The Petawatt beamline at the Vulcan laser facility is capable of delivering pulses with 500J of energy in <500fs, and has been operational as a user facility since 2003; being used to study laser matter interactions under extreme conditions. In addition to this short-pulse beamline there is a single long pulse beamline capable of 250J with durations from 0.5 to 6ns. In this paper we present our plans to add an auxiliary beamline to this facility based on Optical Parametric Chirped Pulse Amplification (OPCPA) using LBO as the non-linear crystal. This new beamline will have a dedicated laser area where the seed will be generated, stretched and amplified before being transported to the target area for compression and delivery to target. The beamline will be implemented in 2 phases the first phase will see the development of a 7J <30fs capability with the second phase increasing the delivered energy to 30J. This additional beamline will open up the potential for novel pump probe experiments when operated with the existing PW and long pulse beamlines.
We designed and produced optical coatings for broad bandwidth high reflection (BBHR) of femtosecond (fs) pulses for high energy petawatt (PW) lasers. These BBHR coatings consist of TiO2/SiO2 and/or HfO2/SiO2 layer pairs formed by reactive E-beam evaporation with ion-assisted deposition in Sandia’s Large Optics Coating Facility. Specifications for the HR band and center wavelength of the coatings are for 45° angle of incidence (AOI), P polarization (Ppol), with use of the coatings at different AOIs and in humid or dry/vacuum environments providing corresponding different HR center wavelengths and spectral widths. These coatings must provide high laserinduced damage threshold (LIDT) to handle the PW fluences, and also low group delay dispersion (GDD) to reflect fs pulses without distortion of their temporal profiles. We present results of LIDT and GDD measurements on these coatings. The LIDT tests are at 45° or 65° AOI, Ppol in a dry environment with 100 fs laser pulses of 800 nm line center for BBHR coatings whose HR band line centers are near 800 nm. A GDD measurement for one of the BBHR coatings whose design HR center wavelength is near 900 nm shows reasonably low and smoothly varying GDD over the HR band. Our investigations include BBHR coatings designed for 45° AOI, Ppol with HR bands centered at 800 nm in dry or vacuum environments, and featuring three options: all TiO2/SiO2 layer pairs; all HfO2/SiO2 layer pairs; and TiO2/SiO2 inner layer pairs with 5 outer HfO2/SiO2 layer pairs. LIDT tests of these coatings with 100 fs, 800 nm line center pulses in their use environment show that replacing a few outer TiO2 layers of TiO2/SiO2 BBHR coatings with HfO2 leads to ~ 80% higher LIDT with only minor loss of HR bandwidth.
We designed an optical coating based on TiO2/SiO2 layer pairs for broad bandwidth high reflection (BBHR) at 45-deg angle of incidence (AOI), P polarization of femtosecond (fs) laser pulses of 900-nm center wavelength, and produced the coatings in Sandia’s large optics coater by reactive, ion-assisted e-beam evaporation. This paper reports on laser-induced damage threshold (LIDT) tests of these coatings. The broad HR bands of BBHR coatings pose challenges to LIDT tests. An ideal test would be in a vacuum environment appropriate to a high energy, fs-pulse, petawatt-class laser, with pulses identical to its fs pulses. Short of this would be tests over portions of the HR band using nanosecond or sub-picosecond pulses produced by tunable lasers. Such tests could, e.g., sample 10-nm-wide wavelength intervals with center wavelengths tunable over the broad HR band. Alternatively, the coating’s HR band could be adjusted by means of wavelength shifts due to changing the AOI of the LIDT tests or due to the coating absorbing moisture under ambient conditions. We had LIDT tests performed on the BBHR coatings at selected AOIs to gain insight into their laser damage properties and analyze how the results of the different LIDT tests compare.
We have designed and produced an optical coating suitable for broad bandwidth high reflection (BBHR) at 45° angle of
incidence (AOI), P polarization (Ppol) of petawatt (PW) class fs laser pulses of ~ 900 nm center wavelength. We have
produced such BBHR coatings consisting of TiO2/SiO2 layer pairs deposited by ion assisted e-beam evaporation using
the large optics coater at Sandia National Laboratories. This paper focuses on laser-induced damage threshold (LIDT)
tests of these coatings. LIDT is difficult to measure for such coatings due to the broad range of wavelengths over which
they can operate. An ideal test would be in the vacuum environment of the fs-pulse PW use laser using fs pulses
identical to of the PW laser. Short of this ideal testing would be tests over portions of the HR band of the BBHR coating
using ns or sub-ps pulses produced by tunable lasers. Such tests could be over ~ 10 nm wide wavelength intervals whose
center wavelengths could be tuned over the BBHR coating’s operational band. Alternatively, the HR band of the BBHR
coating could be adjusted by means of wavelength shifts due to changing the AOI of the LIDT tests or due to absorbed
moisture by the coating under ambient conditions. We conduct LIDT tests on the BBHR coatings at selected AOIs to
gain insight into the coatings’ laser damage properties, and analyze how the results of the different LIDT tests compare.
KEYWORDS: Modeling, Mirrors, High power lasers, Point spread functions, Adaptive optics, Wavefronts, Motion models, Tolerancing, Off axis mirrors, Near field optics
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.
KEYWORDS: Optical amplifiers, Picosecond phenomena, Near field optics, Mirrors, Diagnostics, Near field, Silicates, Pulsed laser operation, Glasses, High power lasers
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.
O. Chekhlov, E. Divall, K. Ertel, S. Hawkes, C. Hooker, I. Ross, P. Matousek, C. Hernandez-Gomez, I. Musgrave, Y. Tang, T. Winstone, D. Neely, R. Clarke, P. Foster, S. Hancock, B. Wyborn, J. Collier
We describe two development projects: Astra-Gemini: a Petawatt class system based Ti: Sapphire amplifiers and a
10 PW upgrade for the Vulcan laser. The design concepts, features of the optical design of amplifiers and compressors
are presented. Radial delay compensation techniques used for a 3-x beam expander are discussed.
David Neely, Colin Danson, Ric Allott, F. Amiranoff, E. Clark, Chris Clayton, J. Collier, A. Dangor, A. Djaoui, Christopher Edwards, P. Flintoff, Daniel Gordon, P. Hatton, Mark Harman, M. Hutchinson, K. Krushelnick, G. Malka, Victor Malka, A. Modena, Z. Najmudin, David Pepler, Ian Ross, M. Salvati, M. Santala, M. Tatarakis, M. Trentelman, T. Winstone
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 beam's 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.
Colin Danson, Ric Allott, S. Angood, G. Booth, J. Collier, A. Damerell, Christopher Edwards, P. Flintoff, J. Govans, S. Hancock, P. Hatton, S. Hawkes, M. Hutchinson, Michael Key, C. Hernandez-Gomez, John Leach, W. Lester, David Neely, Peter Norreys, M. Notley, David Pepler, C. Reason, D. Rodkiss, Ian Ross, W. Toner, M. Trentelman, J. Walczak, R. Wellstood, T. Winstone, R. Wyatt, B. Wyborn
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.
Colin Danson, L. Barzanti, Christopher Edwards, S. Edwards, C. Harrison, C. Mistry, David Neely, Peter Norreys, David Pepler, D. Rodkiss, Ian Ross, W. Toner, T. Winstone, F. Walsh, R. Wyatt
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.
Christopher Edwards, L. Barzanti, Colin Danson, Michael Key, David Neely, Peter Norreys, David Pepler, W. Toner, F. Walsh, T. Winstone, Marcus Hutchinson, Ian Mercer, D. Wilson, F. Zhou
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.
Colin Danson, L. Barzanti, Chungu Zenghu, A. Damerell, Mike Dooley, Christopher Edwards, S. Hancock, Michael Key, R. Mahadeo, M. Miller, Peter Norreys, C. Ollman, David Pepler, D. Rodkiss, Ian Ross, M. Smith, P. Taday, W. Toner, K. Wigmore, T. Winstone, R. Wyatt, Shen Luan, F. Beg, Angus Bell, A. Dangor, Marcus Hutchinson, P. Lee, Ian Mercer, Roland Smith, F. Zhou, A. Fews
A Chirped Pulse Amplification (CPA) mode of operation is being developed on the VULCAN high power Nd:glass laser system, at the Rutherford Appleton Laboratory (RAL). Experiments have been carried out using an interim configuration yielding pulses of up to 30 J on target of 2.4 picoseconds length at focused intensities up to 4 X 1017 W cm-2, with contrast ratio of 106. In the CPA technique the amplification of a stretched pulse to high energy followed by recompression provides a means of delivering a higher peak power to target than can be propagated through the laser system due to non-linear effects and component damage thresholds. In the system described here a grating pair is used to stretch a transform limited pulse of 2 ps, to 80 ps prior to amplification to high energy (80 J). The linear stretch produced by the gratings enables the pulse to be recompressed without pedestal. Recompression to the 10 TW level by a second grating pair is carried out in a vacuum propagation and reflective focusing system to avoid non-linear effects in air, windows and lenses.
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