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Ferreiro T.I.,Scottish Universities Physics Alliance | Sun J.,Scottish Universities Physics Alliance | Reid D.T.,Scottish Universities Physics Alliance
Optics Express | Year: 2011

Carrier-envelope-offset (CEO) and pulse-repetition frequencies of a Ti:sapphire-pumped femtosecond optical parametric oscillator were locked to uncertainties of 0.09 Hz and 0.16 mHz respectively, with the CEO beat signal linewidth being stabilized to 15 Hz (instrument limited). In-loop phase-noise power spectral density measurements showed a contribution of our servo electronics to the comb-line frequency uncertainty of up to 110 Hz. Complementary time-series data implied an in-loop comb instability of 2 × 10-11 (1-s gate time), matching the Rb-stabilized reference used and verifying that dual servo-control of the CEO and repetition frequencies was effective in stabilizing the comb to at least this precision. © 2011 Optical Society of America.


Zhang Z.,Scottish Universities Physics Alliance | Gu C.,Scottish Universities Physics Alliance | Gu C.,Tianjin University | Sun J.,Scottish Universities Physics Alliance | And 3 more authors.
Optics Letters | Year: 2012

Two asynchronous, broadband 3.3 μm pulse trains with a stabilized repetition-rate difference of up to 5 kHz were generated using an ultrafast optical parametric oscillator. The two oscillation channels, each producing ∼100 mW average power, ran essentially independently, and weak non-phase-matched sum-frequency mixing between them provided a timing signal that indicated when the asynchronous pulses coincided. The system has immediate applications in incoherent asynchronous optical sampling and, with additional carrier-envelope-offset stabilization, could be applied to coherent dual-frequency-comb spectroscopy. © 2012 Optical Society of America.


Yelland E.A.,Scottish Universities Physics Alliance | Yelland E.A.,University of Edinburgh | Yelland E.A.,University of St. Andrews | Barraclough J.M.,University of St. Andrews | And 5 more authors.
Nature Physics | Year: 2011

The emergence of superconductivity at high magnetic fields in URhGe is regarded as a paradigm for new state formation approaching a quantum critical point. Until now, a divergence of the quasiparticle mass at the metamagnetic transition was considered essential for superconductivity to survive at magnetic fields above 30 T. Here we report the observation of quantum oscillations in URhGe revealing a tiny pocket of heavy quasiparticles that shrinks continuously with increasing magnetic field, and finally disappears at a topological Fermi surface transition close to or at the metamagnetic field. The quasiparticle mass decreases and remains finite, implying that the Fermi velocity vanishes due to the collapse of the Fermi wavevector. This offers a novel explanation for the re-emergence of superconductivity at extreme magnetic fields and makes URhGe the first proven example of a material where magnetic field-tuning of the Fermi surface, rather than quantum criticality alone, governs quantum phase formation. © 2011 Macmillan Publishers Limited. All rights reserved.


Reid D.T.,Scottish Universities Physics Alliance
Optics Express | Year: 2011

Ultrashort-pulse evolution inside a optical parametric oscillator is described by using a nonlinear-envelope-equation approach, eliminating the assumptions of fixed frequencies and a single χ(2) process associated with conventional solutions based on the three coupled-amplitude equations. By treating the interacting waves as a single propagating field, the experimentally-observed behaviors of singly and doubly-resonant OPOs are predicted across near-octave-spanning bandwidths, including situations where the nonlinear crystal provides simultaneous phasematching for multiple nonlinear processes. © 2011 Optical Society of America.


Zhang Z.,Scottish Universities Physics Alliance | Sun J.,Scottish Universities Physics Alliance | Gardiner T.,National Physical Laboratory United Kingdom | Reid D.T.,Scottish Universities Physics Alliance
Optics Express | Year: 2011

We report the generation of 200-nm-bandwidth mid-infrared pulses at 3.5-μm from an optical parametric oscillator incorporating a 25-mm MgO:PPLN crystal and synchronously-pumped by chirped pulses from a fiber-amplified Yb:KYW laser. A long nonlinear crystal permits efficient transfer of the pump bandwidth into the idler pulses, achieves exceptional passive stability and enables pumping using chirped pulses directly from a fiber-amplifier, avoiding the need to use lossy pulse-compression optics. © 2011 Optical Society of America.


Lamour T.P.,Scottish Universities Physics Alliance | Reid D.T.,Scottish Universities Physics Alliance
Optics Express | Year: 2011

Sub-250-fs pulses with energies of up to 650 nJ and peak powers up to 2.07 MW were generated from a cavity-dumped optical parametric oscillator, synchronously-pumped at 15.3 MHz with sub-400-fs pulses from an Yb:fiber laser. The average beam quality factor of the dumped output was M2 ∼1.2 and the total relative-intensity noise was 8 mdBc, making the system a promising candidate for ultrafast laser inscription of infrared materials. © 2011 Optical Society of America.


McMahon M.I.,Scottish Universities Physics Alliance | Ackland G.J.,Scottish Universities Physics Alliance
Nature Materials | Year: 2010

Ab initio calculations have shown that aluminum undergoes transition to a significant structure when it is subjected to extremely high pressures despite being a simple system. Quantum mechanical calculations reveal that aluminum is the simplest metal that undergoes a phase transition from hexagonal close-packed to body-centered cubic at 0.38 TPa. The use of aluminum as a standard in experiments makes predictions on its structure at extremely high densities critical. Researchers have addressed this issue by using the method of Ab Initio Random Structure Searching (AIRSS) to study the structure of aluminum at pressures of 10 TPa. They have predicted aluminum transforms to an open-packed incommensurate host-guest structure that is stable to above 8 TPa in place of the simple close-packed structures found at lower pressures. AIRSS has an advantage over methods that converge to a single optimum solution, as it can identify complex structures that are metastable at the calculated pressure.


Ivanistsev V.,Scottish Universities Physics Alliance | O'Connor S.,Scottish Universities Physics Alliance | Fedorov M.V.,Scottish Universities Physics Alliance
Electrochemistry Communications | Year: 2014

In this paper we present a unified view on charge-driven structural transitions in the electrical double layer in ionic liquids and summarise molecular-scale mechanisms of the ionic liquid structural response to the surface charge. © 2014 Elsevier B.V.


Borthakur S.,Johns Hopkins University | Heckman T.,Johns Hopkins University | Strickland D.,Johns Hopkins University | Wild V.,University of St. Andrews | And 2 more authors.
Astrophysical Journal | Year: 2013

We present a study exploring the impact of a starburst on the properties of the surrounding circumgalactic medium (CGM): gas located beyond the galaxy's stellar body and extending out to the virial radius (∼200 kpc). We obtained ultraviolet spectroscopic data from the Cosmic Origins Spectrograph (COS) probing the CGM of 20 low-redshift foreground galaxies using background QSOs. Our sample consists of starburst and control galaxies. The latter comprises normal star-forming and passive galaxies with similar stellar masses and impact parameters as the starbursts. We used optical spectra from the Sloan Digital Sky Survey to estimate the properties of the starbursts, inferring average ages of ∼200 Myr and burst fractions involving ∼10% of their stellar mass. The COS data reveal highly ionized gas traced by C IV in 80%(4/5) of the starburst and in 17%(2/12) of the control sample. The two control galaxies with C IV absorbers differed from the four starbursts in showing multiple low-ionization transitions and strong saturated Lyα lines. They therefore appear to be physically different systems. We show that the C IV absorbers in the starburst CGM represent a significant baryon repository. The high detection rate of this highly ionized material in the starbursts suggests that starburst-driven winds can affect the CGM out to radii as large as 200 kpc. This is plausible given the inferred properties of the starbursts and the known properties of starburst-driven winds. This would represent the first direct observational evidence of local starbursts impacting the bulk of their gaseous halos, and as such provides new evidence of the importance of this kind of feedback in the evolution of galaxies. © 2013. The American Astronomical Society. All rights reserved.


Grant
Agency: GTR | Branch: EPSRC | Program: | Phase: Training Grant | Award Amount: 3.99M | Year: 2014

The Scottish Doctoral Training Centre in Condensed Matter Physics, known as the CM-DTC, is an EPSRC-funded Centre for Doctoral Training (CDT) addressing the broad field of Condensed Matter Physics (CMP). CMP is a core discipline that underpins many other areas of science, and is one of the Priority Areas for this CDT call. Renewal funding for the CM-DTC will allow five more annual cohorts of PhD students to be recruited, trained and released onto the market. They will be highly educated professionals with a knowledge of the field, in depth and in breadth, that will equip them for future leadership in a variety of academic and industrial careers. Condensed Matter Physics research impacts on many other fields of science including engineering, biophysics, photonics, chemistry, and materials science. It is a significant engine for innovation and drives new technologies. Recent examples include the use of liquid crystals for displays including flat-screen and 3D television, and the use of solid-state or polymeric LEDs for power-saving high-illumination lighting systems. Future examples may involve harnessing the potential of graphene (the worlds thinnest and strongest sheet-like material), or the creation of exotic low-temperature materials whose properties may enable the design of radically new types of (quantum) computer with which to solve some of the hardest problems of mathematics. The UKs continued ability to deliver transformative technologies of this character requires highly trained CMP researchers such as those the Centre will produce. The proposed training approach is built on a strong framework of taught lecture courses, with core components and a wide choice of electives. This spans the first two years so that PhD research begins alongside the coursework from the outset. It is complemented by hands-on training in areas such as computer-intensive physics and instrument building (including workshop skills and 3D printing). Some lecture courses are delivered in residential schools but most are videoconferenced live, using the well-established infrastructure of SUPA (the Scottish Universities Physics Alliance). Students meet face to face frequently, often for more than one day, at cohort-building events that emphasise teamwork in science, outreach, transferable skills and careers training. National demand for our graduates is demonstrated by the large number of companies and organisations who have chosen to be formally affiliated with our CDT as Industrial Associates. The range of sectors spanned by these Associates is notable. Some, such as e2v and Oxford Instruments, are scientific consultancies and manufacturers of scientific equipment, whom one would expect to be among our core stakeholders. Less obviously, the list also represents scientific publishers, software houses, companies small and large from the energy sector, large multinationals such as Solvay-Rhodia and Siemens, and finance and patent law firms. This demonstrates a key attraction of our graduates: their high levels of core skills, and a hands-on approach to problem solving. These impart a discipline-hopping ability which more focussed training for specific sectors can complement, but not replace. This breadth is prized by employers in a fast-changing environment where years of vocational training can sometimes be undermined very rapidly by unexpected innovation in an apparently unrelated sector. As the UK builds its technological future by funding new CDTs across a range of priority areas, it is vital to include some that focus on core discipline skills, specifically Condensed Matter Physics, rather than the interdisciplinary or semi-vocational training that features in many other CDTs. As well as complementing those important activities today, our highly trained PhD graduates will be equipped to lay the foundations for the research fields (and perhaps some of the industrial sectors) of tomorrow.

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