Bernardo Jaduszliwer

Alkali reactions with wall coating materials used in atomic resonance cells

It is well known that the chemisorption of various chlorosilane materials on glass atomic storage vessel walls results in surface coatings which inhibit electronic‐ and nuclear‐spin relaxation. In the present study the chemical reaction of rubidium, and by analogy other alkali metals, with dichlorodimethylsilane‐treated glass surfaces has been studied. We find evidence that rubidium reacts with a freshly prepared coating to produce H2 and a volatile silicon‐containing species. The most reasonable reaction process is postulated to be rubidium reacting with residual silanol groups (Si‐OH) found on the surface. As the reaction proceeds these groups would disappear, thus reducing the spin‐relaxation rate associated with the surface. We believe that this reaction results in the ‘‘curing’’ of wall coatings reported by other investigators. Concurrently, the gaseous reaction products become impurities within the system. The spin‐relaxation cross section of the silicon‐containing species is expected to be less tha...

All-Optical Integrated rubidium Atomic Clock

We report on progress in the development of an All-Optical Integrated Micro-Primary Atomic Clock (AO-IMPAC). The operattion of the clock is based on an inhomogeneously broadened rubidium optical transition used for stabilization of a Kerr optical frequency comb generated in a high-Q whispering gallery mode (WGM) microresonator. We have demonstrated the initial operation of this clock built in a physics package with dimensions 5 × 6 × 1.2 cm. The clocks long term stability approaches 3 × 10−13 at about 2 × 104 s integration time. The measured value is limited by the noise floor of the measurement setup.

All-optical integrated atomic clock

We describe a novel architecture for realization of a miniature all-optical atomic clock. We show theoretically that a hyperparametric oscillator based on a whispering gallery mode resonator can be used as a miniature frequency divider for the clock. Such a frequency divider allows for transferring the long term frequency stability from the optical frequency domain to the RF frequency domain. We present some details for the clock that utilizes the thermally stable isoclinic point of the inhomogeneously broadened D1 line of 87Rb for frequency stabilization, and report on progress towards its experimental realization.

Atomic velocity distributions in a hydrogen beam effusing out of a radio frequency discharge dissociator

We have measured atomic hydrogen velocity distributions in an effusive beam coming out of a rf discharge dissociator by using a magnetic deflection technique. Dissociator pressures varied between 0.028 and 0.340 Torr. At low dissociator pressures the measured atomic velocity distributions were narrower than the expected beam Maxwellians; at higher pressures they were indistinguishable from beam Maxwellians at the dissociator wall temperature, indicating full thermalization of the atoms prior to exiting the dissociator. Monte Carlo simulations of the thermalization process within the dissociator reproduce these results, and point out the important role of vibrational excitation of the background hydrogen molecules as an energy loss mechanism. Our results are significant when designing magnetic state selectors for spin‐ or hyperfine‐polarized atomic hydrogen beams.

Development of a fiber optic chemical dosimeter network for use in the remote detection of hydrazine propellant vapor leaks at Cape Canaveral Air Force Station

Fiber optic chemical dosimeters are being developed for use in the remote detection of toxic rocket propellant vapors, (hydrazine and its derivatives, and nitrogen tetroxide) that are used at Air Force and civilian rocket launch sites. The dosimeters employ colorimetric indicators that react selectively and irreversibly with the propellant vapors to yield chemical compounds that absorb laser light launched into a fiber optic network. The dosimeters are fabricated by dispersing the reagent within either a porous cladding or a porous distal end coating, that is prepared by a low temperature sol-gel technique. Remote field- scale detection of hydrazine vapor in a few hundreds of ppb-min integrated dose regime has been demonstrated with a network that is approximately equals 1 kilometer in length and the use of a low power (10 mW) diode laser. We have also assembled a computer model of a multimode fiber optic dosimeter network for prediction of the operational capabilities of a multiplexed system containing 100 dosimeters. The model was encoded in both spreadsheet and BASIC formats. It was used to evaluate the performance of a field-scale, remote fiber optic detection system incorporating discrete chemical vapor dosimeters in serial, parallel, or hybrid serial/parallel topologies. Additionally, we have begun exploratory work utilizing chemical reagents that react reversibly with hydrazine vapor to develop hydrazine vapor concentration sensors that could be deployed in a similar fashion on a remote fiber optic network to detect hydrazine vapor in the ppb regime.

Buffer gas consumption in rubidium discharge lamps

We present a physics-based empirical model of a newly discovered potential failure mode of rubidium atomic clocks: exhaustion of the noble gas buffer in the rubidium discharge lamp. We attribute the buffer gas loss to noble gas ion capture (NIC) by the glass walls of the lamp. The noble gas ions are produced by multistep ionization in collisions with discharge electrons. The model explains the observed pressure dependence of the buffer gas loss rate, and predicts an extremely high sensitivity of the loss rate to discharge electron temperature. That prediction is confirmed by comparison with experimental data. The model needs further work to be fully validated. We propose that longest lamp life can be achieved by minimizing noble gas light emission while keeping Rb light emission at the level required to achieve the desired atomic clock performance.

Current‐to‐voltage amplifier with a high voltage isolated input

The measurement of very low currents collected on electrodes held at high voltages is a commonly encountered experimental problem, since a commercial electrometer’s input can usually be floated only at a few tens of volts. We have run into this problem when attempting to measure the gain of the first dynode of an electron multiplier of the type used on cesium‐beam atomic clocks. In order to solve it, we have designed, built, and tested a current‐to‐voltage (transresistance) amplifier whose input can be floated up to ±2000 V, while providing a ground‐referenced low‐impedance output capable of driving a voltmeter or chart recorder. This very flexible instrument can measure currents in the 10−12 –10−7‐A range, has a 1‐Hz bandwidth, and it can be built at a cost of a few hundred dollars.

Injection current calibration of diode laser wavelengths

Abstract When performing precision spectroscopy experiments, it is often necessary to incorporate a stabilized, high finesse Fabry-Perot etalon to provide frequency markers. We show that when the experiments use diode lasers, this technique can be replaced by precision measurements of the laser injection current. We examine the relationship between injection current and optical frequency for three TJS single-mode AlGaAs diode lasers and show that, to the limit of our measurement accuracy, the relationship is linear. By using the hyperfine structure of the D 2 line of cesium as our frequency reference, we are able to determine optical frequencies inside a 9.4 GHz range to within a few MHz; furthermore, we show that we can extrapolate this calibration several GHz beyond the calibration range. This optical frequency-calibration technique is very simple to implement and should be widely applicable.

Field test of fiber optic hydrazine dosimeters at Cape Canaveral

We tested seventy-two hydrazine fuel fiber optic dosimeters for periods up to three months or Cape Canaveral in order to determine the effect of the local environment on its lifetime and sensitivity. The dosimeters were deployed at a diverse group of sites including fuel, oxidizer, and hydrocarbon fuel storage and transfer locations, a salt spray corrosion test facility, a satellite processing area, an estuarine marsh, a paint storage locker, and several indoor locations including chemical laboratory fume hoods and bathrooms. In addition, a group were set aside in a sealed enclosure for control purposes. The dosimeters were retrieved at monthly intervals and exposed to measured doses of hydrazine vapor to determine the effects of the field exposure on their hydrazine response. Our analysis indicated that 90% of the exposed dosimeters were able to sense hydrazine at a dose detectivity of less than 15 ppb-hr, a value that meets the current hydrazine sensing requirement. Consequently, we are planning to deploy a full scale, continuously operating fiber optic system for detecting potential hydrazine leaks during launch operations at Cape Canaveral.

Remote fiber optic dosimeter for detecting hydrazine vapor

A fiber optic chemical dosimeter has been developed for use in the remote detection of vapors of toxic amine rocket fuels (hydrazine and its substituted derivatives) that are used at U.S. Air Force and civilian launch sites. The dosimeter employs a colorimetric indicating reagent immobilized in a porous sol-gel cladding on multimode fiber. This reagent reacts selectively with the fuel vapor to produce a strongly absorbing cladding that introduces light propagation losses in the fiber; these losses indicate the presence of hydrazine (N2H4) vapor. The absorption occurs over a broad spectral range ideally suited for interrogation by semiconductor diode lasers. We have shown that the dosimeter yields an average hydrazine detectivity of 2.3 ppb-hr with a standard deviation of 1 ppb-hr, a value that meets U.S. Air Force current detection requirements. Prolonged exposures of the dosimeter to laboratory air have not adversely affected the dosimeter. Additionally, its response to ammonia vapor has been determined to be 9200 times smaller than its response to hydrazine vapor.