Nobel-winning science is key to Australian research: ultra-fast laser physics

•Half of the 2018 Nobel Prize for Physics has been awarded to Gérard Mourou and Donna Strickland for their method of generating high-intensity, ultra-short optical pulses.
•Ultra-fast laser physics key to development of future electronics at FLEET’s Swinburne and Monash nodes
The ultra-fast laser pulsing technique developed by Mourou and Strickland has had enormous impact across the fields of chemistry, physics and biology, and provides the basis for important scientific approaches used in FLEET’s research.
FLEET researchers Assoc. Professor Jeff Davis (Swinburne University of Technology) and Dr. Agustin Schiffrin (Monash University) both make use of the technique in their research.
The development of chirped-pulse amplification (CPA) by Mourou and Strickland enabled the generation of intense ultrashort laser pulses with durations of femtoseconds (1 fs = a millionth of a billionth of a second) or less.
This has led to important discoveries in nonlinear optics and to the advent of ultrafast spectroscopy, femtochemistry and attosecond physics, which have enabled discoveries in many scientific fields.
The most important advances enabled by CPA are both utilised in FLEET research:
•The ability to monitor ultrafast processes, on femtosecond and even attosecond timescales.
•Creation of strong peak laser intensities, leading to nonlinear phenomena.
Electrons move very quickly – on the timescale of femtoseconds, or even faster. This means that tracking an electron in an electronic circuit, solar cell or chemical reaction requires experimental probes operating at similar speeds.
Understanding – and ultimately controlling – such ultrafast electronic behaviour can potentially open to door to novel ultrafast electronics technologies.
“When you want to measure how fast something is moving, you need a starter’s gun to set things going and something to stop the clock”, explains FLEET CI Jeff Davis at Swinburne.
“In a 100 m race, this is straightforward because the time taken to run 100m is slow compared with how fast you can push the buttons on a stopwatch.
“But when you want to measure the precise evolution of electrons, which can change their properties or their state in femtoseconds, you need to be able to start and stop the clock much, much faster. We use femtosecond laser pulses to achieve this.”
CPA allows for the reliable generation of a train of high-energy, ultrashort laser pulses, where each pulse has an ultrashort duration (as small as a few femtoseconds), and is produced every microsecond, i.e., a million pulses per second.
Jeff Davis’s Swinburne lab uses femtosecond laser pulses to investigate novel, complex materials that could be used in a future generation of low-energy electronics.
“These extremely short-duration pulses are necessary to measure the evolution of sub-atomic particles such as electrons,” says Professor Davis. “Spectroscopy measurements can then be performed in a reasonable time, allowing sufficient data to be acquired to minimise noise levels on weak signals.”
Swinburne University of Technology has the highest concentration of ultrafast laser systems in the southern hemisphere, many relying on the technique developed by Strickland and Mourou. In fact, Swinburne was the first lab in Australia to install one of these amplified laser systems, in 1998.
At Monash, FLEET CI Agustin Schiffrin will use ultrashort laser pulses to probe and control the electronic properties of nanomaterials on ultrafast timescales.
“In a material, the motion of an electron can unfold at timescales as short as a few femtoseconds, or even less”, says Dr Schiffrin.
“Experimental probes that allow for accessing such ultrafast timescales – such as the laser pulses generated by CPA – will pave the way to novel, ultrafast electronics technologies.”
As well as probing novel and complex materials, these high-energy ultrashort laser pulses can be used to alter and control the properties of these materials, driving them to change state, becoming novel quantum states of matter.
“In FLEET, we are developing ways to change two-dimensional materials from being trivial insulators into what are known as topological insulators, and back again,” explains Professor Davis.
Topological insulators are a relatively new state of matter, recognised by the 2016 Nobel Prize in Physics, which have the fascinating property that they don’t conduct electricity through their interior, but around the edges the electrical current can flow without resistance, and hence without energy loss.
FLEET will take advantage of this unique property to develop a new generation of topological electronic devices that do not waste energy as they switch.
The proposed technology could also potentially switch much faster than current, silicon-based electronics.
“Ultrafast laser pulses allows exquisite control over the properties of the material, giving us the potential for ultrafast switching,” says Davis.
“This exquisite control and our ultrafast measurement of dynamics will allow us to fully understand these phase transitions, allowing us to optimise their control in future devices.
Davis and Schiffrin describe it as “fundamental science, but with an immediate application.”
“These experiments enhance our fundamental understanding of topological phase transitions, and we use this knowledge in our investigations of future ultra-low energy, topologically-based electronics.”
ARC Centre of Excellence in Future Low-Energy Electronics Technologies
FLEET is an Australian Research Council-funded Centre of Excellence bringing together over a hundred Australian and international experts to develop a new generation of ultra-low energy electronics.
The impetus behind such work is the increasing challenge of energy used in computation, which uses 5–8% of global electricity and is doubling every decade.
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