Abstract
Synchronously-pumped OPOs (OPOs) are now well-established as versatile sources of ultrashort pulses from the UV and visible to the near- and mid-IR. However, access to the deep-IR spectral regions beyond ~4.5 μm is fundamentally limited by the multi-phonon absorption in oxide-based QPM materials, placing a practical upper wavelength limit of ~4 μm in all such OPOs [1]. The new nonlinear material, CdSiP2 (CSP), has the important capability for parametric generation beyond ~6 μm with direct pumping at ~1.06 μm [2-4]. However, the use of the KLM femtosecond (fs) Ti:sapphire laser, the workhorse of ultrafast technology, is fundamentally precluded by two-photon absorption cutoff below ~1 μm in CSP. Here, we demonstrate a novel internal-cascaded pumping scheme that overcomes this fundamental limitation. In this scheme, the CSP fs OPO is synchronously pumped internal to a MgO:PPLN fs OPO in a coupled-cavity geometry. The new architecture enables access to high intracavity signal intensities to reach the CSP fs OPO threshold, while providing a pump at ~1 μm to avoid two-photon absorption in the crystal. A schematic of the intracavity-cascaded OPO (ICOPO) synchronously pumped by the KLM fs Ti:sapphire laser is shown in Fig. 1.
© 2015 IEEE
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