An analysis based on the comparison between singularities of speckle phase and pseudophase in the practice of optical vortex metrology is carried out by measuring the phase map of the speckle pattern obtained from the transmitted light through binary diffusers. In the characterization of the core structure of both phase singularities, the variation of the measured parameters is produced by means of in-plane linear displacements and rotations of the scattered speckle fields. These fields are addressed by using similar displacements of the binary phase masks recorded in a spatial light modulator (SLM). We complete these comparisons by measuring out-of-plane variations of the core structure parameters. In addition, we verified that the phase map of the transmitted light beam through the binary diffusers recorded in SLMs is actually characterized by a speckle phase with vortices of unitary charge. The presented analysis would be helpful for understanding the scope and limitations of the use of the singularities of speckle phase and pseudophase as position marking, and also for speckle measurement of in-plane rigid-body displacements of binary diffusers dynamically controlled by means of SLMs.
The determination of ocular pupil diameter and gaze direction is important in various psychophysical and cognitive tests and can be accomplished using commercial, academic or open-source devices. In this work we develop a table-top pupillometer eyetracker termed Blick, the hardware costs 50 dollars and the software is open source (https://github.com/abianchetti/blick). The hardware is mounted in a portable holder and comprises an illumination system (two infrared LEDs generating 0.13 W/m<sup>2</sup> at 22 cm) and a detection system (containing an USB camera, an infrared filter and a 16mm lens system) The software, programmed in C++ using OpenCV and cvblob libraries, processes eye images in real time and supplies plots and tables of pupil diameter and gaze direction and a video of the eye. As applications, capturing the right eye of six young emmetropes and after performing the pixel-mm and homographic calibrations (required to determine diameter in mm and gaze direction), we conduct three tests. The corresponding tasks are to detect mistakes in three series of four poker cards, to recognize letters F between distractors and to write a sentence via eye movements using Blick as eye tracker and the tool Dasher (MacKays´s Cambridge Group). We obtain that Blick´s performance is satisfactory (errors being 0.05 mm in pupil diameter and 1 degree in gaze direction); that there are slight pupil dilations when subjects used to playing cards find mistakes and when some subjects find targets and, finally, that Blick can be employed as eyetracker to allow communication of disabled persons.