A team from the Vienna University of Technology has developed a way of using a medium to shorten intense laser pulses, in a breakthrough made more significant due to the importance of ultra-short laser pulses in advanced atomic and molecular research. Extremely short infrared laser pulses are a common tool for investigating the quantum world, as they can detach electrons from their atoms, accelerate electrons and also help monitor the dynamics of chemical reactions.
Creating these laser pulses has remained a complex process. As such short pulses combine different colors due to the various wavelengths involved, when they travel through a medium they move at different speeds, with the pulses becoming longer and longer, creating a dispersion effect. However, this new study, as reported in the journal Nature Communications [Balciunas et al. Nat. Commun. (2015) DOI: 10.1038/ncomms7117], reversed the process, demonstrating how to compress laser pulses by a factor of 20 by sending them through a gas-filled hollow fiber, with each laser pulse being only one oscillation of light.
Inside this special fiber is a specially designed nanostructure called a “kagome” (a traditional Japanese woven bamboo pattern) that allows the short wavelengths to travel through the fiber quicker than longer ones, providing undistorted transmission. The non-linear interaction between the light and the gas atoms makes different wavelengths travel at different speeds – when these opposing effects are combined, it has the effect of compressing the laser pulse so that the pulses all come out at the same time, with the pulse also being short and very intense, attaining a peak power of one gigawatt.
The various pulse wavelengths have commonly been manipulated using intricate mirror systems to carry out the pulse compression. In this research, they tested the technology by focusing the pulse onto a target of xenon gas, thus ionizing the xenon atoms. The specific shape of the laser pulse influences the direction that the electrons torn from the xenon atoms are sent.
This new and straightforward pulse compression approach should make it much easier and cheaper for laboratories to develop single-cycle infrared pulses, and could lead to generating even shorter pulses. The scientists now hope to use the tabletop technology to carry out a range of new measurements, and expect other researchers to take up the concept, especially as such a small laser system could potentially enhance attosecond science and ultrafast lasering.