T. B. Winstone

The Vulcan 10 PW project

The aim of this project is to establish a 10 PW facility on the Vulcan laser system capable of being focussed to intensities of at least 1023 Wcm−2 and integrate this into a flexible and unique user facility This paper will present progress made in Phase one developing the 10PW Front End as well as the concept for the new Vulcan 10 PW facility. The new facility will be configured in a unique way to maximise the scientific opportunities presented through a combination with the existing capabilities already established on Vulcan. This ground breaking development will open up a range of new scientific opportunities.

Recent developments on the Vulcan High Power Laser Facility

We present details of a refurbishment and development programme that we have undertaken on the Vulcan Nd:Glass laser system to improve delivery to its two target areas. For target area petawatt in addition to replacing the gratings in the compressor chamber we have installed a new diagnostic line for improved pulse length measurement and commissioned a high energy seed system to improve contrast. In target area west we have replaced a grating on the high energy short pulse line and improved the focal spot quality. Both areas have been re-commissioned and their laser parameters measured showing that the pulse in petawatt has been measured below 500fs and focused to a spot size of 4μm the two short pulse beam lines in target area west have been measured as short as 1ps and have been focused to 5μm.

The 10 PW OPCPA Vulcan laser upgrade

We present the progress that has been made in developing 10PW capability for the Vulcan laser. These pulses will have focused intensities ≫1023 Wcm−2, which represents orders of magnitude increases in intensity currently available. This will be achieved by generating pulses with energies greater than 300J and with durations less than 30fs using the technique of optical parametric chirped pulse amplification, OPCPA [1].

Central Laser Facility High Power Laser Capabilities Applied to X-Ray Laser Science

Soft X-ray lasers have been developed at the Central Laser Facility (CLF) of the Science and Technology Facilities Council over the last three decades by an active UK and international research community. The Vulcan Nd:glass Laser has been the primary drive system for these developments, providing pump pulses from nano- to pico- seconds, firing one shot every 20 minutes. An upgraded Vulcan facility is due to come on line in September 2008 with dual pico-second high energy beam lines (1 ps, 100 J and 10 ps, 500 J) combined with long pulse (80 ps, 40 J — 4 ns, 300 J) capability. Recent developments in laser technology have meant that the CLF has increased its ultra short pulse capabilities. The Ti:Sapphire Astra-Gemini laser facility, which came on-line in early 2008, gives 20 second shot turnaround times and ultra short pulses (30fs, 15J). The new opportunities which these drive systems enable for soft x-ray laser science, source development and applications will be presented.

Pulse generation and shaping using the ultra-high power laser system -- VULCAN

VULCAN is a multi-beam, multi-terawatt laser facility based on Nd:glass operating at 1053 nm. The system is highly versatile, supplying four experimental areas with laser radiation at a range of pulse durations from 700 fs to 20 ns, at fundamental frequency, frequency doubled, or, as a limited option, frequency tripled wavelengths. Beams are available in a number of geometries dictated by the university based programs, which at present include: cluster; line focus including x-ray laser oscillator/amplifier geometry; backlighting; probing; and chirped pulse amplification (CPA) configurations. The system has eight beams which can deliver synchronized long and short pulses including two beams which can deliver subpicosecond CPA pulses. The CPA capabilities on VULCAN are an integral part of the laser system, not only delivering sub-picosecond pulses, but allowing uncompressed pulses and multi-pulses to be delivered to the target areas synchronized with the nanosecond pulses. This paper describes the system configuration, details the means of pulse synchronization and presents some of the pulse manipulation techniques used on VULCAN to provide the laser requirements for the experimental program.

High-power laser parabola focus modelling at the Central Laser Facility

For many years parabolic mirrors have been used as the primary focusing optics of short pulse high power lasers. Pushing the boundaries of the highest focused intensities requires not only increases in peak laser power but also exploring the limits of focal spot size. Modelling has been performed at the Central Laser Facility to evaluate the performance and tolerance of the alignment of a variety of off-axis parabolic mirrors and their limitations in correcting beam aberrations. Practical considerations such as debris shields and optic mounting have also been assessed for their effects on the focal spots.

Focused intensities of 1020 Wcm-2 with the upgraded Vulcan CPA interaction facility

There has been considerable interest in the last 10 years in the physics of ultra-high power laser interactions. With all high power lasers such as Vulcan there is a limit to the energy that can be extracted from laser amplifiers at short pulse-lengths due to the intensity dependent non-linear refractive index. The technique of Chirped Pulse Amplification has overcome the classic limit and has resulted in massive increases in focused intensity. The large increase in on target intensity is achieved by a substantial, usually orders of magnitude, reduction in pulse duration while at the same time maintaining comparable pulse energy and focusability.

Multi-terawatt frequency doubling of picosecond pulses for plasma interactions

Frequency doubling a large aperture sub ps, chirped pulse amplified (CPA) 1053 nm beam for laser matter interaction studies was investigated at the Central Laser Facility. Efficiencies > 50 percent were achieved using a 4 mm thick KDP crystal to convert a 140 X 89 mm 700 fs beam. Measurements of the 527 nm beams focal spot quality when the doubling crystal was driven at high intensities 200 GWcm-2 are presented. Using data from 2 and 4 m thick 25 mm diameter test crystals, the optimum crystal thickness in terms of conversion efficiency is reviewed for 1053 nm CPA systems in the 0.3-3 ps region and options for fourth harmonic production discussed.

Characterisation of Large Aperture Frequency Doubled Picosecond Pulses

A single molecule in a ctystal matrix is a very good example of an electronic two-level system [ l ] . We illustrate some well-known and some less usual effects of the interaction between an electronic two-level and a laser field with a new system, dibenz-anthanthrene in a naphthalene crystal (21. We studied the optical Saturation of the molecule, and the bunching of fiuorescence photons due to a metastabie triplet manifold, in which we could resolve two triplet sublevels. The triplet population rates and triplet lifetimes are so low that the bottleneck effect of the triplet may be neglected, We also observed variations of the single molecule radiative linewidths, which we attribute to spontaneous emission modifications by surface effects [2]. Pump-probe experiments were also performed on this System with near-resonanl fields. We observed the iight-shift of the transition, with strong deviations from the well-known perturbative expression when the pump is close to resonance. The hyper. Raman resonance corresponds to the absorption of two pump photons and to the emission of a probe photon by stimulated emission, It would appear as an amplification of the probe beam, bul we detect it by an increase in excited state population. Multiphotonic sub-harmonic oscillations also appear for strong pump and probe beams. These oscillations are related to a kicked-oscillator dynamics of the Bloch vector in the total laser field resulting of the beating of pump and probe beams [2]. We performed further experiments by applying an RF field to the single molecule in the laser field. Because the dipole moments in the ground and excited states are different, the RF interacts with the nutating Bloch vector, leading lo so-called Rabi resonances, which can be simply intiipreted in the dressed molecule picture.

Optimization of system design and performance to generate >10 20 Wcm -2

We report focused intensities of > 1019 Wcm-2, with subpicosecond operation of the VULCAN Nd:glass laser at the Rutherford Appleton Laboratory using chirped pulse amplification (CPA) techniques. This paper describes novel aspects of the system including: picosecond and subpicosecond diode pumped oscillators; the use of a regenerative amplifier and system optimization. The ultrashort pulse generated from an additive pulse modelocked LMA oscillator was stretched from 0.5 ps to approximately 200 ps in a double pass grating system and amplified from 1 nJ to 50 J, in phosphate glass amplifiers with a final beam aperture of 150 mm diameter. The stretched pulse was recompressed using a pair of gratings (300 X 150 mm, 1740 lines per mm) and focused using an off-axis parabola to avoid nonlinear effects from transmissive optics. The compressed pulse was monitored using a suite of diagnostics to determine the focusability, pulsewidth, and spectrum. We also describe the current system development program, which is in progress and designed to achieve intensities of approximately 1020 Wcm-2 to target.