[1] [1] Schmit J, Creath K, Wyant J C. Surface profilers, multiple wavelength, and white light interferometry [M]. Wiley & Sons, 2007.

[2] [2] Cohen D K, Ayres J D, Cochran E. R. Apparatus and method for automatically focusing an interference microscope: U.S, 5122648 [P]. 1992.

[3] [3] Swinford R W, Aziz D J, Guenther B W, et al. Automated minimization of optical path difference and reference mirror focus in white-light interference microscope objective: U.S, 6552806 [P]. 2003.

[4] [4] Deck L L. Method and apparatus for automated focusing of an interferometric optical system: U.S, 5208451 [P]. 1993.

[5] [5] Cohen D K, Gee W H, Ludeke M, et al. Automatic focus control: the astigmatic lens approach [J]. Appl. Opt(S0003-6935), 1984, 23(4): 565-570.

[6] [6] Mansuripur M. Analysis of astigmatic focusing and push-pull tracking error signals in magnetooptical disk systems [J]. Appl. Opt(S0003-6935), 1987, 26(18): 3981-3986.

[7] [7] Quercioli F, Mannoni A, Tiribilli B. Correlation optical velocimetry with a compact disk pickup [J]. Appl. Opt(S0003-6935), 1997, 36(25): 3672-6375.

[8] [8] Zhang J H, Cai L L. An auto-focusing measurement system with the piezoelectric translator [C]// Proceedings of International Conference on Robotics and Automation, Albuquerque, N M, USA, April 20-25, 1997: 2801-2806.

[9] [9] Bartoli A, Poggi P, Quercioli F, et al. Fast One-Dimensional Profilometer with a Compact Disc Pickup [J]. Appl. Opt(S0003-6935), 2001, 40(7): 1044-1048.

[10] [10] Fan K C, Lin C Y, Shyu L H. The development of a low-cost focusing probe for profile measurement [J]. Meas. Sci. Technol(S0957-0233), 2000, 11(1): 1-7.

[11] [11] Fan K C, Chu C L, Mou J I. Development of a low-cost autofocusing probe for profile measurement [J]. Meas. Sci. Technol(S0957-0233), 2001, 12(12): 2137-2146.

[12] [12] Liu C H, Li Z H. Application of the astigmatic method to the thickness measurement of glass substrates [J]. Appl. Opt(S0003-6935), 2008, 47(21): 3968-3972.

[13] [13] Hsu W Y, Lee C S, Chen P J, et al. Development of the fast astigmatic auto-focus microscope system [J]. Meas. Sci. Technol(S0957-0233), 2009, 20(4): 1-9.

[14] [14] Liu C H, Yeh S C, Huang H L. Thickness measurement system for transparent plates using dual digital versatile disc (DVD) pickups [J]. Appl. Opt(S0003-6935), 2010, 49(4): 637-643.

[15] [15] Islam N, Parkin R M, Jackson M R, et al. Development of a novel profile measurement system for actively planed surfaces [J]. Measurement(S0263-2241), 2011, 44(2): 466-477.

[16] [16] Hnilicka B, Voda A, Schroder H J. Modeling the characteristics of a photodetector in a DVD player [J]. Sensors and Actuators A-Physical(S0924-4247), 2005, 120(2): 494-506.