HOLLOW CYLINDRICAL WAVE-GUIDES FOR USE AS EVANESCENT FLUORESCENCE-BASED SENSORS - EFFECT OF NUMERICAL APERTURE ON COLLECTED SIGNAL

Hollow cylindrical waveguide sensors permit conventional capillary inj ection techniques for flowing precise volumes of a liquid sample throu gh the sensor while exciting and collecting fluorescence by use of eva nescent fields. Both a ray-optics model and experimental data show tha t fluorescence collected from bulk or thin-layer fluorescent samples i ncreases strongly as the numerical aperture (N.A.) increases and is ma ximized when the N.A. of the excitation-collection optic matches the w aveguide N.A. The dependence of fluorescence on N.A. closely resembled that reported previously for solid cylindrical waveguides. Mode mixin g reduced the strength of this dependence and should be minimized to i ncrease collected fluorescence. (C) 1997 Optical Society of America.