2-PHOTON EXCITATION PROFILES IN CYLINDRICAL CAPILLARIES

Poor detection limits of two-photon excited fluorescence in cylindrica l capillaries are attributed to photothermal expansion and beam astigm atism. Photothermal expansion is demonstrated for excitation in a 1 cm cell and is inferred for the larger diameter capillaries. Astigmatism is caused by focal differences between rays in a plane Longitudinal t o the capillary and rays in a plane transverse to the capillary. Data were obtained by integrating the fluorescence from variously sized cyl indrical and square capillaries, and by photographing the fluorescence within a 1 cm cell.