Submitted Paper

In-line spectral interferometry in infrared laser filaments in gasesPavel Polynkin

We discuss recent experiments and computer simulations on the propagation of intense ultrashort laser pulses at infrared wavelengths in air and argon. We conduct our experiments using two different laser sources. Our first source is a shortwave-infrared, two-cycle, carrier-envelope phase (CEP)-stable OPCPA at 1.7 um center wavelength. We observe the CEP-dependent interference between the third harmonic and the supercontinuum contributions to the white-light emission in the far field. Our second laser source is a CEP-unstable, femtosecond, mid-infrared OPCPA at 3.9 um center wavelength. In this case, multiple harmonics of the fundamental are detected in the visible and near-infrared. We present evidence for the CEP-dependent interferences in the harmonic spectra. The CEP-dependence of the generated white-light spectra may be used for inline, single-shot measurements of the CEP in CEP-unstable sources. This technique could enable experiments that require CEP control, by post-selecting the data and correlating it with the simultaneous inline CEP measurements.