The use of non-contact ultrasonic detection techniques is essential to develop an apparatus capable of inspecting components in service, operating in adverse environmental conditions or whose surfaces are challenging to access. Among these techniques, Gas-Coupled Laser Acoustic Detection (GCLAD) is based on measuring the deviation that a laser beam sustains when intersecting an ultrasonic wavefront. The method has been recently developed, being hence unestablished in the non-destructive testing (NDT) field. The objective of the present work is to expand knowledge on the physical operating principles of the GCLAD system; this is obtained by investigating, both theoretically and experimentally, the influence of specific working parameters on the detected signals with the aim of maximizing the ultrasonic amplitude. These analyses are essential for proposing effective non-destructive investigation methodologies benefitting from the employment of the GCLAD technique. Based on the information obtained and from an NDT standpoint, test configurations are proposed with a different relative arrangement between the GCLAD system and the structure; these configurations provide peculiar results also based on the type of wave under investigation (surface or bulk waves). Finally, to highlight the capabilities of the GCLAD system in inspections of mechanical pieces, signals detected experimentally on a component (i.e., a railway axle) are presented in the presence and absence of a surface defect.

非接触式超声波检测技术的使用对于开发一种能够检查使用中的组件，在不利的环境条件下运行或表面难以接近的设备至关重要。在这些技术中，气体耦合激光声学检测（GCLAD）是基于测量与超声波前相交时激光束所承受的偏差。该方法是最近开发的，因此在非破坏性测试（NDT）领域中尚未建立。当前工作的目的是扩展有关GCLAD系统物理操作原理的知识；这是通过在理论上和实验上研究特定工作参数对检测到的信号的影响而获得的，目的是最大程度地提高超声幅度。这些分析对于提出受益于GCLAD技术使用的有效非破坏性调查方法至关重要。根据获得的信息并从NDT的角度出发，提出了GCLAD系统与结构之间相对布置不同的测试配置。这些配置还根据所研究的波的类型（表面波或体波）提供了特殊的结果。最后，为了突出显示GCLAD系统在检查机械零件中的功能，在存在或不存在表面缺陷的情况下，都会在组件（即铁路车轴）上通过实验检测到的信号会呈现出来。建议的测试配置在GCLAD系统和结构之间具有不同的相对布置；这些配置还根据所研究的波的类型（表面波或体波）提供了特殊的结果。最后，为了突出显示GCLAD系统在检查机械零件中的功能，在存在或不存在表面缺陷的情况下，都会在组件（即铁路车轴）上通过实验检测到的信号会呈现出来。建议的测试配置在GCLAD系统和结构之间具有不同的相对布置；这些配置还根据所研究的波的类型（表面波或体波）提供了特殊的结果。最后，为了突出显示GCLAD系统在检查机械零件中的功能，在存在或不存在表面缺陷的情况下，都会在组件（即铁路车轴）上通过实验检测到的信号会呈现出来。