Compressive sensing has been widely used in image compression and signal recovery techniques in recent years; however, it has received limited attention in the field of optical measurement. This paper describes the use of compressive sensing for measurements of photovoltaic (PV) solar cells, using fully random sensing matrices, rather than mapping an orthogonal basis set directly. Existing compressive sensing systems optically image the surface of the object under test, this contrasts with the method described, where illumination patterns defined by precalculated sensing matrices, probe PV devices. We discuss the use of spatially modulated light fields to probe a PV sample to produce a photocurrent map of the optical response. This allows for faster measurements than would be possible using traditional translational laser beam induced current techniques. Results produced to a 90% correlation to raster scanned measurements, which can be achieved with under 25% of the conventionally required number of data points. In addition, both crack and spot type defects are detected at resolutions comparable to electroluminescence techniques, with 50% of the number of measurements required for a conventional scan.
Measurement of the laser beam propagation factor M2 is essential in many laser applications including materials
processing, laser therapy, and lithography. In this paper we describe the characterisation of a prototype device using a
cross-distorted diffraction grating known as an Image Multiplex (IMP(R)) grating, to measure the M2 value of laser beams.
The advantage of the IMP(R) grating instrument lies in its ability to simultaneously image nine positions along the beam
path. This enables beam propagation parameters to be calculated both for pulsed lasers and lasers with rapidly changing
propagation characteristics. This is in contrast to the scanned technique recommended by the ISO, which is relatively
slow and in practice can only be easily used with cw sources. The characterisation was accomplished by comparison of
results from the IMP(R) grating device with those obtained using the accepted methodology described in the ISO 11146
series of standards through measurements conducted by the National Physical Laboratory. The scope of the work also
included provision of a traceability route to international standards, and an uncertainty budget, to allow the intended user
community to have confidence in measurements obtained when using the device, and to enable them to use it as part of
their quality framework.
Wavefront sensors, particularly those of the Hartmann-Shack type are now available in commercial form from several manufacturers. They have found increasing use in medical and industrial applications and, for consistent measurements over a range of instruments and measurement situations, traceability of measurement is essential.
We have investigated the use of simple artefacts such as an optical plate and a plano-convex lens, used with a point source, to generate prescribed values of optical aberration. Measured values obtained with Hartmann-Shack sensors are verified by comparison with calculated results and measurement by other means.
Conference Committee Involvement (3)
Optical Instrument Science, Technology, and Applications III
10 April 2024 | Strasbourg, France
Optical Instrument Science, Technology, and Applications II
13 September 2021 | Online Only, Spain
Optical Instrument Science, Technology, and Applications
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