Detection and identification of gaseous species is crucial in applications spanning through defence and security, bio-medical, environmental monitoring and various others. Many techniques have been demonstrated over the years, with some demonstrating sensitivity to different molecules with concentrations as low as parts-per-quadrillion. However, such technologies are usually complicated with limited applicability beyond the lab. Therefore, there is still need for development of lightweight, compact and portable sensing devices that will bring the high sensitivity sensing into the field.
In this project we aim to place our focus on one of the laser-based spectroscopic techniques – photoacoustic spectroscopy (PAS). Here the wavelength of an excitation source is chosen such that it is coincident with a molecular absorption of the compounds of interest. When these molecules are within the excitation range, a portion of that radiation is absorbed which in turn leads to weak heating – and thus a change in density. Modulation of the incident wave causes an associated modulation in density, resulting in a periodic pressure – or sound – wave. This sound wave can subsequently be detected with a microphone-type arrangement. It is an ideal laser-based gas trace detection technique as it allows to combine rugged, highly compact topology with potentially very high specificity (as conferred by the laser linewidth), selectivity (from laser tunability) and, potentially, sensitivity (matching that of laboratory-based techniques).
An exciting opportunity exists to develop and refine the spectroscopic work of the team at the Fraunhofer centre by combining their laser-based systems with the extensive expertise of Dr Michael Lengden gas sensing group, to generate novel sensing modalities.
The prospective student will be exposed to the laboratory-based experimental laser physics, as well as opto-mechanical, electronic and spectroscopic instrumentation design. In parallel, she/he will study all the aspects of the acoustic detection modules, such as spectrophones design and manufacture, their characterisation and calibration. As such this represents an ideal challenge for a candidate exhibiting strength in experimental physics, as in encompasses photonics and acoustics, electronics and associated instrumentation.
There is a strong desire to translate laboratory-based success into field-deployable demonstrators, and so a desire to engage with mechanical design and with potential end users is also highly desirable.
(a) How does the project fit with the scope of CDT Applied Photonics?
The proposed project will focus on the development of the detection and sensing techniques based on the photoacoustic effect. It will comprise of the development and characterization of miniature photoacoustic transducers, optical systems enabling this phenomenon as well as the instrumentation required to drive the system. All these aspects of the technology will be explored in the context of applications targeting relevant problems of our customers. As such we believe that this proposed project perfectly fits the scope of this CDT’s programme, in that it is a sensor technology underpinned by photonics technology, and will involve a high component of engineering and technology transfer.
(b) What are the key academic and industrial research questions the project aims to answer?
The root question we seek to answer over the course of this study is: can established photo-acoustic techniques be enhanced and translated to the spectrally-potent fingerprint region; and if so can the resulting technology be miniaturised and automated such that it can find utility in front line homeland security / environmental monitoring applications? Although the photoacoustic effect is well established, its use in sensing extra-laboratory applications is still limited. These limitations often come from the size and complexity of relevant system and in this project we aim to drive the development of solutions that can find direct applications in the field. From the design of acoustic cells and optical systems characterised by superior performance, through the development of measurement techniques simplifying the testing procedure to the miniaturisation and ruggedization of relevant systems, this project will explore ways of marrying exceptional performance with portability and ease of operation.
(c) Where is the novelty of the project, and in what industrial / academic context?
The project will bring together state of the art developments in Quantum-Cascade excitation lasers operating in the spectroscopically potent 7-10um spectral fingerprint region; low cost, high performance 3D-printed acoustic spectrophones and deep-infrared, low-loss optical enhancement cavities. Specifically, this project will merge the know-how and experience in manufacturing of miniature, 3D-printed photoacoustic cells from the Centre for Microsystems and Photonics (CMP) at the University of Strathclyde, and the unique position of Fraunhofer Centre for Applied Photonics in development and application of optical systems. Among other things, the prospective student will explore new molecule excitation schemes, novel cell designs, ways to reduce the noise and calibrate the detector and finally new fields of applications.
(d) What is the methodology to be used, and what will the student actually be doing?
During this project the student will be predominantly based at the premises of Fraunhofer CAP, however thanks to the geographical proximity between the company and the academic group (the same floor of the same building) she/he will enjoy direct access to both teams, enhancing the first hand exposure for the activities in both teams. The student will be responsible for (a) designing, manufacturing and characterising the miniature acoustic cells; (b) characterising commercial and in-house QCL systems; (c) optical cavity design; (d) instrumentation [optical cavity locking techniques, low-level signal recovery, including digital lock-in amplifiers]. She/he will be responsible for the development of the whole infrastructure of given experiment, data collection and analysis. When appropriate, the student will be involved in commercial projects exploiting the resulting technology.
(e) What makes this a doctoral thesis project rather than a shorter piece of work?
The photoacoustic spectroscopy is a very potent technique and although a single aspect of the above work programme could be considered in a short term task, in this programme we envisage the student to build up an extensive know-how on principles, implementation and exploitation of this technology. Our vision is for the student to be responsible for a comprehensive overview of the current state of the art, and then a ‘ground up’ design and integration activity to result in an optimised device. It is particularly suited to the engineering Doctorate programme as he / she will be expected to work beyond fundamental bottom-line performance and develop high TRL demonstration modules for exploitation in various gas spectroscopy applications, stand-off photoacoustic spectroscopy and various other concepts based on the photoacoustic effect. Although from industrial perspective the student may be involved in a portfolio of different projects, photo-acoustic spectroscopy sits at the core of all the work in this programme which will make for a coherent body of results fully fulfilling the level of doctoral thesis.
CDT Essential Criteria
A Masters level degree (MEng, MPhys, MSc) at 2.1 or equivalent.
Desire to work collegiately, be involved in outreach, undertake taught and professional skills study.
- First- or upper-second degree background in physics, preferably with specialisation in laser physics or acoustics
- Strong ability and desire to set-up experimental systems and put theory into practice
- Ability to work with as part of a wider team, and demonstrate initiative when tasked with lone working.
- Desire to interact with industrial end-users
- Knowledge of programming languages such as Matlab, Labview or Python
- Experience in setting up optical and laser-based systems
- Industrial background and experience in executing commercial projects
This applications-focused EngD Programme is centred on developing advanced and ultrasensitive molecular sensors based upon laser-based spectroscopy techniques. The project will be divided between the Centre for Microsystems and Photonics (CMP) at the University of Strathclyde, and the Fraunhofer Centre for Applied Photonics in Glasgow – the first Fraunhofer centre in the UK.
Such a collaboration plays to the strengths and aspirations of both institutions who share a common desire to contribute to the knowledge-based economy through high-technology innovation.
The applicant will work in a vibrant, collegiate and supportive environment with access to state-of-the-art laboratory infrastructure and scientific expertise.
We are a professional R&D organisation, and as such maintain core hours of operation. However, we are flexible in our approach and welcome such discussions.