Shortwave infrared (SWIR) cameras are becoming increasingly attractive due to the improving size, resolution and decreasing prices of InGaAs focal plane arrays (FPAs). The rapid development of competitively priced HD performance SWIR cameras has not been matched in SWIR imaging lenses with the result that the lens is now more likely to be the limiting factor in imaging quality than the FPA. Adapting existing lens designs from the visible region by re-coating for SWIR will improve total transmission but diminished image quality metrics such as MTF, and in particular large field angle performance such as vignetting, field curvature and distortion are serious consequences.
To meet this challenge original SWIR solutions are presented including a wide field of view fixed focal length lens for commercial machine vision (CMV) and a wide angle, small, lightweight defence lens and their relevant design considerations discussed. Issues restricting suitable glass types will be examined. The index and dispersion properties at SWIR wavelengths can differ significantly from their visible values resulting in unusual glass combinations when matching doublet elements. Materials chosen simultaneously allow athermalization of the design as well as containing matched CTEs in the elements of doublets.
Recently, thinned backside-illuminated InGaAs devices have made Vis.SWIR cameras viable. The SWIR band is sufficiently close to the visible that the same constituent materials can be used for AR coatings covering both bands. Keeping the lens short and mass low can easily result in high incidence angles which in turn complicates coating design, especially when extended beyond SWIR into the visible band. This paper also explores the potential performance of wideband Vis.SWIR AR coatings.
We present a passively Q-switched, diode end-pumped, 1μm Nd:YAG laser with a single pulse energy in excess of 40mJ. To our knowledge, this is the highest single pulse energy reported for a passively Q-switched end-pumped laser. We achieved this with a novel pump scheme, which uses an engineered diffuser to create the necessary uniform gain distribution for efficient passive Q-switching. The system consists of a 3kW, 808nm, diode-laser stack pump source, and a set of collimating optics, with the engineered diffuser, to homogenise and couple the pump beam into the end of a 20mm diameter Nd:YAG laser rod. Q-switching is achieved with a Cr:YAG saturable absorber within a plane-parallel cavity. The 40mJ value was achieved despite a pump coupling efficiency of only 55%; hence we believe higher energies are achievable. The beam parameter product and pulse width were measured to be 12mm mRad and 18ns, respectively, which are consistent with those required for designation. We have investigated the pulse-to-pulse timing jitter of our system, which has been previously cited as the main drawback when implementing passive Q-switching for designation applications. We have achieved a reduction in timing jitter from 16 μs to 3.2 μs by environmental isolation of the laser resonator.
A new high performance silicon complementary bipolar technology is introduced. In addition a novel process 'enhancement' technique based on a local oxidation is described and demonstrated and NPN devices with cut-off frequencies up to 45GHz and PNP devices of 20GHz have been fabricate. We propose that the technique we have used will allow specific transistors within a circuit to be optimized, as required.
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