By Research Support Instruments (RSI)
Airborne acoustic waves create travelling changes in the air's density, a.k.a a sound wave. The changes in density also produce changes in the air's index of refraction. A light beam traveling through this section will deflect slightly from its intended path. A position-sensitive photodetector that receives the light beam could translate the acoustic signals into electrical signals without any mechanical components. This is the concept of Gas-coupled Laser Acoustic Detection, or GCLAD. This type of detection has been demonstrated before as the light traveled through acoustic fields in liquids or solids, but was first demonstrated in air by Dr. James N. Caron. (Caron, James N., et al. Materials Evaluation 58.5 (2000).) Since the discovery, the instrumentation has evolved such that highly resolved waveforms have been detected in both the ultrasonic and audio frequency ranges. GCLAD was first developed at the University of Delaware as an alternative method to detect ultrasound after it has been transmitted through a solid material, primarily for composite materials. This technique, coupled with a pulsed laser, creates a laser-based ultrasound system.
