Diamond Raman lasers (DRLs) have been the subject of extensive research in the recent years. Continuous-wave and pulsed, intra- and extra-cavity DRLs emitting from UV to IR have been demonstrated . The majority of these studies were carried out in the steady-state mode, when the pump pulse duration is longer than the dephasing time in diamond. Less work has been done on the transient mode, when the pulse duration is shorter than the dephasing time: DRLs under femtosecond (fs) pumping in synchronously-pumped cavities has been demonstrated , and supercontinuum (SC) generation in diamond under fs pumping has been reported . The major mechanism for SC generation under fs laser pumping is believed to be self-phase modulation (SPM). It has been shown before that this effect can be significantly reduced when using the Bessel beam pumping. In this work we present a first comparison study of the effect of Gaussian and Bessel pump beams on the spectral properties of nonlinear frequency conversion in diamond in transient mode.
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