Yusof, Mohd Farid Mohamad, et al. “Axial Calibration of QPD Signal Based on Stuck Bead Method for Optical Trapping Applications”. International Journal of Engineering & Technology, vol. 7, no. 4.30, Nov. 2018, pp. 371-3, https://doi.org/10.14419/ijet.v7i4.30.22320.