15 Oct 2015

Ultra-fast lasers

From Our Changing World, 9:34 pm on 15 October 2015

By Alison Ballance

“An optical frequency comb allows you to do measurements more precisely than any other technique in existence.”
Miro Erkintalo, 2015 Rutherford Discovery Fellow, University of Auckland

Physicist Miro Erkintalo holds an ultra-fast laser developed at the University of Auckland.

Physicist Miro Erkintalo holds an ultra-fast laser developed at the University of Auckland that he says is worth more than its weight in gold. On the research bench behind are optical fibres which are essentially an unpacked version of the box. Photo: RNZ / Alison Ballance

Bar code scanners, CD and DVD players, blu-ray players, laser printers – lasers are everywhere.

“Laser is an acronym for light amplification by stimulated emission of radiation,” explains University of Auckland physicist Miro Erkintalo. “So essentially a laser is a device that is capable of laser light. And laser light is very unique form of light that is essentially coherent – both spatially and temporally – and it’s basically much brighter than ordinary light.

Although the physics of lasers is well understood, Miro says there is always a push to develop new kinds of lasers and that’s a key part of his research. He says it’s often the case that the development of a new kind of laser will lead to new applications, and he cites how the development of a cheap blue laser led to blu-ray technology

Miro works on ultra-fast lasers, although he says they’re more accurately described as ultra short pulsed lasers since they emit vast numbers of ultra short pulses per second (and since the speed of light can’t actually go faster than itself).

"A single one of these short pulses lasts just hundreds of femtoseconds, and one femtosecond is to one second what one second is to 32 million years,” says Miro. “Basically these pulses are the shortest things that humans have ever created."

Miro says they try to create ultra short-pulsed lasers that are robust and can be used for micro-machining, for example, in industrial environments where there is a lot of noise, high temperatures and mechanical vibrations.

“Because you are packing a certain amount of energy in a short duration, it means these lasers have very high peak power and that allows you to leverage non-linear optical effects. You can use it, for example, for high-resolution microscopy, and it is used in biomedical imaging to allow you to see further into tissue. You can also use ultra short-pulsed lasers to look at the dynamics of very short chemical reactions”.

Research lab using optical lasers.

Miro Erkintalo's lab works on ultra short-pulsed lasers, optical frequency combs and micro-resonators, and they are looking to develop new kinds of lasers with new industrial and research applications. Photo: RNZ / Alison Ballance

University of Auckland researchers have already developed ultra-fast laser technology, with pulses of about 140 femtoseconds, that has been licensed to Southern Photonics and is sold internationally. Miro says the resulting piece of equipment, which is portable, is worth more per gram than gold, which makes it an excellent export commodity.

Miro’s lab works on optical frequency combs, which is a light source whose spectrum consists of equi-distantly spaced spectral components. Because the distance between each of the colours - or frequencies - is known it can be used as a ruler to measure unknown optical frequencies.

Optical frequency combs can also be used to create optical atomic clocks, which are so precise they won’t gain or lose a second, even over billions of years. This area of research, using optical frequency combs, was awarded a Nobel Prize in 2005.

Mira says that an exciting new development in the field of ultra-fast lasers is the use of microresonators, which allow you to put in a single laser light and create all the colours of the rainbow, in other words an optical frequency comb. In 2013 Miro was awarded a Faststart Marsden Fund award for research into 'Microresonator frequency combs: Fiber-optic physics to the rescue.'

Miro Erkintalo is talking about “Rulers of light” as part of the Royal Society of New Zealand’s International Year of Light and Light-based Technologies Ten by Ten lecture series. His talk is in Dunedin at 5.30pm on Thursday 22 October.

Also next week Justin Hodgkiss talks on ‘The solar revolution’ in Rotorua 5.30pm Thursday 22 October, and Cather Simpson is talking on ‘Making light work’ in Wanaka at 6pm Friday 23 October.

You can hear Cather and Justin in an Our Changing World feature from 2013 marking 50 years of the laser.