Fig. 1. Schematic of the focus-plane drift measurement system with non-symetric optical beam

Fig. 2. Mechanical layout of the focus-plane drift measurement system

Fig. 3. Flowchart of drift correction system

Fig. 4. Optical spot shape and location at the detection plane simulated by ZEMAX software. (a) -1 μm defocus; (b) in focus; (c) +1 μm defocus; (d) relationship between sample drift and max spot radius; (e) relationship between sample drift and centroid X coordinate of the detected optical spot

Fig. 5. Intensity profiles of reflected spots obtained by the linear camera with a 10× objective. (a) Detected stray beam when there is no sample slide; (b) stray light and reflected light from two sample surfaces detected after placing the sample on a cover glass slide; (c) reflected spots from the two surfaces of glass coverslip when the stray beam is blocked

Fig. 6. Intensity profiles of reflected spots obtained by the linear CCD with a 60× oil-immersion objective. (a) Profile with 3/4 incident beam blocked; (b) profile with 1/2 incident beam blocked; (c) relationship between the displacement of the light spot on the detector and the drift of the sample

Fig. 7. Close-loop drift correction

Fig. 8. Long-term imaging of oral epithelial cells. (a) Image at beginning without drift correction; (b) image after 20 h without drift correction; (c) image at beginning with drift correction; (d) image after 20 h with drift correction

Fig. 9. Quantitative analysis of long-term imaging. (a) SSIM evaluation; (b) Brenner evaluation