Cover Picture: Laser Phys. Lett. 3/2012

Abstract

High-order harmonic generation is realized in a semi-infinite gas cell using a commercial, amplified Ti:Sapphire system operating at 5 kHz and delivering 30 fs pulses at 800 nm. A schematic of the experimental setup is shown in Cover Picture. Using an f = 100 cm focusing lens placed ≈97 cm from the pinhole, intensities of ≈1 × 10¹⁴ W/cm² are produced. The pulses are not CEP-stabilized, which is unproblematic because we are investigating the interference of quantum paths of the same half cycle [8]. The target chamber is filled with 75 mbar of argon and terminated by a 100 µm pinhole, causing an abrupt transition to vacuum. As shall be discussed below, this geometry does not favor either the long or the short quantum paths. In the analyzer chamber the generated XUV radiation is dispersed spectrally by a reflective flat-field grating (1000 lines/mm, Hitachi), positioned ≈1035 mm downstream from the pinhole, and impinges upon a micro-channel plate (MCP, Hamamatsu) with a fluorescent back screen. This signal is imaged onto a CCD camera, enabling us to resolve the harmonic radiation both in angle and frequency in the far field, i.e. in the (ω, θ) domain. (Cover picture: S.M. Teichmann, D.R. Austin, et al. pp. 207–211, in this issue) (© 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)