COLLINEAR TYPE-II 2ND-HARMONIC-GENERATION FREQUENCY-RESOLVED OPTICAL GATING FOR USE WITH HIGH-NUMERICAL-APERTURE OBJECTIVES

Ultrashort-pulse lasers are now commonly used for multiphoton microsco py, and optimizing the performance of such systems requires careful ch aracterization of the pulses at the tight focus of the microscope obje ctive. We solve this problem by use of a collinear geometry in frequen cy-resolved optical gating that uses type II second-harmonic generatio n and that allows the full N.A. of the microscope objective to be used . We then demonstrate the technique by measuring the intensity and the phase of a 22-fs pulse focused by a 20x, 0.4-N.A. air objective. (C) 1998 Optical Society of America OCIS codes: 140.7090,320.7100, 320.716 0.