Compact, ultra-sensitive gas sensing techniques

气态物质的检测和识别在国防和安全、生物医学、环境监测等应用中至关重要。多年来已经证明了许多技术，其中一些技术对浓度低至每四分之一的不同分子表现出灵敏度。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，仍然需要开发将高灵敏度感测带入该领域的轻质、紧凑和便携式感测装置。在这个项目中，我们的目标是把我们的重点放在光热家庭的激光光谱技术，特别是在光声光谱。这里，选择激发源的波长，使得其与感兴趣的化合物的分子吸收一致。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。入射波的调制引起密度的相关调制，导致周期性的压力波或声波。随后可以用麦克风类型的装置检测该声波。它是一种理想的基于激光的气体痕量检测技术，因为它允许将坚固的高度紧凑的拓扑结构与潜在的非常高的特异性（如由激光线宽所赋予的）、选择性（来自激光可调谐性）和潜在的灵敏度（与基于实验室的技术相匹配）相结合。一个令人兴奋的机会存在，通过将他们的激光系统与Michael Lengden博士气体传感小组的广泛专业知识相结合，开发和完善Fraunhofer中心团队的光谱工作，以产生新的传感模式。未来的学生将接触到实验室为基础的实验激光物理，以及光机械，电子和光谱仪器设计。与此同时，她/他将学习声学检测模块的所有方面，如光谱仪的设计和制造，它们的特性和校准。因此，这对在实验物理学方面表现出实力的候选人来说是一个理想的挑战，因为它包括光子学和声学，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器，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.