研究目的
To characterize beam splitters using Mueller matrix ellipsometry and apply this to calibrate a six-channel Stokes polarimeter, reducing measurement errors.
研究成果
The proposed characterization method based on Mueller matrix ellipsometry effectively extracts all polarization distortion parameters of beam splitters, leading to reduced residual errors in Mueller matrix fitting. Applied to a six-channel Stokes polarimeter, it reduces the general error of Stokes vector measurements from 3% to 1% and achieves thickness measurement errors within 1 nm for SiO2 films, comparable to commercial MME performance. Future work should focus on improving measurement stability and refining the model for skew effects.
研究不足
The method assumes identical PBSs in calibration for simplicity, which may introduce small errors. The relationship between tilt angle and circular birefringence is not precise, and depolarization effects from other sources (e.g., sample or multiple reflections) are not fully accounted for. Measurement stability of the polarimeter needs improvement, as uncertainties are higher than commercial instruments.
1：Experimental Design and Method Selection:
A theoretical analysis method based on Mueller matrix ellipsometry is proposed to characterize beam splitters by considering polarization distortions such as depolarization, linear birefringence, circular birefringence, linear dichroism, and circular dichroism. The method involves fitting Mueller matrices using a least-squares algorithm.
2：Sample Selection and Data Sources:
Two types of beam splitters (polarization beam splitter and non-polarization beam splitter) from Thorlabs are used. Mueller matrices are measured using a commercial Mueller matrix ellipsometer (ME-L from Wuhan Eoptics Technology). Standard SiO2 thin film samples of various thicknesses are used for validation.
3：List of Experimental Equipment and Materials:
Equipment includes a He-Ne laser (632.8 nm, 5 mW from THORLABS), linear polarizers, wave plates (quarter-wave and half-wave), beam splitters (NPBS and PBS from Thorlabs), photomultiplier tubes (PMTs), a commercial Mueller matrix ellipsometer (ME-L from Wuhan Eoptics Technology), rotation mounts, motorized stages, and a personal computer for data acquisition.
4：8 nm, 5 mW from THORLABS), linear polarizers, wave plates (quarter-wave and half-wave), beam splitters (NPBS and PBS from Thorlabs), photomultiplier tubes (PMTs), a commercial Mueller matrix ellipsometer (ME-L from Wuhan Eoptics Technology), rotation mounts, motorized stages, and a personal computer for data acquisition.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The calibration involves measuring the fast axes and retardances of wave plates and Mueller matrices of beam splitters with the MME. Then, in situ calibration of the Stokes polarimeter is performed by modulating the polarization state with a rotating polarizer and fitting the intensity data to extract optical parameters. The system is used to measure SiO2 thin films, and results are compared with MME measurements.
5：Data Analysis Methods:
Data analysis uses least-squares fitting algorithms to extract effective optical parameters from Mueller matrices. Stokes vectors are calculated, and ellipsometric angles (ψ, Δ) are derived to determine film thickness and refractive index. Residual errors and general errors are quantified to evaluate performance.
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