Study And System Optimization Of Simultaneous Phase-shifting Interferometer For Measurement Of The Height Of Living Cells

Cell volume is important information in terms to understand the biomedical problemssuch as cellular development and homeostasis and pathological cell growth defines cancerin metazoans. The precision measurement of the height value of cell is more difficultywhile considering that the2D plane shape of cells can be easy observed and measured bytraditional optical microscopic instruments. Based on the modern optical measuringtechnology, making full use of the phase character of light, we can realize measurementwith nanoscale even higher accuracy. Temporal Phase-shifting Method is a kind ofadvances phase measurement method combining optical interferometry and microscopy. Inthis way, using CCD/CMOS digital imaging device to record the vision field, we can get aserial of cell interference patterns with certain phase changes. Using digital imageprocessing and pixel joint operation, cell height information can be extracted accurately.We researched in the principle of phase-shifting interferometry measuring method andestablished mathematical model used to analysis the detail process of interference imagingand polarization phase shifting. We also found the key factors to improve pattern stripescontrast and light uniformity which would provide theory guidance for design andoptimization of optical structure. We analyzed several common phase extraction algorithmsand phase unwrapping algorithms. A new algorithm which synthesizes the advantages ofthe branch-cut method and the quality-guide method is put forward. In this new algorithm,branch-cut method is applied firstly to unwrapping the most parts on the pattern, and thenquality-guided method is utilized for unwrapping the rest parts. We gather phase-shiftinterferograms of cell specimens by Phase-Shifting Interference Microscopy in thelaboratory and use the new algorithm to unwrapping the phase of interference pattern. Theresults show that this new phase unwrapping method is effective and practical in theprocessing of cell interferograms.We built a phase-shifting interference microscopy systems which was based ondual-angle incident to achieve height value of cells even the refractive index of cell innerenvironment was unknown. We designed a light splitting device which could divide theincident beam into four spatial separated parallel beams. We equipped a phase-shiftingsystem behind the light splitting system which was composed by quarter-wave plate and four pieces of polarizer. This system enable that we get four different phase changesthrough one photographic process of the digital camera, improving the real-timemeasurement abilities. This Spatial phase-shifting interferometry microscopy systemeliminated phase-shifting errors and time-delay errors and improved the reliability of themeasurements compared with the original system.