XPW based self-referenced spectral interferometry for few-cycle pulse characterization in the short wavelength IR

Abstract

Femtosecond pulses in the short-wavelength infrared spectral range (1-2.5 m) are nowadays available from commercial optical parametric amplifiers (OPA). Further spectral broadening and compression of these pulses potentially leads to table-top, few-cycle pulse laser sources. The full temporal characterization of these sources is important for most applications.In this work, we present a measurement device based on Self-Referenced Spectral Interferometry (SRSI) [1] that uses Cross-Polarized Wave Generation (XPW) [2] as a temporal nonlinear filter. The device is capable of single shot temporal measurement and spectral phase characterization of femtosecond pulses down to a few optical cycles in the 1-2.5 m spectral range. Fig. 1Single-shot measured spectrum (black solid line), spectral phase (red squares) and pulse intensity (inset-black) of few cycle pulses at 1400 nm (a), 1600 nm (b), 1700 nm (c) and 1950 nm (d). The measured XPW spectra (blue dashed line) and retrieved XPW FL pulses (inset blue) are also shown. Figure 1 shows single-shot SRSI measurements of sub-50 fs pulses at 1400 nm (a), 1700 nm (c) and 1950 nm (d) [3]. After nonlinear spectral broadening by filamentation in Xenon and correction of the residual group delay dispersion, 2.5 cycle pulses at 1600 nm have been generated and successfully characterized with our device (Fig. 1, b). As a consistency check, we verified that the XPW spectrum (Fig. 1, dashed blue line) is broader and the FL duration shorter than those of the pulse to be measured (Fig. 1, insets).These results show the excellent capability of the SRSI device to perform accurate single-shot characterization of nearly bandwidth limited pulses over the full 1.2-2.5 m spectral range. Moreover, the presented setup could be directly used for characterization of broadband pulses in the 1-5 m spectral range provided that a suitable high-resolution spectrometer is available making it a very simple and yet powerful diagnostic tool.