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

We demonstrate the generation of sub-cycle pulses in the infrared (1340 nm) with a peak power of 27 GW using soliton self-compression. …

By exploiting soliton dynamics in gas-filled hollow capillary fibres, we generate tuneable few-femtosecond pulses from the vacuum …

Soliton dynamics in large-core gas-filled hollow capillary fibres can create high-energy sub-femtosecond and few-femtosecond pulses …

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

Recent Publications

You can filter our full list of publications here.

Infrared femtosecond laser pulses are important tools both in strong-field physics, driving x-ray high-harmonic generation, and as the basis for widely tunable, if inefficient, ultrafast sources in the visible and ultraviolet. Although anomalous material dispersion simplifies compression to few-cycle pulses, attosecond pulses in the infrared have remained out of reach. We demonstrate soliton self-compression of 1800-nm laser pulses in hollow capillary fibers to subcycle envelope duration (2 fs) with 27-GW peak power, corresponding to attosecond field transients. In the same system, we generate wavelength-tunable few-femtosecond pulses from the ultraviolet (300 nm) to the infrared (740 nm) with energy up to 25μJ and efficiency up to 12%, and experimentally characterize the generation dynamics in the time-frequency domain. A compact second stage generates multi-microjoule pulses from 210 to 700 nm using less than 200 μJ of input energy. Our results significantly expand the toolkit available to ultrafast science.

We demonstrate an efficient scheme for the generation of broadband, high-energy, circularly polarized femtosecond laser pulses in the deep ultraviolet through seeded degenerate four-wave mixing in stretched gas-filled hollow capillary fibers. Pumping and seeding with circularly polarized 35 fs pulses centered at 400 nm and 800 nm, respectively, we generate idler pulses centered at 266 nm with 27 μJ of energy and over 95% spectrally averaged ellipticity. Even higher idler energies and broad spectra (27 nm bandwidth) can be obtained at the cost of reduced ellipticity. Our system can be scaled in average power and used in different spectral regions, including the vacuum ultraviolet.

Resonant dispersive wave (RDW) emission in gas-filled hollow waveguides is a powerful technique for the generation of bright few-femtosecond laser pulses from the vacuum ultraviolet to the near infrared. Here, we investigate deep-ultraviolet RDW emission in a hollow capillary fiber filled with a longitudinal gas pressure gradient. We obtain broadly similar emission to the constant-pressure case by applying a surprisingly simple scaling rule for the gas pressure and study the energy-dependent dispersive wave spectrum in detail using simulations. We further find that in addition to enabling dispersion-free delivery to experimental targets, a decreasing gradient also reduces the pulse stretching within the waveguide itself, and that transform-limited pulses with 3 fs duration can be generated by using short waveguides. Our results illuminate the fundamental dynamics underlying this frequency conversion technique and will aid in fully exploiting it for applications in ultrafast science and beyond.

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).

Experimental Facilities

LUPO consists of three clean-room like optics laboratories totalling 150 m^2 of lab-space. Each laboratory has a specific target:

  • One laboratory is dedicated to fundamental high-energy ultrafast optics.
  • One is dedicated to industrial ultrafast light sources at high average power and repetition rate.
  • And one to the application of bright deep-ultraviolet light to healthcare technology.

We currently have four primary laser sources:

  • A 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. Combined with 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.
  • An Amplitude Tangor laser, operating at up to 100 W and 0.5 mJ energy with 500 fs pulses. This system can be scaled in repetition rate up to 40 MHz.
  • A Pharos system from Light Conversion producing 200 fs and up to 0.2 mJ of energy, along with 4th and 5th harmonic conversion.
  • A 1 J single-frequency Nd:YAG laser system with up to 4th harmonic output.

Our experimental philosophy tends towards building our own devices and systems rather than buying commercial 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 measurement 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 retrieve 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 fibre 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 currently have several open post-doc positions, please get in touch for details.

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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