Narrow-band and directed ultrasound generated by laser arrays

Pulsed laser arrays have been used to modify the characteristics of laser generated ultrasound and produce both narrowband and directed ultrasonic signals. One advantage of using this technique over the use of a single high power laser pulse is that the generation can be kept in the thermoelastic regime and thus surface damage can be avoided. A repetitively pulsed laser source can be used to reduce the bandwidth of an ultrasonic signal. In order to take advantage of this narrowband generation, the detection electronics can be tuned to the generation frequency or signal processing techniques can be used. A spatially and temporally modulated array of laser sources can also be used to enhance acoustic pulse amplitudes in specific directions. The result of each of these methods is to increase the signal-to-noise ratio of the system