Abstract

We report observations and analysis of high harmonic generation driven by a superposition of fields at 1290 nm and 780 nm. These fields are not commensurate in frequency, as in previous experiments such as Ref. [1], and the superposition leads to an increase in the yield of the mid-plateau harmonics of more than two orders of magnitude compared to using the 1290 nm field alone. Significant extension of the cut-off photon energy is seen even by adding only a small amount of the 780 nm field. Fig. 1 plots the observed yield enhancements against harmonic energy and scanned over the temporal delay between the peaks of the two pulse envelopes. The figure shows two different intensity ratios, as stated in the caption. In both cases yield enhancement of up to two orders of magnitude is seen below 40 eV, together with smaller enhancements up to 80 eV, the limit of the MCP detector. This is a promising route to provide a greater photon number in attosecond pulse production [2], for applications in XUV imaging and time-resolved experiments [3].

© 2011 Optical Society of America