https://link.springer.com/content/pdf/10.1016%2FS1044-0305%2802%2900384-7.pdf

A two-dimensional quadrupole ion trap mass spectrometer.

Atomic clocks have been instrumental in science and technology, leading to innovations such as global positioning, advanced communications, and tests of fundamental constant variation. Timekeeping precision at 1 part in 10 18 enables new timing applications in relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests of physics beyond the standard model. Here, we describe the development and operation of two optical lattice clocks, both using spin-polarized, ultracold atomic ytterbium. A measurement comparing these systems demonstrates an unprecedented atomic clock instability of 1.6 × 10 –18 after only 7 hours of averaging.

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An atomic clock with $10^{-18}$ instability

Micromotion of ions in Paul traps has several adverse effects, including alterations of atomic transition line shapes, significant second-order Doppler shifts in high-accuracy studies, and limited confinement time in the absence of cooling. The ac electric field that causes the micromotion may also induce significant Stark shifts in atomic transitions. We describe three methods of detecting micromotion. The first relies on the change of the average ion position as the trap potentials are changed. The second monitors the amplitude of the sidebands of a narrow atomic transition, caused by the first-order Doppler shift due to the micromotion. The last technique detects the Doppler shift induced modulation of the fluorescence rate of a broad atomic transition. We discuss the detection sensitivity of each method to Doppler and Stark shifts, and show experimental results using the last technique.

Minimization of ion micromotion in a Paul trap

▪ Abstract Laser ablation of in situ metals has recently made it possible to immerse a large number of different metal atoms and ions and small clusters of metal atoms in liquid helium (He) and thus study their absorption and emission spectra in the visible region. Atoms and molecules are readily picked up by large ( ≥ 103 atoms) He droplets, and their spectra are sensitively detected through the use of either beam depletion following absorption or laser-induced fluorescence. Within the past three years, a wide variety of molecules, ranging from OCS to large organic molecules such as amino acids and a number of van der Waals complexes and even large metal clusters, have been embedded in He droplets and studied either in infrared or in the visible region. These results are discussed here in detail, and the evidence for the effect of superfluidity on the spectral features is reviewed.

Spectroscopy of atoms and molecules in liquid helium

Characteristics of mass selective axial ion ejection from a linear quadrupole ion trap in the presence of an auxiliary quadrupole field are described. Ion ejection is shown to occur through coupling of radial and axial motion in the exit fringing fields of the linear ion trap. The coupling is efficient and can result in extraction of as much as 20% of the trapped ions. This, together with the very high trapping efficiencies, can yield high sensitivity mass spectral responses. The experimental apparatus is based on the ion path of a triple quadrupole mass spectrometer allowing either the q2 collision cell or the final mass analysis quadrupole to be used as the linear trap. Space charge induced distortions of the mass resolved features while using the pressurized q2 linear ion trap occur at approximately the same ion density as reported for conventional three-dimensional ion traps. These distortions are, however, much reduced for the lower pressure linear trap possibly owing to the proposed axial ejection mechanism that leads to ion ejection only for ions of considerable radial amplitude. RF heating due to the high ejection q-value and the low collision frequency may also contribute. Two hybrid RF/DC quadrupole-linear ion trap instruments are described that provide high sensitivity product ion scanning while operated in the linear ion trap mode while also retaining all conventional triple quadrupole scan modes such as precursor ion and neutral loss scan modes. Copyright © 2002 John Wiley & Sons, Ltd.

A new linear ion trap mass spectrometer

We present test results for a short-term frequency standard, 40 K Compensated Sapphire Oscillator (CSO). Included are measured resonator Q values, cryocooler vibration data, silver spacer construction process, and copper wall sensitivity. The 40 K CSO design goals are a frequency stability of 1/spl times/10/sup -14/ ( 1 second /spl les/ /spl tau/ /spl les/ 100 seconds), a year or more continuous operation, and a compact rack-mount configuration. The 40 K CSO bridges the gap of two previous technologies: 10 K CSO and 77 K CSO. In particular, the 10 K CSO incorporated a Gifford-McMahon type of cryocooler with no cryogens, while the 77 K CSO developed thermo-mechanical compensation operating at 80 K. The 40 K CSO can serve as an independent oscillator or as a "slaved" local oscillator controlled by atomic standards like the Hg ion trap, enabling their inherent performance.

Cryo-cooled sapphire oscillator with mechanical compensation

Adiabatic frequency modulation of a superconducting resonator has been achieved by pulsed microwave interference. The technique has been shown to produce phase‐coherent variable‐frequency pulse‐power gain.

Pulsed frequency modulation of superconducting resonators

We describe the present status of the State University of New York at Stony Brook Superconducting Heavy-Ion LINAC (SUNYLAC). The LINAC will extend at very modest cost the capabilities of the existing FN tandem Van de Graaff into the energy range 5-10 MeV/A for light heavy-ions from oxygen to bromine. The active elements are 43 lead-plated copper superconducting resonators of the split-loop type optimized for either velocity s=v/c=0.055 or s=0.10. Phase and amplitude of each resonator is independently set through RF-feedback controllers interfaced to an overall computer control system. Full scale construction work began in July, 1979 following the in-beam demonstration of a prototype LINAC module containing 4 low-s resonators, and the majority of the installation work on the beam transport and refrigeration systems was completed in the summer of 1980. The project is now well into its final assembly and testing phase, with the completion of assembly scheduled in early 1982. We describe details of the design of key elements of the LINAC and the initial operating experience with the injection beam path, helium refrigerator and first production accelerator module. The progress of a continuing program aimed at optimizing crucial aspects of the LINAC is also reviewed.

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Status of the Stony Brook Superconducting Heavy-Ion Linac

The preliminary design details for two sapphire whispering gallery mode phase stabilizers are presented. The sapphire resonators are cooled in individual liquid nitrogen dewars to an operating temperature of approximately 80 K. Each operates to stabilize the phase of an 8.1 GHz signal derived from a quartz crystal oscillator operating at 100 MHz. Ultra-low phase noise (-80 dB/Hz at 1 Hz offset) is projected due to the high resonator Q (3*10/sup 7/ at 80 K). The temperature of the thermally uncompensated sapphire resonators is stabilized by RF heating to a value approximately 3 degrees above that of a liquid nitrogen bath. Oscillator configurations which can further reduce oscillator phase noise are discussed and analyzed. These circuit improvements should provide crystal-oscillator type performance in a room-temperature 10 GHz (X-band) oscillator using a whispering gallery mode sapphire resonator with an intrinsic Q of 2*10/sup 5/. A general description of the oscillator systems and the thermal design considerations together with design details and analysis for the microwave aspects is presented. >

http://ieeexplore.ieee.org/iel2/117/4483/00177547.pdf

Ultra-low noise microwave phase stabilizer using sapphire ring resonator

In order to provide frequency standards for the Deep Space Network (DSN) which are more stable than present-day hydrogen masers, a research task was established under the Advanced Systems Program of the TDA to develop a Hg-199(+) trapped ion frequency standard. The first closed-loop operation of this kind is described. Mercury-199 ions are confined in an RF trap and are state-selected through the use of optical pumping with 194 nm UV light from a Hg-202 discharge lamp. Absorption of microwave radiation at the hyperfine frequency (40.5 GHz) is signaled by atomic fluorescence of the UV light. The frequency of a 40.5 GHz oscillator is locked to a 1.6 Hz wide atomic absorption line of the trapped ions. The measured Allan variance of this locked oscillator is currently gamma sub y (pi) = 4.4 x 10 to the minus 12th/square root of pi for 20 is less than pi is less than 320 seconds, which is better stability than the best commercial cesium standards by almost a factor of 2. This initial result was achieved without magnetic shielding and without regulation of ion number.

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G.J. Dick

Papers

Cryo-cooled sapphire oscillator with mechanical compensation

Pulsed frequency modulation of superconducting resonators

Status of the Stony Brook Superconducting Heavy-Ion Linac

Ultra-low noise microwave phase stabilizer using sapphire ring resonator

The JPL trapped mercury ion frequency standard