HIGH-ENERGY, FEW-CYCLE LASER BEAMLINE FOR RELATIVISTIC INTERACTION WITH ALIGNED NANOSTRUCTURES

Abstract

Ultra-high intensity lasers have been used to produce a variety of sources of intense radiation and energetic particles through the irradiation of nanostructured targets, including high-brightness x-ray sources, energetic collimated sources of ion and electron beams, and quasi-monoenergetic pulses of neutrons. However, these experiments have been constrained to the use of multi-cycle laser pulse drivers with duration of 30-50 fs or longer. This work presents results from the development and commissioning of a new relativistic-intensity laser beamline for solid target interaction experiments with pulses in the few-cycle regime. Application of these laser pulses to nanostructured targets will produce a unique and mostly unexplored plasma regime in which the driving pulse duration is shorter than the time scale of ion motions. The scaling of few-cycle pulse compression to the multi-terawatt regime is demonstrated here by the performance of a laser beamline based on the spectral broadening of Ti:sapphire pulses in a large-bore hollow-capillary fiber and subsequent recompression. The millimeter fiber waveguide presents a unique geometry for spectral broadening in the Ti:sapphire spectral range that results in an exceptionally high energy throughput and its performance has been characterized over a wide range of gas pressure conditions. The compressed output pulses of 15 mJ energy and 6.9 fs duration set a new record for the peak power of post-compressed pulses in the <10 fs regime. A new reverse pressure gradient operation mode has been introduced and applied to allow for operation of the hollow-capillary fiber beyond the usual peak power limit set by the onset of self focusing. The output of the beamline has been focused to a relativistic intensity of 6.5  1018 W/cm2 and relativistic electrons have been accelerated by the irradiation of solid flat and nanostructured targets and characterized by a custom-built magnetic spectrometer. This beamline will allow for relativistic laser-matter interactions with nanostructured targets in a new and unexplored few-cycle pulse duration regime.