Determining the complete optical behavior of anisotropic samples using ptychography is always a difficult problem. We propose a novel birefringence measurement method based on mixed-state ptychography that can simultaneously obtain the azimuth angle and retardation of anisotropic samples in a single scan. By using a reference system transformation, the two mutually orthogonal object states are unambiguously retrieved, and their errors are greatly reduced. The normalized root mean square errors of the obtained azimuth angle and retardation are 0.0011 and 0.0041, respectively. This method offers more rapid data acquisition; compared to interferometric based methods, it has the advantages of unlimited field of view and a simpler, more stable setup. Further, it opens a new possibility for investigating anisotropic samples by means of mixed-state ptychography.
In a high power laser system, the stress in large-aperture optical component could affect the system beam quality and safe operation. But studies on stress distribution and influence mainly focus on the finite element analysis. A new stress measurement method for large-aperture sample, which combines the ptychography with the polarization measurement technique, is presented. The birefringent sample is placed in the parallel probe-forming path. By the complex amplitude reconstructions of probes carrying stress information under different polarization states, the separation of two principal stress components is realized and quantitative full-field stress information is provided. The theoretical derivation and experimental implementation about how to extract strong stress information from phase are illustrated. The feasibility of this method is verified through a classic diametrically compressed disc, and the result for each stress component agrees well with the theoretical model. The proposed method avoids the scanning movement of sample and has a simple structure and strong anti-interference ability. It can be further combined with single-shot PIE techniques for rapid and online measurement, which provides a practical measurement means for the study of stress in large-aperture optics.
Although it is a simple and convenient birefringence analysis instrument, the traditional planar polariscope is difficult to use for the quantitative measurement of phase retardation and azimuth angle. A novel 2D quantitative birefringence measurement method based on ptychographic iterative engine (PIE) in a planar polariscope is proposed. The birefringent sample is placed in the parallel probe-forming path. By inserting an isotropic diffractive object with good modulation property for the probe, the ptychographic scan measurements are performed under two different dark-field states. The amplitudes and phases of the two probes containing different birefringence information were reconstructed, and the phase retardation and azimuth angle obtained with a simple and straightforward extraction approach. The approach was verified using a classic diametrically compressed disc. The proposed method solves the problem of quantitative birefringence measurement in planar polariscopes by introducing the phase information. It reduces the PIE scans and shortens the data collection time, which provides a practical measurement means for birefringence in materials, biophysics and opto-mechanical system.
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