Quadrupole ion traps and trap arrays: geometry, material, scale, performance

Quadrupole ion traps are reviewed, emphasizing recent developments, especially the investigation of new geometries, guided by multiple particle simulations such as the ITSIM program. These geometries include linear ion traps (LITs) and the simplified rectilinear ion trap (RIT). Various methods of fabrication are described, including the use of rapid prototyping apparatus (RPA), in which 3D objects are generated through point-by-point laser polymerization. Fabrication in silicon using multilayer semi-conductor fabrication techniques has been used to construct arrays of micro-traps. The performance of instruments containing individual traps as well as arrays of traps of various sizes and geometries is reviewed. Two types of array are differentiated. In the first type, trap arrays constitute fully multiplexed mass spectrometers in which multiple samples are examined using multiple sources, analyzers and detectors, to achieve high throughput analysis. In the second, an array of individual traps acts collectively as a composite trap to increase trapping capacity and performance for a single sample. Much progress has been made in building miniaturized mass spectrometers; a specific example is a 10 kg hand-held tandem mass spectrometer based on the RIT mass analyzer. The performance of this instrument in air and water analysis, using membrane sampling, is described.

Adaptive neural network in a hybrid optical/electronic architecture using lateral inhibition

We report the optical implementation of a neural network based on a nearest matched filter algorithm and extensive lateral inhibition. Extremely rapid learning is demonstrated in pattern recognition and autonomous control applications, without introducing processing artifacts such as spurious states and ambiguous solutions. The optical implementation is achieved with a reconfigurable, bipolar mask-type crossbar switch based on an inexpensive liquid crystal spatial light modulator.

Reconfigurable bipolar analog optical crossbar switch

A differential technique is proposed for obtaining bipolar analog {-1 . . . 0 . . . 1} inputs, outputs, and connection weights in a mask-type optical crossbar switch. The technique compensates for the limitations of current component technology and permits the use of inexpensive, low-contrast spatial light modulators for reconfigurable switching matrices. The conclusions of this work may be extended to design improvements in a wide variety of optical computing implementations.

Mirror surface autocovariance functions and their associated visible scattering

Visible scattering is measured and compared with predictions based upon surface roughness measurements. The results indicate two scales of roughness, a short scale of the order of 1 microm and a long scale ranging from 30 to 150 microm. A study of the relative amount of scattering from the two scales shows that the short scale accounts for all the scattering for scattering angles larger than 3 degrees . Furthermore, the analysis demonstrates the importance of spatial frequency bandwidth limits in optical scattering and finish measurements for a particular class of highly polished mirror surfaces.