Effects of Broadband Laser Generated Ultrasound on Array Gain

Abstract

The array gain model for laser phased arrays was derived using an assumption that ultrasound from each array source interferes with each other. However, laser generated ultrasound is broad band and ultrasound from each array source may not interfere with each other. A theoretical model called the frequency modulation of phased arrays (FMLPA) was developed and experimentally verified for use when ultrasound from each array member does not interfere with each other. It was experimentally verified that current array gain equations still apply when ultrasound from array members interfere with each other. The FMLPA can be used to create new techniques for measuring weld penetration depth, crack location, and dimensions of objects.