Laboratory of Ultrafast Physics and Optics

Welcome to the Laboratory of Ultrafast Physics and Optics @ Heriot-Watt University (LUPO).

We use nonlinear optics to create new light sources with tailored, and extreme, spectral and temporal properties.

Examples include the generation of high energy single-cycle pulses in both the ultraviolet (especially the vacuum region), and the mid-infrared, new techniques for broadband white-light supercontinuum generation, the production of ultrafast electric field waveforms called optical attosecond pulses (pulses shorter than one million billionth of a second in the visible and ultraviolet), and the design and construction of high-energy few-cycle ultrafast fibre lasers.

Our work is a symbiotic mix of experimentation and numerical modelling. We make use of nature’s full landscape of materials, laser beam geometries and nonlinear effects, but our favourite system is hollow waveguides (such as photonic crystal fibres and capillaries) filled with gases, liquids, and plasmas.

We use these light sources for both fundamental science (such as the physics of nonlinear optics, ultrafast light-gas interactions, new ways of driving strong-field physics, advanced spectroscopy), and for applications in healthcare, advanced manufacturing and the semiconductor industry.

Projects

High-energy soliton dynamics in hollow capillary fibres for self-compression and deep and vacuum ultraviolet generation

Time-resolved photoelectron imaging of molecular dynamics with our deep and vacuum ultraviolet pulse sources

Nonlinear optics in gas-filled microstructured optical fibres

New techniques for the characterization and application of ultrafast optical pulses

We develop a world-leading nonlinear pulse propagation code

People

Principal Investigator

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Prof. John C. Travers

Professor of Physics

Research Associates

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Dr. Federico Belli

Research Associate

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Dr. Christian Brahms

Research Associate

PhD Students

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Teodora F. Grigorova

PhD Student

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Athanasios Lekosiotis

PhD Student

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Mohammed Sabbah

PhD Student

Recent & Upcoming Talks

Optical soliton dynamics can cause extreme alteration of the temporal and spectral shape of a propagating light pulse. Recently we have …

We experimentally investigate the different regimes of optical nonlinear dynamics that can be accessed in hollow capillary fibres by …

We report a remarkably efficient experimental scheme for the generation of high energy ultra-short pulses by means of four-wave mixing …

Recent Publications

You can filter our full list of publications here.

We demonstrate a spectral broadening and compression setup for carrier-envelope phase (CEP) stable sub-10-fs Ti:sapphire oscillator pulses resulting in 3.9 fs pulses spectrally centered at 780 nm. Pulses from the oscillator with 2 nJ energy are launched into a 1 mm long all-normal dispersive solid-core photonic crystal fiber and spectrally broadened to more than one octave. Subsequent pulse compression is achieved with a phase-only 4f pulse shaper. Second harmonic frequency resolved optical gating with a ptychographic reconstruction algorithm is used to obtain the spectral phase, which is fed back as a phase mask to the shaper display for pulse compression. The compressed pulses are CEP stable with a long term standard deviation of 0.23 rad for the CEP noise and 0.32 rad for the integrated rms phase jitter. The high total throughput of 15% results in a remaining pulse energy of about 300 pJ at 80 MHz repetition rate. With these parameters and the ability to tailor the spectral phase, the system is well suited for waveform sensitive photoemission experiments with needle tips or nanostructures and can be easily adapted to other sub-10 fs ultra-broadband Ti:sapphire oscillators.

We report on a highly-efficient experimental scheme for the generation of deep-ultraviolet ultrashort light pulses using four-wave mixing in gas-filled kagomé-style photonic crystal fiber. By pumping with ultrashort, few μJ, pulses centered at 400 nm, we generate an idler pulse at 266 nm, and amplify a seeded signal at 800 nm. We achieve remarkably high pump-to-idler energy conversion efficiencies of up to 38%. Although the pump and seed pulse durations are ~100 fs, the generated ultraviolet spectral bandwidths support sub-15 fs pulses. These can be further extended to support few-cycle pulses. Four-wave mixing in gas-filled hollow-core fibres can be scaled to high average powers and different spectral regions such as the vacuum ultraviolet (100-200 nm).

We demonstrate high-energy resonant dispersive-wave emission in the deep ultraviolet (218 to 375 nm) from optical solitons in short (15 to 34cm) hollow capillary fibres. This down-scaling in length compared to previous results in capillaries is achieved by using small core diameters (100 and 150 μm) and pumping with 6.3 fs pulses at 800 nm. We generate pulses with energies of 4 to 6 μJ across the deep ultraviolet in a 100 μm capillary and up to 11 μJ in a 150 μm capillary. From comparisons to simulations we estimate the ultraviolet pulse to be 2 to 2.5 fs in duration. We also numerically study the influence of pump duration on the bandwidth of the dispersive wave.

Optical soliton dynamics can cause extreme alteration of the temporal and spectral shape of a propagating light pulse. This occurs at up to kilowatt peak powers in glass-core optical fibres and at the gigawatt level in gas-filled microstructured hollow-core fibres. Here, we demonstrate optical soliton dynamics in large-core hollow capillary fibres. This enables scaling of soliton effects by several orders of magnitude to the multi-millijoule energy and terawatt peak power level. We experimentally demonstrate two key soliton effects. First, we observe self-compression to sub-cycle pulses and infer the creation of sub-femtosecond field waveforms—a route to high-power optical attosecond pulse generation. Second, we efficiently generate continuously tunable high-energy (1–16 μJ) pulses in the vacuum and deep ultraviolet (110 nm to 400 nm) through resonant dispersive-wave emission. These results promise to be the foundation of a new generation of table-top light sources for ultrafast strong-field physics and advanced spectroscopy.

Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherent and broadband radiation, but so far the generation of few-femtosecond pulses using this technique has not been demonstrated. Using in-vacuum frequency-resolved optical gating, we directly characterize tuneable 3 fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses.

Experimental Facilities

LUPO is currently based in one large ultrafast optics laboratory, with a second laboratory for high average power and repetition rate experiments under construction.

We have a single 10 m long vibration isolated optical table.

Our primary laser source is a commercial ti:sapphire oscillator, regenerative amplifier and single-pass amplifier chain (Coherent Legend Elite Duo USX) producing 8.5 mJ, 26 fs, 800 nm pulses at 1 kHz repetition rate.

This can be fed into a TOPAS optical parametric amplifier (Light Conversion) producing 25 fs pulses with up to 1.4 mJ at idler wavelengths as long as 2500 nm.

Our experimental philosophy tends towards building our own devices and systems rather than buying commerical products. Some examples of instrumentation we have built include:

  • State of the art FROG and XFROG devices, including SHG, SFG and SD devices covering the UV to infrared, and a ptychographic PG-FROG capable of simultaneous mesaurement from the deep UV (200 nm) to infrared (the broadest spectral bandwidth ever achieved)
  • A vacuum ultraviolet spectrometer covering from 50 nm to 800 nm, which can be operated in a fully calibrated mode to retreive VUV pulse energies
  • A UV (180 nm) to mid-infrared (10 μm) scanning spectrometer
  • A pulse compression system, providing sub 5 fs pulses at over 1 mJ pulse energy
  • Stretched hollow capillary fiber setups with over 4 m capillary lengths
  • High pressure gas cells and hollow fibre setups which can work up to 150 atmospheres, or at high-vacuum
  • Active laser beam stabilization system
  • Vacuum beam-lines for characterisation and application experiments
  • Pump-probe delay lines for two colour experiments, along with high energy SHG and THG setups

Join Us!

Our work is based at the Heriot-Watt campus just outside the wonderful city of Edinburgh, and close to the beautiful nature, horrible history and terrible weather of Scotland.

For an idea of the research directions we are heading in, please see our project pages.

PhD scholarships

We currently have two exciting PhD scholarships for research on the next generation of advanced table-top light sources. As a PhD student you’ll make use of nonlinear optics in gas-filled hollow-core fibres to create unique light sources for fundamental science, healthcare, advanced manufacturing and the semiconductor industry. Topics available include ultrafast light-gas interactions, broadband white-light supercontinuum generation, ultrafast high-power deep-ultraviolet sources, and the design and construction of high-energy few-cycle ultrafast fibre lasers. These projects span both fundamental physics through to device engineering, and can be tailored to your specific interests and abilities. Please contact us for more information.

Post-doc positions

We do not currently have any open post-doc positions, but this is very likely to change in the next few months. We are always interested to hear from candidates proposing fellowship applications based at the LUPO laboratories.

What will you be doing?

All positions require candidates to work extensively both as experimentalists in the lab, and on numerical codes to model our experiments.

Experimental work will involve:

  • Performing and creating rigorous and systematic experiments to explore new physical phenomena
  • Working with ultrafast optical setups, including pulse compression, synthesis and measurement
  • Tuning and maintaining high energy ultrafast oscillator, amplifier and parametric amplifier systems
  • Developing and constructing a high-pressure gas to high-vacuum laser beam-line for infrared, vacuum and extreme ultraviolet experiments
  • Building optical characterization devices such as Mid-IR, VUV and EUV spectrometers, and pulse measurement devices such as FROGs. Including the development of new pulse characterization techniques in the VUV region
  • Programming instrument control and data acquisition systems (in python)
  • Working with electronic and mechanical engineers and CAD models

Our experimental philosophy tends towards building our own devices and systems rather than buying commerical products. This ensures we have greater technical expertise and that our experiments do exactly what we want.

Numerical work will involve:

  • Running existing simulation codes and processing their results
  • Helping to develop new models and algorithms to simulate pulse propagation, the material response, and other aspects of our experiments
  • Coding in Julia, python, C++ and Fortran (don’t worry, mostly Julia and python)

Requirements

You will be expected to:

  • Have a good command of English
  • Write excellent papers
  • Be eager and good at presenting your results at international scientific conferences around the world
  • Be willing to work in collaborations at other laboratories
  • Have a good sense of fun and a healthy perspective on life

PhD candidates must have:

  • An excellent academic performance record from a good scientific institution
  • A proven interest in our field of research
  • Hands-on experience with any of the above experimental skills will be a major advantage
  • The will to learn, work hard, be creative and have fun!

Postdoctoral candidates must have all of the PhD requirements, but also:

  • Evidence of producing excellent experimental work in an optical laboratory
  • A proven record in multiple of the above mentioned skills and techniques
  • A clear explanation of why they want to join our group and the scientific direction they are heading

If you are interested, then please contact us, explaining why.

Consulting

We are happy to provide consultancy services.

Gas-filled hollow fibre systems

We offer the design and installation of gas-filled hollow fibre setups for pulse compression, spectral broadening and frequency conversion, including to the vacuum and deep ultraviolet. This includes systems based on our HISOL concept using stretched hollow capillary fibres, and also systems based on hollow-core microstructured fibres.

Modelling of light propagation in optical fibres

Modelling of light propagation in hollow fibres with our unique software. This work can include, for example: the design and optimization of a multitude of frequency conversion and supercontinuum generation schemes in optical fibres, including conventional photonic crystal fibre and gas-filled optical fibres; optimization of spectral flatness, noise instabilities, and polarization evolution in supercontinuum systems; parameter region optimization (i.e. reducing sensitivity to pump pulse and environmental conditions).

Instrumentation

Design and construction of our specialised instruments, such as state of the art FROG and XFROG devices, including SHG, SFG and SD devices covering the UV to infrared.

Please contact us for more information.

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