Signal nonlinearity measurements and corrections in MWIR and LWIR HgCdTe H2RG arrays for NEO Surveyor

The depletion region around each p-n junction in HgCdTe HAWAII-2RG detector arrays decreases in volume as charge is collected, causing the pixel capacitance to change continuously throughout an integration period. This changing capacitance manifests as a steadily decreasing measured signal rate while observing a constant flux. Ignoring this nonlinear response to signal accumulation can lead to underestimating the number of detected pho- tons by as much as 10%. Presented here are two methods, one simple and one complex, of measuring this signal nonlinearity and a theoretical framework behind a nonlinearity correction method. Additionally, experimental data are compared with simulations to explain methods to reduce noise in the nonlinearity measurement and identify deviations from the expected behavior that merit further study. © SPIE. Downloading of the abstract is permitted for personal use only.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Modulation transfer function measurements of HgCdTe long wavelength infrared arrays for the Near-Earth Object Surveyor

The modulation transfer function (MTF) is a useful measure in image quality analysis and performance budget determination. Sensitive long wavelength infrared (LWIR) detectors for astronomical space telescopes require slight modifications to the existing MTF measurement methods due to the increased prevalence of high dark current pixels. Presented here are the specifics of a modified slanted edge method to determine the MTF in λc > 10 μm HgCdTe detectors to be used with the planned Near-Earth Object Surveyor Mission. The measured MTF at Nyquist using 6 μm light is 0.22 ± 0.02 and is 0.25 ± 0.02 using 10 μm light for both 250 and 350 mV of applied reverse bias. These measurements are from edge spread functions with median signal values around 50% of the well depth, as the MTF is expected to change with signal value due to two brighter-fatter type effects. The expected trends caused by the influences of these two effects and the expected trends with wavelength of absorbed photons are all observed. © 2022 Society of Photo-Optical Instrumentation Engineers (SPIE).Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Blooming in H2RG arrays: Laboratory measurements of a second brighter-fatter type effect in HgCdTe infrared detectors

Improved measurement and calibration of detector behaviors will be crucial for future space missions, particularly those aiming to tackle outstanding questions in cosmology and exoplanet research. Similarly, many small detector effects, such as the nearest-neighbor interactions of the brighter-fatter effect and interpixel capacitance, will need to be considered to ensure measured signals are truly astronomical in origin. Laboratory measurements confirming the existence of an additional brighter-fatter type effect in HAWAII-1RG and HAWAII-2RG HgCdTe infrared arrays with cutoff wavelengths ranging from 5.7 to 16.7 μm are presented. This effect is similar in nature to the blooming observed in charge-coupled devices and is characterized by a pixel spontaneously sharing a current with its neighbors upon reaching saturation, serving to make the brightest sources appear fatter. In addition to exploring the cause and mechanism of current sharing for this effect, measurements for several arrays show the magnitude of the shared current is greater than 60% of the incoming photocurrent hitting the saturated pixel. A proof-of-concept correction method for this effect is also described along with the necessary next steps to improve this correction and investigate the amplitude of other nearest-neighbor interactions. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The World at America\u27s Doorstep: Service Learning in Preparation to Teach Global Students

Immigration trends in the United States necessitate the preparation of new K-12 teachers to teach diverse populations and to recognize the capabilities of immigrant and refugee children. Transformative learning that results from service learning offers a promising opportunity for preservice teachers to gain awareness and change their attitudes toward these children. This study examined the role of service learning where undergraduate education students tutored at a local refugee agency or elementary school. An analysis of their journal entries indicated changes in beliefs and attitudes toward refugee and other immigrant children, including the acknowledgement of their motivation and determination when confronted by challenges not faced by students born in the United States