Fig. 2: Implementation of broadband UV to blue-green generation.

a Pump pulses from a 1 GHz Ti:sapphire comb enter a 35 mm long photonic-crystal fiber to create 650–1150 nm supercontinuum (SC) pulses, which are launched into an MgO:PPLN waveguide (inset). Replica pump pulses are co-launched into the waveguide and overlapped with infrared SC components to achieve a broadband SHG and SFM comb, which is filtered by a Fabry–Pérot etalon to produce a 30 GHz astrocomb. All beamsplitters are non-polarizing: 1 and 2 have low GDD at 800 nm and reflectivities (transmissions) of 30 and 50% respectively; 3 is a low-reflectivity beam sampler; 4 is a broadband 750–1050 nm 50% reflector; and 5 is a 30% reflector and is followed by a 410 nm narrowband filter (6) to select pump SHG light used for Fabry–Pérot etalon locking. Half-wave plates (HWP) are used to prepare the pump and SC light into vertical polarizations before the waveguide. b Delay-resolved output from the MgO:PPLN waveguide, recorded by incrementing the temporal overlap between the pump and SC pulses using an optical delay line in the 800 nm pump channel. The offset of the delay axis is arbitrary, with the origin set to the delay which yielded the most intense SFM signal. Line cuts at 30 and 800 fs illustrate the enhanced spectral coverage and intensity achieved from the SFM process, spanning a spectral gap from 400–430 nm. c Photograph of the UV to blue-green supercontinuum generated by the MgO:PPLN waveguide at optimal delay between the pump and supercontinuum pulses. d Spectra of the fundamental pulses (red shading) and the SHG/SFM field (blue shading) generated in the MgO:PPLN waveguide. The shape and bandwidth of the SHG/SFM spectrum after Fabry–Pérot filtering (solid blue line) is preserved.