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Honeywell Aerospace is implementing on behalf of the Canadian Space Agency the Quantum Encryption and Science Satellite (QEYSSat), a Canadian-owned and operated scientific and technology demonstration mission aimed at developing the next-generation of secure communications infrastructure backed by quantum physics. The mission management is led by the Canadian Space Agency and the science is led by the Institute for Quantum Computing at the University of Waterloo. Quantum key distribution (QKD) is a method for issuing, via single-photon transmission, verifiably-confidential encryption keys between two parties. This capability is a powerful tool for the transfer of sensitive data (e.g. financial transactions, health records, etc.), however current terrestrial QKD networks are limited to a few hundred kilometres in geographic reach between nodes. The QEYSSat mission will use a satellite receiver as a trusted node to demonstrate the distribution of secure keys between ground stations separated by at least 400 km. In addition, Honeywell intends to fly an optical intersatellite link (OISL) terminal as a hosted payload on this mission. The QEYSSat mission will utilize both weak coherent pulse (WCP) sources and entangled photon sources in an uplink configuration to study the performance of QKD, and to perform Bell tests of long-range quantum entanglement. Honeywell is building the QKD receiver terminal consisting of a front-end telescope, a precision pointing and tracking system and single-photon detectors. Major technical challenges include polarization management throughout the optical chain, accurate pointing and tracking, and suppression of background and stray light sources. To address these challenges, Honeywell is leveraging its existing commercial optical communications solutions to meet the more stringent performance requirements for space-based QKD. The QKD terminal architecture consists of an afocal front-end telescope, a wide FOV high-precision pointing and tracking assembly, a polarization analyzer and single-photon photodetector system. A large-diameter on-axis telescope for geostationary optical communications forms the basis for the terminal’s front-end optics, and Honeywell’s commercial Optical Pointing and Tracking Relay Assembly for intersatellite Communications (OPTRAC) has been adapted as a quantum-ready pointing and tracking unit (QTRAC). For each element, substantial effort has been made to develop an optical system that preserves single-photon states with high fidelity despite the large number of optical surfaces in the chain. The optical assembly for the QKD terminal was developed and tested at the breadboard level in 2020; this paper will highlight the development and testing of these units as well as the overall architecture and concept of the QEYSSat mission.

Avalanche photodiodes (APDs) are well-suited for single-photon detection on quantum communication satellites as they are a mature technology with high detection efficiency without requiring cryogenic cooling. They are, however, prone to significantly increased thermal noise caused by in-orbit radiation damage. Previous work demonstrated that a one-time application of thermal annealing reduces radiation-damage-induced APD thermal noise. Here we examine the effect of cyclical proton irradiation and thermal annealing. We use an accelerated testing environment which emulates a realistic two-year operating profile of a satellite in low-Earth-orbit. We show that repeated thermal annealing is effective at maintaining thermal noise of silicon APDs within a range suitable for quantum key distribution throughout the nominal mission life, and beyond. We examine two strategies -- annealing at a fixed period of time, and annealing only when the thermal noise exceeds a pre-defined limit. We find both strategies exhibit similar thermal noise at end-of-life, with a slight overall advantage to annealing conditionally. We also observe that afterpulsing probability of the detector increases with cumulative proton irradiation. This knowledge helps guide design and tasking decisions for future space-borne quantum communication applications., Comment: 7 pages, 8 figures

The purpose of this study was to optimize the best granulation techniques for development of tablet dosage form. The present study explains comparative study of different wet granulation techniques including Planetary mixer granulation, Rapid mixer granulation, Fluid bed granulation with Direct compression method. Similar formulations were used to evaluate Planetary mixer granulation, Rapid mixer granulation and Fluid bed granulation method. The granules prepared by different techniques were evaluated for particle size distribution, porosity, spherisity, bulk density, flow property and compressibility, compatibility and tablet properties of Diclofenac sodium tablet. The fluid bed granulation technique had superior flow properties, compressibility, compactibility measured by Kawakita, Hekel, Walker and Leuenberger equation. The granules prepared by Fluid bed granulation showed better tablet properties (weight uniformity, hardness, friability and disintegration, drug content, dissolution) and accelerated stability study compared to other granulation techniques so finally, it was concluded that Diclofenac sodium tablets prepared by using fluid bed granulation which meets the required specification compared to other wet granulation techniques and direct compression method. Key words: Granulation technique, Flowability, compressibility, compactibility, Diclofenac sodium tablet.

Type-II strained-layer superlattices (T2SLs) are receiving increased interest as mid-wave infrared (MWIR) and long-wave infrared detector absorbers due to their potential Auger suppression and ability to be integrated into complex device structures. Although T2SLs show promise for use as infrared detectors, further investigation into the effects of high energy particle radiation is necessary for space-based applications. In this presentation, the effects of both 4.5 MeV and 63 MeV proton radiation on the carrier lifetime of MWIR InAs/InAsSb T2SLs will be shown. The 63 MeV proton radiation study will focus on the carrier lifetime of MWIR InAs/InAsSb T2SL samples of varying donor density. These results reveal a Shockley-Read-Hall (SRH) lifetime associated with a radiation induced defect level, which is not dependent on the donor density of the T2SL. Using 4.5 MeV proton radiation, the dependence of carrier lifetime on relative trap density in MWIR T2SLs samples is studied by varying the particle fluence. A comparison of these two radiation studies shows similar lifetime effects that will be discussed in detail. These results give insight into the viability of Ga-free T2SLs for space applications.

Aims In the present study, to investigate its chemical stability and the in vitro sun protection factor (SPF) of Rosa kordesii petal extract in a gel formulation. Methods Due to its antioxidant and photoprotective properties, R. kordesii is a promising candidate for use in cosmetic and pharmaceutical formulations. A high performance liquid chromatography method was used to evaluate the chemical stability using R. kordesii extract as marker at 5, 25 and 45 °C for 3–4 months. The sun protection factors were analyzed by ultraviolet (UV) spectrophotometry using samples irradiated with UVB lamp. Results The chemical stability of the R. kordesii root extract gel was determined according to the concentration of R. kordesii extracts at different storage temperatures (5, 25 and 45 °C) for 3–4 months. It is screened for in vitro sun protection factor in the R. kordesii extract and of its gel formulation and determines Photostability of the isolated R. kordesii extract and SPF. Conclusion This study has shown that the R. kordesii petal extract gel is stable for at least 3–4 months when stored at 5 and 25 °C. It is essential for collection of similar data for different plants and their flowers, as well as other parts. This proved activity of plant showed its importance and prophylactic utility in anti-solar formulation. This will be a better, cheaper and safe alternative to harmful chemical sunscreens that used now a days in the industry.

Weather satellite instruments require detectors with a variety of wavelengths ranging from the visible to VLWIR. The Cross-track infrared Sounder (CrIS) is a Polar Orbiting interferometric sensor that measures earth radiances at high spectral resolution, using the data to provide pressure, temperature and moisture profiles of the atmosphere. The pressure, temperature and moisture sounding data are used in weather prediction models that track storms, predict levels of precipitation etc. The CrIS instrument contains SWIR (lambda(sub c) (is) approximately 5 micrometers at 98 K), MWIR (lambda(sub c) (is) approximately 9 micrometers at 98 K) and LWIRs (lambda(sub c) (is) approximately 15.4 m at 81 K) bands in three Focal Plane Array Assemblies (FPAAs). CrIS detectors are 850 micrometers diameter detectors with each FPAA consisting of nine photovoltaic detectors arranged in a 3 x 3 pattern. Molecular beam epitaxy (MBE)-grown Hg1-xCdxTe material are used for the detectors fabricated in a modified Double Layer Planar Heterostructure (DLPH) architecture. Each detector has an accompanying cold preamplifier. SWIR and MWIR FPAAs operate at 98 K and the LWIR FPAA at 81 K, permitting the use of passive radiators to cool the detectors. D* requirements at peak 14.01 micrometers wavelength are greater than 5.0E+10 Jones for LWIR, greater than 7.5E+10 Jones at 8.26 micrometers for MWIR and greater than 3.0E+11 Jones at peak 4.64 micrometers wavelength for SWIR. All FPAAs exceeded the D* requirements. Measured mean values for the nine photodiodes in each of the LWIR, MWIR and SWIR FPAAs are D* = 5.3 x 10(exp 10) cm-Hz1/2/W at 14.0 micrometers, 9.6 x 10(exp 10) cm-Hz1/2/W at 8.0 micrometers and 3.4 x 10(exp 11) cm-Hz1/2/W at 4.64 micrometers.

Weather satellite instruments require detectors with a variety of wavelengths ranging from the visible to VLWIR. One of the remote sensing applications is the geostationary GOES-ABI imager covering wavelengths from the 450 to 490 nm band through the 13.0 to 13.6 μm band. There are a total of 16 spectral bands covered. The Cross-track infrared Sounder (CrIS) is a Polar Orbiting interferometric sensor that measures earth radiances at high spectral resolution, using the data to provide pressure, temperature and moisture profiles of the atmosphere. The pressure, temperature and moisture sounding data are used in weather prediction models that track storms, predict levels of precipitation etc. The CrIS instrument contains SWIR (λc ∼ 5 μm at 98K), MWIR (λc ∼ 9 μm at 98K) and LWIRs (λc ∼ 15.5 μm at 81K) bands in three Focal Plane Array Assemblies (FPAAs). GOES-ABI contains three focal plane modules (FPMs), (i) a visible-near infrared module consisting of three visible and three near infrared channels, (ii) a MWIR module comprised of five channels from 3.9 μm to 8.6 μm and (iii) a 9.6 μm to 13.3 μm, five-channel LWIR module. The VNIR FPM operates at 205 K, and the MWIR and LWIR FPMs operate at 60 K. Each spectral channel has a redundant array built into a single detector chip. Switching is thus permitted from the primary selected array in each channel to the redundant array, given any degradation in performance of the primary array during the course of the mission. Silicon p-i-n detectors are used for the 0.47 μm to 0.86 μm channels. The thirteen channels above 1 μm are fabricated in various compositions of Hg1-xCdxTe, and in this particular case using two different detector architectures. The 1.38 μm to 9.61 μm channels are all fabricated in Hg1-xCdxTe grown by Liquid Phase Epitaxy (LPE) using the HDVIP detector architecture. Molecular beam epitaxy (MBE)-grown Hg1-xCdxTe material are used for the LWIR 10.35 μm to 13.3 μm channels fabricated in Double layer planar heterostructure (DLPH) detectors. This is the same architecture used for the CrIS detectors. CrIS detectors are 850 μm diameter detectors with each FPAA consisting of nine photovoltaic detectors arranged in a 3 x 3 pattern. Each detector has an accompanying cold preamplifier. SWIR and MWIR FPAAs operate at 98 K and the LWIR FPAA at 81 K, permitting the use of passive radiators to cool the detectors. D* requirements at peak wavelength are ≥ 5.0E+10 Jones for LWIR, ≥ 9.3E+10 Jones for MWIR and ≥ 3.0E+11 Jones for SWIR. All FPAAs exceeded the D* requirements. Measured mean values for the nine photodiodes in each of the LWIR, MWIR and SWIR FPAAs are D* = 5.3 x 1010 cm-Hz1/2/W at 14.0 μm, 1.0 x 1011 cm-Hz1/2/W at 8.0 μm and 3.1 x 1011 cm-Hz1/2/W at 4.64 μm.

Improvement of bio-availability of poorly water soluble drugs presents one of the furthermost challenge in drug formulations. One of the most admired and commercially viable formulation approach for this challenge is solid self micro emulsifying drug delivery system (S-SMEDDS). There are many techniques to convert liquid SMEDDS to solid, but an adsorption technique is simple and economic. Hence aim of present study was to develop S-SMEDDS of poorly water soluble drug Telmisartan (TEL) using Aerosil 200 as solid carrier. Liquid SMEDDS was prepared using Acrysol EL 135, Tween 80 and PEG 400 as oil, surfactant and co-surfactant and was converted to S-SMEDDS by adsorbing it on Aerosil 200. Prepared S-SMEDDS was evaluated for flow properties, drug content, reconstitution properties, DSC, SEM, in-vitro drug release and ex-vivo intestinal permeability study. Results showed that prepared S-SMEDDS have good flow property with 99.45 ± 0.02% drug content. Dilution study by visual observation showed that there was spontaneous micro emulsification and no sign of phase separation. Droplet size was found to be 0.34 µm with polydispersity index of 0.25. DSC thermogram showed that crystallization of TEL was inhibited. SEM photograph showed smooth surface of S-SMEDDS with less aggregation. Drug releases from S- SMEDDS were found to be significantly higher as compared with that of plain TEL. Ex-vivo intestinal permeability study revealed that diffusion of drug was significantly higher from S-SMEDDS than that of suspension of plain TEL. Study concluded that S-SMEDDS can effectively formulated by adsorption technique with enhanced dissolution rate and concomitantly bioavailability.DOI: http://dx.doi.org/10.3329/icpj.v1i12.12451 International Current Pharmaceutical Journal 2012, 1(12): 414-419

InAs1−x Sb x material with an alloy composition of the absorber layer adjusted to achieve 200-K cutoff wavelengths in the 5-μm range has been grown. Compound-barrier (CB) detectors were fabricated and tested for optical response, and J dark–V d measurements were taken as a function of temperature. Based on absorption coefficient information in the literature and spectral response measurements of the midwave infrared (MWIR) nCBn detectors, an absorption coefficient formula α(E, x, T) is proposed. Since the presently suggested absorption coefficient is based on limited data, additional measurements of material and detectors with different x values and as a function of temperature should refine the absorption coefficient, providing more accurate parametrization. Material electronic structures were computed using a k·p formalism. From the band structure, dark-current density (J dark) as a function of bias (V d) and temperature (T) was calculated and matched to J dark–V d curves at fixed T and J dark–T curves at constant V d. There is a good match between simulation and data over a wide range of bias, but discrepancies that are not presently understood exist near zero bias.

The COM DEV Mission Development Group has recently launched a nanosatellite mission called NTS (Nanosatellite Tracking of Ships). NTS is a space trial, intended to provide proof-of-concept validation for a COM DEV AIS (Automatic Identification System) radio that has been specifically designed to receive ship AIS transmissions from low Earth orbit. The AIS system uses the very high frequency (VHF) band and provides detailed information about each equipped vessel. Not only does this system provide information such as the location of a vessel, but it also provides heading, engine status and other crucial information about the ship. Designed for terrestrial use, the AIS system traditionally has a range of only 100 km and uses a local self-organized time-division multiple access (SO-TDMA) scheme to ensure transmissions from all ships in any self-organized cell do not overlap. Receiving these signals from a space platform presents an opportunity to provide wide area monitoring of shipping activity. Detection of AIS signals from space will provide a new capability to track and monitor large maritime vessels even when there are large distances from traditional shore based detection systems. The NTS program was designed to be a low cost demonstration satellite and provide rapid risk mitigation to assist in the development of a future constellation of spacecraft that could provide operational AIS from space (AIS-S) reception and dissemination. The scope of the NTS program was kept to a minimum with focus on the design, development and demonstration of a new payload. The nanosatellite bus was developed using a combination of pre-existing designs by the University of Toronto Institute of Aerospace Studies/Space Flight Laboratory (UTIAS/SFL). The resulting bus design was a combination of their CanX-2 and Generic Nanosatellite Bus. The NTS spacecraft is able to provide the capability to detect AIS signals from low earth orbit with multiple, short AIS signal collection cycles over its planned mission lifetime. The paper presents an overview of the NTS spacecraft, mission concept and preliminary results obtained from the flight.

Increasing very long-wave infrared (VLWIR, λ c ≈ 15 μm) pixel operability was approached by subdividing each pixel into four interdigitated subpixels. High response is maintained across the pixel, even if one or two interdigitated subpixels are deselected (turned off), because interdigitation provides that the preponderance of minority carriers photogenerated in the pixel are collected by the selected subpixels. Monte Carlo modeling of the photoresponse of the interdigitated subpixel simulates minority-carrier diffusion from carrier creation to recombination. Each carrier generated at an appropriately weighted random location is assigned an exponentially distributed random lifetime τ i, where 〈τ i〉 is the bulk minority-carrier lifetime. The minority carrier is allowed to diffuse for a short time dτ, and the fate of the carrier is decided from its present position and the boundary conditions, i.e., whether the carrier is absorbed in a junction, recombined at a surface, reflected from a surface, or recombined in the bulk because it lived for its designated lifetime. If nothing happens, the process is then repeated until one of the boundary conditions is attained. The next step is to go on to the next carrier and repeat the procedure for all the launches of minority carriers. For each minority carrier launched, the original location and boundary condition at fatality are recorded. An example of the results from Monte Carlo modeling is that, for a 20-μm diffusion length, the calculated quantum efficiency (QE) changed from 85% with no subpixels deselected, to 78% with one subpixel deselected, 67% with two subpixels deselected, and 48% with three subpixels deselected. Demonstration of the interdigitated pixel concept and verification of the Monte Carlo modeling utilized λ c(60 K) ≈ 15 μm HgCdTe pixels in a 96 × 96 array format. The measured collection efficiency for one, two, and three subelements selected, divided by the collection efficiency for all four subelements selected, matched that calculated using Monte Carlo modeling.

Spectral response of detectors can be modeled using a stack matrix approach. The different material layers that make up the detector form the optical stack. Light intensity is proportional to the square of the amplitude of the electromagnetic field’s electric field component. Using the electric component of light, the model takes into account the reflective and transmission coefficients at the interface between two adjacent layers and the phase difference during propagation within each layer. The transition from one optical layer to another and the propagation within an optical layer can be formulated as 2 × 2 matrices; their multiplication through every optical layer makes up the stack matrix that defines the optical properties of the detector. Knowing the complex index of refraction for each layer in the detector, the intensity of light can be calculated at any point in the detector structure, which can then be used to determine the response of the detector as a function of wavelength. This model shows fairly good agreement with the experimental data, even revealing fine structure and etalon effects. Using this model, the detector can be designed to meet specific spectral characteristics. The spectral response model was used on high-density vertically interconnected photodiode front-side-illuminated photodiodes.

We demonstrated a device with a unique planar architecture using a novel approach for obtaining low arsenic doping concentrations in long-wavelength (LW) HgCdTe on CdZnTe substrates. HgCdTe materials were grown by molecular beam epitaxy (MBE). We fabricated a p-on-n structure that we term P +/π/N + where the symbol “π” is to indicate a drastically reduced extrinsic p-type carrier concentration (on the order of mid 1015 cm−3); P + and N + denote a higher doping density, as well as a higher energy gap, than the photosensitive base π-region. Fabricated devices indicated that Auger suppression is seen in the P +/π/N + architecture at temperatures above 130 K and we obtained a saturation current on the order of 3 mA on 250-μm-diameter devices at 300 K with Auger suppression. Data shows that about a 50% reduction in dark current is achieved at 300 K due to Auger suppression. The onset of Auger suppression voltage is 450 mV at 300 K and 100 mV at 130 K. Results indicate that a reduction of the series resistance could reduce this further. A principal challenge was to obtain low p-type doping levels in the π-region. This issue was overcome using a novel deep diffusion process, thereby demonstrating successfully low-doped p-type HgCdTe in MBE-grown material. Near-classical spectral responses were obtained at 250 K and at 100 K with cut-off wavelengths of 7.4 μm and 10.4 μm, respectively. At 100 K, the measured non-antireflection-coated quantum efficiency was 0.57 at 0.1 V under backside illumination.

Time series and Fourier-transform data on high-density vertically integrated photodiodes (HDVIP) at 0 and 50 mV reverse bias in the dark have been studied. The detectors have a cutoff wavelength λc (60 K) of 10.5 μm. Examination of the detector current time series and Fourier-transform curves of these devices reveals a variety of interesting characteristics: (i) time series displaying switching between four states characteristic of random telegraph signal (RTS) noise, the noise current power spectrum having Lorentzian or double Lorentzian type characteristics, (ii) time series data exhibiting wave-like characteristics with the noise current power spectrum being 1/f2-like at low frequencies, (iii) time series having a mean value independent of time with the noise current power spectrum being white, and (iv) time series nearly independent of time with the noise current power spectrum having 1/f characteristics. Although from a single array, the excess noise characteristics at low (mHz) frequencies were varied, most of the detectors measured fell into one of these four categories. The predominance of detectors examined had minimal excess low-frequency noise down to ~ 10 mHz. Detectors that displayed RTS noise in reverse bias were repeatable under subsequent measurement. However, when measured at zero bias, the same detectors exhibited no RTS noise, the noise current power spectrum being white in nature.

The Cross-Track Infrared Sounder (CrIS) program [an instrument on the National Polar-Orbiting Operational Environmental Satellite System (NPOESS)] requires photodiodes with spectral cutoffs denoted by short-wavelength infrared [γc(98 K) ∼5.1 µm], midwavelength infrared [γc(98 K) ∼9.1 µm], and long-wavelength infrared (LWIR) [γc(81 K) ∼15.5 µm]. The CrIS instrument also requires large-area (850-µm-diameter) photodiodes with state-of-art performance. Molecular beam epitaxy (MBE) is used to grow n-type short-wavelength infrared, midwavelength infrared, or LWIR Hg1−xCdxTe on latticematched CdZnTe. Detectors with p-type implants 7 µm in diameter are used to constitute the 850-µm-diameter lateral collection diodes (LCDs). The photodiode architecture is the double-layer planar heterostructure architecture.

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1−xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-µm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10−15A/Hz1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth in(f = 1 Hz, Vd = −60 mV, and Δf = 1 Hz) to dark current Id(Vd = −60 mV) was αSW-d = in/Id ∼ 1 × 10−3. The SWIR detectors measured at 0 mV under illuminated conditions had median αSW-P = in/Iph ∼ 7 × 10−6. For mid-wave infrared (MWIR) detectors, αMW-d = in/Id ∼ 2 × 10−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-µm-diameter MWIR detectors under illuminated conditions at 98 K and −60 mV bias resulted in αMW-P = in/Iph = 4.16 ± 1.69 × 10−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, αMW-P, in the mid 10−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, αLW-d = in/Id ∼ 6 × 10−6, for the best performers. The majority of the LWIR detectors exhibited αLW-d on the order of 2 × 10−5. The photo-induced 1/f noise had αLW-P = in/Iph ∼ 5 × 10−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.

This paper investigates 1/f noise performance of very-long-wavelength infrared (VLWIR) Hg1-xCdxTe (cutoff wavelengths λc = 15 µm and λc = 16 µm) photodiodes at 78 K, where detector current is varied by changing detector area, detector bias, and illumination conditions. Holding detector bias and temperature constant, the 1/f noise current is proportional to the detector current. Significant nonuniformity is observed in the noise data for each detector area because of the varying detector quality. Defects are presumed resident in the detectors to produce greater nonuniformity in 1/f noise as compared to dark current at 100-mV reverse bias. For λc = 16 µm, 4-µm-radius, diffusion-limited diodes at 78 K and 100-mV reverse bias, the average dark current is Id = 9.76 ± 1.59 × 10-8A, while the average noise current measured at 1 Hz is in = 1.01 ± 0.63 × 10-12A/Hz1/2. For all detector areas measured, the average ratio in 1-Hz bandwidth is αD = in/Id = 1.39 ± 1.09 × 10-5. The 1/f noise was also measured on one diode as a function of detector-dark current as the applied bias is varied. In the diffusion-limited portion of this detector's current-voltage (I-V) curve, to about 130 mV, the 1/f noise was independent of bias. For this diode, the ratio αD = in/Id = 1.51 ± 0.12 × 10-5. The 1/f noise associated with tunneling currents is a factor of 3 greater than the 1/f noise associated with diffusion currents, αT = in/IT = 5.21 ± 0.83 × 10-5. In addition, 1/f noise was measured on detectors held at - 100 mV and 78 K under dark and illuminated conditions. The measured ratios αp ∼ αD ∼ 1.5 × 10-5 were about the same for the dark and photon-induced diffusion currents. Therefore, the diffusion current appears to have a unique value of α as compared to the tunneling current. This may be indicative of unique noise-generation mechanisms associated with each current.

State-of-the-art large-area photovoltaic (PV) detectors fabricated in HgCdTe grown by molecular beam epitaxy (MBE) have been demonstrated for the Crosstrack Infrared Sounder (CrIS) instrument. Large-area devices (1 mm in diameter) yielded excellent electrical and optical performance operating at 81 K for λc ∼ 15 µm, at 98 K for λc ∼ 9 µm, and λc ∼ 5-µm spectral cutoffs. Fabricated detectors have near-theoretical electrical performance, and Anti Reflection coated quantum efficiency (QE) is greater than 0.70. Measured average RoA at 98 K is 2.0E7 Ωcm2, and near-theoretical QEs greater than 0.90 were obtained on detectors with λc ∼ 5-µm spectral cutoffs. These state-of-the-art large-area PV detector results reflect high-quality HgCdTe grown by MBE on CdZnTe substrates in all three spectral bands of interest.

Very long wavelength infrared (VLWIR; 15 to 17 µm) detectors are required for remote sensing sounding applications. Infrared sounders provide temperature, pressure and moisture profiles of the atmosphere used in weather prediction models that track storms, predict levels of precipitation etc. Traditionally, photoconductive VLWIR (λc >15 µm) detectors have been used for sounding applications. However, photoconductive detectors suffer from performance issues, such as non-linearity that is 10X – 100X that of photovoltaic detectors. Radiometric calibration for remote sensing interferometry requires detectors with low non-linearity. Photoconductive detectors also suffer from non-uniform spatial optical response. Advances in molecular beam epitaxy (MBE) growth of mercury cadmium telluride (HgCdTe) and detector architectures have resulted in high performance detectors fabricated in the 15 µm to 17 µmm spectral range. Recently, VLWIR (λc ∼ 17 µm at 78 K) photovoltaic large (1000 µm diameter) detectors have been fabricated and measured at flux values targeting remote sensing interferometry applications. The operating temperature is near 78 K, permitting the use of passive radiators in spacecraft to cool the detectors. Detector non-AR coated quantum efficiency >60% was measured in these large detectors. A linear response was measured, while varying the spot size incident on the 1000 µm detectors. This excellent response uniformity, measured as a function of spot size, implies that low frequency spatial response variations are absent. The 1000 µm diameter, λc ∼ 17 µm at 78 K detectors have dark currents ∼160 µA at a −100 mV bias and at 78 K. Interfacing with the low (comparable to the contact and series resistance) junction impedance detectors is not feasible. Therefore a custom pre-amplifier was designed to interface with the large VLWIR detectors operating in reverse bias. A breadboard was fabricated incorporating the custom designed preamplifier interfacing with the 1000 µm diameter VLWIR detectors. Response versus flux measurements were made on the large VLWIR detectors and non-linearity

Long wavelength infrared molecular beam epitaxy (MBE) grown p-on-n Hg1−xCdxTe double layer planar heterostructure (DLPH) detectors have been characterized to determine the dominant mechanisms limiting their performance. Material defects have been identified as critical factors that limit 40K performance operability. This effort has concentrated on identifying microscopic defects, etch pit density (EPD) and relating these defects to the device performance. Visual inspection indicates defect densities as high as 105 per cm2 with a spatial extent as observed by atomic force microscope in the range of micrometers extending several micrometers beneath the surface. At high EPD values (greater than low 106 cm−2) zero bias resistance (R0) at 40K decreases as roughly as the square of the EPD. At 78K, however, measured R0 is not affected by the EPD up to densities as high as mid-106 cm−2. Visual defects greater than 2–3 µm than ∼2 µm in size (micro-void defects) result in either a single etch pit or a cluster of etch pits. Large variations in a cross-wafer etch pit distribution are most likely a major contributor to the observed large spreads in 40K R0. This study gives some insight to the present limitation to achieve higher performance and high operability for low temperature infrared applications on MBE grown HgCdTe material.

Excess low frequency noise is investigated for the first time in infrared MBE grown LWIR Hg1−xCdxTe double layer planar heterostructure (DLPH) detectors grown on lattice matched substrates. LWIR detectors having R0Aopt values at 40K in the 101–107 Θ-cm2 range have been characterized as a function of temperature between 120 and 20K. Detectors with R0Aopt≥103Θ-cm2 at 40K have theoretical diffusion limited performance down to 78K and detectors with R0Aopt ≥105 Θ-cm2 at 40K are within a factor of two of theoretical diffusion limited performance for T>65K. Activation energies extracted from noise (Vd=−100 mV) and dark current (Vd=−100 mV) vs temperature measurements were detector dependent. The activation energy for detectors with R0Aopt≈106 Θ-cm2 at 40K is ∼0.90*Eg to 0.99*Eg. The noise measured between 78 and 105K in the intermediate performance (R0Aopt∼103–104 Θ-cm2 at 40K) detectors are higher than the noise measured in the higher performance (R0Aopt∼105–107 Θ-cm2) detectors. In addition, the excess low frequency noise and the dark current at −100 mV in the intermediate and poor (R0Aopt∼101 Θ-cm2) performance detectors are temperature independent. For each detector measured, the activation energy extracted from noise (Vd=−100 mV) vs temperature measurements is equal to the activation energy extracted from the total dark current (Vd=−100 mV) vs temperature measurements. For different dark current mechanisms, the excess low frequency noise varies with temperature and also with area within statistical accuracy in the same manner as the total dark current through the detector. At 78K, the Tobin14 expression holds in the general sense for equal area detectors dominated by different current mechanisms and also for detectors with a wide range of implant dimensions (Aimp=3.85×10−7 cm2 to Aimp=6.25×10−4 cm2). Following measurements, the detectors were stripped of the passivation and overlaying metal layers and dressed by a defect etch to reveal defects in each detector. A correlation among noise, leakage current and defect type has been determined for each detector.

The current-voltage characteristics and quantum efficiencies of double layer planar heterostructure photodiodes were investigated. Results are reported on devices with cutoff wavelengths of 1.8, 2.4, and 3.3 µm. For these respective devices, the dominant currents for temperatures >250,>200,>150K are diffusion currents limited by shallow Shockley-Hall-Read (SHR) processes. The remarkable result is that the electrical and optoelectronic properties of these devices of diverse cut-off wavelength can be explained by simple models using independently measured layer parameters such as the minority carrier lifetimes. For all three cases, the analysis suggests that the same shallow (SHR) centers located at 78% of the energy gap are causing the observed effects. These traps located in then-type base of the device are not influenced by the magnitude of n-type doping and this observation was used to significantly improve the performance of the devices and validate the predictive capability of the models used in the analysis. The shallow centers appear to be process induced rather than grown-in. This assertion is based on the observation that changes in the annealing process led to an order of magnitude improvement in the minority carrier lifetime.

The capability of growing state-of-the-art middle wavelength infrared (MWIR)-HgCdTe layers by molecular beam epitaxy (MBE) on large area silicon substrates has been demonstrated. We have obtained excellent compositional uniformity with standard deviation of 0.001 with mean composition of 0.321 across 1.5″ radii. R0A as high as 5 × 107 ω-cm2 with a mean value of 7 × 106 Θ-cm2 was measured for cut-off wavelength of 4.8 µm at 77K. Devices exhibit diffusion limited performance for temperatures above 95K. Quantum efficiencies up to 63% were observed (with no anti-reflection coating) for cut-off wavelength (4.8–5.4) µm @ 77K. Excellent performance of the fabricated photodiodes on MBE HgCdTe/CdTe/Si reflects on the overall quality of the grown material in the MWIR region.

Mid wavelength infrared p-on-n double layer planar heterostructure (DLPH) photodiodes have been fabricated in HgCdTe double layers grown in situ by liquid phase epitaxy (LPE), on CdZnTe and for the first time on CdTe/sapphire (PACE-1). Characterization of these devices shed light on the nature of the material limits on device performance for devices performing near theoretical limits. LPE double layers on CdZnTe and on PACE-1 substrates were grown in a horizontal slider furnace. All the photodiodes are p-on-n heterostructures with indium as the n-type dopant and arsenic the p-type dopant. Incorporation of arsenic is via implantation followed by an annealing step that was the same for all the devices fabricated. The devices are passivated with MBE CdTe. Photodiodes have been characterized as a function of temperature. R0Aimp values obtained between 300 and 78K are comparable for the two substrates and are approximately a factor of five below theoretical values calculated from measured material parameters. The data, for the PACE-1 substrate, indicates diffusion limited performance down to 110K. Area dependence gives further indications as to the origin of diffusion currents. Comparable R0Aimp for various diode sizes indicates a p-side origin. R0A and optical characteristics for the photodiodes grown on lattice-matched CdZnTe substrates and lattice mismatched PACE-1 are comparable. Howover, differences were observed in the noise characteristics of the photodiodes. Noise was measured on 50 × 50 µm devices held under a 100 mV reverse bias. At 110K, noise spectrum for devices from the two substrates is in the low 10−15 A/Hz1/2 range. This value reflects the Johnson noise of the room temperature 1010 Ω feedback resistor in the current amplifier that limits the minimum measurable noise. Noise at 1 Hz, −100 mV and 120K for the 4.95 µm PACE-1 devices is in the 1–2 × 10−14 A/Hz1/2, a factor of 5–10 lower than previously grown typical PACE-1 n+-on-p layers. Noise at 120K for the 4.60 µm PACE-1 and LPE on CdZnTe was again below the measurement technique limit. Greatest distinction in the noise characteristics for the different substrates was observed at 163K. No excess low frequency noise was observed for devices fabricated on layers grown by LPE on lattice-matched CdZnTe substrates. Photodiode noise measured at 1Hz, −100 mV and 163K in the 4.60 µm PACE-1 layer is in the 1–2×10−13 A/Hz1/2, again a factor of 5–10 lower than previously grown PACE-1 n+-on-p layers. More variation in noise (4×10−13−2×10−12 A/Hz1/2) was observed for devices in the 4.95 µm PACE-1 layer. DLPH devices fabricated in HgCdTe layers grown by LPE on lattice-matched CdZnTe and on lattice-mismatched PACE-1 have comparable R0A and quantum efficiency values. The distinguishing feature is that the noise is greater for devices fabricated in the layer grown on lattice mismatched substrates, suggesting dislocations inherent in lattice mismatched material affects excess low frequency noise but not zero bias impedance.

The molecular beam epitaxy (MBE) growth technology is inherently flexible in its ability to change the Hg1−xCdxTe material’s bandgap within a growth run and from growth run to growth run. This bandgap engineering flexibility permits tailoring the device architecture to the various specific requirements. Material with active layer x values ranging from ∼0.198 to 0.570 have been grown and processed into detectors. This wide range in x values is perfectly suited for remote sensing applications, specifically the National Polar Orbiting Environmental Satellite System (NPOESS) program that requires imaging in a multitude of infrared spectral bands, ranging from the 1.58 to 1.64 µm VSWIR (very short wave infrared) band to the 11.5 to 12.5 µm LWIR (longwave infrared) band and beyond. These diverse spectral bands require high performance detectors, operating at two temperatures; detectors for the VSWIR band operate near room temperature while the SWIR, MWIR (mid wave infra red), LWIR and VLWIR (very long wave infrared) detectors operate near 100K, because of constraints imposed by the cooler for the NPOESS program. This paper uses material parameters to calculate theoretical detector performance for a range of x values. This theoretical detector performance is compared with median measured detector optical and electrical data. Measured detector optical and electrical data, combined with noise model estimates of ROIC performance are used to calculate signal to noise ratio (SNR), for each spectral band. The SNR are compared with respect to the meteorological NPOESS system derived focal plane. The derived system focal plane requirements for NPOESS are met in all the spectral bands.

Short wave infrared (SWIR) devices have been fabricated using Rockwell’s double layer planar heterostructure (DLPH) architecture with arsenic-ion implanted junctions. Molecular beam epitaxially grown HgCdTe/CdZnTe multilayer structures allowed the thin, tailored device geometries (typical active layer thickness was ∼3.5 µm and cap layer thickness was ∼0.4 µm) to be grown. A planar-mesa geometry that preserved the passivation advantages of the DLPH structure with enhanced optical collection improved the performance. Test detectors showed Band 7 detectors performing near the radiative limit (∼3-5X below theory). Band 5 detector performance was ∼4-50X lower than radiative limited performance, apparently due to Shockley-Hall-Read recombination. We have fabricated SWIR HgCdTe 256 × 12 × 2 arrays of 45 um × 45 µm detector on 45 µm × 60 µm centers and with cutoff wavelength which allows coverage of the Landsat Band 5 (1.5−1.75 µm) and Landsat Band 7 (2.08−2.35 µm) spectral regions. The hybridizable arrays have four subarrays, each having a different detector architecture. One of the Band 7 hybrids has demonstrated performance approaching the radiative theoretical limit for temperatures from 250 to 295K, consistent with test results. D* performance at 250K of the best subarray was high, with an operability of ∼99% at 1012 cm Hz1/2/W at a few mV bias. We have observed 1/f noise below 8E-17 AHz 1/2 at 1 Hz. Also for Band 7 test structures, Ge thin film diffractive microlenses fabricated directly on the back side of the CdZnTe substrate showed the ability to increase the effective collection area of small (nominally

United States. Defense Advanced Research Projects Agency (DARPA under contract N66604-09-C-3652)

Multiply damaged sites (MDS) are defined as greater than/equal to two lesions within 10-15 bp and are generated in DNA by ionizing radiation. In vitro repair of closely opposed base damagesor =2 bp apart results in a double strand break (DSB). This work extends the in vitro studies by utilizing clusters of uracil DNA damage as model lesions to determine whether MDS are converted to DSBs in bacteria. Lesions were positioned within the firefly luciferase coding region, transformed into bacteria (wild-type, uracil DNA glycosylase-deficient, ung-, or exonuclease III and endonuclease IV-deficient, xth-nfo-) and luciferase activity measured following repair. DSB formation was expected to decrease activity. Two closely opposed uracils separated byor =7 bp decreased luciferase activity in wild-type and xth-nfo-, but not ung- bacteria. Growth of bacteria to obtain plasmid-containing colonies demonstrated that the plasmid was destroyed following the mis-repair of two uracils positioned 7 bp apart. This study indicates a DSB is formed when uracil DNA glycosylase initiates repair of two closely opposed uracilsor =7 bp apart, even in the absence of the major apurinic endonucleases. This work supports the in vitro studies and demonstrates that DNA repair is not always advantageous to cells.

We present an investigation of the lepton energy distributions in the inclusive semileptonic weak decays of heavy baryons performed within a relativistic quark model formulated on the light front (LF). Using the heavy-quark LF distribution functions related to the equal time momentum wave functions taken from the Kalman--Tran--D'Souza model we compute the electron energy spectra and the total semileptonic widths of the Lambda_Q and Xi_Q (Q=c,b) baryons and confront the results with existing data., Comment: Latex, 5 pages, 3 figures. Talk presented by Calvin Kalman at the 5th International Conference on Hyperon, Charm and Beauty Hadrons, Vancouver, June 2002

We present an investigation of the inclusive semileptonic decay widths of the heavy baryons Lambda_Q and Xi_Q, (Q=b,c) performed within a relativistic constituent quark model, formulated on the light-front. In a way conceptually similar to the deep-inelastic scattering case, the H_Q baryon inclusive width is expressed as the integral of the free Q-quark partial width multiplied by a bound-state factor related to the Q-quark distribution function in the H_Q. The non-perturbative meson structure is described through the quark-model wave functions, constructed via the Hamiltonian light-front formalism using as input the Kalman-Tran-D'Souza equal time wave functions. A link between spectroscopic quark models and the H_Q decay physics is obtained in this way. It is shown that the bound-state effects and the Fermi motion of the b-quark remarkably reduce the decay rate with respect to the free-quark result. Our predictions for the BR(Lambda_c ->X_s e nu_e) and BR(Lambda_b->X_c e nu_e) decays are in good agreement with existing data., 6 pages, latex, espcrc2.sty (included), 3 figures. The invited talk presented by C.S.K. at the 4-th International Conference on Hyperons, Charm and Beauty Hadrons, Valencia, June 27-30, 2000

Optical quantum communication utilizing satellite platforms has the potential to extend the reach of quantum key distribution (QKD) from terrestrial limits of ~200 km to global scales. We have developed a thorough numerical simulation using realistic simulated orbits and incorporating the effects of pointing error, diffraction, atmosphere and telescope design, to obtain estimates of the loss and background noise which a satellite-based system would experience. Combining with quantum optics simulations of sources and detection, we determine the length of secure key for QKD, as well as entanglement visibility and achievable distances for fundamental experiments. We analyze the performance of a low Earth orbit (LEO) satellite for downlink and uplink scenarios of the quantum optical signals. We argue that the advantages of locating the quantum source on the ground justify a greater scientific interest in an uplink as compared to a downlink. An uplink with a ground transmitter of at least 25 cm diameter and a 30 cm receiver telescope on the satellite could be used to successfully perform QKD multiple times per week with either an entangled photon source or with a weak coherent pulse source, as well as perform long-distance Bell tests and quantum teleportation. Our model helps to resolve important design considerations such as operating wavelength, type and specifications of sources and detectors, telescope designs, specific orbits and ground station locations, in view of anticipated overall system performance.

Balanced splicing of retroviral RNAs is mediated by weak signals at the 3' splice site (ss) acting in concert with other cis elements. Moloney murine sarcoma virus MuSVts110 shows a similar balance between unspliced and spliced RNAs, differing only in that the splicing of its RNA is, in addition, growth temperature sensitive. We have generated N-nitroso-N-methylurea (NMU)-treated MuSVts110 revertants in which splicing was virtually complete at all temperatures and have investigated the molecular basis of this reversion on the assumption that the findings would reveal cis-acting elements controlling MuSVts110 splicing thermosensitivity. In a representative revertant (NMU-20), we found that complete splicing was conferred by a G-to-A substitution generating a consensus branchpoint (BP) signal (-CCCUGGC- to -CCCUGAC- [termed G(-25)A]) at -25 relative to the 3' ss. Weakening this BP to -CCCGAC- [G(-25)A,U(-27)C] moderately reduced splicing at the permissive temperature and sharply inhibited splicing at the originally nonpermissive temperature, arguing that MuSVts110 splicing thermosensitivity depends on a suboptimal BP-U2 small nuclear RNA interaction. This conclusion was supported by results indicating that lengthening the short MuSVts110 polypyrimidine tract and altering its uridine content doubled splicing efficiency at permissive temperatures and nearly abrogated splicing thermosensitivity. In vitro splicing experiments showed that MuSVts110 G(-25)A RNA intermediates were far more efficiently ligated than RNAs carrying the wild-type BP, the G(-25)A,U (-27)C BP, or the extended polypyrimidine tract. The efficiency of ligation in vitro roughly paralleled splicing efficiency in vivo [G(-25)A BP > extended polypyrimidine tract > G(-25)A,U(-27)C BP > wild-type BP]. These results suggest that MuSVts110 RNA splicing is balanced by cis elements similar to those operating in other retroviruses and, in addition, that its splicing thermosensitivity is a response to the presence of multiple suboptimal splicing signals.

Until recently the geographic distribution of infection due to human immunodeficiency virus type 2 (HIV-2) had excluded North America. We report the first two cases of such infection in Canada. Both people came from endemic areas of western Africa and were asymptomatic. The results of a commercial enzyme immunoassay specific for HIV-1 antibody were positive in both cases, but those of the Western blot technique were indeterminate. The Western blot technique specific for HIV-2 antibody and the indirect fluorescent antibody test were used to verify the presence of HIV-2 antibody.

DURING the course of mass breeding of Microbracon brevicornis in the parasite laboratory of the Entomology Division of this Institute for the purpose of exporting them to the United States of America for the control of pink boll worm in the cotton belt of that country, it was necessary to maintain a stock of pupae of the parasite in cold storage at a temperature of 10 ± 3° C. It was observed that the adults emerging from the chilled pupae which had been in cold storage from 10 to 75 days showed dark pigmentation ranging from dark grey to jet black, as against the distinctly brown individuals obtained from unchilled pupae.