Abstract

It is an established fact that laser imaging through a high-scattering medium like biological tissue is possible with short pulse gates or broadband coherent long pulse gates. Short optical pulses (100 fs-30 ps) can be used with various short gates to separate the first image bearing portions of the optical pulse from the scattered light that comes later, long broadband pulses have some advantages over short pulses such as higher ANSI limit for incident laser energy. It was recognized that holography can be used as a gate for long laser pulses.¹ However, it requires equal light intensities in two interfering beams for a good contrast. It is desirable to have gates with a good contrast to keep exposure levels ίο a minimum. Recently, we showed that a nonlinear optical process, coherent anti-Stokes Raman scattering (CARS), provides a high contrast coherent gate. CARS has the disadvantage of one-dimensional imaging or short interaction length, which limits conversion efficiency.

© 1993 Optical Society of America