Optical EngineeringTwofold spatial resolution enhancement by two-photon exposure of photographic film
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Two-photon absorption of photosensitive media can produce interference fringes with double spatial frequency. This requires the employment of multiple-frequency beams, which interfere with one another to produce a stationary image with double spatial resolution. The required beams were produced by frequency filtering of broadband radiation from a cw mode-locked femtosecond Ti:sapphire laser (? = 790 nm) in a dispersion-free pulse shaper. Then the two multifrequency rays converged from opposite edges of a lens, focusing on Kodak commercial film. The laser intensity was high enough to produce a two-photon exposure. The doubling of the spatial frequency of the interference pattern has been observed, but the contrast ratio of the pattern was limited by competition from the more usual one-photon absorption. Laser pulse parameters for a single-pulse two-photon exposure have been estimated.