The short and the shorter of it: Infrared laser pulses

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  • Published: Feb 1, 2015
  • Channels: Infrared Spectroscopy
thumbnail image: The short and the shorter of it: Infrared laser pulses

Self-shortening lasers

A new technology that leads to self-shortening laser pulses could make short infrared pulses more accessible and cheaper, involving as it does sending an initial infrared laser pulse into a hollow fibre filled with gas. (Copyright: TU Wien)

A new technology that leads to self-shortening laser pulses could make short infrared pulses more accessible and cheaper, involving as it does sending an initial infrared laser pulse into a hollow fibre, or capillary, filled with xenon gas.

Ultrashort laser pulses are widely important tools in atomic and molecular research, making them even shorter is always a goal for scientists hoping to capture events that happen on unimaginably small timescales. Now, the team of T. Balciunas, G. Fan and A. Baltuska at the Vienna University of Technology, Austria, working with C. Fourcade-Dutin, F. Gerome and F. Benabid at the University of Limoges, France, T. Witting at Imperial College London, UK, A. A. Voronin and A. M. Zheltikov of the M.V. Lomonosov Moscow State University, Russia, and G. G. Paulus of the Friedrich-Schiller-University, Germany, has demonstrated a new approach to compressing an intense laser pulse by a factor of twenty (the resulting pulse length being 4.5 femtoseconds) by sending it through a hollow fibre. This compressed pulse consists of just one single oscillation of light, although it is requires only bench-top apparatus and so is much simpler and less expensive than any earlier setups. The team publishes details in the journal Nature Communications.

Noble choice

The team explains how an infrared laser pulse can sent into a hollow, but gas-filled, fibre, the interior of which is designed to have a "basket weave", or Kagome lattice, structure to make a novel waveguide material. The Kagome nanostructure was designed and fabricated by Benabid's research group. The nanostructured basket weave leads to a nonlinear interaction between the light and the gas within the special fibre makes different wavelengths travel at different velocities. The components with longer wavelengths travel faster than the short wavelength components. The fibre's internal nanostructure allows short wavelengths to travel through the fibre faster than longer ones. This leads to a compression of the laser pulse. It is as if a long line of marathon runners were all to reach the race finish line at the same time. The foreshortened pulse is also much more intense than normal, reaching a peak of a gigawatt of power at the capillary exit.

Of course, it is more than thirty years since scientists first observed self-shortening of ultrashort laser pulses as they pass through a negative dispersion waveguide when an optical soliton was first seen. The new approach to short laser pulses is, however, scalable, unlike those earlier experiments, allowing high energy shortened pulses to be generated. It also precludes the need for an intricate setup of mirrors to compress the laser into a single pulse. The work might now allow researchers to push the realm of infrared pulses from the femtosecond to the attosecond timescale a thousand times shorter. Careful choice of the noble gas used to fill the capillary can be used to change the energy of the pulse.

Ionisation pulse

The team in Vienna has already shown how their short laser pulses can be used to ionize xenon gas. The profile of the ultrashort laser pulse can affect the direction in which xenon's electrons are removed from the atom and so reveal more about the ionisation process than was possible previously. The team suggests that their high-energy ultrashort pulses will have applications in attosecond and field-sensitive measurements, such as above threshold ionisation (ATI) electron spectrometry, coincidence momentum imaging and terahertz (THz) generation in plasma.

Related Links

Nature Commun, 2015, 6, online: "A strong-field driver in the single-cycle regime based on self-compression in a kagome fibre"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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