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Raman Laser Group

• Overview
• Key Research Areas
• Emphasis on collaboration
• Projects for Students
• Contacts

Overview

Diode-pumped Raman lasers are practical and efficient sources of laser output at otherwise "hard to reach" wavelengths. Based on conventional Nd laser technology, they use stimulated Raman scattering (SRS) in nonlinear crystals to shift the output wavelength further into the infrared, with conversion efficiencies typically as high as 70%. When combined with frequency doubling, efficient conversion to the yellow orange spectral regions, and the UV region can occur as well as the creation of devices with multi-wavelength and wavelength-selectable ouptut.

In recent years, we have enjoyed great success in targeting the yellow-orange spectral region for medical and defence applications, and developed techniques for obtaining wavelength-selectable output across the green-yellow-red spectral region.

The main focus of our current research program over the next 2 years are the development of continuous-wave yellow Raman lasers, the development of UV Raman-based laser sources, investigating novel resonator configurations and using single crystal diamond as Raman medium. 

Key Research Areas

Raman lasers are unique in a number of ways and the physics involved gives rise to interesting and unusual effects.  It is an understanding of this physics which has enabled us to develop such innovative laser devices and novel ways of operating them.  We have research projects aimed at understanding the optical field dynamics of Raman lasers, through a combination of experimental and numerical modelling studies. The main project areas under investigation are detailed below.  Areas not listed include terahertz Raman lasers, and anti-Stokes Raman lasers.

Continuous-wave Raman lasers

We have recently made advances which enable us to obtain cw operation of yellow lasers.  The best results to date are 4.3 W fully cw output at 588nm, and 5 W output at 588nm (50% duty cycle).   These lasers are practical, efficient diode-pumped devices, with diode to yellow efficiency up to 15%.  Ongoing research is aimed at improving improve the conversion efficiency, power scaling, device miniaturisation and demonstrating wavelength-selectable output between green, yellow and red wavelengths.

UV Raman-based laser sources

This program concerns the development of crystalline Raman laser-based sources which operate in the UV spectral region.  Based on well-established, robust Nd laser technology, these sources will operate at discrete wavelengths in the UV spectral regions.  It is anticipated that around 30 different wavelengths in the range 266nm to 400nm can be generated by appropriate choice of laser and Raman media and resonator design. We will also explore means by which output can be easily switched between two or more of these wavelengths

In preliminary experiments we have achieved 250mW at 289nm.  Lower powers up to 50mW at 8 wavelengths between 266nm and 308nm by frequency conversion of a Q-switched green laser producing 1.2W at 532nm

Diamond Raman lasers

We have recently launched a programme to exploit the extraordinary optical and physical properties of diamond and create novel laser devices of enhanced capability. Owing to diamond’s high Raman gain, outstanding thermal conductivity and very broad optical transmission, diamond is very promising for realizing miniature devices of high average output power and very wide wavelength range (from the so-called terahertz region to the deep ultraviolet). In late 2008, we reported the first externally-pumped diamond Raman laser and our ongoing efforts aim to explore the large range of advantages provided by this exceptional material. We have recently demonstrated highly efficient diamond Raman lasers,  and projects are underway in the generation of ultraviolet and long wave infrared laser output and output power scaling. 

Mode locked Raman lasers

We have recently shown that by pumping a Raman laser with an inexpensive green picosecond laser, we can simultaneously convert the pulse wavelength to the more useful yellow/orange/red wavelengths and compress the pulse to shorter durations. Short-pulse yellow lasers have applications in areas such as two photon microscopy, in which two yellow photons can excite the common ultraviolet absorptions of biological species.

Numerical modelling of Raman lasers

Raman lasers are unique in a number of ways and the physics involved gives rise to interesting and unusual effects.  It is an understanding of this physics which has enabled us to develop innovative laser devices and novel ways of operating them. 
 
Recent numerical modelling studies of cw Raman lasers have been highly beneficial at elucidating the optical field dynamics of Raman lasers, with verification by experimental studies. We propose to expand these modelling studies further to address various issues relating to the performance and features of a range of cw and pulsed Raman lasers.

Emphasis on Collaboration

Many of our research programs have involved a strong collaboration aspect with industry partners who have an interest in co-developing laser sources with output characteristics to match the requirements for their applications.  Devices have been developed in partnership with DSTO (Defence Science and Technology Organisation), a medical laser manufacturer, and we have also seen the formation of a spin-off company, Lighthouse Technologies to commercialise some of our Raman laser technology. 

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.

jobs.ac.uk advertised position, "Wavelength-agile lasers for biophotonics". Lasers play a crucial role in biological imaging; for example two-photon microscopy allows some of the most detailed images of live cells to be taken. We will develop new lasers sources to fulfill the needs of this and other applications, creating sub-picosecond laser sources with the necessary wavelength agility by harnessing the power of Raman shifting.  There is the opportunity to spend periods of time at Strathclyde University, UK, to apply our laser sources to real-world problems such as molecular uncaging. A second, related project is described here.

PhD Projects in Diamond and Micro-optical Raman laser systems now available for 2010 start. Contact Rich Mildren.

Acknowledgements

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

Contacts