Speaker
Description
The Modulation Transfer Function (MTF) is an important performance
metric for all position sensitive pixelated imaging detectors. Many
methods of determining MTF experimentally in the optical wavelength
region have been presented in the literature over the years, and
generally involve projection of a known test pattern of some kind. Laser
speckle MTF measurements are of interest for small pixels because they
do not require refractive optics in the projection, and are therefore
not restricted by the implied optical information limit.
The laser speckle MTF method works by preparing a light field consisting
of the speckle pattern resulting from random reflections of a laser from
a rough surface. This light field is then band limited (by means of an
aperture) and linearly polarised. The resulting intensity distribution
at the sensor some distance away has known second order statistics and a
known power spectrum, and thus the MTF can be obtained by a Fourier
Transform.
The method has been well known and used for many years. However,
conventional measurements using this technique cannot recover
information above the Nyquist Frequency of the sensor. We present a
modification of the laser speckle technique which allows recovery of the
MTF beyond Nyquist in small pixel CMOS APS detectors. We contrast our
suggested improvement with two previous approaches to recover
super-Nyquist information in laser speckle measurements, compared to
which it is simpler and cheaper though with some tradeoffs.
We present results from the measurement of MTF on two commercial CMOS
APS devices of different pixel sizes at two wavelengths, and compare the
result on the larger pixel size with a conventional optically projected
MTF test pattern measurement.
We remark that this technique will be used, alongside others, in the
characterisation of the MTF of the science cameras for the MAGIS-100
atom interferometer.
| Your name | Daniel Philip Weatherill |
|---|---|
| Institute | University of Oxford |
| Email address | daniel.weatherill@physics.ox.ac.uk |
