Non-Contact Ultrasound Sensing Platform Towards In-Vivo Applications Based on Terahertz Photoacoustic Effect and Laser Vibrometry

Ultrasound is a versatile modality for non-invasive inspection. However, close contact between an object and transducers is usually required to capture ultrasound signals, limiting the flexibility of inspection. To tackle this challenge, we propose a novel system that generates ultrasound in aqueous materials by irradiating them with modulated continuous-wave terahertz waves based on the photoacoustic effect and detects the ultrasound signals by means of laser Doppler vibrometry. This system enables the completely non-contact generation and detection of ultrasound in aqueous samples. While all-optical laser ultrasound systems have recently been considered, our approach can produce continuous wave ultrasound, making it advantageous for arbitrary wave modulation, high signal-to-noise ratio, and compact system integration. As a preliminary experiment, we verified the system using plastic bottles filled with liquid as test objects, and showed that the proposed system could generate and measure the ultrasound in aqueous samples without contact.