Talking Papers
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Radiation sensing fibres - talking papers #5
Imagine:
- clothing that can detect radiation
- a tiny probe to reduce side effects of cancer treatment
Work from a PhD student mixes together two IPAS research themes and demonstrates a novel dosimetry architecture capable of supporting these and many other innovations.
It's a great story on the way IPAS can boost the career of young researches through access to world leaders in six discipline spanning research themes. PhD student Christopher Kalnins has been with IPAS since commencing honours, just a few short years ago. Even before finishing his PhD, Christopher is now lead author on a significant research paper published in Optical Materials Express which shows a novel architecture for dosimetry - the measurement of radiation in an environment. He has been able to mix together expertise from two of the six IPAS trans-disciplinary research themes, namely 'Optical Materials & Structures' and 'Chemical & Radiation Sensing'. Normally a student would have to choose between the opportunity to work on the development of a new material or the testing of the application of a new material in a field of science.
Armed with some fairly rudimentary radiation sources, shields and detectors, a few home-made black boxes (literally!) to keep things dark and a rather basic soft fluoride phosphate glass drawn to a fiber of very simple geometry Christopher was able to demonstrate and measure Optically Stimulated Luminescence or OSL. I spent some time with Chris to talk about his work and to take a look at some of the equipment he used.
It turns out that one of the major challenges in this work was the 'signal to noise ratio', meaning a fairly weak signal in the presence of a lot of background noise. To overcome this challenge Christopher used a bundle of six fibres and went to great pains to eliminate as much background noise, in this case - light, as possible. The lab used looks like a fairly traditional darkroom, with windows blacked out and a 'safe' red light in which it is possible to see equipment. Closer inspection shows that any piece of equipment with a screen or light has been modified by disabling or removing any such light. The next step was for Christopher to build a black box with a lid to contain most of the equipment. Finally, he had to learn to operate his equipment by feel in total darkness as even the 'safe-light' interfered with the results. Listen to this short audio recording for more detail.
Working with IPAS director Professor Tanya Monro and theme leaders Heike Ebendorff-Heidepriem & Nigel Spooner, Christopher published the findings of his work in a paper entitled "Radiation dosimetry using optically stimulated luminescence in fluoride phosphate optical ï¬ÂÂÂÂÂÂÂÂÂÂbres" published in Optical Materials Express by the Optical Society of America. This paper marks the first demonstration of an intrinsic architecture for OSL meaning the fibre acts as both the sensing and light guiding component. From the paper:
In this study we focus on advancing the intrinsic ï¬ÂÂÂÂÂÂÂÂÂÂbre architecture, for the purposes of distributed and environmental sensing in situations where an increase in the radiation ï¬ÂÂÂÂÂÂÂÂÂÂeld is possible. There are many potential environments that would beneï¬ÂÂÂÂÂÂÂÂÂÂt from this method of sensing, primarily any environment in which leakage of ionising radiation from equipment or facilities could potentially occur.
This paper shows shows this novel intrinsic platform / architecture is feasible. Further work to improve the signal noise ratio, starting with new materials then repeating the whole exercise with more precise detectors has already begun. Some time in the not too distant future we may see radiation sensing fibres woven into clothing or formed into tiny probes that measure radiation doses inside a patient during cancer therapy.
Mike Seyfang for IPAS “talking papers” series.
- - - the information below may help the reader to better understand the paper - - -
Definitions:
OSL - Optically Stimulated Luminescence: Optically stimulated luminescence or (OSL) is a method for measuring doses from ionizing radiation (commonly known as radioactive radiation) , wikipedia has a definition that mentions two important application areas.
PhotoDarkening - has been defined as: the phenomenon that the optical power losses in a medium can grow when the medium is irradiated with light at certain wavelengths.
Scintillation - can be defined as: a flash of light produced in a transparent material by an ionization event.
Units:
luminescence - cnts / g / microJ: counts of photons emitted per gram of material per micro joule of energy
scintillation - cnts / s: counts of photons emitted per second
dose - Gray (Gy) is the SI unit of absorbed dose. Joules of energy absorbed per kilogram of material
radiation BQ - emissions per sec: One Becquerel is that quantity of a radioactive material that will have 1 transformations in one second
Links:
paper - http://digital.library.adelaide.edu.au/dspace/handle/2440/68551
YouTube - http://youtu.be/yFB8Kqp-_pk
Audio - http://media.ipas.edu.au/2012/TalkingPapers05ChrisTanya.mp3
Mike Seyfang for IPAS “talking papers” series.
Diamonds inside &ndashw medium fuantum inftion– talking papers serinbsp;#4
Quantum information science prbe a next big t. Diamond nano-crystals can be made to exhibit quantum behaviour through single photon emission but are extremely fiddly to manipulate. Microstructured optical fibres provide a great platform for interacting light with matter and transmitting information over potentially large distances at very low cost. By mixing diamond nano-crystal powder into tellurite glass & taking it through a well established process to create microstructured fibre, IPAS researchers have paved the way for future work that might give us ways to create simple, effective, cheap technologies that bridge quantum/classical, potonic/electronic & nano/micro/macro scale environments. These technologies could well provide industry with new tools for the creation of devices that can send perfectly secure quantum messages, re-define the standard for how we measure light intensity & create new types of sensors.
The paper “Diamond in Tellurite Glass: a New Medium for Quantum Information” published in Advanced Materials shows the world a new hybrid material with implications for quantum information processing and is understandably attracting quite a lot of attention. The fundamental question posed by this research is: if diamond nano-crystal powder is mixed into molten glass, will the special properties of those crystals be retained in a useful way? To answer this question the team made several ‘billets’ of tellurite glass mixed with diamond nano-crystals, extruded them into structured ‘pre-form’ rods which were then drawn into Micro-structured Optical Fibres‘MOF’. Team members from the University of Melbourne then examined the fibres to see how the crystals were distributed in the glass and performed tests to see if they retained their special single photon emission property.
As Melbourne based collaborator Andrew Greentree explains in the audio that accompanies this writing, the diamond nano-crystals are commercially available and were carefully selected for their emission properties and likely ability to survive the fibre fabrication process.
These particular crystals have a nitrogen vacancy colour centre that emits light (as single photons) at a rate of about one every 10 nano-seconds. This is a very bright emission that can be seen through a microscope – unlike the tiny (30 nm diameter) crystals themselves. That said, special skills and a computer controlled microscope were required to find and count the crystals in a section of the special tellurite glass fibre.
Matt Henderson gives us a sense of how tricky it was to mix the diamond powder into the glass and to prevent bad things from happening to the tiny nano-crystals at high temperatures. While the crystals did mix with the molten glass, they tended to ‘clump together’ in these early fabrication runs. Using even smaller quantities of diamond powder and distributing it more evenly throughout the glass will be a focus of future work. Matt also points out that it is not exactly easy to find small numbers of tiny crystals in a ‘huge’ (about the width of a human hair and a few centimetres long) piece of fibre. These images show the light emitting from the diamond nano-crystals as a laser is aimed into the fibre.
The great news is that despite the perils of exposing the diamond nano-crystals to a rather harsh process and their tendency to clump together in the glass, it is still possible to detect single photon emission from a piece of the special micro structured fibre. This is shown in the classic ‘V’ dip in the chart at figure 3c in the paper. The challenge for future research will be to fabricate a much smaller fibre with far fewer diamond nano-crystals and to couple that fibre with a laser in such a way that exactly one photon is emitted each and every time the laser is fired. A source like this could be used to send perfectly secure quantum messages, re-define the standard for how we measure light intensity & react that nano particle with its environment to create new sensors.
Pretty cool eh? IPAS director Prof Tanya Monro thinks so and is particularly optimistic about the potential for this approach which harnesses properties unique to the nano-scale in a platform that is able to be fabricated and manipulated at the macro or micro scale. This blend of materials science, photonics & nano-tech is definitely an area to keep an eye on – and watch out when a cheap, reliable, robust single photon source is developed. I think that will turn out to be one of those ‘tipping points’ we will look back on, possibly through the output device of our shiny new quantum computer.
Mike Seyfang for IPAS “talking papers” series.
Psst: Looking for a really sensitive in Vivo sensor? – talking papers series, #3
The whisper is that IPAS are looking to work with people who need to measure proteins or other bio-molecules “in-Vivo” thanks to a new sensing architecture demonstrated in the paper “Highly efficient excitation and detection of whispering gallery modes in a dye-doped microsphere using a microstructured optical fiber”
Work led by Alexandre Francois shows that whispering gallery modes (WGM) can be excited and detected in dye doped micro spheres via a microstructured optical fibre (MOF). By sticking a tiny sphere to the end of a very thin fibre and running a series of experiments Alex & Kris have demonstrated a new architecture for sensors that not only works but provides a substantial increase in excitation & collection efficiency. The overall efficiency of this robust architecture is 200 times greater than that of more conventional schemes.
The curiously named “whispering gallery mode” refers to a special kind of resonance that occurs when light is trapped within a resonator by total internal reflection. I remember sitting in an IPAS seminar in which Kris Rowland eloquently and with much wit described WGMs using a picture like the one below:
To quote Kris from that presentation “A whispering gallery mode is said to exist when a light wave bouncing around the perimeter of a resonator returns in phase. This means that after one round trip, when the wave “catches its tail”, the wave overlaps itself identically.“
So, exactly how does one precisely position a tiny (10 micrometer) polystyrene sphere on the end of a very thin (130 micrometer) glass fibre? To get those dimensions in perspective, consider that a human hair is typically around 18-80 micrometre in diameter. It turns out that after a bit of ‘playing around’ (quite literally so, according to this audio grab from IPAS director, Prof Tanya Monro) the sphere tends to centre itself on one of the three holes in the MOF and stick there by a combination of electrostatic and surface forces. The end result – a compact and robust architecture for applications such as localized in-vivo/vitro biosensing.
Which leads us to the future…
IPAS are now actively looking for researchers with questions that can (only) be answered by “in vivo” measurement of bio-molecules. There is rich medical information that we cannot currently measure by taking measurements of externally accessible bodily fluids or with existing sensing technologies. This new technique opens up the possibility of increasing out understanding of the origins of disease and our response to treatment at a local level inside our bodies. Imagine, for example, being able to measure the response of a tumor to a new cancer treatment in real time ( “in vivo” and “in situ”). It is hoped that the development of specific sensors based on this newrchitecture will be extremely useful.
To paraphrase Tanya from the audio interviews that accompany this story:
“one day clinicians may have a little kit of spheres that have been functionalised to detect all their favorite bio markers and make a clinical decision on which ones to pick up on the end of a fibre and stick into the patient”.
Ouch!
Mike Seyfang for IPAS “talking papers” series
A new platform for ion sensing in small volumes – talking papers series, #2
This paper delivers on Professor Monro’s vision of new platforms for sensing that push the boundaries of what can be done with extremely versatile micro-structured optical fibres when resarchers take a trans-disciplinary approach to their collaboration. It is well known that these fibres have the potential to deliver results in real-time, in-situ, by directly accessing tiny volumes of fluids smaller than those typically found in living cells. The work done for the paper “Fluorescence-Based Aluminum Ion Sensing using a Surface Functionalized Microstructured Optical Fiber“ combines commercially available chemicals with micro-structured fibres in a way that retains the useful characteristics of each, thus paving the way for a new platform in (ion) sensing. I spoke to two of the paper’s authors and IPAS director Professor Tanya Monro to find out more about the achievements and challenges in this important quest.
Stephen Warren-Smith and Sabrina Heng joined forces under Tanya’s guidance and with support from Andrew Abell, worked in the space between their two disciplines – Physics and Chemistry. Sabrina and her colleagues adapted an existing commercially available synthetic compound (a ‘flurophore’ called lumogallion). This new ‘compound 3′ is designed to stick to the glass surfaces of the micro-structured fibre while retaining or enhancing fluorescence in the presence of aluminium ions. Sabrina tells me they made good progress with ‘compound 3′ because it only takes a few steps to make, is made from low cost ingredients and provides a reasonably high yield.
Compound ’3′ – modified Lumogallion
While the compound did bind well to the fibre surface, it did so in such a way that may have impacted on sensitivity and was easily removed. There is room for improvement here. Stephen tells me there are many ways in which the binding may be improved – by tweaking the chemistry of the flurophore and/or that of the polyelectrolyte intermediate layer to which the fluorophore attaches. Alternatively, there are other ways to approach the coating (or ‘functionalisation’) of the micro-structured fibres to try in future research. One of the challenges faced is in quantifying (or even seeing) the extent to which the flurophore has coated the fibre surface – the subject of current work by other IPAS researchers. Tanya informs me that this is the first time IPAS has produced a variant of a known flurophore that has been adapted to enable surface functionalisation. This approach means there is great potential for development that benefits from the economy of scale.
Small scale of flushing equipment
Something that surprised me while collecting photographs of the equipment used in this research was the small scale of everything. While the paper does contain phrases such as “approximately 2 mL of the reaction mixture was used for the experiment” I did not imagine the nitrogen pumping apparatus, or the fluorescence cuvettes at a realistic scale. Stephen reminded me that one of the key features of micro-structured optical fibres is their tiny (less than a human hair) outer diameters which makes them ideal for sensing in-situ. Furthermore, they can be as short (or long) as required to transmit the fluorescence information from the sample to the detector. As you can hear in this short audio recording with Prof Monro, Stephen’s experimental work is the first to record this type of “dip-sensing” that works in only a few nano-litres of liquid.
Only 2x600mm lengths of the specially enhanced fibre were used for this work – and working lengths of 60mm after surface coating (or ‘functionalisation’) were used to perform the sensing measurements. I recorded some audio from a conversation with Stephen which gives a great behind the scenes look at the remarkable teamwork required to envisage, design, create and characterise this new platform for sensing. It goes something like this…
The micro-structured fibre lengths were flushed with a saline solution of polyelectrolyte (PAH) for 30 mintues. Each 600mm length of fibre had to be cleaned by pumping water through for 30 minutes then dried by flushing with nitrogen gas for a futher 30 minutes. Visual inspection was done using an optical microscope which is quite fiddly and laborious – especially since it is not possible to see fluids inside – only the meniscus that forms at the barrier between fluid and air can be seen.
Early work on the chemical attachment concept originated with Dr Markus Pietsch who is now at the University of Cologne hospital in Germany. Fellow IPAS researcher Alexandre Francois suggested the polyelectrolyte approach which first binds an intermediate layer to the glass fibre via electrostatic forces. The modified flurophore then attaches chemically to this intermediate layer via covalent bonds. Roger Moore (no, not that one!) found a way to ‘inflate’ the tiny holes inside the ’wagon-wheel’ fibre using positive gas pressure during the drawing process. This is needed to avoid blockage of the holes during the flushing and coating steps required to functionalise the surface and to enable liquid sample to enter the holes during dip sensing. Peter Hoffmann (now deputy director of IPAS) provided access to a Typhoon imager used in the glass slide characterisation. The whole effort was made possible thanks to funding from the DSTO and ARC for Tanya Monro’s Federation Fellowship program.
This paper opens the door to a whole new platform for sensing that will allow IPAS to build tools for further research and to partner with industry in developing products with a diverse range of applications in fields from medicine, the environment and agriculture through to defence industries. The commercial opportunity for sensors based on this platform are enhanced by some of the new discoveries and potential for cost effective scale.
Cleaving machine
Fluorescence (dramatised for visual effect)
Mike Seyfang for IPAS “talking papers” series
‘Printing’ lasers as tools for IPAS research – talking papers series, #1
Recent work published by IPAS senior researcher David Lancaster brings the team a step closer to being able to ‘print’ (or burn / write) highly specialized lasers required for further research into a wide range of photonics and advanced sensing technologies. With the right kind of industry partner, this work could lead to extremely fast and cheap ways to fabricate lasers for the mass market. Earlier this week I caught up with David to discuss his recently published paper “Fifty percent internal slope efficiency femtosecond direct-written Tm3+:ZBLAN waveguide laser”.
On the way to David’s office at the Institute for Photonics and Advanced Sensing (IPAS) at the University of Adelaide I had one last read through the abstract of this curiously titled paper. Having circled the words ‘doped’, ‘pumped’, ‘resonator’ my attention was grabbed by the final phrases ‘the most efficient laser’ (created in a glass host) via ‘femtosecond waveguide writing’. I figured I would ask about ‘writing a waveguide’ in glass first, then tackle the mysterious ‘fifty percent internal slope efficiency’.
Our conversation began with a brief description of using a precisely focussed laser beam to create tiny ‘bubbles’ of plasma that altered the all important refractive index property of the host glass. (The host glass in this case being a heavy-metal fluoride called ZBLAN). David showed me some microscope images of these tiny bubbles arranged in various patterns and very patiently explained how these patterns created wave-guides similar to those already being fabricated in the IPAS labs. (By a process of extruding molten glass into cylindrical pre-forms which are then re-heated and drawn to the same geometry but less than the thickness of a human hair). I have to admit that I really did not understand how these dots that are ‘written’ (or ‘burned’) into the host glass could do anything useful. Then an object on David’s bookshelf caught my attention – it was a glass cube that had a three dimensional image of a racing car burned (written or 3D-printed) into it.
Then the penny dropped – I knew these glass art works were created by making a design using C.A.D. software then ‘printing’ the three dimensional design into the glass using tightly focussed laser beams to burn (or ‘write’) tiny holes at various x,y,z coordinates. David (and his collaborators at Macquarie University) are doing the same thing – designing three dimensional patterns (that resemble those of the micro-structured fibres fabricated in the IPAS labs) in software and ‘printing’ (or writing) them into the host glass. So there it is – using a laser to ‘write’ (or print / burn) a structure that can guide light (waveguide) in such a way that it can behave as a new laser. It turns out that this technique has been around for a while – the surprise finding described in this paper is just how efficient the resulting laser produced by this inherently fast and cheap process is. We are talking around 12 seconds to write a small batch of lasers at a cost of hundreds of dollars for short runs in lab conditions – plenty of room for dramatic cost reductions in a large-scale commercial process.
So that covers the ‘Femtosecond direct-written Tm3+:ZBLAN waveguide laser’ half of the title, or nearly. Femtosecond (1×10-15 seconds) is unit of the extremely brief duration of each pulse of the tightly focussed writing laser. Each tiny dot is written into the host glass in a few such pulses. Tm3+ is the form of rare-earth ionThulium that emits the photons we desire when excited by another “pump” laser. ZBLAN is our heavy-metal fluoride host glass that has been ‘doped’ with Tm3+ as mentioned earlier.
What, then, is the big deal about the “Fifty percent internal slope efficiency”? Well, it is a good numeric indicator for the efficiency and therefore usefulness of the resulting waveguide laser. At the time this work was being undertaken the best researchers could manage for a similar regime was around 2%. The highest efficiency ever reported for any type of directly written waveguide laser in glass was 21% (for lasers that work in much less elusive wavelengths). The techniques explored by IPAS gave an extremely encouraging result on first try with plenty of room for improvement and customization. The high internal slope efficiency translates to very user-friendly output that is inherently low-loss and thermally efficient. This means that much less engineering is required to manage heat (a problem for most lasers). Furthermore this host/dopant combination is very stable and not particularly prone to ‘self-erasing’ – a problem in many direct written waveguide lasers.
So what for the future of this technique? David tells me he is confident that his team will be able to design waveguide geometries that include the ‘resonator’ function (which was provided by a pair of external mirrors at each end) of the waveguide laser. This removes the need for a whole bunch of engineering and makes for a very useful laser produced entirely with this rapid and cheap technique. Next the team plan to experiment with and characterize combinations of slightly different host glass, dopant and waveguide geometry which will enable IPAS to design and manufacture lasers with very specific properties and to chase those elusive long (mid-infrared) wavelengths that are particularly useful in high end applications.
Speaking of applications, David is optimistic about the potential uses of this technique to develop low cost tools for sensing in general and gave a couple of example scenarios that should be possible. One is in the area of tissue imaging – which requires lasers with very specific characteristics to ‘see through’ various types of internal organs etc. Another is in the area of coherent L.I.D.A.R. which currently requires very expensive specialised lasers. The military are always interested in lasers that work in the mid-infrared beacause that is where they can see heat. Spectroscopy is another area that could benefit from small, cheap, portable lasers that will enable sensing to move out of the labs and into the field – for example to detect contaminants or pathogens in-situ.
In a subsequent chat with Prof. Tanya Monro, Director of IPAS, I learned how the idea of being able to create new & specialised tools for research is entirely consistent with her vision for ‘platform technologies’ coming out of the Institute. The work described in this paper creates a pathway to accessible and scaleable technologies that will produce cheap, robust and useful lasers at wavelengths that currenly require expensive and bulky equipment which can only be operated by experts.
IPAS would like to acknowledge the State Government (the PSRF in particular) for funding this work, the collaborators at Macquarie University and the ANFF facilities.
If this story has captured your imagination, take a listen to these brief audio comments from Associate Professor David Lancaster and IPAS Director, Professor Tanya Monro.
Mike Seyfang for IPAS “talking papers” series
