Characterization of retardance spatial variations over the aperture of liquid-crystal variable retarders.

We present a comparison of two experimental methods to measure retardance as a function of applied voltage and as a function of position over the aperture of liquid-crystal variable retarders. These measurements are required for many applications, particularly in polarimetry. One method involves the scan of an unexpanded laser beam over the aperture, and the other uses an expanded beam from a LED and a CCD camera to measure the full aperture with a single measurement.

Broadband extended source imaging Mueller-matrix polarimeter.

An imaging Mueller matrix polarimeter, named the red-green-blue (RGB)950, takes images of medium-sized (tens of centimeters) objects by using a very bright source, large polarization state generator, and high-quality camera. Its broadband extended light source switches between red, green, blue, and near-infrared light to allow taking polarimetric images for comparison with RGB camera images. The large diffuse source makes shadow transitions gradual and spreads out the specular reflected spot into a larger less conspicuous area.

Permitted experimental errors for optimized variable-retarder Mueller-matrix polarimeters.

An optimized Mueller-matrix polarimeter is simulated. The polarimeter is optimized by finding the configurations of the polarization state generator and polarization state analyzer that give the minimum condition number. Noise is included in the measurement of the polarimeter intensities, and the eigenvalue calibration procedure is used to reduce the errors in the final Mueller matrix.

Experimental limits for eigenvalue calibration in liquid-crystal Mueller-matrix polarimeters.

A numerical study is carried out to find the experimental conditions necessary for the eigenvalue calibration procedure to work correctly in a liquid-crystal variable-retarder-based Mueller-matrix polarimeter. Using the error between the simulated experimental Mueller matrix in a polarimeter with errors and the expected ideal Mueller matrices for four calibration samples, the maximum experimental errors are estimated for a successful eigenvalue calibration. It is found that the retarder axes' orientations have smaller permitted errors than the retardation values.

Calibration and data extraction in nonoptimized Mueller matrix polarimeters.

We present a method for calibration and data extraction for a nonoptimized Mueller matrix polarimeter. The advantage of this type of method is a reduction in measurement time for multiwavelength systems or in systems with slow response times. The calibration process requires the measurement of four known polarization devices.

Direct inversion methods for spectral amplitude modulation of femtosecond pulses.

In the present work, we applied an amplitude-spatial light modulator to shape the spectral amplitude of femtosecond pulses in a single step, without an iterative algorithm, by using an inversion method defined as the generalized retardance function. Additionally, we also present a single step method to shape the intensity profile defined as the influence matrix. Numerical and experimental results are presented for both methods.