SIte-directed mutagenesis and the associated site-specific fluorescent labeling of proteins can be used to rationally design reagentless fluorescent molecular senors. The phosphate binding protein (PBP) and calmodulin (CaM) bind to phosphate and calcium in a highly specific manner. These ions induce a hinge motion in the proteins, and the resultant conformational change constitutes the basis of the sensor development. By labeling each protein at a specific site with environment-sensitive fluorescent probes, these conformational changes can be monitored and related to the amount of analyte ion present. In this study, the polymerase chain reaction was used to construct mutants of PBP and CaM that have a single cysteine at positions 197 and 109, respectively. Each protein was site-specifically labeled through the sulfhydryl group of the introduced cysteine residue at a single location with an environment-sensitive fluorescent probe. Characterization of the steady-state fluorescence indicated an enhancement of signal intensity upon binding of the analyte ion. Highly sensitive and selective and selective sensing systems for phosphate and calcium were obtained by using this approach.

Species selective and sensitive films were designed and fabricated for sensing explosives such as TNT. The molecular recognition host reagents were functionalized and covalently attached to a surface acoustic wave (SAW) transducer surface for detecting nitroaromatic species in gas phase. The selectivity and sensitivity of the film are based on host- guest interaction between the host reagent and gas phase species. The film fabrication employs molecular self- assembly technique to construct stable and organized films. The self-assembled monolayer film containing permethylated beta-cyclodextrin can detect o-nitrotoluene at 60 parts per billion. The multilayer films based on covalently attached cyclodextrin polymers can detect o-nitrotoluene at 600 parts per trillion.

We present a new approach to array fabrication for multianalyte sensing. Sensor arrays are prepared in a random fashion such that each sensor in the array occupies a different location from fiber to fiber. Using optical encoding schemes, the identity of each sensor can be ascertained and registered on the detector. The approach alleviates the need for preregistration of each sensing element during the array fabrication process.

In this work we present three novel optical approaches towards the implementation of bio-and chemical sensors. First we describe an absorbance spectroscopic techniques developed on a waveguide platform that features a sensitivity enhancement of 4 orders of magnitude compared to the conventional transmission measurements of ultra-thin films. Next we show a waveguide Zeeman interferometric technique, which is based on the relative phase change between the TE and TM waveguide modes, applied as a sensor platform. Finally an external-cavity laser, a semiconductor laser combined with a single mode optical fiber and a Bragg grating reflector, was built to work as an active sensor where the analyte species were incorporated inside the resonant cavity to increase sensitivity.

Biosensors combine a biological recognition mechanisms with a physical transduction technique. In nature, the transduction mechanism for high sensitivity molecular detection is modulation of cell membrane ionic conductivity, through specific ligand - receptor binding induced switching of ion channels. This effects an inherent signal amplification of 6-8 orders of magnitude, corresponding to the total ion flow arising from the single channel gating event. Here we describe the first reduction of this principle to a practical sensing device, which is a planar impedance element composed of a macroscopically supported synthetic bilayer membrane incorporating ion channels. The membrane and ionic reservoir are covalently attached to an evaporated gold surface. The channels have specific receptor groups attached which permit switching of the channels by analyte binding to the receptors. The device may then be made specific for the detection of a very wide range of analytes, including proteins, drugs, hormones, antibodies, DNA, etc., currently in the 10^-7-10^-12 M range. It also lends itself readily to microelectronic fabrication, the optimum sensitivity range of the device may be tuned over several orders of magnitude.

The LIGO Project is a joint effort between the California Institute of Technology and the Massachusetts Institute of Technology to build and operate a novel astronomical observatory that directly senses gravitational waves, and in doing so open a new observational window to the universe. Installation of detector components is planned to begin in the spring of 1998 with the first data run at the designed strain sensitivity of h approximately 2 X 10^-23 m/(root) Hz scheduled to begin in 2002.

We report improvements to our atom-interferometer based Sagnac gyroscope which uses stimulated Raman transitions to manipulate atomic wavepackets of cesium atoms. Using counter-propagating high-flux atomic beams, we form two interferometers with opposite Sagnac phase shifts that share key components such as Raman atomic state manipulation beams. Subtracting the two interferometer signals allows the common-mode rejection of spurious noise sources and various systematic effects. Preliminary results indicate a short term sensitivity of 3 X 10^-9 (rad/s) (root) Hz.

We describe the coupling of a magneto-optical trap to amass separator for the ultra-sensitivity detection of selected radioactive species. As a proof of principle test, we have demonstrated the trapping of approximately 6 million $_82)Rb atoms using an ion implementation and heated foil release method of introducing the sample into a trapping cell with minimal gas loading. Gamma-ray counting techniques were used to determine the efficiencies of each step in the process. By far the weakest step in the process is the efficiency of the optical trap itself. Further improvements in the quality of the nonstick dryfilm coating on the inside of the trapping cell and the possible use of larger diameter laser beams are indicated. In the presence of a large background of scattered light, this initial work achieved a detection sensitivity of approximately 4,000 trapped atoms. Improved detection schemes using a pulsed trap and gated photon detection method are outlined. Application of this technology to the areas of environmental monitoring and nuclear proliferation are foreseen.

In a ceramic vapor cell we have created a robust Sr magneto- optical trap that stores about 10⁸ atoms with lifetimes > 200 ms. We eliminate the 5p ¹P₁ yields 4d¹D₂ yields 5p ³P₂ leak and achieve a 10-fold improvement in trap lifetime by re-pumping the 5p ³P_0,2 dark states with 679 nm and 707 nm light. The observed lifetime is now limited by cold collision losses, and we have preliminary measurements of the 2-body loss rate. Direct readout of the trap velocity distribution is possible using the narrow 5s^{2 1}S₀ yields 5p ³P₁ intercombination line at 689 nm. We can also cool with this narrow transition and have achieved a 40-fold 1D velocity compression for about 5 percent of the trapped atoms by applying this second-stage cooling.

High detection sensitivities of quantum absorptions are important in many research fields of physics, chemistry and biology. In this paper we present our latest results on the ultrasensitive molecular overtone spectroscopy using the cavity-enhanced frequency modulation (FM) technique. The principle of this method makes use of a high-finesse external cavity to enhance the intrinsic resonance contrast, while an FM modulation approach provides short-noise limited signal recovery. Ideal matching of the FM sideband frequency to the cavity free-spectral-range makes the detection process insensitive to laser frequency noise relative noise relative to the cavity, while at the same time overcomes the cavity bandwidth limit.Working with a 1064-nm Nd:YAG laser, we have obtained sub-Doppler overtone resonances of HCCD, HCCH and CO₂ molecules. A detection sensitivity of 5 X 10^-13 of integrated absorption over 1-s averaging time has been achieved. The resultant high signal- to-noise ratio of the weak resonance produces excellent laser frequency stabilization.

We consider a binary mixture of two overlapping Bose- Einstein condensates in two different hyperfine states of ⁸⁷Rb with nearly identical magnetic moments. Such a system has been simply realized through application of radio frequency and microwave radiation which drives a two-photon transition between the two states. The nearly identical magnetic moments afford a high degree of spatial overlap, permitting a variety of new experiments. We discuss some of the conditions under which the magnetic moments are identical, with particular emphasis placed on the requirements for a time-averaged orbiting potential magnetic trap.

We summarize all experimental studies of Bose-Einstein condensation in dilute atomic gases reported thus far and discuss the experimental techniques used to produce, manipulate and observe nanokelvin samples of atoms.

We report Bose-Einstein condensation of large numbers of ⁸⁷Rb atoms in a magnetic time-averaged potential trap. Over 1.5 X 10⁹ atoms, initially captured in the TOP trap, are evaporatively cooled down to temperatures near 100 nK. Condensates of up to 2 X 10⁵ atoms at peak densities higher than 10¹⁴ cm^-3 are observed.

The significance of quantum computation for cryptography is discussed. Following a brief survey of the requirements for quantum computational hardware, an overview of the ion trap quantum computation project at Los Alamos is presented. The physical limitations to quantum computation with trapped ions are analyzed and an assessment of the computational potential of the technology is made.

A miniature, elliptical ring rf ion trap has been sued in recent experiments toward realizing a quantum computer in a trapped ion system. With the combination of small spatial dimensions and high rf drive potentials, around 500 V amplitude, we have achieved secular oscillation frequencies in the range of 5-20 MHz. The equilibrium positions of pairs of ions that are crystallized in this trap lie along the long axis of the ellipse. By adding a static potential to the trap, the micromotion of two crystallized ions may be reduced relative to the case of pure rf confinement. The presence of micromotion reduces the strength of internal transitions in the ion, an effect that is characterized by a Debye-Waller factor, in analogy with the reduction of Bragg scattering at finite temperature in a crystal lattice. We have demonstrated the dependence of the rates of internal transitions on the amplitude of micromotion, and we propose a scheme to use this effect to differentially address the ions.

We discuss frequency standards based on laser-cooled ¹⁹⁹Hg⁺ ions confined in cryogenic rf traps. In one experiment, the frequency of a microwave source is served to the ions' ground-state hyperfine transition at 40.5 GHz. For seven ions and a Ramsey free precession time of 100 s, the fractional frequency stability is 3.3 (2) X 10^-13 (tau) ^-1/2 for measurement times (tau) < 2 h. The ground-state hyperfine interval is measured to be 40 507 347 996.841 59 (14) (41) Hz, where the first number in parentheses is the uncertainty due to statistics and systematic errors, and the second is the uncertainty in the frequency of the time scale to which the standard is compared. In a second experiment under development, a strong-binding cryogenic trap will confine a single ion used for an optical frequency standard based on a narrow electric quadrupole transition at 282 nm. The bandwidth of the laser used to drive this transition is less than 10 Hz at 563 nm.

Secondary Neutral Mass Spectrometry using resonant laser ionization can provide for both high useful yields and high discrimination while maintaining high lateral and depth resolutions. An example of the power of the method is measurement of the isotropic composition of Mo and Zr in 1-5 micrometers presolar SiC and graphite grains isolated form the Murchison CM2 meteorite for the first time. These grains have survived the formation of the Solar System, and isotopic analysis reveals a record of the stellar nucleosynthetic processes known as s-, p-, and r-process. Successful isotopic analysis of these elements requires both high selectivity and high efficiency. Resonant ionization spectroscopy is particularly useful and flexible in this application. While the sensitivity of this technique has often been reported in the past, we focus here on the very low noise properties of the technique. We further demonstrate the efficacy of noise removal by two complimentary methods. First we use the resonant nature of the signal to subtract background signal. Second we demonstrate that by choosing the appropriate resonance scheme background can often be dramatically reduced.

Application of high resolution ICP-AES to selected problems of importance in the nuclear industry is a growing field. The advantages in sample preparation time, waste minimization and equipment cost are considerable. Two examples of these advantages are presented in this paper, burnup analysis of spent fuel and analysis of major uranium isotopes. The determination of burnup, an indicator of fuel cycle efficiency, has been accomplished by the determination of ¹³⁹La by high resolution inductively coupled plasma atomic emission spectroscopy (HR-ICP-AES). Solutions of digested samples of reactor fuel rods were introduced into a shielded glovebox housing an inductively coupled plasma and the resulting atomic emission transmitted to a high resolution spectrometer by a 31 meter fiber optic bundle. Total and isotopic U determination by thermal ionization mass spectrometry is presented to allow for the calculation of burnup for the samples. This method of burnup determination reduces the time, material, sample handling and waste generated associated with typical burnup determinations which require separation of lanthanum from the other fission products with high specific activities. Work concerning an alternative burnup indicator, ²³⁶U, is also presented for comparison. The determination of ²³⁵U:$_238)U isotope ratios in U-Zr fuel alloys is also presented to demonstrate the versatility of Hr-ICP-AES.

Laser wave-mixing spectroscopy is presented as a sub-Doppler method that offers not only high spectral resolution, but also excellent detection sensitivity. It offers spectral resolution suitable for hyperfine structure analysis and isotope ratio measurements. In a non-planar backward- scattering four-wave mixing optical configuration, two of the three input beams counter propagate and the Doppler broadening is minimized, and hence, spectral resolution is enhanced. Since the signal is a coherent beam, optical collection is efficient and signal detection is convenient. This simple multi-photon nonlinear laser method offers un usually sensitive detection limits that are suitable for trace-concentration isotope analysis using a few different types of simple analytical atomizers. Reliable measurement of hyperfine structures allows effective determination of isotope ratios for chemical analysis.

Photon burst mass spectrometry has been used to measure ⁸⁵Kr in a sample with an abundance of 6 X 10^-9. Improvements in detection efficiency by the use of avalanche photodiodes cooled to liquid nitrogen temperature are reported, which should make possible measurement of ⁸⁵Kr at the ambient atmospheric abundance of 10^-11.

We describe recent results of experiments probing single molecules in the surface of spherical microcavities. Effects of spatial photoselection have been recently observed through changes in the single-molecule fluorescence photon statistics. In addition to being a sensitive probe of the highly interesting boundary region between classical and quantum mechanics, cavity-modified spontaneous emission and the possibility of single-molecule stimulated emission hold exciting promise as a means of exceeding sensitivity limitations such as photobleaching and absorption saturation in single molecule fluorescence detection. Ongoing efforts such as fluorescence imaging of single molecules on the surface of microspheres and attempts to observe single- molecule stimulated emission will also be described.

Heterogeneity in the environments of molecules affects their photophysical parameters. Changes in the local environments or changes within the molecules themselves produces fluctuations in the photophysical parameters. We have explored the fluorescence lifetime and intensity fluctuations of Rhodamine 6G on silica using time correlated single photon counting combined with near-field and far- field scanning optical microscopies, and fluorescence photon-pair correlation measurements in far-field microscopy. In the most recent work, we find complex behavior in the fluorescence lifetime and emission intensity in the millisecond to minute time range that must be associated with changes in both the non-radiative and the radiative decay rates.

Laser wave mixing is presented as a sensitive detection method for absorbance measurements in flowing liquid analytes. Wave mixing is an unusually sensitive multi-photon nonlinear optical method since the analytical signal is generated as a coherent laser beam. Since the bright signal is visible to the naked eye, optical alignment is convenient. For liquid analytes in continuously flowing cells, we have demonstrated excellent detection sensitivity levels using various wave-mixing optical configurations and laser sources. Since it is an optical absorption method, laser wave-mixing detection offers excellent detection sensitivity for both fluorescing and non-fluorescing analytes. Hence, one does not have to label non-fluorescing analytes with tags in order to obtain good detection sensitivity in wave-mixing detection methods. Sensitivity detection of analytes in their native form offers many obvious advantages especially when interfaced to popular capillary separation methods. Since the analyte laser probe volume is very small, wave-mixing detection is suitable for on-column detection in various capillary electrophoresis or micro liquid chromatography systems.

High intensity nonresonant multiphoton ionization has been used in conjunction with time-of-flight mass spectrometry to perform highly sensitive, quantitative, chemical analysis. To achieve quantification of all elements simultaneously and obtain uniform detection efficiencies, all species, regardless of ionization potentials, should be saturated in a single, well-defined volume. To aid in this analysis, 3D potentials intensity distributions of high power laser beams were imaged at a nd near their focus. The cross-sectional intensity distributions of the fundamental and higher order harmonics of a 35-ps Nd:YAG laser beam showed near Gaussian profiles. For nonresonant multiphoton ionization of sputtered or gaseous atoms and molecules, high laser beam quality combined with high power density led not only to photo-ionization saturation of species with quite different ionization potentials, but also to sharply defined ionization volumes. Experiments were performed on the nonresonant multiphoton ionization of species from solid samples and from gaseous samples using well-characterized, high intensity laser beams. The result, driving relative sensitivity factors almost to unity, demonstrate quantitative compositional analysis.

We have developed and begun to field test a very sensitive method for real-time measurements of single-ring aromatic hydrocarbons in ambient air. In this study, we focus on the efficient 1 + 1 resonance enhanced multiphoton ionization (REMPI) of the BTEX species in the narrow region between 266 and 267 nm. We particularly emphasize 266.7 nm, a wavelength at which both benzene and toluene exhibit a sharp absorbance feature and benzene and its alkylated derivatives all absorb. An optical parametric oscillator system generating 266.7 nm, a REMPI cell, and digital oscilloscope detector are mounted on a breadboard attached to a small cart. In the first field test, the cart was wheeled through the various rooms of a chemistry research complex. Leakage of fuel through the gas caps of cars and light trucks in a parking lot was the subject of the second field test. The same apparatus was also used for a study in which the performance of the REMPI detector and a conventional photoionization detector were compared as a BTEX mixture was eluted by gas chromatography. Among the potential applications of the methodology are on-site analysis of combustion and manufacturing processes, soil gas and water headspace monitoring, space cabin and building air quality, and fuel leak detection.