Compact, ultra-sensitive gas sensing techniques

气体物种的检测和识别在国防和安全、生物医学、环境监测和各种其他领域的应用中至关重要。多年来，已经证明了许多技术，其中一些技术对浓度低至百万分之几的不同分子表现出了敏感性。然而，这些技术通常很复杂，在实验室之外的适用性有限。因此，仍然需要开发轻便、紧凑和便携的传感设备，将高灵敏度的传感带到现场。在这个项目中，我们的目标是将我们的重点放在基于激光的光谱技术的光热家族上，特别是光声光谱。在这里，激发源的波长被选择为与感兴趣化合物的分子吸收相一致。当这些分子在激发范围内时，一部分辐射被吸收，这反过来导致弱加热--从而改变密度。入射波的调制导致密度上的相关调制，从而产生周期性的压力波或声波。随后可以利用麦克风类型的布置来检测该声波。它是一种理想的基于激光的气体痕迹检测技术，因为它允许将坚固、高度紧凑的拓扑结构与潜在的非常高的特异性(由激光线宽赋予)、选择性(来自激光的可调谐性)和潜在的灵敏度(与基于实验室的技术相匹配)相结合。现在有一个令人兴奋的机会来开发和完善弗劳恩霍夫中心团队的光谱工作，将他们的基于激光的系统与Michael Lengden博士气体传感小组的广泛专业知识相结合，以产生新的传感模式。未来的学生将接触到以实验室为基础的激光物理实验，以及光机械、电子和光谱仪器设计。同时，她/他将研究声学探测模块的方方面面，例如分光机的设计和制造、其特性和校准。因此，对于在实验物理领域表现出实力的候选人来说，这是一个理想的挑战，因为它涵盖了光子学和声学、电子学和相关仪器。人们强烈希望将基于实验室的成功转化为可现场部署的演示，因此，参与机械设计和潜在最终用户的愿望也是非常可取的。

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 the photothermal family of the laser-based spectroscopic techniques and especially on the photoacoustic spectroscopy. 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.