Scientists from US, Canada and France win 2018 Nobel Prize in Physics

Last week, Arthur Ashkin, Gerard Mourou and Donna Strickland were jointly awarded the Nobel Prize in Physics 2018.

The inventions being honoured this year have revolutionised laser physics. Extremely small objects and incredibly rapid processes are now being seen in a new light. Advanced precision instruments are opening up unexplored areas of research and a multitude of industrial and medical applications.

Arthur Ashkin invented optical tweezers that grab particles, atoms, viruses and other living cells with their laser beam fingers. This new tool allowed Ashkin to realise an old dream of science fiction — using the radiation pressure of light to move physical objects. He succeeded in getting laser light to push small particles towards the centre of the beam and to hold them there. Optical tweezers had been invented.

A major breakthrough came in 1987, when Ashkin used the tweezers to capture living bacteria without harming them. He immediately began studying biological systems and optical tweezers are now widely used to investigate the machinery of life.

Donna Strickland, the first woman to win the Nobel Prize in Physics in 55 years, and Gérard Mourou paved the way towards the shortest and most intense laser pulses ever created by mankind.

Their revolutionary article was published in 1985 and was the foundation of Strickland’s doctoral thesis. Using an ingenious approach, they succeeded in creating ultrashort high-intensity laser pulses without destroying the amplifying material. First they stretched the laser pulses in time to reduce their peak power, then amplified them, and finally compressed them. If a pulse is compressed in time and becomes shorter, then more light is packed together in the same tiny space — the intensity of the pulse increases dramatically.

Strickland and Mourou’s newly invented technique, called chirped pulse amplification, CPA, soon became standard for subsequent high-intensity lasers. Its uses include the millions of corrective eye surgeries that are conducted every year using the sharpest of laser beams.

Ultrafast laser physics — key to Australian research

The ultrafast laser pulsing technique developed by Mourou and Strickland has had a significant impact across the fields of chemistry, physics and biology. One example is materials research at the FLEET Centre of Excellence (Swinburne University of Technology and Monash University), an Australian Research Council-funded research centre.

FLEET researchers Associate 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 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 used 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.

“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,” said FLEET CI Jeff Davis at Swinburne.

“In a 100 m race, this is straightforward because the time taken to run 100 m 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, ie, 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. The field of study is referred to as ultrafast ‘femtosecond’ spectroscopy.

“These extremely short-duration pulses are necessary to measure the evolution of sub-atomic particles such as electrons,” said 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 is said to have 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 FLEET, we are developing ways to change two-dimensional materials from being trivial insulators into what are known as topological insulators, and back again,” said 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. “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”.

Image caption: Associate Professor Jeff Davis, Swinburne University of Technology.