Researchers at Swinburne University of Technology in Australia have discovered a new way to generate bright beams of coherent extreme UV radiation using a table-top setup that could be used to produce high resolution images of tiny structures at the nanoscale.
A table-top laser setup is used to illuminate a gas cell of argon with two intense beams of ultrashort laser pulses at different wavelengths. One beam (at the infrared wavelength of 1400 nm) generates ‘high-order harmonics’ in the extreme UV (at wavelengths of 15–30 nm) as a seeding beam, while the effect of the second overlapping ‘pump’ beam (at a wavelength of 800 nm) is to amplify the extreme UV radiation by a process known as optical parametric amplification.
“The new table-top system may offer a cost-effective and convenient alternative to large-scale, multi-million-dollar facilities such as synchrotrons or free-electron lasers, which, until now, were the only way to generate bright coherent beams of extreme UV radiation,” says Professor Lap van Dao in Swinburne’s Centre for Quantum and Optical Science, who led the research.
“The new and unique aspect of this work is the realization of optical parametric amplification of the high harmonic radiation in the extreme UV region, where the very high order (nonlinear) response of the illuminated medium needs to be considered,” the professor continues.
The advantage of the novel extreme-UV laser system is that the intensity of high harmonic radiation by optical parametric amplification is enhanced by one to two orders of magnitude compared with just having high harmonic radiation on its own.
The discovery could be a game-changer in the field. “The potential impact for future imaging systems is the generation of intense coherent beams at still shorter wavelengths, including the water window region (wavelengths 2–4 nm), which would allow imaging of structures on the nano-scale and high contrast imaging of biological molecules, for example, by coherent diffraction imaging, and possibly dynamical (functional) imaging of biological molecules,” van Dao says.
The next step for the team, he continues, was to extend this technique to shorter wavelengths, including the water window region (at wavelengths 2–4 nm) by illuminating helium gas or by using a longer wavelength laser beam, for example, 2000 nm, to generate the high order harmonic seeding beam. “This would allow imaging of structures on the nano-scale and high contrast imaging of biological molecules, for example, by coherent diffraction imaging, and possibly dynamical (functional) imaging of biological molecules,” van Dao says.
Written by Sandra Henderson, research editor Novus Light Technologies Today