Pulsed and cw confocal microscopy: a comparison of resolution and contrast

Scanning confocal microscopy using pulsed illumination is investigated theoretically and experimentally. The point-spread-function of a confocal microscope operating with pulsed illumination is derived and compared to its continuous wave counterpart. High aperture confocal images of scattering point-like objects are recorded with pulses of 220 fs, and with a continuous beam. The images are compared paying particular attention to differences in resolution and contrast. Whereas no significant change in resolution has been observed for pulsed mode, the contrast of scanning reflection microscopy is enhanced when pulsed operation is employed. For ultrashort transform-limited pulses (<50 fs) a significant increase of resolution is predicted. This resolution increase amounts to 20% at a pulse of 10 fs.