Laser-based ultrasound (LBU) is a technique where high-frequency elastic waves are generated and detected in material using lasers. In this non-contact technique, a laser pulse generates ultrasound by locally heating the material, relying on thermoelastic or ablative mechanisms. The ultrasonic response is subsequently measured with an optical interferometer or vibrometer. LBU offers advantages over traditional transducer-based ultrasound such as eliminating the need for couplant and transducer load on the part, while also enabling higher scanning speeds and a wider application temperature range, among other advantages. However, LBU has seen limited industrial adoption because setups are often unwieldly, involving free space lasers and sensitive optics. Here, a novel, fully fiberized thermoelastic LBU system is demonstrated. This system utilizes a hollow core anti-resonant single mode fiber to couple the pulse laser light and a custom commercial fiber interferometer. The fiber outputs and beam shaping optics are sealed within a miniaturized sensing head. The result is a small, portable, environmentally robust, and remote fiber sensor, capable of optically generating and detecting ultrasound. This sensing head is then integrated into a 4-axis high precision lathe to perform in-situ on-machine thickness gauging. We demonstrate system performance by measurements before and after cutting operations and comparison with ex-situ CMM measurements. The LBU system, including theory and the on-machine measurements, are presented.
Stobbe et al. (Wed,) studied this question.