IN THIS SECTION
1. New Sources and Active Materials
There is a serious shortage of compact, reliable, powerful and preferably solid state laser sources in the mid infrared spectral region. Most laser materials require the active material - often a lanthanide ion such as erbium or holmium in its trivalent state - as a dopant in a 'host' material. The properties of the host are critical to the laser's success. It must obviously be transparent to the required laser wavelength, but additionally it must show low non radiative relaxation for the upper energy level utilized in the laser. Fortunately these two requirements are compatible, one solution is to use hosts containing heavy atoms and no oxygen ('low phonon energy hosts'). This leads to three of our research programs.
1.1 Chalcogenide Glass Films
In the solid state our interests centre on thin films of gallium-lanthanum sulphide (Ga2S3-La2S3)
Because oxygen or hydrogen contamination would cause unacceptable loss in our films the chamber is constructed to a high vacuum standard (10-7 Torr) and is fitted with a load lock to reduce exposure to air and provide rapid substrate change. The substrate can be both heated and, more unusually, cooled to below minus one hundred degrees centigrade which proves advantageous for these amorphous films. Substrate oscillation during deposition provides improved uniformity, whilst large, rotating targets give reproducible films and freedom from GLS target thermal damage.Twin targets are provided for simultaneous deposition and will enable control of dopant levels and GLS composition without the need to fabricate new targets for each desired dopant etc. Deposition may be carried out under vacuum, inert gas, oxygen or hydrogen sulphide.
The chamber is working extremely well and producing large numbers of high quality films. Our attention is now turning to analysing the properties of these films, understanding their relationship to the glass structure, and optimising them for device performance. This includes infrared and visible spectroscopy, kinetics measurements on dopants, measurement of the photomodification effect (and development of novel instrumentation for this), ellipsometry, X-ray diffraction, and we hope in the near future to utilise RBS and EXAFS.
Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is a technique used to determine short-range interatomic correlations in a solid. It involves the measurements of the X-ray absorption coefficient u of atoms as a function of photon energy E. In general the absorption coefficient is a decreasing function of E, but discontinuous increases, i.e absorption edges, occur when an X-ray photon having higher energy than the binding energy of a core electron is absorbed by the atom, exciting the electron to a continuum state.
EXAFS oscillations carry information on local atomic arrangements around the absorbing atom, such as the type and number of neighbouring atoms and their distance away from the absorbing atoms.
The availability of intense sources of continuous X-radiation, particularly in the form of dedicated storage rings, has stimulated the development of X-ray techniques for structure determination. EXAFS spectroscopy has been known for over 60 years, but it is only in the last two decades that advances in the physical theory of EXAFS and in data analysis have changed the technique from a scientific curiosity to a quantitative tool for structure determination.
In this group, the EXAFS experiments are carried out using the synchrotron radiation source at the EPSRC Daresbury Laboratory in the UK. The source is actually the electron storage ring which is capable of holding a beam of electrons at energies up to 2 GeV and currents of approximately 200 mA for many hours. We make measurements at the sulphur, gallium and lanthanum edges to determine the structure of our GLS bulk samples and thin films, and to determine the structural effects of photomodifying the films.
Rivers PE, Rutt HN and Asal R, High sensitivity mapping of refractive index across a surface using a dual beam differential reflectance technique, Measurement Science and Technology, 9, 1998, pp. 86-94
Asal R and Rutt HN, Optical properties of laser ablated gallium lanthanum sulphide chalcogenide glass thin films prepared at different deposition laser densities Optical Materials, 8, 1997, pp. 259-268
Asal R, Rivers PE and Rutt HN, A structured study of gallium lanthanum sulphide glass bulk and thin films by x-ray absorption fine structure spectroscopy, Journal of Physics: Condensed Matter, 9 pp.6217-6230, 1997
Asal R, Rivers PE and Rutt H N, Optical properties and local structures of gallium lanthanum sulphide/oxide thin film for waveguide lasers, poster presented at QE13 Conference, Cardiff, UK, 1997
Asal R, Rivers PE and Rutt HN, Gallium lanthanum sulphide films for waveguides devices, CLEO '96 Conference on Laser and Electro Optics, paper CWG6, Los Angeles, June 1996
Asal R, Rivers PE and Rutt HN, Laser Ablation Deposition of Ga2S3-La2S3 Glass Films, Materials Research Society Symposium Proceedings 1996, vol. 397, p. 253
Gill DS, Eason RW, Zaldo C, Rutt HN and Vainos NA, Characterisation of Ga-La-S chalcogenide glass thin film optical waveguides, fabricated by pulsed laser deposition, Journal of Non-Crystalline Solids, 191 pp 321-326, 1995
Eason RW, Youden KE, Grevatt T, Rutt HN, Deol RS, Wylangowski G and Gill DS, Pulsed laser deposition of Ga-La-S chalcogenide glass films for optical waveguide applications, AIP Conference Proceedings 288, Laser Ablation: Mechanisms and Applications II, Knoxville 1993, p. 583
Youden KE, Grevatt T, Eason RW, Rutt HN, Deol RS and Wylangowski G, Pulsed laser deposition of Ga-La-S chalcogenide glass films for optical waveguides,Applied Physics Letters, 63 (12) 1993, pp. 1601-1603
2. Medical Applications of Infrared Spectroscopy
Mid-infrared (MIR) spectroscopy is so specific that not only can chemical compounds be identified, but individual isotopic species are distinguishable from one another thereby, allowing measurement of isotopic ratios. The infrared spectroscopic measurement of isotopic ratios is based upon the isotopic shift in the spectrum of the tracer molecule. When a particular atom in a molecule is replaced by its isotope it remains chemically identical to the original in every way except for a change in total mass associated with the number of neutrons present, eg addition of a neutron to 12CO2 produces a 13CO2 molecule. 13CO2 and 12CO2 are known as isotopomers of carbon dioxide. The increment in mass between two isotopomers leads to their infrared absorption spectrum being slightly off-set from one another.
This can form the basis for convenient, non-invasive medical tests by measuring the change of the ratio in a breath sample related to the ratio in a sample taken after the administration of a 13C labelled dose. Such tests are known as isotopic breath tests and can be used for the investigation of metabolism, bacterial colonisation and organ function. The most prominent use of the 13CO2/12CO2 ratio test is for the detection of Helicobacter Pylori, a bacteria found in the duodenum. Helicobacter Pylori is recognized as the major aetiological factor of non- autoimmune gastritis, as well as gastric and duodenal ulcers. It has been shown that eradication of the Helicobacter Pylori promotes healing of these and greatly decreases the chance of recurrence. The bacteria is also associated with gastric cancer, with Helicobacter Pylori being given the same carcinogenic classification as cigarette smoke. Recently there has been much activity to develop a 13C-erythromycin (C37H67NO13) breath test for determining in-vivo cytochrome P4503A4 (CYP3A4) activity. This is an enzyme associated with the metabolism of a large number of endogenous and exogenous compounds. Many of the new drugs are CYP3A4 substrates and knowledge of the patients in-vivo CYP3A4 activity will allow precise prescription of tailored drug doses.
However, the widespread routine clinical use of isotope breath tests is limited by the requirement of an Isotope Ratio Mass Spectrometer (IRMS). The IRMS is very sensitive but has the disadvantages of being a large, complex instrument requiring a specialised technician and also has high capital and maintenance costs. The instrument produced from this project is intended to replace the mass spectrometer's analytical role in such isotopic ratio breath tests, making the technique far more accessible and affordable, thus moving the technology out of the research establishments and into the hospitals and health clinics. The challenge therefore, is to design a compact, low cost, highly reliable instrument with minimal restrictions on its usability.
One of the first things to be considered was whether or not infrared spectroscopy was a suitable way of measuring the 13CO2/12CO2 ratio. The nature of a diagnostic instrument requires it to be reliable and the risk of spurious results minimised as the dangers of a misdiagnosis leading to an incorrect treatment are obvious. Such a risk is manifested by any metabolic products or by-products that are excreted from the body via the respiratory system and also by any exogenous contaminants that are present in the patient's breath sample. Also the absorption bands of other CO2 isotopomers and hotbands need to be taken into consideration. Our initial work has confirmed in detail that other substances present on the breath will not invalidate the result.
The method of measuring the isotope ratio requires a precision measurement very much higher than is usual in infrared measurements, and we are in the process of designing a device with a novel configuration which promises very high accuracy and freedom from drifts due to changes in sample pressure, temperature etc. Use of an alternative isotope ratio to that of 13CO2/12CO2 is also being investigated along with a novel technique of high precision frequency selectivity.
After further investigation using computer simulations we will be seeking industrial collaborators in the medical instrumentation field.
Mansfield C and Rutt H N, Development of an Infrared Diagnostic Instrument for the Measurement of CO2 Isotope Ratios in Breath, SPIE International Symposium on Systems and Technologies for Clinical Diagnostics and Drug Discovery II, V.3603, pp36-48, San Jose, California January 1999
- The International Foundation for Helicobacter and Intestinal Immunology,
- The Japanese Helicobacter Page
Dr C Mansfield recently completed his PhD on this subject, and we are seeking a student to continue the work with the construction of an instrument. 3. Novel Infrared Image Modulators
The new generation of thermal imagers employing pyroelectric detector arrays have eliminated the need for high speed mechanical scanning and cryogenic cooling typical of older systems. As such they offer the prospect of compact, low cost systems of high reliability and possibly consumer market penetration for this 'ex-military' technology.
They do however have a major disadvantage in that a 'chopper', a mechanical shutter to periodically interrupt the infrared image is vital to the operation of pyroelectric arrays. This re-introduces a mechanical device which ideally should be all solid state. A solution to this problem has been sought for some years.
We have developed a new all solid state shutter for the eight to fourteen micron thermal image band. Preliminary results show excellent modulation - over 98% 'on' state transmission would be achieved by the simple addition of an antireflection coating, with less than 10% 'off' state. This greatly exceeds the performance achieved elsewhere, and is in a very practical form suitable for large area image modulation over the full thermal image band.
We have recently taken out a patent on the device and obtained a substantial two year contract from DERA Malvern to proceed with its optimisation. We are seeking further support for alternative embodiments and applications of the device from industrial sources.
P D Fairley, H N Rutt, Novel Germanium Infrared Modulator, J. Phys D, Applied Physics, Volume 33 pp2837-2852 2000
P D Fairley, H N Rutt, Microwave PCD technique applied to extraction of carrier parameters in a germanium IR modulator, submitted to Semiconductor Science and Technology, 2000.
Fairley PD and Rutt HN, Mid-infrared Optoelectronic materials & devices, 17-18th September 1996, Lancaster University
Fairley PD and Rutt HN, Germanium induced absorption chopper, SIOE '97, University of Wales, Cardif, 24-26th March 1997, IOP
Patent, Joint with DERA, H N Rutt, R Watton, P Manning
19/9/95 - Infrared modulating device - 95/9078.1
Dr P Fairley recently completed his PhD on optically powered operation of the modulator, and we are seeking a student to continue with work on an electrically operated device.
4. Multi-Quantum-Well Far Infrared Lasers
Coherent electromagnetic wave sources in submillimeter or far infrared (FIR) region 30-300 µm can be used as local oscillator sources for communications, remote sensing, radar, astronomy and applied in spectroscopy. FIR multi-quantum-well (MQW) lasers utilizing intersubband transitions have potential in this spectral region and have advantages in efficiency, size and cost.
- Design of MQW FIR lasers
- Physics of MQW FIR lasers
- Inhomogeneous effect on MQW FIR lasers
- Laser device processing
- FIR laser characterization
- Emitter in mid-IR
- Gas sensing
Z Xin, H N Rutt, and H A Tan, Electron Lifetime Measurement in Stepped Quantum Wells for Far Infrared Lasers , Semiconductor and Integrated Optoelectronics (SIOE '2000). 17-19 April 2000, Aberdare Hall, Cardiff, Wales.
Z Xin and H N Rutt, Effect of inhomogeneity on quantum well far-infrared lasers, Journal of Applied Physics, 83, 1998, p. 1491
Z Xin and H N Rutt, Optimization of intersubband QW Far IR Lasers, SIOE'97, Cardiff, UK,1997.
Z Xin and H N Rutt, Design of Intersubband Quantum Well Far Infrared Lasers, Semicond. Sci. Technol., 12(1997), pp. 1129-1134.
Z Xin and H N Rutt, Effect of inhomogeneity on quantum well far-infrared lasers, presented in QE13, Cardiff, UK, 1997.
Z Xin and H N Rutt, Effect of inhomogeneity on quantum well far-infrared lasers, to be published: Journal of Applied Physics, February 1998.
Z Xin and H N Rutt, Inhomogenous broadening in quantum well far-infrared lasers, in preparation
5. Other Activities
The group has a range of other activities arising from the need for specialist instrumentation arising in other areas of our work and also from specific problems identified through industrial contacts. These have included, for example the design and construction of a wide range infrared polarizer and analysis of possible improvements in SPRITE based thermal imagers.
Rutt H N, Optimisation of SPRITE integration and readout lengths, SPIE International Symposium on Optics, Imaging and Instrumentations, San Diego, July 1994, Paper No 2274, pp 126-135
Rutt H N, Optically pumped mid infrared laser action in the monohaloacetylenes, 20th International Conference on Infrared and Millimetre Waves, Paper T 7.5, 11-15 December, Orlando, Florida, USA, 1995
Rutt H N , Letter on "Far infrared radiation - another view", published in OE Reports, March 1994, pp 8 and 15
Rutt H N, Letter on "Etalon effects in laser mirrors", Optical Engineering, 34 (6), (COM 1124), June 1995, pp 1838-1839
Rutt H N, A low-cost, ultra-wide range infrared polarizer, Measurement Science Technology, 6, 1995, pp 1124-1132
Rutt H N, Optically pumped mid infrared laser action in the monohaloacetylenes, Optical Communications, 120 (5/6), October 1995, pp 287-294
Rutt HN,Angular tolerances and trapped internal reflections in wedged high refractive index Brewster's angle plates, Journal of Infrared Physics and Technology, 58, 1997
Huang X, Chandler PJ, Townsend PD and Rutt HN, Ion-implanted lanthanum fluoride waveguides, Nuclear Instruments and Methods in Physics Research B, 127-128, 1997, pp. 533-536
Coleman A P, Nieuwenhuyzen M, Rutt H N and Seddon K R, Novel Ionic Media for Liquid Lasers, J. Chem. Soc. Chem. Communications, 23, pp. 2369-2370, 1995
Coleman A P and Rutt H N, Inorganic solvent systems for lanthanide ions, Optical Materials, 5, 1996
Patent, University of Southampton, H N Rutt
26/8/95 - Diode laser - 9517545
6. Group Facilities
Although a new group, we are steadily establishing a core of excellent experimental facilities for infrared material and device fabrication and characterisation.
Our major facilities now include a very highly specified PE2000 Fourier Transform Infrared (FTIR) spectrophotometer operating over an exceptionally wide range of 0.64 microns to beyond 100 microns at high resolution (0.2 wavenumbers.) Visible spectroscopy is also available, and furnaces for glass target fabrication. We have recently purchased a closed cycle cryostat which achieves a 6K ultimate temperature in half an hour, and very high cooling powers at 10K (2W) for cryogenic semiconductor work and material characterisation. Precision calibrated black body sources are available for detector calibration, and a wide range of laser sources including near infrared diodes, 1.15, 3.39, 5 micron region and 9-11 micron gas lasers for test purposes. We have both pulsed TEA and CW carbon dioxide lasers. Additionally the group has a wide range of detectors and supporting electronics including high speed 'boxcar' facilities.
A new addition to the armoury, due to arrive in late 2000, is a Carey Eclipse Spectrofluorimeter. This machine, new on the market, will give us a visible and near infrared fluorescence measurement capability, and has both excitation and emission monochromators. We plan to fit our variable temperature, 6K closed cycle cryostat to it.
For waveguide measurements we have a Metricon prism coupler. This permits measurement of both TE and TM modes in thin film waveguides, to determine film thickness and index. It also provides loss measurement. We have modified our instrument so that measurements can be made at a series of different wavelengths across the red and near infared spectrum (0.633um to 1.6um.) This gives an invaluable insight into loss mechanisms, and direct results at device relevant wavelengths. Recently the group has expanded its facilities with the purchase of an Edwards Auto 306 coating plant. It is equipped with high speed turbo molecular pumping, a large chamber and a wide range of evaporation and monitoring facilities. It will permit the fabrication of laser mirrors, antireflection coatings and waveguide layers in a facility dedicated to the group and in which the use of infrared relevant materials (chalcogenides etc) is acceptable. Another recent purchase is a high power, 500mW, single transverse mode tuneable diode laser which covers a range of 965nm to over 1000nm (1 micron). It is equipped with a broad band isolator and will be an invaluable addition to our laser pumping capabilities. This chamber has now been enhanced with the addidition of a low energy ion beam, which can be used for substrate cleaning and ion beam assisten deposition (IBAD.)
7. New Grants
Recently we have won several new grants. We are very grateful to the funding agencies for their continued support!
A major new EPSRC grant funds work on our novel Multiple Quantum Well Far Infrared lasers, including growth of MQW structures at the Sheffield III-V facility, and collaboratively with Prof Colin Stanley at Glasgow University.
We participate in the EPSRC program on the FELIX free electron laser, and Prof Rutt is one of the joint investigators on the EPSRC FELIX contract. He is also the EPSRC representative to the FELIX program advisory committee. A grant from the Rank Prize Funds both enabled us to purchase the Edwards 306 coating unit and will also supplement a three year PhD studentship with an extra £1500 per year. The work will be on novel infrared lasers, and would suite a physicist or physical chemist. We do not want to give all our novel ideas away here, so if you are interested contact Prof Rutt! Secondly jointly with Dr Rob Eason of the ORC we have won a substantial new EPSRC grant entitled 'Laser Ablative Deposition of Epitaxial Thin Film Waveguide Optical Devices.' We are very pleased to strengthen our ORC links in this way. The program will build on the great success Rob has had recently with GGG films, and our own work on ablating chalcogenides. Finally, Dr Greg Parker as principle investigator together with Prof Rutt and Dr Bob Greef in Chemistry have won an EPSRC grant for 'Two and Three Dimensional Photonic Band Gap Structures in Si and Si/Ge'. from the 1996 Microstructured photonics material programme. One interest here is whether photonic bandgap structures can be made in high refractive index, infrared transparent germanium and silicon germanium alloys.
8. Plans for the Future
9. Infrared Physics and Technology
Prof Rutt is editor-in-chief of the Elsevier Journal 'Infrared Physics and Technology.' The journal publishes papers covering a very wide range of material in its subject area, covering for example detectors, infrared instruments and systems, infared lasers and materials etc etc, right across the IR spectrum from the NIR to the sub millimetre.You will find the details at Infrared Physics & Technology. If you are working in the IR we would be happy to receive your papers - and feel free to contact Prof Rutt to discuss any proposals for review articles or special issues etc. We are very happy to consider special issues based on the proceedings of small, relevant specialist meetings, or organised by a guest editor. If you are active in the IR and would like to become more actively involved we may shortly have some spaces on the honorary editorial board.
Copyright University of Southampton 2006