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Light Applications and Source Engineering Research:

LASER Group

• Overview
• Key Research Areas
• Collaboration
• Projects for Students
• Contacts

Overview

We are a team of physicists with strong backgrounds in laser theory, linear and nonlinear optics, system design, and practical device engineering for laser based scientific and industrial led applications. We have over 30 years combined experience in laser physics, including developing cerium lasers, copper and gold vapour lasers, liquid and solid dye lasers, Nd lasers, Ti:sapphire lasers, Yb:S-FAP lasers, high power ultraviolet lasers,  

We explore the physics and engineering of novel laser sources with unique characteristics targetted for specific applications, and explore novel applications of our lasers. Current major laser development project areas include: ultraviolet cerium lasers, where we have recently demonstrated the first ever mode-locked and continuous wave cerium lasers; ultrafast microchip lasers where we are attempting to bridge the energy-pulse duration gap between ultrafast low pulse energy mode-locked oscillators and conventional millijoule kHz nanosecond gain-switched lasers.  Applications research includes high speed imaging including colour coded particle image velocimetry, CARS microspectroscopy for forensics investigations, and ultraviolet autofluorescence biophotonics.

Key Research Areas

Cerium Lasers - the Ti:Sapphire of the UV

Cerium lasers are efficient, broadly tunable all solid state ultraviolet lasers which are arguably the Ti:sapphire laser of the ultraviolet. Cerium lasers provide a very attractive route to tunable ultraviolet when compared to a frequency doubled dye laser or frequency tripled Ti:sapphire laser: It makes sense to get to the ultraviolet by harmonic generation from a fixed wavelength pump laser (eg Nd:YAG) where the peak power and beam quality are higest, and then pump a tunable ultraviolet (cerium) laser, rather than frequency doubling or tripling a lower peak power tunable laser. By generating ultraviolet directly from a UV laser (rather than by harmonic conversion) the uv temporal, spectral and spatial characteristics can be better controlled. We believe that cerium should be considered an ultraviolet analog of the remarkably versatile infrared Ti:sapphire laser.

We have a long running and extensive research program on developing novel cerium lasers beginning with broadly tunable high power and miniature kHz pulsed systems, and most recently we achieved two major breakthroughs in ultraviolet lasers:

Continuous wave cerium lasers: Using a modelocked picosecond 266 nm pump laser we have demonstrated the first ever continuous wave cerium laser. This opens up exciting new opportunities for developing stable continuous wave tunable ultraviolet lasers.

Mode-locked cerium lasers: By synchronously pumping with a picosecond 266 nm pump laser we have demonstrated the first ever mode-locked cerium laser. Cerium has sufficient bandwith to support direct generation of few femtosecond pulses directly in the ultraviolet at wavelengths where the single cycle limit is of order 900 attoseconds. To reach this potential we need to implement dispersion control and Kerr-lens modelocking.  Read a review of these experiments here.

Ultrafast Microchip Lasers

We are developing sub 20 ps microchip lasers aimed at bridging the gap between low pulse rate (MHz), low pulse energy ultrafast mode-locked lasers and high pulse energy nanosecond pulsed Q-switched lasers. Our aim is to push the pulse duration of microchip lasers down to the minimum possible so that robust microchip laser technology can be accessed for applications ranging from laser micromachining to nonlinear optical microscopy (including CARS microspectroscopy).

High Speed Imaging

We are using multispectral and continuum laser sources for novel high speed imaging applications including particle image velocimetry. Our unique approach is to use high pulse energy continuum sources for colour coded imaging applications where colour is used to code an extra dimension of information (eg a third spatial dimension, or give time information).  For example, by illuminating a volume of space with a dispesed rainbow of colours and recording a colour image of scattering particles, the colour of each particle can give us an extra spatial dimension of information. This is illustrated in the picture to the right where the foreground particles are blue and the background particles are red.  

UV Biophotonics Applications

Cerium lasers conveniently operate at wavelengths corresponding to many important UV excitation bands for naturally autofluorescent biological compounds. We are exploring uv autofluorescence application in Biophotonics using our miniature tunable ultraviolet cerium lasers.

Using a miniature 1 mW cerium laser we scanned protein gel electrophoresis plates to determine the concentration limits for detection. Detection limits for many proteins matched conventional dye based fluorescence detection, meaning considerable potential cost savings for proteomics. 

Novel mode locking for ultrafast lasers

Mode locking is a method of persuading a laser source to generate a train of short pulses rather than giving a smooth "continuous wave" (CW) output. A train of pulses in the time domain means that the laser output contains a set of evenly-spaced frequencies in the frequency domain - these frequencies are the different longitudinal cavity modes of the laser oscillator, all oscillating with their phases locked together. The laser then outputs a train of short pulses, with the period between pulses close to the round-trip time of the laser cavity. We can see then that the inside the laser cavity there is a single pulse rattling back and forth, of which a little leaks out of the cavity each time it reflects from the output coupler.

There are lots of ways of doing this, but they fall into two types; either active ways where we generate the mode locking forces (e.g. AO modelocking, synchronous pumping), or passive ways where the pulse itself generates the locking force (e.g. Kerr lens, saturable mirrors, colliding pulse). Passive locking generates far shorter pulses since as the pulse gets shorter the mode locking forces it is itself creating get stronger and stronger.

Mode locked lasers are important for generating picosecond and femtosecond pulses for a huge range of applications, including generating the highest possible laser powers (petawatts), measuring fast chemical and physical events, and industrial applications such as material processing.

Collaboration

We will continue to establish collaborative links with research organisations and companies who have an interest in developing laser sources, laser applications  or laser-based instrumentation, and invite expressions of interest from such organisations.

Projects for Students

A range of projects within the key research areas described above are available for interested students, including honours, masters and PhD and also exchange scholars.  These can be tailored to suit applicants strengths or particular interests (eg. theoretical, experimental, industry-related). Interested candidates should contact one of the research staff listed below. Refer also to information on scholarships are exchange opportunities.

Acknowledgements

Our research is supported by Australian Research Council and University project funding. 

Contacts