Pulsed Laser Deposition

The Pulsed Laser Deposition (PLD) Group is led by Professor Rob Eason and currently consists of five members:

• Professor Rob Eason (Group Leader and also Deputy Head of School (Education))
• Dr Christos Grivas (Senior Research Fellow)
• Dr Tim May-Smith (Post Doctoral Research Assistant)
• Mr Mark Darby (PhD student)
• Miss Rossana Gazia (PhD student)

PLD is a versatile technique for growing thin films and can be applied to a very wide range of materials. A pulsed laser (usually ultra-violet (UV) wavelength) is used to ablate a target, and a plasma plume is formed by the ejected material; the plasma plume then expands away from the target surface and interacts with the chamber atmosphere until it reaches the substrate, where it is deposited as a thin film. The substrate can be heated to assist with nucleation and allow crystal growth, and a background gas can be used to help control the film composition. The PLD process covers many different areas of physics and chemistry, and an increasing understanding of what drives the mechanisms behind successful depositions is critical for the continuous improvement of future films and devices. Several deposition parameters must be carefully optimised before high quality films can be produced. A major advantage of the technique is the occurrence of stoichiometric transfer. This allows complex multi-component materials to be grown and has the added benefit that targets can be adapted easily from small pieces of bulk material.

14 Jan 08 - Novel crystal growth with multi-beam laser deposition technique
Researchers are using multiple targets and multiple lasers to grow a range of unique films whose properties can be tuned.

5 Jan 07 - Arrival of a new vacuum chamber. This new chamber will fulfil the role of a fabrication facility for thick and multilayer designer planar waveguide structures made from garnet crystals. The state-of-the-art chamber has been specifically designed to take advantage of a laser trio system.

November 06 - New book release. Pulsed Laser Deposition of Thin Films: Applications-Led Growth of Functional Materials (Hardcover) by Professor Rob Eason is available to order now. This text summarizes the wide range of different pulsed laser deposition applications areas that are either current or newly emerging. A must-have resource for scientists, technologists and development engineers who have a need to grow and pattern, to apply and use thin film materials.

Recent activities have been focussed on the rebuilding of the PLD lab and equipment, whilst femtosecond-PLD experiments have continued in the Femtosecond Applications of Science and Technology laboratory (FAST-lab).

The main group research interest is to use PLD grown thin films to fabricate optical devices such as waveguide amplifiers and lasers, and thin-disk lasers. Due to the successes achieved in the past with garnet crystals and sapphire, research continues to be centred around oxide crystals such as these, but the group is also interested in the deposition of glasses for new applications. We are also continually striving to understand the PLD process more and find new techniques which will enable us to make better films and devices in the future. The main projects currently underway are summarised below. All of these projects are supported within the ORC Portfolio grant.

• Optimisation of garnet crystal growth by PLD: can laser deposited films approach the quality of bulk crystal?

Recent results have shown that thick Nd:Gd₃Ga₅O₁₂(GGG) films with propagation losses as low as 0.1 dBcm^-1 can be fabricated by PLD. However, spectroscopic, compositional and structural analysis showed that the films were still some way away from bulk crystal quality and there is a continued interest in improving the quality and consistency of films in an attempt at realising the most efficient and highly optimised devices. Also, when growing GGG films with thicknesses above 50 µm, there is a need for precise compositional control to prevent the deleterious effects of stress which can occur in non-stoichiometric films.

• A comparison of femtosecond-PLD to nanosecond-PLD and its potential for the deposition of new materials

The recent availability of femtosecond lasers with the potential for clean ablation and particulate-free deposition has generated interest from PLD groups worldwide. The aims of this project are to establish if there are any real benefits from using femtosecond lasers as ablation sources in PLD and trial a range of different materials to find out if the altered mechanisms involved allow the growth of new materials or old materials for which nanosecond-PLD has been found to be unsatisfactory in the past. This project is to form the basis of Mark Darby’s PhD, who is in the receipt of an Industrial CASE studentship from QinetiQ for this work.

• High power diode-pumped crystal planar waveguide devices by PLD

The aim of this project is to fabricate thick and multilayer waveguide structures suitable for pumping by diode stacks. Such types of structures would present an efficient means of brightness enhancement and wavelength manipulation, and with the ever increasing amount of power available in diode-stack form, there is scope for achieving output powers beyond 100 W from a well optimised device with good thermal management. The planar waveguide geometry is well suited to diode-pumping, and in particular, side-pumping offers the advantage of performing lasing, pumping (from one or two sides) and thermal management each on a unique axis. PLD grown devices also have the advantage that heating relaxes stresses due to thermal expansion mismatch between the substrate and film, since growth occurs at high temperatures (~800 °C).

• Pushing the limits with multi-target tri-laser PLD: what can be achieved with three targets, three lasers and three plumes?

The goal of this project is to establish what the new fabrication possibilities are when three targets are available with three separate laser systems and three different plumes to mix and vary. Advances have been made previously with experimental enhancements to the standard PLD setup, such as dual plume cross-beam techniques and linearly expanded multi-target systems for large-area deposition, but perhaps for the first time, the capability to perform several of these enhancements at the same time has been designed into a deposition system. We have great expectations for multi-target tri-laser PLD and this exploratory project is essential for us to find out what works well and what doesn’t, and to define the limitations (if any) of the system. This project is likely to form the basis of Rossana Gazia’s PhD, who is a recent addition to the group from 2006.

• Designer crystal planar waveguide and thin-disk devices by multi-target tri-laser PLD

The intention in this project is to bring together the new advantages of multi-target tri-laser PLD with the plenitude of post-processing techniques and skills within the ORC to ultimately produce designer devices that could make the next generation of planar waveguide and thin-disk lasers. We aim to successfully apply advances such as spatial dopant profiles in waveguide and thin-disk form, material customisation and optimisation (e.g. spectroscopic for tuning absorption and maximising efficiency, structural and compositional for minimal film stress and optical loss), in-situ micro-structuring by techniques such as masking and ablative removal, and grading of layers to produce structures with distributed stress and custom refractive index profiles for optimal modal control of pump and laser light. The outcome of this project relies heavily on the success of the others, since only the combination of excellent film quality and highly refined fabrication processes and techniques will allow us to make devices with low losses and high operational efficiencies.

If you are considering doing a PhD with the ORC, projects with the PLD Group would appeal to those with good problem solving and lab-based skills, as PLD encompasses laser use, surface science diagnostics, modelling, vacuum technology, and device processing and operation. Visit the PhD pages to find out more about our PhD programme and how to apply.

The wealth of fabrication, processing and analysis equipment available within the University makes Southampton a highly rewarding place to do PLD. Interaction with other groups gives us the rare ability to see films through from optimisation and fabrication, all the way to post-processing and device operation. The PLD group interacts with the following:

• Infrared Science and Technology Group, led by Professor Harvey Rutt (ORC). The UV lasers and lab for PLD are shared with the IRST Group who have a joint interest in the use of PLD for the deposition of chalcogenide films such as gallium lanthanum sulphide (GLS). Past interactivity has included the growth of zinc sulphide, lead germanate and gallium lanthanum sulphide glass films.
• Optical Parametric Oscillators Group, led by Professor David Shepherd (ORC). Interactivity provides essential skills exchange for waveguide device processing, testing and performance optimisation.
• Advanced Solid State Sources Group, led by Professor Andy Clarkson (ORC). Interactivity provides essential skills exchange for waveguide and thin-disk device processing, testing and performance optimisation.
• Novel Glass and Fibre Group, led by Professor Dan Hewak (ORC). The Novel Glass and Fibre Group are greatly interested in the conversion of in-house made bulk glasses into a thin film medium and PLD is an attractive way of achieving this if the long-standing problems with the deposition of glasses can be circumvented.
• EPSRC UK National Crystallography Service – based in the School of Chemistry, University of Southampton. The X-ray diffractometers provided by the EPSRC UK NCS are critical for the optimisation of deposition parameters and identification of films when depositing crystals. 
• Laser and Plasma Applications Group, led by Professor James Lunney – Physics Department, Trinity College Dublin. Recent collaboration with the Laser and Plasma Applications Group has been focussed on the differences in plasmas produced by femtosecond and nanosecond ablation, and the possible effects of these differences on crystal and glass film growth.

We are always interested to hear from academic groups and industry about potential collaborations. If you are interested in collaborating with us, please go ahead and contact Professor Rob Eason directly.

Beyond the projects described above with the ultimate goal of designer structures, there are many potential uses for PLD that are still relatively unexplored. The following list summarises some possible research directions for the future of optical films and devices by PLD. 

• Combinatorial PLD: The anticipated success of multi-target and laser PLD could lead to a new application for PLD in combinatorial science. The availability of three target sources allows trigonal intermediate mixing of materials and could offer a quick way of finding useful new material compositions. 
• Multi-Enhanced PLD: With so many different enhancements to PLD available that focus on improving one characteristic of films, an interesting challenge for the future could be to combine several of these at once to make bigger overall improvements to film quality.
• Horizontally integrated ‘on-chip’ structures: The integration of multiple layers for different functions side-by-side on the same substrate is a highly desirable achievement for optical devices. For example, integration of a laser-ion doped area of film with a saturable absorber area of film could allow the fabrication of a self-Q-switched planar waveguide laser. 
• Optimisation by complete feedback loop: It is important for any device fabrication group to achieve a complete feedback loop where the actual operational performance of the devices becomes the parameter by which optimisation in production steps occurs. This is a step that we strongly desire to take in the near future, and is admittedly also a critical test for PLD to pass if it is to make the transition from experimental technique to routine fabrication facility for future optical devices.

The PLD group at Southampton has on many occasions led the way in making the often elusive step of converting PLD grown films into actual devices. The following list (starting with the most recent first) highlights some of the main important achievements throughout the history of the group.

• Growth of a multilayer garnet crystal film.

T. C. May-Smith, D. P. Shepherd, R. W. Eason. Growth of a multilayer garnet crystal double-clad waveguide structure by pulsed laser deposition. Thin Solid Films (2007), in press. 

• Growth of a Yb₃Al₅O₁₂ (YbAG), Y₃Ga₅O₁₂ (YGG), Nd,Cr:Y₃Sc₂Al₃O₁₂ (Nd,Cr:YSAG), Cr:Gd₃Sc₂Al₃O₁₂ (Cr:GSAG) and Nd,Cr:Gd₃Sc₂Ga₃O₁₂ (Nd,Cr:GSGG) by PLD.

T. C. May-Smith. Pulsed laser deposition of thick multilayer garnet crystal films for waveguide laser devices. PhD Thesis (April 2005).

• Diode-pumped laser operation of a 50 µm thick Nd:GGG film.

T. C. May-Smith, J. Wang, J. I. Mackenzie, D. P. Shepherd, R. W. Eason. Diode-pumped garnet crystal waveguide structures fabricated by pulsed laser deposition. CLEO/QELS, Long Beach, California, 21-25 May CMFF7 (2006).

• Laser operation of rib waveguides based on Ti:sapphire films grown by PLD.

C. Grivas, D. P. Shepherd, T. C. May-Smith, R. W. Eason, M. Pollnau. Single transverse mode Ti:sapphire rib waveguide laser. Optics Express Vol. 30 pp. 210-215 (2005). 

• Effect of self-imaging observed in a YAG capped Nd:GGG film.

T. C. May-Smith, C. Grivas, D. P. Shepherd, M. S. B. Darby, R. W. Eason. Pulsed laser deposition of thick multilayer garnet films for cladding-pumped planar waveguide laser devices. CLEO/IQEC, San Francisco, California, 16-21 May CthE2 (2004). 

• Ti:sapphire rib waveguides, based on Ti:sapphire films grown by PLD, as fluorescence sources.

C. Grivas, T. C. May-Smith, D. P. Shepherd, R. W. Eason, M. Pollnau, M. Jelinek. Broadband single transverse-mode fluorescence sources based on ribs fabricated in pulsed laser deposited Ti:sapphire waveguides. Applied Physics A Vol. 79 pp. 1195-8 (2004).

• Low loss of 0.1 dBcm^-1 observed in a lasing 40 µm thick Nd:GGG film.

C. Grivas, T. C. May-Smith, D. P. Shepherd, R. W. Eason. Laser operation of a low loss (0.1dB/cm) Nd:Gd₃Ga₅O₁₂ thick (40 micron) planar waveguide grown by pulsed laser deposition. Optics Communications Vol. 229 (1-6) pp. 355-61 (2004). 

• Growth of a 135 µm thick GGG film.

T. C. May-Smith, C. Grivas, D. P. Shepherd, R. W. Eason, M. J. F. Healy. Thick film growth of high optical quality low loss (0.1dBcm^-1) Nd:Gd₃Ga₅O₁₂ on Y₃Al₅O₁₂ by pulsed laser deposition. Applied Surface Science Vol. 223 pp. 361-371 (2004).

• Characterisation of the effect of particulate density on film loss and laser threshold.

S. J. Barrington, T. Bhutta, D. P. Shepherd, R. W. Eason. The effect of particulate density on performance of Nd:Gd₃Ga₅O₁₂ waveguide lasers grown by pulsed laser deposition. Optics Communications Vol. 185 pp. 145-52 (2000). 

• Establishment of a CO₂ laser substrate heating system.

S. J. Barrington, R. W. Eason. Homogeneous substrate heating using a CO₂ laser with feedback, rastering, and temperature monitoring. Review of Scientific Instruments Vol. 71 (11) pp. 4223-5 (2000). 

• Growth of lead germanate glass.

S. J. Barrington, S. Mailis, A. A. Anderson, R. Greef, W. S. Brocklesby, H. N. Rutt, R. W. Eason, N. A. Vainos, C. Grivas. UV induced refractive index changes in lead germanate glass waveguides grown by pulsed laser deposition. Photosensitivity in Optical Waveguides and Glasses, Lake Lucerne, Switzerland, 13-18 July (1998). 

• Laser operation of a Ti:sapphire planar waveguide.

A. A. Anderson, R. W. Eason, L. M. B. Hickey, M. Jelínek, C. Grivas, D. S. Gill, N. A. Vainos. A Ti:sapphire planar waveguide laser grown by pulsed laser deposition. Optics Letters Vol. 22 (20) pp. 1556-58 (1997). 

• Low loss of 0.5 dBcm^-1 observed in a lasing 8 µm thick Nd:GGG film.

A. A. Anderson, C. L. Bonner, D. P. Shepherd, R. W. Eason, C. Grivas, D. S. Gill, N. Vainos. Low loss (0.5 dB/cm) Nd:Gd₃Ga₅O₁₂ waveguide layers grown by pulsed laser deposition. Optics Communications Vol. 144 pp. 183-86 (1997).

• Growth of Ti:sapphire crystalline films.

A. A. Anderson, R. W. Eason, M. Jelinek, L. M. B. Hickey, C. Grivas, C. Fotakis, K. Rogers, D. Lane. Waveguiding and crystallographic properties of single crystal Ti:sapphire layers produced by pulsed laser deposition. CLEO-Europe, Hamburg, Germany, September CTuG8 79 (1996). 

• Laser operation of a PLD grown Nd:GGG film.

D. S. Gill, A. A. Anderson, R. W. Eason, T. J. Warburton, D. P. Shepherd. Laser operation of an Nd:Gd₃Ga₅O₁₂ thin-film optical waveguide fabricated by pulsed laser deposition. Applied Physics Letters Vol.69 (1996). 

• Growth of crystalline GGG films.

D. S. Gill, R. W. Eason, J. Mendiola, P. J. Chandler. Growth of crystalline Gd₃Ga₅O₁₂ thin-film optical waveguides by pulsed laser deposition. Applied Physics Letters Vol. 25 pp. 36982 (1995).

• Growth of crystalline KNbO₃ films.

C. Zaldo, D. S. Gill, R. W. Eason, J. Mendiola, P. J. Chandler. Growth of KNbO₃ thin films on MgO by pulsed laser deposition. Applied Physics Letters Vol. 65 (4) pp. 502-504 (1994).

• Growth of chalcogenide glass GLS films.

K. E. Youden, T. Grevatt, R. W. Eason, H. N. Rutt, R. S. Deol, G. Wylangowski. Pulsed laser deposition of Ga-La-S chalcogenide glass thin film optical waveguides. Applied Physics Letters Vol. 63 (12) pp. 1601-1603 (1993).

T.C.May-Smith, Pulsed laser deposition of thick multilayer garnet crystal films for waveguide laser devices PhD Thesis - Apr 2005

S.J.Barrington, Planar waveguide devices fabricated by pulsed laser deposition PhD Thesis - Aug 2001

A.A.Anderson, Crystalline planar waveguide lasers fabricated by pulsed laser deposition PhD Thesis - Sep 1998 

D.S.Gill, Fabrication and characterisation of thin film optical waveguides by pulsed laser deposition PhD Thesis - Jan 1996

K.E.Youden, Fabrication and characterisation of photorefractive thin films and waveguides PhD Thesis - Dec 1992

During the past ten years or so, funding has been obtained predominantly from EPSRC for specific research projects. Additional funding has also been generated from Qinetiq, the EU and the University of Crete.

Click here for a list of the group's publications to date.