A Study On Design Of Polarimetric Measurement System For Biomedical Applications

Polarization imaging techniques are capable of probing the structural and optical properties of turbid media.As a label-free,non-destructive method,polarization imaging has shown many potential applications in biomedical studies and clinical practices.Polarization techniques can be used for the clinical diagnosis provided that the accurate and fast polarimetric measurement systems are established.However,as there are many error sources and complex error transfer functions in a polarimetric measurement system,resulting in huge difficulties to achieve accurate polarimetric measurements.Since the polarimetric measurement is based on many different light intensity measurements,it’s also not easy to fulfill a real-time polarimetric measurements system.To cope with those problems,in this thesis,we systematically research the polarimetric modulation devices,the design of the polarimetric measurement system,and the biomedical applications of the real-time polarimetric microscopy.First,we systematically research the design theory for polarimetric measurement system.The theoretical framework "Denoise-Optimization-Calibration" is established and validated by experiments.With the aim of mininmizing the noises transmitted through the matrix inversion from the error sources to the polarization solutions(Stokes vector or Mueller matrix),we propose an optimization indicator based on the singular value decomposition,which provides estimations for all errors in the polarization solutions.Using the GLP,we also study the influence of the number of the analyzing channels to the optimization.For accurate polarimetric measurements,the systematic error sources should be minimized by calibration.We summarize two calibration methods for the systematic errors in the polarizing elements,and propose a new calibration method for the residual polarization errors in the non-polarizing elements.Then,the 60 Mueller matrix measurement system is proposed to cope with the beam wander caused by the rotation of the polarizing elements.Last but not the least,the "step-by-step"optimization and calibration methods are proposed to improve the polarimetric measurement performance for targeted scenes.Second,we research the polarimetric modulation devices.A new polarimeter for the simultaneous measurement of all Stokes parameters in a single shot is presented.The GRIN lens polarimeter(GLP)consists of only a GRIN lens,a polarizer,an imaging lens and a CCD,without mechanical movements or electrical signal modulation or the division of amplitude components.This design takes advantage of the continuous spatial distributions of birefringence value and fast axis direction of a GRIN lens and derives the state of polarization(SOP)of the incident beam from the characteristic patterns on the CCD images.It is pointed out that many optimization techniques,although developed for other types of Stokes polarimeters,can also be applied to the GLP because the GRIN lens can traverse all possible retardance and fast axis modulations.Using the above modulation methods and the design theory for polarization measurement system,we present a division of focal plane(DoFP)polarimeter based polarization microscope,which is capable of imaging both the Stokes vector and the Mueller matrix.The Mueller matrix measurement can help us completely understand the polarization properties of the sample and the Stokes vector measurement is a simultaneous technology.Experiment results show that the characteristic features of many biomedical samples can be observed in the "polarization staining" images using the circularly polarized light as illumination.In this way,the DoFP polarization microscope has the capacity for real-time polarization monitoring of dynamic processes in biological samples.