High harmonic emission from a superposition of multiple unrelated frequency fields

• Published in: Optics express 2010-03, Vol.18 (7), p.6853-6862
• Main Authors: Siegel, T, Torres, R, Hoffmann, D J, Brugnera, L, Procino, I, Zaïr, A, Underwood, Jonathan G, Springate, E, Turcu, I C E, Chipperfield, L E, Marangos, J P
• Format: Article
• Language: English
• Subjects: Aluminum Oxide - chemistry; Electromagnetic Fields; Electrons; Equipment Design; Ions; Lasers; Nonlinear Dynamics; Normal Distribution; Optics and Photonics; Photons; Physics - methods; Titanium - chemistry
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.18.006853

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 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. These observations are explained by calculations performed in the strong field approximation. Most importantly we find that enhancement is found to arise as a consequence of both increased ionization in the sum-field and modification of the electron trajectories leading to an earlier return time. The enhanced yield even when using modest intensity fields of 5 x 10(13) Wcm(-2) is extended to the 80 eV range and is a promising route to provide a greater photon number for applications in XUV imaging and time-resolved experiments at a high repetition rate.