Attosecond Technology

Project overview

Contents

• Overview
• New technology
• New science
• New UK capability
• Training of young scientists

Overview

Fig. 1: Photograph of the few-cycle source.

The fundamental processes of chemistry, biology and material science are mediated by electronic and nuclear motions of the constituent atoms. The electronic motions inherent to these systems have attosecond time-scales (1 attosecond = 10^-18 sec) which are too fast to resolve with current technology.

This Basic Technology project aims to develop the technological tools to study electron motion in matter with both attosecond time-scale resolution and sub-Ångstrom spatial resolution. Underpinned by extreme-ultraviolet (EUV) light sources producing attosecond duration light pulses, these tools open the door not only for real-time observation but also time-domain control of electron dynamics on the atomic scale.

This project represents a set of front-line technological challenges in laser engineering, optical pulse diagnostics, extreme ultraviolet optics, molecular physics and energy/momentum resolved electron detection.

Our team comprising scientists from Imperial College London, University College London, the universities of Oxford, Reading Birmingham, and the Rutherford Appleton Laboratory (CCLRC) has brought together a range of expertise to tackle these challenges. As we have developed the technology, new science has followed, for example we have made the fastest ever measurement of molecular dynamics. The project has also succeeded in training more than a dozen doctoral students and fostering a new UK attosecond science community. It has also transferring new technology to the UK science base thereby increasing both the expertise and the capacity to do attosecond science in the UK.

Fig. 2: Pulsed gas valve with kHz repetition rate - designed and built inhouse.

Fig. 3: Vacuum compatible, piezo-actuacted delay stage for the focusing of XUV and IR beams.

New technology

Hollow-Fibre Pulse Compressor - see Fig. 1. We have developed an optical system that compresses high power (100GW) near IR femtosecond pulses to the “few-cycle” limit, i.e. to durations approaching 5 fs, with carrier-envelope phase stabilisation. These pulses- amongst the shortest, highest power pulses in the world - are used to generate attosecond EUV pulses via the process of High Harmonic Generation.

Novel pulsed-valve (Fig. 2) developed to deliver gas plumes to laser interaction experiments at kHz repetition rates and with high backing pressures.

“Jitter-free” EUV delay stage. This highly stable piezo-actuated two-part Mo/Si mirror allows optical and EUV (13nm) pulses to be precisely delayed with respect to each other (<50 attsecond resolution). This is used to measure the duration of attsoecond EUV pulses.

We developed a vibration isolation technology to allow optics in vacuum beamlines to be stabilised with interferometric stability relative to external optics. This is vital for attosecond resolution pump-probe experiments.

Fig. 5: Experimental measurements of half-cycle cut-offs in high harmonic generation on the cover of Nature Physics.

Fig. 4: BBC website coverage of an experiment undertaken as part of the Attosecond Technology project.

New science

Fastest ever view of molecular motion - Science, 312, p424, April 2006

New technique for measuring the “carrier-envelope phase” of ultrafast light pulses - Nature Physics 3, p62, Jan 2007

New capability

Attosecond beamline at Imperial College London. This state-of-the-art vacuum beamline is used for the generation, filtering, focusing and delivery of attosecond EUV and few-cycle near-IR pulses in pump-probe configuration to a range of experiments (e.g. molecular physics and surface science studies).

Our pulse compression technology has been transferred to the Astra laser (TA1) at RAL giving this user facility high-power 10fs capability.

Our beamline and laser systems technology as well as expertise is being transferred to the Astra-Artemis Project at RAL. Due to be completed in early 2009 this user-facility will provide few-cycle, carrier-envelope phase stablised pulses at a range of wavelength (including EUV) to user experiments. Attosecond capability is projected after a second phase of development.

Fig. 6: Part of the attosecond beamline at Imperial College London.

Fig. 7: Hollow fibre pulse compression facility at Rutherford Appleton Laboratories - technology transferred from Imperial College London.

Fig. 8: Schematic of the laboratory for the Artemis project at the Rutherford Appleton Laboratory.

Training of young scientists

Centred at Imperial College London, the project has connected a number of UK universities and institutes – in many cases creating new bridges between research areas and research groups.

PhD students connected with the project during a one-day symposium they organised in Dec 2005 at RAL. Training of researchers has been one of the most important outcomes of the project.

An international workshop was held in April 2006 as part of this Basic Technology project. Funded by EPSRC, the ESF and through commercial sponsorship it attracted more than 120 delegates from the UK and overseas, including twenty field-leading invited speakers. The workshop also provided an opportunity to showcase the UK attosecond project. Free registration was provided for all students.

Fig. 9: PhD students at a project meeting in 2005.

Fig. 10: Delegates attending the Ultrafast Dynamic Imaging Workshop, held at Imperial College London in 2006.