Efficient spectral broadening and recompression of 200 fs pulses from a monolithic Yb-FCPA to 66 fs

Ytterbium doped fiber chirped pulse amplifiers (FCPAs) are attractive sources to replace their solid-state counterparts in applications like micromachining, for example for manufacturing photonic devices in bulk glass substrates. For such applications, a pulse duration of several tens of fs is often considered to be optimal so that one can write features with a sub-wavelength precision. However, the shortest attainable pulse duration from μJ -level Yb-doped FCPAs is limited to ~160 fs because of gain narrowing in such systems. Therefore, spectral broadening of the output of the Yb-doped FCPA is needed to allow recompression to several tens of fs. Many methods to obtain spectral broadening are rather lossy (e.g. white light generation in a bulk substrate followed by spatial filtering) or produce pulses that are difficult to compress (e.g. spectral broadening in highly nonlinear or photonic crystal fibers). In a bid to obtain well-compressible pulses with a high energy-efficiency, we couple the compressed output pulses from our monolithic Yb-doped FCPA into a 20 cm long piece of polarization maintaining (PM) large mode area (LMA) fiber.