in the sample, the spatial coherence of the interferometric signal may be destroyed when the sample is rotated at specific angles. In fact, the intensity of light passing through the zero-order quarter wave plate is various while in different principal angles despite the incident light is unpolarized. It also can explain why only the range in 0 ~ 20 of the orientation angle of LB is measured. The composite structure of the sample will induce some difficulties in the calibration in successive measurements. Secondly, the dispersion effect has an influence on the measured intensity and the width of interferometric signals, and the use of this light source requires an effective dispersion compensation scheme. So, we may not achieve enough dispersion compensation in this study. Additionally, a polymer polarizer (LLC2-82-18S, OPTIMAX Co.) baked in an oven at 150 C for 100 min are served as a testing sample for the LB and LD properties. Due to the prolonged exposure of the polarizer to a high-temperature environment, the input light leaks through one of the LD axes. Thus, as expected, the measured value of linear dichroism has a value of 0.9864 closed to 1 and the measured value of the phase retardance is found to be 19.2262 . In comparison with the previous study [12], the result is slight different because the central wavelength of the light in the Mueller OCT system is different from that in Stokes polarimeter. However, it also can confirm that the proposed analytical model enables the parameters of hybrid samples with both LB and LD properties to be accurately determined. 20.5 Conclusions and Discussions This study has developed a Mueller OCT to measure the Mueller matrix expression of an anisotropic sample with a high depth resolution. According to the measured Mueller matrix, an analytical model based on use of the differential calculation method and both considering the forward and backward measured beams to extract effective parameters of a composite sample containing LB and LD properties measured by the Mueller OCT is proposed. In the calculation by using a genetic algorithm, the model is suitable for the LB/LD composite sample and able to provide the measurement over the full range. α, optical axis orientation 9.91E-04 21.0461 17.3938 11.5358 6.055 0 5 10 15 20 25 Input α (Degree) Measured α (Degree) Theoretics Experiments β, Phase retardation 90.4994 89.2145 91.1071 90.6149 89.7836 60 65 70 75 80 85 90 95 100 Input α (Degree) Measured β (Degree) Theoretics Experiments θd, orientation angle of LD 128.4142 101.3711 123.5166 50.2721 127.8188 0 20 40 60 80 100 120 140 160 180 Input α (Degree) Measured θd (Degree) Experiments D, Linear Dichroism 0.0119 0.0303 0.0203 0.0351 0.0396 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 5 10 15 20 0 5 10 15 20 0 5 10 15 20 0 5 10 15 20 Input α (Degree) Measured D Experiments a b c d Fig. 20.4 Comparison of theoretical and experimental results for (a) optical axis orientation angle of LB; (b) phase retardation of LB; (c) orientation angle of LD; (d) linear dichroism 188 C.-C. Liao and Y.-L. Lo
RkJQdWJsaXNoZXIy MTMzNzEzMQ==