Tunable ultra-violet lasers
A/Prof David Coutts and Dr David Spence
We have Open projects for MSc or PhD in this area!
There are many applications that require lasers with ultra-violet output, including defense applications such as detection of airbourne pathogens and excitation of biological and chemical species. While there are many hundreds of different materials from which a laser can be made, the great majority operate in the infra-red or visible regions of the spectrum - think of ubiquitous Nd:YAG, tunable Ti:Sapphire, or dye lasers. Lasers that operate directly in the UV are far less common - the KrF gas excimer laser is the best-known, operating at 248 nm. Of course UV output can always be generated by frequency up-conversion of visible or IR lasers, and combined with frequency down-conversion in optical parameteric conversion almost any desired wavelength across the deep UV to far infrared can be created. The trouble is that these systems are prone to be complex, inefficient, hard to use, and hard to tune.
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We are working on an exciting group of cerium-doped crystals. These solid-state laser crystals laser directly in the UV, and moreover are widely tunable. The two most common crystals are Ce:LiCAF (Ce: Li Ca Al F) which lases between 280 nm and 315 nm, and Ce:LiLuF which lases between 305 nm and 338 nm. These are the only tunable lasers that directly provide output in this region. By directly producing the tunable light, these lasers can be compact, simple, reliable and easy to use. Our research has concentrated on making cerium lasers smaller and cheaper, so that they are suitable to be used in applications, and for commercial collaboration. We now make lasers that fit in a shoe-box and cost a few thousand dollars. We have also pushed for shorter pulse durations, generating laser pulses as short as a few hundred picoseconds, and have developed new tuning methods so that one-piece monolithic lasers can be tuned (see article in the magazine "Photonics Spectra") |
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We crossed many technical hurdles along the way. Quality of the laser cyrstals is paramount to acheiving efficient operation. Colour centres and excited state absorption are the two major problems that affect the laser operation. Colour centres are defects or impurities in the crystal that can trap electrons, and which absorb light (in severe cases making the crystals appear coloured, hence the name...) and reduce the efficiency of the laser. Excited state absorption is a catch-all term for unwanted absorption of light by ions in the upper laser laser, which again causes unwanted losses and can in severe case mean the material will never lase. We find that compact laser cavities and short pump pulses lead to more efficient laser operation, with a reduction in the effects of colour centres. Extremely short microchip-lasers operate extremely well, and lend themselves to new architectures that can be developed to generate picosecond pulses.
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Cerium lasers have the potential to provide continuous wave tunable UV output and may possibly be mode locked to generate ultrafast UV pulses. In principle a cerium mode locked laser could generate pulses as short as 3 femtoseconds - m uch shorter than can be generated with Ti:Sapphire oscillators. These ultrafast UV pulses have many application in femtosecond chemistry and surface science. More... |
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MSc and PhD studenship projects
The following are some of our ongoing and new projects, which are suitable for new Masters and PhD projects. More projects are also being offered in the Lasers and Photonics CORE.
Short Pulse and Tunable Microchip Lasers
Microchip lasers are solid-state lasers where the laser mirrors are directly coated on a thin piece of laser material. Such lasers find many applications e.g. laser ranging, biophotonics, and materials processing. Building upon exciting preliminary results, we propose to study a new class of microchip lasers which is broadly tunable. For example we will use Ti:Sapphire and cerium based laser crystals and incorporate wedge etalon tuning elements. Systems for generating very short pulses (down to few 10's of ps) will also be investigated, including novel master oscillator-power amplifier techniques. We will also use these lasers for nonlinear optics including nonlinear microscopy. The project will involve both experimental and some laser modeling work and would suit a student with an interest in lasers and optics.
Contact dcoutts@ics.mq.edu.au
Tunable Ultraviolet Continuous-wave Laser Sources
The goal of this project is to investigate the use of mode-locked lasers for pumping continuous wave (CW) lasers. The project will focus on the laser material Ce:LiCAF that is widely tunable in the ultraviolet spectral region. Experiments using this short lifetime material as well as using Ti:Sapphire crystals that have a far longer lifetime will carried out, and interpreted using numerical modeling. The noise characteristics, frequency tuning and laser threshold properties will be studied, and compared to experiments that use a CW pump source. Spectroscopic applications of the CW ultraviolet source will be investigated.
Contact dspence@ics.mq.edu.au