Observation of broadband forward hyper-Raman emission with high intensity focused laser beams

We show that the well known multiphoton destructive interference, which leads to hyper-Raman gain suppression in the weak pumping regime, no longer occurs under strong pumping conditions. In contrast to the weak pumping case, where no forward hyper-Raman can be observed and strong backward hyper-Raman occurs, forward hyper-Raman emission is found to be much stronger under strong pumping conditions. The emission spectrum acquires new characteristics due to the ac Stark effect introduced by the strong laser field. The frequency spectrum of the forward hyper-Raman is no longer determined by the laser bandwidth, instead a continuum of forward hyper-Raman emission is observed with the width being determined by the peak power density. We will present here a comparison between strong and weak pumping regimes.