High-peak-power surface high-harmonic generation at extreme ultra-violet wavelengths from a tape

Abstract

Solid-based surface high-harmonic generation from a tape is experimentally studied. By operating at mildly relativistic normalized laser strengths a 0 Շ 0:2, harmonics up to the 17th order are efficiently produced in the coherent wake emission (CWE) regime. CWE pulse properties, such as divergence, energy, conversion efficiency, and spectrum, are investigated for various tape materials and drive laser conditions. A clear correlation between surface roughness and harmonic beam divergence is found. At the measured pulse properties for the 15th harmonic (conversion efficiency $6:5 Â 10 À7 , divergence $7 À 15 mrad), the 100-mJ-level drive laser produces several MWs of extreme ultra-violet pulses. The spooling tape configuration enables multi-Hz operation over thousands of shots, making this source attractive as a seed to the few-Hz laser-plasma-accelerator-driven free-electron laser (FEL). Models indicate that these CWE pulses with MW level powers are sufficient for seed-induced bunching and FEL gain. V C 2013 AIP Publishing LLC. [http://dx.

Megawatt level surface high-harmonic generation from thin, replenishing, solid tapes

“…The affect the surface roughness plays on the divergence of the harmonic signal is explored in greater detail in Ref. [8].…”

“…Here we present a novel solid target configuration based on a tape [8,9], allowing for hundreds of meters (5 mm between successive shots) of solid target to be spooled through the laser focus, allowing for over 10 5 shots on target before needing to change tape. Such a source could be applied to seeding an FEL.…”

Staged acceleration experiments

“…This PM [12] has a laser energy throughput of 80%, no laser mode or pointing degradations, and has been fully characterized and improved to provide uninterrupted operation at a repetition rate of 1 Hz for hours of run time. Its long term stability was demonstrated in a multi-week experimental campaign on High-Harmonic Generation from a tape [13,14]. In order to minimize the chance of damaging the second stage target, the PM was equipped with an active feedback system.…”

Spectral characterization of laser-driven solid-based high harmonics in the coherent wake emission regime

“…For the studies presented in this paper, as well as for our proposed free-electron laser (FEL) seeding application [4], the CWE regime was chosen due to its high conversion efficiency and stable source characteristics arising from the quasi-linear laser scaling [7,15]. The CWE-based SHHG pulses can be described as a sequence of individual attopulses, each separated by approximately one laser period.…”

“…On the other hand, surface HHG (SHHG) relies on the interaction of the laser with a high-density (overcritical) plasma, such that the target acts as a mirror with accompanying XUV emission from its surface. SHHG has been demonstrated to produce megawatt-level pulses (within an individual harmonic) in relatively compact >100 mJ laser configurations [3,4]. With target replenishing systems such as rotating mirrors [3,5] or spooling tapes [4] to mitigate single-shot target destruction, an important hurdle to SHHG-based high-power applications has been overcome.…”