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For the first time to the best of our knowledge, a simultaneous 10.6 mum CO(2) laser pulse has been used to enhance the Laser Induced Breakdown Spectroscopy (LIBS) emission from a 1.064 mum Nd:YAG laser induced plasma on a hard target. The enhancement factor was on the order of 25 to 300 times, depending upon the emission lines observed. For an alumina ceramic substrate the Al emission lines at 308 nm and Fe impurity line at 278 nm showed an increase of 60x and 119x, respectively. The output energy of the Nd:YAG laser was 50 mJ/pulse focused to a 1 mm diameter spot to produce breakdown. The CO(2) laser pulse had a similar energy density of 40 mJ/mm(2). Timing overlap of the two laser pulses within 1 microsecond was important for enhancement to be observed. An observed feature was the differential enhancement between different elemental species and also between different ionization states, which may be helpful in the application of LIBS for multi-element analysis.

We have developed a simple, noncontact, fiber-optic proximity sensor, using a laser micromachined tap on a single multimode optical fiber. The fiber end is placed near a target surface, and a beam of light is incident from the fiber onto the target. Some fraction of this light is reflected or scattered by the target and coupled back into the fiber. The amount recoupled into the fiber is dependent on the distance between the fiber end and the target surface as well as on other parameters such as the target's surface roughness. The fiber-optic tap allows us to monitor both the initial amount of light launched down the fiber toward the target and the amount of backreflected light from the target. For a known environment and target surface, variations in source intensity can be compensated for by monitoring the ratio of the two counterpropagating beams.

There is a great need for easy-to-fabricate and versatile fiber optic signal processing systems in which optical fibers are used for the delay and storage of wideband guided lightwave signals. We describe the design of the least-mean-square algorithm-based fiber optic adaptive filters for processing guided lightwave signals in real time. Fiber optic adaptive filters can learn to change their parameters or to process a set of characteristics of the input signal. In our realization we employ as few electronic devices as possible and use optical computation to utilize the advantages of optics in the processing speed, parallelism, and interconnection. Many schemes for optical adaptive filtering of electronic signals are available in the literature. The new optical adaptive filters described in this paper are for optical processing of guided lightwave signals, not electronic signals. We analyzed the convergence or learning characteristics of the adaptive filtering process as a function of the filter parameters and the fiber optic hardware errors. From this analysis we found that the effects of the optical round-off errors and noise can be reduced, and the learning speed can be comparatively increased in our design through an optimal selection of the filter parameters. A general knowledge of the fiber optic hardware, the statistics of the lightwave signal, and the desired goal of the adaptive processing are enough for this optimum selection of the parameters. Detailed computer simulations validate the theoretical results of performance optimization.

A CO(2)-laser-based laser ablative chemical etching (LACE) technique was used for the rapid (milliseconds) fabrication of micrometer-scale taps in the cladding of multimode silica optical fibers. In the initial experiments the optical-quality surfaces of the etched groove directionally radiate approximately one third of the total tap output. The fraction of the guided optical energy tapped out can be easily and precisely controlled by the laser parameters. The radiation patter from the tap is in reasonably good agrement with initial theoretical calculations. This novel LACE-based tap manufacturing technique permits computer-controlled, rapid, and inexpensive fabrication of the high-quality fiber-optic taps needed for realizing various fiber-optic signal-processing, interconnection, monitoring, and sensor systems.

An improved photoelastic modulator (PEM) employing two piezoelectric transducers and incorporating a new ir zmc selenide (ZnSe) optical element is described. The 0.64-cm thick PEM is capable of obtaining quarter-wave retardation from 0.55 microm to 13.0 microm. Previously no single, high quality, low static strain PEM element existed for this wavelength range. We have also constructed other PEM's using optical elements composed of fused quartz, calcium fluoride, and KRS-5. The important optical and mechanical properties are measured and compared.

A multimode integrated optical bistable switch using a LiNbO(3) phase modulator in a noncavity configuration was constructed and tested. Bistability and discriminator operation were observed in this device using a He-Ne laser.

Laser calorimetry was used to measure the optical absorption of several candidate window materials for application at CO laser wavelengths. These materials include KCl, CaF(2), SrF(2), and ZnSe. The long, thin bar technique was used to separate bulk and surface absorption contributions by means of their time dependencies. One sample of KCl, known to be low absorbing at 10.6 microm, exhibited no measurable absorption within the sensitivity of the calorimeter (beta(t) < 2 x 10(-6) cm(-1)). The absorption coefficients measured for two samples of CaF(2) at 5.41 microm were higher than those measured by other investigators at 5.25 microm, but, when fitted to an exponential dependence on wavelength, compared favorably with currently measured values. To compare results from different laboratories, precise definition of the spectral power distribution is essential. The surface absorption was, in all cases, small relative to similar measurements at 10.6 microm; in several cases it was not separable from bulk absorption by the technique used.