One of the primary goals of HgCdTe linear-mode avalanche photodiode arrays is to provide a 1kx1k pixels format, @15 μm pitch, near-infrared (0.9 to 2.5 μm) detector suitable for ultra-low background astronomical applications and long integration times. Such science goals impose very strict detector requirements, namely a dark current <0.001 [e−/pix/sec] and a sub-electron read noise. The Institute for Astronomy (IfA), University of Hawaii has partnered with Leonardo Company to develop such devices, using fine control of the photodiode process to enable noise-free amplification of the charge carriers and a readout circuit optimized for minimal glow. We discuss the first results of the tests conducted at the IfA on this new device operated in our cryogenic testbed. We report the values of dark current, read noise and conversion gain, as well as its cosmetic qualities that we have measured at a temperature of 50K. The measured dark current of these devices at low bias voltages is of ∼3 [e-/pix/ksec] (ksec=1000 seconds). We show that this dark current is dominated by the glow emitted by the ROIC of the detector when it is being read out. The intrinsic dark current of these devices is consistent with zero, with a best estimate of ∼0.1 [e-/pix/ksec]. The glow coming from the ROIC is measured to be ∼0.08 [e-/pix/frame], or 1 [e-/pix] every ∼12 frames. The read noise of these devices starts around ∼10 [e-/pix/frame] at a bias voltage of 3V, and decreases by a factor of 1.3 with each +1V increment of the bias voltage, in agreement with theory. It is reduced to ∼2 [e-/pix/frame] at a bias voltage of 8V.
Eyesafe military laser range finder systems that incorporate carbon dioxide lasers operating at 10.59 microns have been successfully developed and are currently in production for both the U.S. and foreign military services. The development of carbon dioxide laser rangefinders for Fire Control applications has provided high performance, eyesafe capability to both heavy combat vehicles and air defense platforms. The distinct wavelength compatibility provided by a long wavelength laser in conjunction with long wavelength Forward Looking Infrared (FLIR) detection systems positions the CO2 laser range finder system as unique in the ability to provide ranging capability to FLIR recognizable targets and eye safety. First order modeling of expected performance versus system design parameters has provided a basis for understanding the key performance factors and their relationship to necessary design trade-offs. The successful implementation of the laser range finder design required the development of an array of CO2 laser system components that provide both the transmitted laser pulse and the ability to detect the target reflected return. A modular design approach to the CO2 laser system components has led to several successful programs that incorporate identical key technologies thereby reducing the overall cost of all CO2 laser range finder programs.
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