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Frequency conversion of subnanojoule femtosecond laser pulses in a microstructure fiber for photochromism initiation.

Microstructure fibers with multiple submicron cores are used to frequency-convert unamplified 0.3-nJ, 80-fs pulses of 800-nm Ti: sapphire laser radiation to the spectral range of 400 - 500 nm. This frequencyupconverted radiation is then employed to induce reversible changes in the absorption spectrum of spiropyran molecules through photochromic transformations in a solid-phase spiropyran/PMMA sample. Microstructure fibers are thus shown to enhance the capabilities of low-power femtosecond lasers, making unamplified ultrashort pulses suitable for photochemical and micromachining applications.