Laboratory of Ultrafast Physics and Optics

Welcome to the Laboratory of Ultrafast Physics and Optics @ Heriot-Watt Univeristy (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, and producing ultrafast electric field waveforms called optical attosecond pulses (pulses shorter than one million billionth of a second in the visible and ultraviolet).

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 glass waveguides (such as photonic crystal fibres and capillaries) filled with gases, liquids, and plasmas.

With these light sources we investigate the fundamental physics of nonlinear optics, new ways of driving strong-field physics (such as high-harmonic generation and the creation and evolution of plasma) and advanced spectroscopy.

Projects

What we are working on

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

Meet the LUPO team

Principal Investigator

Avatar

Dr. John C. Travers

Associate Professor of Physics

Research Associates

Avatar

Dr. Federico Belli

Research Associate

Avatar

Dr. Christian Brahms

Research Associate

PhD Students

Avatar

Teodora F. Grigorova

PhD Student

Avatar

Athanasios Lekosiotis

PhD Student

Avatar

Mohammed Sabbah

PhD Student

Recent & Upcoming Talks

We demonstrate soliton self-compression and VUV dispersive-wave emission in argon- and krypton-filled hollow capillary fibre. We …

We demonstrate time-resolved photoelectron velocity-map imaging using tunable DUV pulses generated through resonant dispersive-wave …

We demonstrate that by using short (5-7 fs) driving pulses, optical soliton dynamics can be obtained in hollow capillary fibres less …

We demonstrate soliton self-compression of 0.3 mJ pulses to 2.7 fs in a 3 m long gas-filled hollow capillary fibre. Scaling to higher …

Optical soliton dynamics in a waveguide can cause the extreme alteration of the temporal and spectral shape of a propagating light …

Recent Publications

You can filter our full list of publications here.

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 the extreme alteration of the temporal and spectral shape of a propagating light pulse. They occur at up to kilowatt peak powers in glass-core optical fibres and 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-mJ 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.

We demonstrate, for the first time, the application of rare-gas-filled hollow-core photonic crystal fibers (HC-PCFs) as tunable ultraviolet light sources in femtosecond pump–probe spectroscopy. A critical requirement here is excellent output stability over extended periods of data acquisition, and we show this can be readily achieved. The time-resolved photoelectron imaging technique reveals nonadiabatic dynamical processes operating on three distinct time scales in the styrene molecule following excitation over the 242–258 nm region. These include ultrafast (<100 fs) internal conversion between the S2(ππ) and S1(ππ) electronic states and subsequent intramolecular vibrational energy redistribution within S1(ππ*). Compact, cost-effective, and highly efficient benchtop HC-PCF sources have huge potential to open up many exciting new avenues for ultrafast spectroscopy in the ultraviolet and vacuum ultraviolet spectral regions. We anticipate that our initial validation of this approach will generate important impetus in this area.

We present the results of an experimental and numerical investigation into temporally nonlocal coherent interactions between ultrashort pulses, mediated by Raman coherence, in a gas-filled kagome-style hollow-core photonic-crystal fiber. A pump pulse first sets up the Raman coherence, creating a refractive index spatiotemporal grating in the gas that travels at the group velocity of the pump pulse. Varying the arrival time of a second, probe, pulse allows a high degree of control over its evolution as it propagates along the fiber through the grating. Of particular interest are soliton-driven effects such as self-compression and dispersive wave (DW) emission. In the experiments reported, a DW is emitted at ~300 nm and exhibits a wiggling effect, with its central frequency oscillating periodically with pump-probe delay. The results demonstrate that a strong Raman coherence, created in a broadband guiding gas-filled kagome photonic-crystal fiber, can be used to control the nonlinear dynamics of ultrashort probe pulses, even in difficult-to-access spectral regions such as the deep and vacuum ultraviolet.

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 up to 1.4 mJ at idler wavelengths up to 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!

We do not currently have any open positions. We are always interested to hear from candidates proposing fellowship applications based at the LUPO laboratorties.

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.

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, please send an email to John Travers, explaining why.

Contact