No abstract

We report a new, to the best of our knowledge, measurement method of optical rotatory dispersion (ORD) based on a polarization axis finder (PAF) and digital image processing. The collimated quasi-monochromatic light is output by a monochromator and passes through a polarizer and the chiral samples, and a PAF is employed to modulate the light beam spatially to form an “hourglass” intensity pattern, which is utilized to determine the polarization direction of linearly polarized light. After being recorded by a digital camera, the modulated patterns with and without samples are analyzed by our specially designed digital image processing program to calculate the optical rotation (OR) angle of the chiral substance at a certain wavelength, and the ORD curve can be obtained by fitting a series of OR angles with different wavelengths. The ORD curves of two standard quartz plates with opposite chirality and a glucose solution with different concentrations are measured experimentally, and the fitted coefficients and measurement results agree well with their theoretical values, which indicates that the presented method is an effective and accurate way to determine the ORD of chiral substances conveniently.

Optical rotatory dispersion (ORD) is an important property of chiral material. How to obtain the ORD curve of chiral material quickly and accurately has attracted great attention from researchers. This work presents a measurement method of ORD based on a polarization axis finder (PAF) and a conical lens (CL). The PAF can modulate the collimated broadspectrum beam spatially to form an "hourglass" intensity pattern, and the CL can disperse the polarization information of light of different wavelengths to different positions in space. The use of the PAF and the CL enables the ORD of the sample to be obtained with only a single image. We perform a theoretical analysis of this method to prove it is feasible and verify it experimentally with left-hand quartz (LHQ) as the sample. Both theoretical and experimental results prove that this method is a fast and effective way to determine the ORD of chiral substances.

Polarization is an important property of electromagnetic waves, and measuring their polarization properties fast and precisely is a very important issue in many applications, such as skylight polarization navigation, optical activity measurement, imaging polarimetry, spectroscopic ellipsometry, fluorescence polarization immunoassay and so on. The polarization measurement method based on vector optical field modulation and image processing is a new type of spatial modulation polarization detection technology. The key step of this technique moving to practical application is determined by the effective polarization measuring algorithms with high speed and accuracy. In order to find out the fast and high precision polarization direction calculation methods, the principle of polarization direction measurement based on vector optical field and spatial modulation is introduced briefly, and the basic characteristics of the spatially modulated intensity distribution images are analyzed. According to the properties of spatially modulated image, we have designed and implemented four different polarization direction calculation methods, which are the Radon transform, intensity modulation curve detection, radial integration and image correlation detection, and their working principles and physical thoughts are introduced elaborately. To compare the detailed performance of these four algorithms, an experimental setup has been constructed to collect the images and perform the algorithm verification, and the stability, speed and accuracy of the four algorithms are compared respectively. The research results indicate that all the four methods can achieve stable and reliable polarization direction detection. The three methods of intensity modulation curve detection, radial integration and image correlation detection, can obtain the measurement accuracy of polarization direction better than 0.01 degrees. The intensity modulation curve detection and radial integration own the fast calculation speed relatively, and their overall performances are the best, and they are the most promising methods for realizing real-time and high-precision polarization measurement.