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LeDuc, Henry G.

Publications and source records attributed to LeDuc, Henry G..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Development of the Nano-HEB Array for Low-Background Far-IR Applications

We present an overview of the recent progress made in the development of a far-IR array of ultrasensitive hot-electronnanobolometers (nano-HEB) made from thin titanium (Ti) films. We studied electrical noise, signal and noisebandwidth, single-photon detection, optical noise equivalent power (NEP), and a microwave SQUID (MSQUID) basedfrequency domain multiplexing (FDM) scheme. The obtained results demonstrate the very low electrical NEP down to1.5x10-(sup 2)? W/Hz(sup 1)/(sup 2) at 50 mK determined by the dominating phonon noise. The NEP increases with temperature as ~ T(sup 3)reaching ~ 10-(sup 1)? W/Hz(sup 1)/(sup 2) at the device critical temperature TC = 330-360 mK. Optical NEP = 8.6x10-(sup 1)? W/Hz(sup 1)/(sup 2) at 357mK and 1.4x10-(sup 1)? W/Hz(sup 1)/(sup 2) at 100 mK respectively, agree with thermal and electrical data. The optical couplingefficiency provided by a planar antenna was greater than 50%. Single 8-?m photons have been detected for the first timeusing a nano-HEB operating at 50-200 mK thus demonstrating a potential of these detectors for future photon-countingapplications in mid-IR and far-IR. In order to accommodate the relatively high detector speed (~ ?s at 300 mK, ~ 100 ?sat 100 mK), an MSQUID based FDM multiplexed readout with GHz carrier frequencies has been built. Both the readoutnoise ~ 2 pA/Hz(sup 1)/(sup 2) and the bandwidth > 150 kHz are suitable for nano-HEB detectors.

single-photon↗
NASA NTRS2009

Multiplexing of Hot-Electron Nanobolometers Using Microwave SQUIDs

We have obtained the first data on the multiplexed operation of titanium hot-electron bolometers (HEB). Because of their low thermal conductance and small electron heat capacity nanobolometers are particularly interesting as sensors for far-infrared spectroscopy and mid- and near-IR calorimetry. However, the short time constant of these devices (approximately microseconds at 300-400 mK) makes time domain or audio-frequency domain multiplexing impractical. The Microwave SQUID (MSQUID) approach pursued in this work uses dc SQUIDs coupled to X-band microresonators which are, in turn, coupled to a transmission line. We used a 4-element array of Ti HEBs operated at 415 mK in a He3 dewar with an optical fiber access. The microwave signal exhibited 10-MHz wide resonances at individual MSQUD frequencies between 9 GHz and 10 GHz. The resonance depth is modulated by the current through the bolometer via a change of the SQUID flux state. The transmitted signal was amplified by a cryogenic amplifier and downconverted to baseband using an IQ mixer. A 1-dB per ??/2 responsivity was sufficient for keeping the system noise at the level of ~ 2 pA/Hz1/2. This is more than an order of magnitude smaller than phonon noise in the HEB. The devices were able to detect single near- IR photons (1550 nm) with a time constant of 3.5 ?s. Follow-on work will scale the array to larger size and will address the microwave frequency signal generation and processing using a digital transceiver.

microwave readout↗
NASA NTRS2006

Distributed Antenna-Coupled Transition Edge Sensors

We describe progress toward realizing a new architecture for focal plane arrays for the Submillimeter and Far- Infrared (FIR) bands. This architecture is based on a detector design utilizing distributed hot{electron transition edge sensors (TES) coupled to slot antenna elements. Arrays utilizing this type of detector can be considerably easier to manufacture than membrane-isolated TES arrays, because the need for micro-machining is eliminated. We present background and rationale for this new array architecture and details of a new antenna design for an imaging polarimeter, which yields greater bandwidth than past designs. In addition, we describe a cryogenic facility for testing these arrays.

bolometer↗
NASA NTRS2004

A Wide-Bandwidth, Low-Noise SIS Receiver Design for Millimeter and Submillimeter Wavelengths

In principle, millimeter and submillimeter heterodyne receivers using state-of-the-art SIS detectors are capable of extremely large instantaneous bandwidths with noise temperatures within a few Kelvin of the quantum limit. We are applying modem design tools, such as 3D electromagnetic simulators and Caltech's SuperMix SIS analysis package, to develop a new generation of waveguide SIS mixers with very broad RF and IF bandwidths. Our initial design consists of a double-sideband mixer targeted for the 180- 300 GHz band that uses a single SIS junction excited by a full bandwidth, fixed-tuned waveguide probe on a silicon substrate. The IF output band, limited by the MMIC low-noise IF preamplifier, is 6-18 GHz, providing an instantaneous RF bandwidth of 24 GHz (double-sideband). The SIS mixer conversion loss is predicted to be no more than 1-2 dB (single-sideband) with mixer noise temperatures across the band within 10 Kelvin of the quantum limit. The single-sideband receiver noise temperature goal is 70 Kelvin. The wide instantaneous bandwidth and low noise will result in an instrument capable of a variety of important astrophysical observations beyond the capabilities of current instruments. Lab testing of the receiver will begin in the summer of 2002, and a demonstration on the CSO should occur in the spring of 2003.

Sumner, Matthew↗
NASA NTRS2003

A Broadband Superconducting Detector Suitable for Use in Large Arrays

Cryogenic detectors are extremely sensitive and have a wide variety of applications (particularly in astronomy), but are difficult to integrate into large arrays like a modern CCD (charge-coupled device) camera. As current detectors of the cosmic microwave background (CMB) already have sensitivities comparable to the noise arising from the random arrival of CMB photons, the further gains in sensitivity needed to probe the very early Universe will have to arise from large arrays. A similar situation is encountered at other wavelengths. Single-pixel X-ray detectors now have a resolving power of (Delta)E < 5 eV for single 6-keV photons, and future X-ray astronomy missions anticipate the need for 1,000-pixel arrays. Here we report the demonstration of a superconducting detector that is easily fabricated and can readily be incorporated into such an array. Its sensitivity is already within an order of magnitude of that needed for CMB observations, and its energy resolution is similarly close to the targets required for future X-ray astronomy missions.

Day, Peter K.↗
NASA NTRS2000

Very High Current Density Nb/AlN/Nb Tunnel Junctions for Low-Noise Submillimeter Mixers

We have fabricated and tested submillimeter-wave superconductor-insulator-superconductor (SIS) mixers using very high current density Nb/AlN/Nb tunnel junctions (J(sub c) approximately equal 30 kA/sq cm) . The junctions have low resistance-area products (R(sub N)A approximately 5.6 Omega.sq micron), good subgap to normal resistance ratios R(sub sg)/R(sub N) approximately equal 10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that omega.R(sub N)C = 1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlO(x)/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected receiver noise temperature of T(sub RX) = 110 K (DSB) at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing RF loss in the tuning circuits.

Kawamura, Jonathan↗
NASA NTRS2000

A Dual Polarized Quasi-Optical SIS Mixer at 550-GHz

We describe the design, fabrication, and the performance of a low-noise dual-polarized quasi-optical superconductor insulator superconductor (SIS) mixer at 550 GHz. The mixer utilizes a novel cross-slot antenna on a hyperhemispherical substrate lens, two junction tuning circuits, niobium trilayer junctions, and an IF circuit containing a lumped element 180 deg hybrid. The antenna consists of an orthogonal pair of twin-slot antennas, and has four feed points, two for each polarization. Each feed point is coupled to a two-junction SIS mixer. The 180 deg IF hybrid is implemented using a lumped element/microstrip circuit located inside the mixer block. Fourier transform spectrometer (FTS) measurements of the mixer frequency response show good agreement with computer simulations. The measured co-polarized and cross-polarized patterns for both polarizations also agree with the theoretical predictions. The noise performance of the dual-polarized mixer is excellent, giving uncorrected receiver noise temperature of better than 115 K (DSB) at 528 GHz for both the polarizations.

Chattopadhyay, Goutam↗
NASA NTRS1999

A Hot-electron Direct Detector for Radioastronomy

A hot-electron transition-edge superconducting bolometer with adjustable thermal relaxation speed is proposed. The bolometer contacts are made from a superconductor with high critical temperature which blocks the thermal diffusion of hot carriers into the contacts. Thus electron-phonon interaction is the only mechanism for heat removal. The speed of thermal relaxation for hot electrons in a nanometer-size superconducting bolometer with T(sub c) = 100-300 mK is controlled by the elastic electron mean free path l. The relaxation rate behaves as T(sup 4)l at subkelvin temperatures and can be reduced by a factor of 10-100 by decreasing 1. Then an antenna- or wave guide-coupled bolometer with a time constant approx. = 10(exp -3) to 10(exp -4) s will exhibit photon-noise limited performance at millimeter and submillimeter wavelengths. The bolometer will have a figure-of-merit NEPtau = 10(exp -22) - 10(exp -21) W/Hz at 100 mK which is 10(exp 3) to 10(exp 4) times better (ie: smaller) than that of a state-of-the-art bolometer. A tremendous increase in speed and sensitivity will have a significant impact for observational mapping applications.

Karasik, Boris S.↗
NASA NTRS1994

An SIS Waveguide heterodyne Reciever for 600 GHz - 635 GHz

A waveguide SIS heterodyne receiver using a Nb/A10xNb junction has been built for astronomical observations of molecular tranitions in the frequency range 600GHz - 635GHZ, and has been successfully used at the Caltech Submillimeter Observatory (CSO).

SIS heterodyne receiver molecular transitions↗
NASA NTRS1993

A Prototype Quasi-Optical SIS Array Receiver

We report measurements on a prototype SIS array receiver consisting of a ten-element dipole antenna array with half square micron niobium SIS junctions.

SIS array antenna array mixer array SIS receiver w↗