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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Ultrafast Inverse Chirality-Induced Spin Selectivity Observed by THz Emission

Chirality-induced spin selectivity (CISS) phenomena arise from an interplay among structural chirality, electron spin orientation, and charge current. Steady-state observations such as magnetoresistance offer little insight into the timescales that govern the spin-charge interconversion and often conflate interfacial and bulk phenomena. By contrast, inverse CISS involves the conversion of spin to a charge current. Using terahertz (THz) emission spectroscopy, we directly measured an ultrafast charge current due to inverse CISS with picosecond time resolution. Polarity and polarization analysis of the THz emission map the induced charge current direction upon spin injection. We found that a charge current is generated along the spin orientation that changes direction with stereochemical configuration. These observations directly demonstrate the inherent coupling between spin and charge currents in chiral systems, offering key insights into their fundamental dynamics.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2005

Local oscillator chain for 1.55 to 1.75 THz with 100-(mu)W peak power

We report on the design and performance of a fix-tuned x2x 3x 3 frequency multiplier chain that covers 1.55-1.75 THz. The chain is nominally pumped with 100 mW at W-band. At 120 K the measured output power is larger than 4 (mu)W across the band with a peak power of 100 (mu) W at 1.665 THz. A similar chain operated at room temperature produced a peak power of 21 (mu)W. These power levels now make it possible to deploy multipixel heterodyne imaging arrays in this frequency range.

frequency multiplier↗
DOE OSTI2025

Directional, joule per steradian THz pulses from multi-joule laser irradiation of wires

We report on THz pulses with energy flux exceeding 2.5 J/sr and high directionality, generated from picosecond, joule laser irradiation of microwires. The impact of wire diameter, length, and laser irradiation orientation is explored with the irradiation of 160 μm diameter, 750 μm, sharpened wires at the dull base found to produce the highest energy and shortest wavelength THz pulses among the targets tested. A traveling wave antenna combined with coherent transition radiation model is developed to explain the emission pattern, pulse energy, and spectrum seen.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1992

New approach to the design of Schottky barrier diodes for THz mixers

Near-ideal GaAs Schottky barrier diodes especially designed for mixing applications in the THz frequency range are presented. A diode fabrication process for submicron diodes with near-ideal electrical and noise characteristics is described. This process is based on the electrolytic pulse etching of GaAs in combination with an in-situ platinum plating for the formation of the Schottky contacts. Schottky barrier diodes with a diameter of 1 micron fabricated by the process have already shown excellent results in a 650 GHz waveguide mixer at room temperature. A conversion loss of 7.5 dB and a mixer noise temperature of less than 2000 K have been obtained at an intermediate frequency of 4 GHz. The optimization of the diode structure and the technology was possible due to the development of a generalized Schottky barrier diode model which is valid also at high current densities. The common diode design and optimization is discussed on the basis of the classical theory. However, the conventional fomulas are valid only in a limited forward bias range corresponding to currents much smaller than the operating currents under submillimeter mixing conditions. The generalized new model takes into account not only the phenomena occurring at the junction such as current dependent recombination and drift/diffusion velocities, but also mobility and electron temperature variations in the undepleted epi-layer. Calculated diode I/V and noise characteristics are in excellent agreement with the measured values. Thus, the model offers the possibility of optimizing the diode structure and predicting the diode performance under mixing conditions at THz frequencies.

Jelenski, A.↗
NASA NTRS1998

Low-Loss NbTiN Films for THz SIS Mixer Tuning Circuits

Recent results at 1 THz using normal-metal tuning circuits have shown that SIS mixers can work well up to twice the gap frequency of the junction material (niobium). However, the performance at 1 THz is limited by the substantial loss in the normal metal films. For better performance superconducting films with a higher gap frequency than niobium and with low RF loss are needed. Niobium nitride has long been considered a good candidate material, but typical NbN films suffer from high RF loss. To circumvent this problem we are currently investigating the RF loss in NbTiN films, a 15 K Tc compound superconductor, by incorporating them into quasi-optical slot antenna SIS devices.

Kooi, J. W.↗
NASA NTRS1998

A 2 THz Heterodyne Array Receiver for SOFIA

We proposed to perform a comprehensive design study of a 16-element heterodyne array receiver for SOFIA. The array was designed to utilize hot-electron bolometers in an efficient, low-cost waveguide mount to achieve low noise performance between approx. 1500 and 2400 GHz. Due to the prevailing physical conditions in the interstellar medium, this frequency range is one of the richest in the FIR portion of the spectrum. An array designed for this wavelength range will make excellent use of the telescope and the available atmospheric transmission, and will provide a new perspective on stellar, chemical, and galaxy evolution in the present as well as past epochs. A few of the most important molecular and atomic species which the instrument will sample are CII, OI, CO, OH, NII, and CH. The system used the most sensitive detectors available in an efficient optical system. The local oscillator was a compact CO2 pumped far-infrared laser currently under development for SOFIA. The backend spectrometer was an array acousto-optic spectrometer (aAOS). The spectrometer utilizes proven hardware and technologies to provide broadband performance (greater than or equal to 1 GHz per AOS channel) and high spectral resolution (1 MHz) with the maximum sensitivity and minimum complexity and cost. The proposed instrument would be the fastest and most sensitive heterodyne receiver ever to operate in the 1.5 - 2.4 THz band. One of the key technologies developed for the proposed instrument is the laser micromachining of waveguide structures. These structures provide both the optical link between the instrument and the telescope (via an array of efficient feedhorns) and the impedance transformation between the detectors and free space. With the assistance of funds provided from this grant, we were able to fabricate and test the world's first laser micromachined feedhorns. Figure 1 is a photograph of the 2 THz double feedhorn structure designed and constructed under the auspices of this grant. The quality of the waveguide structure is far better than that obtainable using any other fabrication technique. Figure 2 is the beam pattern obtained from it. The beam parameters are an excellent match to what is expected from theory. The success of this experiment demonstrates the viability of using laser micromachined components in the development of high performance, large format array receivers. Figure 3 is an illustration of the focal plane array concept we developed lot- SOFIA base upon this work. Un- fortunately, our instrument proposal was not selected as a first generation SOFIA instrument. However, we have continued our development efforts and will propose to build a 2nd generation instrument based on the same design concepts. Our work under NAG 2-1057 was very rewarding and we appreciate the opportunity provided by NASA to pursue it. The research led directly to publishing 2 papers (listed below) and the award of an NSF grant to our group to construct a laser micromachining system on the University of Arizona campus.

Walker, Christopher K.↗
NASA NTRS1997

Low Noise in a Diffusion-Cooled Hot-Electron Mixer at 2.5 THz

The noise performance of a Nb hot-electron bolometer mixer at 2.5 THz has been investigated. The devices are fabricated from a 12-nm-thick Nb film, and have a 0.30 micrometer x 0.15 micrometer in-plane size, thus exploiting diffusion as the electron cooling mechanism. The rf coupling was provided by a twin-slot planar antenna on an elliptical Si lens. The experimentally measured double sideband noise temperature of the receiver was as low as 2750 +/- 250 K with an estimated mixer noise temperature of approximately equal 900 K. The mixer bandwidth derived from both noise bandwidth and IF impedance measurements was approximately equal 1.4 GHz. These results demonstrate the low-noise operation of the diffusion-cooled bolometer mixer above 2 THz.

Karasik, B. S.↗
NASA NTRS2001

Nanoklystron: A Monolithic Tube Approach to THz Power Generation

The authors propose a new approach to THz power generation: the nanoklystron. Utilizing silicon micromachining techniques, the design and fabrication concept of a monolithic THz vacuum-tube reflex-klystron source is described. The nanoklystron employs a separately fabricated cathode structure composed of densely packed carbon nanotube field emitters and an add-in repeller. The nanotube cathode is expected to increase the current density, extend the cathode life and decrease the required oscillation voltage to values below 100 V. The excitation cavity is based on ridged-waveguide and differs from the conventional cylindrical re-entrant structures found in lower frequency klystrons. A quasi-static field analysis of the cavity and output coupling structure show excellent control of the quality factor and desired field distribution. Output power is expected to occur through an iris coupled matched rectangular waveguide and integrated pyramidal feed horn. The entire circuit is designed so as to be formed monolithically from two thermocompression bonded silicon wafers processed using deep reactive ion etching (DRIE) techniques. To expedite prototyping, a 600 GHz mechanically machined structure has been designed and is in fabrication. A complete numeric analysis of the nanoklystron circuit, including the electron beam dynamics has just gotten underway. Separate evaluation of the nanotube cathodes is also ongoing. The authors will describe the progress to date as well as plans for the immediate implementation and testing of nanoklystron prototypes at 640 and 1250 GHz.

Siegel, Peter H.↗
NASA NTRS1997

Monte Carlo Simulation of THz Multipliers

Schottky Barrier diode frequency multipliers are critical components in submillimeter and Thz space based earth observation systems. As the operating frequency of these multipliers has increased, the agreement between design predictions and experimental results has become poorer. The multiplier design is usually based on a nonlinear model using a form of harmonic balance and a model for the Schottky barrier diode. Conventional voltage dependent lumped element models do a poor job of predicting THz frequency performance. This paper will describe a large signal Monte Carlo simulation of Schottky barrier multipliers. The simulation is a time dependent particle field Monte Carlo simulation with ohmic and Schottky barrier boundary conditions included that has been combined with a fixed point solution for the nonlinear circuit interaction. The results in the paper will point out some important time constants in varactor operation and will describe the effects of current saturation and nonlinear resistances on multiplier operation.

East, J.↗
NASA NTRS2006

1.9 THz Quantum-cascade Lasers with One-well Injector

We report terahertz quantum-cascade lasers operating predominantly at 1.90 THz with side modes as low as 1.86 THz (lambda approx. equal to 161 micrometers, planck's constant omega approx. equal to 7.7 meV). This is the longest wavelength to date of any solid-state laser that operates without assistance of a magnetic field. Carriers are injected into the upper radiative state by using a single quantum-well injector, which resulted in a significant reduction of free-carrier losses. The laser operated up to a heat-sink temperature of 110 K in pulsed mode, 95 K in continuous wave (cw) mode, and the threshold current density at 5 K was approx. 140 A per square centimeters.

Kumar, Sushil↗
NASA NTRS2004

THz Hot-Electron Photon Counter

We present a concept for the hot-electron transition-edge sensor capable of counting THz photons. The main need for such a sensor is a spectroscopy on future space telescopes where a background limited NEP approx. 10(exp -20) W/H(exp 1/2) is expected at around 1 THz. Under these conditions, the rate of photon arrival is very low and any currently imaginable detector with sufficient sensitivity will operate in the photon counting mode. The Hot-Electron Photon Counter based on a submicron-size Ti bridge has a very low heat capacity which provides a high enough energy resolution (approx.140 GHz) at 0.3 K. With the sensor time constant of a few microseconds, the dynamic range would be approx. 30 dB. The sensor couples to radiation via a planar antenna and is read by a SQUID amplifier or by a 1-bit RSFQ ADC. A compact array of the antenna-coupled counters can be fabricated on a silicon wafer without membranes.

radiation detectors↗
NASA NTRS2011

A 2.5-2.7 THz Room Temperature Electronic Source

We report on a room temperature 2.5 to 2.7 THz electronic source based on frequency multipliers. The source utilizes a cascade of three frequency multipliers with W-band power amplifiers driving the first stage multiplier. Multiple-chip multipliers are utilized for the two initial stages to improve the power handling capability and a sub-micron anode is utilized for the final stage tripler. Room temperature measurements indicate that the source can put out a peak power of about 14 microwatts with more than 4 microwatts in the 2.5 to 2.7 THz range.

Varactor diodes↗
NASA NTRS2016

THz Solar Observations on Board of a Trans-Antarctic Stratospheric Balloon Flight

A new system of two photometers was built to observe the Sun at 3 and 7 THz from space, named SOLART. It has been flown coupled to U.C. Berkeley GRIPS experiment on a NASA stratospheric balloon flight over Antarctica, 19-30 January 2016. The mission was successfully accomplished. We describe the system performance, solar brightness determination and the first THz impulsive burst detected.

Kaufmann, P.↗
NASA NTRS2013

A 294 GHz 0.47m W Caterpillar amplifier based transmitter in 65 nm CMOS for THz data-links

A fully integrated CMOS THz transmitter for short range data-links is presented which provides 0.47 mW of output power to 294 GHz. The output frequency is derived from a 147 GHz on-chip LO and fully differential caterpillar power amplifier combined with a transformer coupled frequency doubler. The transmitter is integrated with an on-chip dipole antenna for use in THz communication systems and consumes a total of 258 mW.

Chang, Mau-Chung Frank↗
NASA NTRS2018

THz Technology for Space Communications

As space instruments become ubiquitous along with advancing capabilities, one of the central challenge is to provide more efficient communication links, between the control center and the instrument or between a cluster of satellites or instruments. Similarly, high-data rate communications between a mother ship and a lander is highly desirable not only for navigation but for science data as well. THz communications systems present a number of advantages in implementing efficient data-links between various scenarios for space applications. This review article will discuss some of the recent advances in solid-state coherent sources that has now made it possible to design and implement THz communication systems specifically for space applications. An example architecture at 240 GHz has been suggested as it is now possible to achieve >100 mW of output power at 240 GHz. With highly sensitive and linear heterodyne mixers, such a system could potentially provide higher data rate capability than in use today.

Jornet, Josep M.↗
NASA NTRS2018

THz technology for space communications

As space instruments become ubiquitous along with advancing capabilities, one of the central challenge is to provide more efficient communication links, between the control center and the instrument or between a cluster of satellites or instruments. Similarly, high-data rate communications between a mother ship and a lander is highly desirable not only for navigation but for science data as well. THz communications systems present a number of advantages in implementing efficient data-links between various scenarios for space applications. This review article will discuss some of the recent advances in solid-state coherent sources that has now made it possible to design and implement THz communication systems specifically for space applications. An example architecture at 240 GHz has been suggested as it is now possible to achieve >100 mW of output power at 240 GHz. With highly sensitive and linear heterodyne mixers, such a system could potentially provide higher data rate capability than in use today.

Jornet, Josep M.↗