Enhanced supercontinuum generation by minute continuous wave seed

Abstract

It is well-known that the properties of the supercontinuum (SC) radiation depend critically on the initial pumping conditions. For instance, if the SC is initiated by noise, namely modulation instability (MI), statistically rare "rogue waves" can be observed with sizable spectral broadening and intensity enhancement in SC. Interestingly, such rouge events can be actively controlled by adding an external weak pulse or by modulating the pump-pulse envelopes. In contrast, we here present that a simple triggering mechanism using an extremely weak continuous wave (CW) can also achieve such "rogue" enhancement. We experimentally demonstrated that a weak CW trigger (∼200,000×weaker than pump) can considerably broaden the SC bandwidth compared to the untriggered SC case (∼100 nm wider). Such enhancement was found to occur when the CW trigger's wavelength falls roughly within the modulation instability gain bandwidth. CW triggering also significantly alters the SC amplitude statistics, i.e. from extreme-value statistics in the untriggered SC to almost normal distribution in the triggered SC. Interferometric measurements also revealed the improvement in the SC coherence when the SC is CW-triggered. The enhanced SC by minute CW triggering only requires the CW-wavelength tuning for optimization and eliminates the necessity of high-precision (down to picoseconds) timing between the pump and the seed as in the pulse-seeding case. It thus offers a more convenient and practical approach to realize an enhanced and stable SC for many applications, especially in which real-time, ultrafast and single-shot spectroscopic measurements are essential. © 2011 SPIE.