FTIR USING ASYNCHRONOUS FEMTOSECOND OPOS: A NEW PARADIGM FOR HIGH-RESOLUTION FREE-SPACE MID-INFRARED SPECTROSCOPY

This proposal for an EPSRC-NPL Postdoctoral Research Partnership addresses the call theme identified as, Photonic Technologies for Optical Remote Sensing in Carbon Capture and Storage and Other Climate Change Applications, and will be conducted in partnership with Dr Tom Gardiner, head of NPL's Environmental Measurement Group.Using their unique infrared differential absorption LIDAR (DIAL) system, NPL's Environmental Measurement Group carries out remote monitoring for the qualification of airborne emissions from industrial installations such as land-fill repositories, petrochemical stacks, cement factories etc. Such quantitative monitoring is an essential procedure in the government's compliance - via carbon taxes imposed on polluters - with the reductions in CO2 and CH4 emissions mandated by the Kyoto Protocol.While being a mature technique, infrared DIAL has reached the limits of its detector technology, and moreover is seriously constrained by its inability to simultaneously measure different gases, a direct consequence of the use of two narrow-linewidth laser wavelengths in the technique. DIAL lacks the ability to obtain true spectroscopic information in a single measurement, and therefore cannot benefit from the sophisticated analysis tools that exist in FTIR to extract the concentrations of multiple species from an absorption spectrum. A system combining the bandwidth and spectral resolution of FTIR, with the remote-sensing facility of DIAL would enhance and extend NPL's technical capability to monitor the emissions of greenhouse gases implicated in climate change.We propose to address this requirement by combining...(a) our world-leading work in femtosecond (fs) FTIR spectroscopy (we were the first group to demonstrate the technique)(b) our world-leading expertise in mid-infrared OPO frequency combs (again, we were the first group to demonstrate a fs OPO frequency comb)Normally FTIR spectroscopy is carried out with thermal sources (globars etc) that produce poorly collimated IR beams that are incompatible with free-space propagation over extended distances. By contrast, the output from a fs OPO has a broad IR bandwidth, approaching that of a thermal emitter, but - critically - has the spatial coherence of a laser, permitting free-space propagation over long distances. A fs OPO therefore provides a route to implementing free-space FTIR across several hundred cm-1 in a single measurement - sufficient to probe the characteristic absorption lines of many chemical species in a single measurement.Conscious of the practical challenges of implementing an interferometric technique over long distances, we propose a novel technical approach, to implement a robust, no-moving-parts FTIR system, which we will progress, in stages, from a bench-top demonstrator to a free-space field-trial at NPL's Teddington site.The concept is based around replacing a mechanically-scanned optical delay line with two asynchronous, phase-coherent mid-IR pulse sequences derived from identical OPOs. Uniquely, this approach is robust, and has the potential to acquire a high (< 0.01 cm-1) resolution spectrum in only a few milliseconds. It offers precisely range-gated detection over propagation distance of potentially 100's of metres, and perhaps further using infrared time-correlated single-photon-counting detection (a technique which the project will have access to at Heriot-Watt).In comparison with DIAL, the technique offers greater spectral discrimination and the ability to simultaneously probe for multiple gases. Furthermore, it is all-solid-state, providing a potentially more compact and efficient solution than DIAL, and avoids the use of dye laser technology, eliminating the associated carccarcinogen hazard. It will extend sensing to new chemical species where suitable DIAL lines are unavailable, and is compatible with heterodyne / RF lock-in detection techniques for improved signal:noise performance.

The principal commercial beneficiary will be NPL, who will benefit from the enhanced technical capability for range-resolved concentration measurements of diverse airborne pollutants, with the potential to increase their revenue from associated consultancy and commercial R&D work. The proposed system will provide quantitative gas concentration measurements of benefit to the Environmental Protection Agency, which will use the data to test the compliance of industrial installations with pollution legislation. Such data will have a consequent impact for government policy makers, for example in terms of the level of carbon taxes imposed on polluters. If the sources developed in the project lead to patentable inventions, these may benefit UK photonics manufacturers who, by licensing the inventions, will be able to bring to market cheaper, more versatile mid-IR ultrafast sources than their competitors. Alternatively, a spin-out company based on the same IP would directly benefit the UK economy by creating new skilled employment, and by attracting further R&D investment into the company from international investors. The research has potential impacts in chemical / biological agent detection of operational interest to the Ministry of Defence for the optical detection of the vapour signatures of improvised explosive devices and landmines. Heriot-Watt's Technology and Research Services (TRS) office is the research and knowledge transfer support unit for the University providing a range of pre-award, exploitation, commercialisation and legal services to academics. Heriot-Watt has an excellent reputation for working successfully with industry and policy makers to apply and exploit knowledge created here. TRS are able to provide support and advice covering a wide spectrum of exploitation activities from successful knowledge exchange applications and PPE activity, to KTPs through to licensing and spin outs. During the project the PI and other relevant staff will ensure that TRS are informed of potential opportunities and we will work with them to ensure that all possible exploitation is pursued and is properly protected by the appropriate means (e.g. collaboration agreements, NDAs, patent applications). At Heriot-Watt, the PI will take responsibility for identifying research outcomes that should be progressed further in order to maximise the opportunity for commercial or other general impact. Evidence of the PI's experience in this activity include: (i) His previous patenting and commercialisation of a pulse measurement instrument in 1997 (ii) Examples of several articles in the non-academic industry literature (iii) His historic cash funding from industry, amounting to 350k over the last 6 years (iv) His short-listing for the current Scottish Enterprise Proof-of-Concept commercialisation competition (v) His appearance as a finalist in the Thales Scottish Technology Prize 2008 Some activities will require the collaboration of colleagues at Heriot-Watt, for example preparing patent applications, market research, or making applications to other specialist commercialisation schemes such as Scottish Enterprise Proof-of-Concept. Staff from TRS will assist with advertising technologies resulting from our research specialist on websites such as University.com and the Innovation Relay Centre. Close interactions of TRS with organisations such as Interface, the ITIs and the investment community will facilitate marketing and commercialisation of our proposed technology. Many of the impact activities have no direct resource implications or are supported by central university services. Knowledge exchange costs associated with the PDRA secondment to NPL are already covered in the core proposal budget.