Simulated system for sensitive laser ultrasonic detection by CFPI based on power amplification using laser injection locking

• A high-sensitivity broadband ultrasonic detector comprised of a confocal Fabry–Perot interferometer modified by laser injection locking has been simulated.
• The specifications of the suggested optical system have been chosen to provide high detection sensitivity and are commercially available.
• By amplifying the weak light reflected from the sample by laser injection locking, sensitivity improvements are expected.
• Two different detection ultrasonic bands have been simulated at 1 GHz and 400 MHz.
• The sensitivity limits of the reflection and transmission modes of CFPI have been compared.

Low sensitivity in the detection of ultrasonic waves is a common problem in optical techniques, unlike in contact methods. To enhance the sensitivity limits for ultrasonic detection, a simulated optical system has been introduced in this study. The proposed system contains a confocal Fabry–Perot interferometer (CFPI) modified by laser injection locking (LIL). The simulation has been performed by evaluating the magnitude and phase response of the complex ultrasonic transfer function of CFPI. Sensitivity limits for the transmission and reflection modes of CFPI have been investigated. The results of numerical simulations in the LABVIEW programme for a proposed optical setup with and without LIL have been presented for detection bandwidths of 400 MHz and 1 GHz. The sensitivity limits for the transmission and reflection systems have been enhanced using LIL by approximately 35%, as clearly demonstrated in this research.