Excess noise generation during spectral broadening in a microstructured fiber

Applied Physics B (Impact Factor: 1.78). 08/2003; 77(2):279-284. DOI: 10.1007/s00340-003-1177-8

ABSTRACT We observe that nanojoule femtosecond pulses that are spectrally broadened in a microstructured fiber acquire excess noise. The excess noise is manifested as an increase in the noise floor of the rf spectrum of the photocurrent from a photodetector illuminated by the pulse train from the laser oscillator. Measurements are made of the intensity dependence of the excess noise for both 100fs and sub-10fs pulses. The excess noise is very strong for 100fs pulses, but barely measurable for sub-10fs pulses. A rigorous quantum treatment of the nonlinear propagation of ultrashort pulses predicts that, for a fixed generated bandwidth, the amount of excess noise decreases with pulse duration, in agreement with the experimental results.

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