Abstract
Intracavity high harmonic generation (iHHG) has proven useful for generating frequency combs in the challenging-to-reach vacuum-ultraviolet (VUV) and extreme-ultraviolet (XUV) spectral regions [1,2]. These combs enable precision spectroscopy of key atomic and molecular transitions in the VUV and XUV through the conversion of high power near-infrared combs inside a passive femtosecond enhancement cavity (fsEC). The first demonstration of iHHG-based frequency comb spectroscopy in the XUV was demonstrated in 2012 [2], however, the use of a single comb restricts measurements to narrow, isolated, atomic transitions. To measure more complex spectra, for example from molecules or Rydberg states, single-comb spectroscopy is often not suitable. Dual-comb spectroscopy (DCS) can overcome these limitations by providing broad-bandwidth, high-resolution spectra with short acquisition times. DCS is a well-established technique in the IR and NIR, however, a straightforward extension to the VUV/XUV would require two separate enhancement cavities and has the additional complication of efficiently overlapping the two XUV beams. In this paper we show that we are able to couple two independent high power fs combs to a single fsEC to greatly simplify our approach towards DCS in the VUV/XUV by eliminating the second cavity and consequently the beam overlap problem. The system can also be configured to enable precise time-resolved measurements of extreme optical nonlinearities using a novel pump-probe technique. See Fig 1(b). This measurement is critical for better understanding intracavity ionization limitations as well as precisely characterizing relative phase shifts between pulse pairs for DCS.
© 2015 IEEE
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