent dyes at the waveguide surface. By recording enhanced TPF signals of Rhodamine B and Lucifer Yellow under resonance conditions, a detection sensitivity of concentrations of approximately one dye molecule per 0.1 microm2 was achieved. For the first time to our knowledge, enhanced TPF signals of a Lucifer Yellow-labeled biomolecule (human self-peptide) in an aqueous environment are demonstrated. These results strongly encourage the use of DGWSs as enhancement platforms in modern biophysics and biotechnology for investigations of biological membranes and cells.
