Charge mobility is a key parameter for understanding the performance of organic semiconductor devices and materials.
A range of techniques is available that can measure charge mobility with varying accuracy and precision. We review the
dark injection transient current method from a metrology perspective with a particular emphasis on quantification of
uncertainties that arise from the technique itself and from the inherent variability of devices and materials. We have
carried out a systematic study of the space-charge-limited dark injection transient current technique as a method of
measuring charge mobility in polymer organic light emitting diodes, paying particular attention to varying the amplitude,
duration and repetition rate of the applied voltage and to environmental factors such as changes in the ambient
temperature. We show that the results of the experiment depend strongly on the previous history of the device and that
both long-term and short-term effects can be identified. As a result, we are able to quantify the contribution of these
effects to the uncertainties associated with estimates of charge mobility obtained using the dark injection method.
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.