Optical parametric amplifiers (OPAs) seeded by a continuum or by parametric generation (OPG) are the prime source of tunable ultrafast radiation. White light seeded OPAs are considered to deliver reproducible pulses, however, they do not render pulses with a clean Gaussian spectrum and a pulse length that is given by the Fourier limit. Even more severely, OPGs are known for large intensity and spectral fluctuations. In the nanosecond regime superior pulses are generated by amplification of monomode cw seed light in dye amplifiers and optical parametric oscillators. For the ultrafast regime the principle has so far not been exploited, due to the small number of seed photons contained within the temporal amplification interval. Yet, the ever increasing availability of low cost diode sources would make it an attractive method.
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