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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
NASA NTRS2011

Cycle Time Reduction in Trapped Mercury Ion Atomic Frequency Standards

The use of the mercury ion isotope (201)Hg(+) was examined for an atomic clock. Taking advantage of the faster optical pumping time in (201)Hg(+) reduces both the state preparation and the state readout times, thereby decreasing the overall cycle time of the clock and reducing the impact of medium-term LO noise on the performance of the frequency standard. The spectral overlap between the plasma discharge lamp used for (201)Hg(+) state preparation and readout is much larger than that of the lamp used for the more conventional (199)Hg(+). There has been little study of (201)Hg(+) for clock applications (in fact, all trapped ion clock work in mercury has been with (199)Hg(+); however, recently the optical pumping time in (201)Hg(+) has been measured and found to be 0.45 second, or about three times faster than in (199)Hg(+) due largely to the better spectral overlap. This can be used to reduce the overall clock cycle time by over 2 seconds, or up to a factor of 2 improvement. The use of the (201)Hg(+) for an atomic clock is totally new. Most attempts to reduce the impact of LO noise have focused on reducing the interrogation time. In the trapped ion frequency standards built so far at JPL, the optical pumping time is already at its minimum so that no enhancement can be had by shortening it. However, by using (201)Hg(+), this is no longer the case. Furthermore, integrity monitoring, the mechanism that determines whether the clock is functioning normally, cannot happen faster than the clock cycle time. Therefore, a shorter cycle time will enable quicker detection of failure modes and recovery from them.

Burt, Eric A.↗
NASA NTRS1983

Laser induced asymmetry and inhomogeneous broadening of the microwave lineshape of a gas cell atomic frequency standard

The possibility of replacing the RF discharge lamp in a rubidium gas cell clock with a single mode laser diode is addressed. Since the short term stability of the rubidium frequency standard is limited by the shot noise of the photodetector, an increased signal-to-noise ratio due to more efficient laser diode optical pumping might improve the short term performance. Because the emission wavelength of the laser diode can be tuned, improved long term performance could be gained through the control of the light shift effect. However, due to the nature of the gas cell frequency standard, various physical phenomena are strongly coupled in their effect on the frequency output, and thus careful consideration must be given to any change in one parameter because of its interrelation with other parameters. Some investigations concerning the coupled effect of the optical and microwave fields in the rubidium atomic clock are reported. It is shown that this type of coupling is an important consideration for any attempt to incorporate a laser diode into a gas cell clock.

Camparo, J. C.↗
DOE OSTI2025

Spin Squeezing with Itinerant Magnetic Dipoles

Entanglement can improve the measurement precision of quantum sensors beyond the shot noise limit. Neutral atoms, the basis of some of the most precise and accurate optical clocks and interferometers, do not naturally exhibit the all-to-all interactions traditionally used to generate such entangled states. On the other hand, these systems exhibit exceedingly high degrees of experimental control over parameters such as temperature, spatial entropy, and itinerancy. In this work, we investigate spin squeezing in a highly coherent itinerant system of neutral atoms with magnetic dipole-dipole interactions. We achieve 7.1 dB of metrologically useful squeezing using finite-range spin-exchange interactions in an erbium quantum gas microscope, and we demonstrate that introducing atomic motion, realizing a dipolar 𝑡−𝐽 model, protects the spin sector coherence at low fillings, significantly improving the achievable spin squeezing in a 2D dipolar system. This work’s protocol can be implemented with most neutral atoms, opening the door to quantum-enhanced metrology in other itinerant dipolar systems, such as molecules or optical lattice clocks, and serves as a novel method for studying itinerant quantum magnetism with long-range interactions.

Atomic, optical & lattice clocks↗
NASA NTRS2009

Optical Injection Locking of a VCSEL in an OEO

Optical injection locking has been demonstrated to be effective as a means of stabilizing the wavelength of light emitted by a vertical-cavity surface- emitting laser (VCSEL) that is an active element in the frequency-control loop of an opto-electronic oscillator (OEO) designed to implement an atomic clock based on an electromagnetically- induced-transparency resonance. This particular optical-injection- locking scheme is expected to enable the development of small, low-power, high-stability atomic clocks that would be suitable for use in applications involving precise navigation and/or communication. In one essential aspect of operation of an OEO of the type described above, a microwave modulation signal is coupled into the VCSEL. Heretofore, it has been well known that the wavelength of light emitted by a VCSEL depends on its temperature and drive current, necessitating thorough stabilization of these operational parameters. Recently, it was discovered that the wavelength also depends on the microwave power coupled into the VCSEL. Inasmuch as the microwave power circulating in the frequency-control loop is a dynamic frequency-control variable (and, hence, cannot be stabilized), there arises a need for another means of stabilizing the wavelength. The present optical-injection-locking scheme satisfies the need for a means to stabilize the wavelength against microwave- power fluctuations. It is also expected to afford stabilization against temperature and current fluctuations. In an experiment performed to demonstrate this scheme, wavelength locking was observed when about 200 W of the output power of a commercial tunable diode laser was injected into a commercial VCSEL, designed to operate in the wavelength range of 795+/-3 nm, that was generating about 200 microW of optical power. (The use of relatively high injection power levels is a usual practice in injection locking of VCSELs.)

Strekalov, Dmitry↗
DOE OSTI2022

Ultra-low loss visible light waveguides for integrated atomic, molecular, and quantum photonics

Atomic, molecular and optical (AMO) visible light systems are the heart of precision applications including quantum, atomic clocks and precision metrology. As these systems scale in terms of number of lasers, wavelengths, and optical components, their reliability, space occupied, and power consumption will push the limits of using traditional laboratory-scale lasers and optics. Visible light photonic integration is critical to advancing AMO based sciences and applications, yet key performance aspects remain to be addressed, most notably waveguide losses and laser phase noise and stability. Additionally, a visible light integrated solution needs to be wafer-scale CMOS compatible and capable of supporting a wide array of photonic components. While the regime of ultra-low loss has been achieved at telecommunication wavelengths, progress at visible wavelengths has been limited. Here, we report the lowest waveguide losses and highest resonator Qs to date in the visible range, to the best of our knowledge. We report waveguide losses at wavelengths associated with strontium transitions in the 461 nm to 802 nm wavelength range, of 0.01 dB/cm to 0.09 dB/cm and associated intrinsic resonator Q of 60 Million to 9.5 Million, a decrease in loss by factors of 6x to 2x and increase in Q by factors of 10x to 1.5x over this visible wavelength range. Additionally, we measure an absorption limited loss and Q of 0.17 dB/m and 340 million at 674 nm. This level of performance is achieved in a wafer-scale foundry compatible Si 3 N 4 platform with a 20 nm thick core and TEOS-PECVD deposited upper cladding oxide, and enables waveguides for different wavelengths to be fabricated on the same wafer with mask-only changes per wavelength. These results represent a significant step forward in waveguide platforms that operate in the visible, opening up a wide range of integrated applications that utilize atoms, ions and molecules including sensing, navigation, metrology and clocks.

Chauhan, Nitesh↗
DOE OSTI2025

Low SWaP Trapped Ion Atomic Clock

For this project we attempted to show signature traits of excellent optical clock performance in a trapped ion system which had an integrated photonic delivery system for all clock algorithm beams. These traits were 1) Contrast for the clock transition, 2) Coherence of the clock transition, and 3) ion lifetime. We were partially successful and were able to demonstrate the clock laser portion of an optical clock with $\sim 4.4 \text{x} 10^{-14}/\sqrt{\tau}$ fractional frequency instability. Additionally, we made progress towards a background-free detection method.

42 ENGINEERING↗
DOE OSTI2020

Detection of the clock transition in thulium atoms by using repump laser radiation

A population transfer from the upper level of the clock transition in thulium atoms to the ground level is demonstrated by using radiation with a wavelength of 402 nm. The method for detecting the clock transition excitation that is not affected by technical fluctuations of the number of atoms in an optical lattice is investigated. The hyperfine splitting of the |4f{sup 12}({sup 3}F{sub 2})5d{sub 5/2} 6s{sup 2}; J = 7/2〉 level in the thulium atom is measured to be 1480(9) MHz. The suggested method for population transfer can be applied to both the hyperfine components of the clock transition intended for compensating Zeeman effect in a thulium optical clock. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1991

Development of an optically-pumped cesium standard at the Aerospace Corporation

We have initiated a research program to study the performance of compact optically-pumped cesium (Cs) frequency standards, which have potential for future timekeeping applications in space. A Cs beam clock apparatus has been assembled. Basic functions of the frequency standard have been demonstrated. Clock signals are observed with optical pumping schemes using one or two lasers. With two laser pumping, we are able to selectively place up to 80 percent of the atomic population into one of the clock transition states. The observed pattern of clock signal indicates that the velocity distribution of the Cs atoms contributing to the microwave signal is beam-Maxwellian. Thus, in the optically-pumped Cs frequency standards, the entire Cs population in the atomic beam could be utilized to generate the clock signals. This is in contrast to the conventional Cs beam standards where only approx. 1 percent of the atoms in the beam are used. More efficient Cs consumption can lead to improved reliability and increased useful lifetime of the clock. Our preliminary results are summarized in this paper

Yat C. Chan↗
NASA NTRS2005

NASA Tech Briefs, April 2005

Gas-Tolerant Device Senses Electrical Conductivity of Liquid Nanoactuators Based on Electrostatic Forces on Dielectrics Replaceable Microfluidic Cartridges for a PCR Biosensor CdZnTe Image Detectors for Hard-X-Ray Telescopes High-Aperture-Efficiency Horn Antenna Full-Circle Resolver-to-Linear-Analog Converter Continuous, Full-Circle Arctangent Circuit Advanced Three-Dimensional Display System Automatic Focus Adjustment of a Microscope Topics covered include: FastScript3D - A Companion to Java 3D; Generating Mosaics of Astronomical Images; Simulating Descent and Landing of a Spacecraft; Simulating Vibrations in a Complex Loaded Structure; Rover Sequencing and Visualization Program; Software Template for Instruction in Mathematics; Support for User Interfaces for Distributed Systems; Nanostructured MnO2-Based Cathodes for Li-Ion/Polymer Cells; Multi-Layer Laminated Thin Films for Inflatable Structures; Two-Step Laser Ranging for Precise Tracking of a Spacecraft; Growing Aligned Carbon Nanotubes for Interconnections in ICs; Multilayer Composite Pressure Vessels; Texturing Blood-Glucose-Monitoring Optics Using Oxygen Beams; Fault-Tolerant Heat Exchanger; Atomic Clock Based on Opto-Electronic Oscillator; Microfocus/Polycapillary-Optic Crystallographic X-Ray Sys; Depth-Penetrating Luminescence Thermography of Thermal- Barrier Coatings; One-Dimensional Photonic Crystal Superprisms; Measuring Low-Order Aberrations in a Segmented Telescope; Mapping From an Instrumented Glove to a Robot Hand; Application of the Hilbert-Huang Transform to Financial Data; Optimizing Parameters for Deep-Space Optical Communication; and Low-Shear Microencapsulation and Electrostatic Coating.

Source record↗
NASA NTRS2011

Whispering Gallery Mode Resonators as Optical Reference Cavities

Highly stabilized lasers are an increasingly valuable tool for metrology. For many applications, however, existing Fabry Perot systems are too bulky and cumbersome. We are investigating the use of miniature monolithic whispering gallery mode resonators as reference cavities for laser stabilization. We seek to exploit the benefit of small size and vibration resistance by suppressing thermally induced frequency fluctuations. We have theoretically investigated the viability of using a thin-film coating to achieve temperature compensation. We have experimentally investigated an active temperature stabilization scheme based on birefringence in a crystalline resonator. We also report progress of laser locking to the resonators.

optical frequency↗
NASA NTRS1966

Radio standards and measurements

Radio standards and frequency measurements - radio waves, atomic time standards, international time unit, and optical radio frequency measurement techniques

ATOMIC CLOCK↗
NASA NTRS2009

Dynamic Self-Locking of an OEO Containing a VCSEL

A method of dynamic self-locking has been demonstrated to be effective as a means of stabilizing the wavelength of light emitted by a vertical-cavity surface-emitting laser (VCSEL) that is an active element in the frequency-control loop of an optoelectronic oscillator (OEO) designed to implement an atomic clock based on an electromagnetically- induced-transparency (EIT) resonance. This scheme can be considered an alternative to the one described in Optical Injection Locking of a VCSEL in an OEO (NPO-43454), NASA Tech Briefs, Vol. 33, No. 7 (July 2009), page 33. Both schemes are expected to enable the development of small, low-power, high-stability atomic clocks that would be suitable for use in applications involving precise navigation and/or communication. To recapitulate from the cited prior article: In one essential aspect of operation of an OEO of the type described above, a microwave modulation signal is coupled into the VCSEL. Heretofore, it has been well known that the wavelength of light emitted by a VCSEL depends on its temperature and drive current, necessitating thorough stabilization of these operational parameters. Recently, it was discovered that the wavelength also depends on the microwave power coupled into the VCSEL. This concludes the background information. From the perspective that led to the conception of the optical injection-locking scheme described in the cited prior article, the variation of the VCSEL wavelength with the microwave power circulating in the frequency-control loop is regarded as a disadvantage and optical injection locking is a solution of the problem of stabilizing the wavelength in the presence of uncontrolled fluctuations in the microwave power. The present scheme for dynamic self-locking emerges from a different perspective, in which the dependence of VCSEL wavelength on microwave power is regarded as an advantageous phenomenon that can be exploited as a means of controlling the wavelength. The figure schematically depicts an atomic-clock OEO of the type in question, wherein (1) the light from the VCSEL is used to excite an EIT resonance in selected atoms in a gas cell (e.g., 87Rb atoms in a low-pressure mixture of Ar and Ne) and (2) the power supplied to the VCSEL is modulated by a microwave signal that includes components at beat frequencies among the VCSEL wavelength and modulation sidebands. As the VCSEL wavelength changes, it moves closer to or farther from a nearby absorption spectral line, and the optical power transmitted through the cell (and thus the loop gain) changes accordingly. A change in the loop gain causes a change in the microwave power and, thus, in the VCSEL wavelength. It is possible to choose a set of design and operational parameters (most importantly, the electronic part of the loop gain) such that the OEO stabilizes itself in the sense that an increase in circulating microwave power causes the VCSEL wavelength to change in a direction that results in an increase in optical absorption and thus a decrease in circulating microwave power. Typically, such an appropriate choice of operational parameters involves setting the nominal VCSEL wavelength to a point on the shorter-wavelength wing of an absorption spectral line.

Strekalov, Dmitry↗
NASA NTRS2007

Cold Atom Source Containing Multiple Magneto-Optical Traps

An apparatus that serves as a source of a cold beam of atoms contains multiple two-dimensional (2D) magneto-optical traps (MOTs). (Cold beams of atoms are used in atomic clocks and in diverse scientific experiments and applications.) The multiple-2D-MOT design of this cold atom source stands in contrast to single-2D-MOT designs of prior cold atom sources of the same type. The advantages afforded by the present design are that this apparatus is smaller than prior designs.

Ramirez-Serrano, Jaime↗
NASA NTRS1973

Optical and infrared masers

Ongoing research progress in the following areas is described: (1) tunable infrared light sources and applications; (2) precision frequency and wavelength measurements in the infrared with applications to atomic clocks; (3) zero-degree pulse propagation in resonant medium; (4) observation of Dicke superradiance in optically pumped HF gas; (5) unidirectional laser amplifier with built-in isolator; and (6) progress in infrared metal-to-metal point contact tunneling diodes.

Source record↗
NASA NTRS2024

Autonomous Navigation of a Lunar Relay Using GNSS and Other Measurements

NASA’s Lunar Communications Relay and Navigation Services (LCRNS) project will establish a relay constellation at the Moon to provide the south pole region with communications and position, navigation, and time (PNT) services. These services will require highly accurate knowledge of position, velocity, and time (PVT) for each relay. This paper explores one approach for performing onboard PVT estimation, the LCRNS PNT Instrument (LPI). This paper considers different configurations of the instrument, specifically different measurement types and clocks, and the resulting navigation performance. Simulation results are first shown for an instrument configuration that uses GPS pseudorange and Doppler measurements with a highly sensitive GPS receiver (i.e., an acquisition and tracking threshold of 23 dB-Hz) and a chip-scale atomic clock (CSAC). The importance of Doppler, clock quality, receiver sensitivity, and optical navigation is examined through comparison of these results to other instrument configurations. Clock quality (i.e., stability) is the strongest determinant of achievable performance, and the inclusion of GPS Doppleralso has a significant effect. Finally, simulation results are compared to two laboratory tests: first a case that includes GPS receiver hardware in the loop, then a case that includes optical navigation and filter flight software in the loop. These agreeclosely with the simulation results and provide evidence the simulation is accurately modeling the instrument under development.

Benjamin W Ashman↗
DOE OSTI2020

Free Space Ramsey Spectroscopy in Rubidium with Noise below the Quantum Projection Limit

In this work, we demonstrate the utility of optical cavity generated spin-squeezed states in free space atomic fountain clocks in ensembles of 390 000 87 Rb atoms. Fluorescence imaging, correlated to an initial quantum nondemolition measurement, is used for population spectroscopy after the atoms are released from a confining lattice. For a free fall time of 4 milliseconds, we resolve a single-shot phase sensitivity of 814(61) microradians, which is 5.8(0.6) decibels (dB) below the quantum projection limit. We observe that this squeezing is preserved as the cloud expands to a roughly 200 μ m radius and falls roughly 300 μm in free space. Ramsey spectroscopy with 240 000 atoms at a 3.6 ms Ramsey time results in a single-shot fractional frequency stability of 8.4(0.2) × 10 –12 , 3.8(0.2) dB below the quantum projection limit. The sensitivity and stability are limited by the technical noise in the fluorescence detection protocol and the microwave system, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2004

Small Mercury Ion Clock for On-board Spacecraft Navigation

I.Small Ion Clock Approach and Heritage: a) No lasers, uwave cavities, cryogenics, atomic beams, etc. b) Ions are electrically shuttled between separate optical and microwave traps. II. Each trap is optimized for its task: quadrupole for optical state selection; multi-pole for microwave clock. a) Very good stability shown in USNO. Timescale running "open loop." III. "Open loop" operation means no self-measurements of frequency offsets: (Zeeman, ion temperature,... etc.) a) Fewer parts and procedures, produces stable output continuously. IV. Ion clock is not so sensitive to temperature fluctuations a) Measured u:nshielded temperature coefficient of few 10(exp -15) per C. b) No bulky temperature isolation needed.

Prestage, John D.↗
DOE OSTI2020

Generalised hyper-Ramsey spectroscopy of two-level atoms in an optically dense medium

The peculiarities of Ramsey resonance and its sensitivity to the light shift from an optically dense medium of cold atoms are investigated. Different composite pulse protocols for clock spectroscopy, including hyper-Ramsey, modified and generalised hyper-Ramsey schemes, are compared. Error signals change significantly due to the processes of absorption and dispersion in the atomic medium. The dependence of the position of the central fringe resonance with a residual uncompensated light shift of the atomic transition is studied with the attenuation of the radiation intensity in the medium taken into account. It is shown that using a combination of generalised hyper-Ramsey error signals allows one to suppress the sensitivity to the light shift for any length of the medium. (laser cooling of atoms)

74 ATOMIC AND MOLECULAR PHYSICS↗