Measuring Young's modulus using a self-mixing laser diode

This paper presents a novel approach for determining the Young’s modulus by using a self-mixing laser diode (SMLD). An SMLD system consists of a laser diode (LD), a microlens and an external target. With a small portion of light backscatterd or reflected by the target re-entering the LD inside cavity, both the amplitude and frequency of the LD power are modulated. This modulated LD power is referred as a self-mixing signal (SMS) which is detected by the photodiode (PD) packaged in the rear of the LD. The external target is the tested sample which is in damping vibration excited by a singular elastic strike with an impulse tool. The vibration information from the tested sample is carried in the SMS. Advanced data processing in frequency-domain is applied on the SMS, from which the resonant frequency of the vibration can be retrieved, and hence Young’s modulus is calculated. The proposed method has been verified by simulations.