Steve B. Brown

A fiber-optic sensor system for monitoring chlorinated hydrocarbon pollutants

We have developed and field-tested a fiber-optic chemical sensor system for use in environmental monitoring and remediation. The system detects chlorinated hydrocarbon pollutants with colorimetry, and is based on an irreversible chemical reaction between the target compound and a specific reagent. The reaction products are detected by their absorption at 560 nm and can be monitored remotely with optical fibers. Continuous measurements are made possible by renewing the reagent from a reservoir with a miniature pumping system. The sensor has been evaluated against gas chromatography standards and has demonstrated accuracy and sensitivity (5 ppbw) sufficient for the environmental monitoring of trichloroethylene and chloroform. Successful preliminary field tests have been conducted in a variety of contamination monitoring scenarios.

High‐efficiency energy extraction in backward‐wave Raman scattering

Pump depletions of 70–75% have been demonstrated for a KrF‐laser‐driven, methane‐gas‐filled backward Raman amplifier and are in agreement with predictions of the Frantz‐Nodvik saturated‐amplifier model. The associated counterpropagating Stokes laser intensity is determined to be ≳3.5 times that of the pump; the corresponding pulse compression ratio is ≈5.

DESIGN OF A CONE-PENETROMETER-COMPATIBLE PROBE AND HOUSING : THE LLNL RAMAN PROBE

An integrated infinity-focused fiber optic probe designed for cone penetrometer and hand-held use and constructed at Lawrence Livermore National Laboratories is described and evaluated for performance. Throughput efficiency is calculated, distance dependence, background levels, and sensitivity to heterogeneity in samples is evaluated. Representative spectra are presented that make use of the major performance advantages of this probe, which are (a) background rejection, (b) low sample light fluences, (c) distant viewing, (d) sample penetration, and (e) sample averaging capability.

Intraoral fiber-optic-based diagnostic for periodontal disease

The purpose of this initial study was to begin development of a new, objective diagnostic instrument that will allow simultaneous quantitation of multiple proteases within a single periodontal pocket using a chemical fiber optic senor. This approach could potentially be adapted to use specific antibodies and chemiluminescence to detect and quantitate virtually any compound and compare concentrations of different compounds within the same periodontal pocket. The device could also be used to assay secretions in salivary ducts or from a variety of wounds. The applicability is, therefore, not solely limited to dentistry and the device would be important both for clinical diagnostics and as a research too.

High-speed fluorescence detection of explosives vapor

High-density optical arrays of fluorescent micrometer sized sensors show promise for detecting low level vapor phase explosives and explosives-like compounds. Imaging software and a high-speed CCD detection system are used to capture changes in a temporal response pattern upon pulsatile vapor delivery to the sensors. Nitroaromatic compounds, such as 2,4-dinitrotoluene (DNT) and 1,3-dinitrobenzene, which are often present on the solid surface above buried landmines, are used to train pattern recognition networks for vapor phase detection. We have demonstrated previously that approximately 9 ppb 2,4-DNT can be detected when signal processing schemes are employed.

Fiber optic sensor for continuous monitoring of chlorinated solvents in the vadose zone and in groundwater: field test results

A fiber optic chemical sensor has been designed for groundwater and vadose zone monitoring of volatile halogenated hydrocarbons. The principle of detection is a quantitative, irreversible chemical reaction that forms visible light absorbing products. This absorption is measured remotely using fiber optics. Modifications of our previous sensor design have resulted in lower detection limits and increased durability. In this paper we describe the measurement system and present the new sensor design along with calibration data and preliminary field test results.

Characterization of the focused output from a selenium soft x-ray laser

The output energy (90 μJ), focal spot diameter (235 μm), and pointing accuracy (±75 μrad) for a 3.7‐cm‐long Se soft x‐ray laser operating at 20.6 and 20.9 nm are reported. Now that this intense soft x‐ray source has been well characterized it may find use in such diverse applications as lithography, contact microscopy, holography, and photoionization pumping.

A non-lensed fiber-optic resonance-enhanced multiphoton ionization probe

We have developed a miniature fiber-optic probe with no focusing optics for in situ analysis of volatile organic compounds (VOCs). The probe uses an optical fiber to transmit a laser pulse to a vapor sample causing it to ionize adjacent to the fiber tip through a resonance-enhanced multiphoton ionization (REMPI) process. The distal end of the optical fiber is contained co-axially within 2-mm-inner-diameter stainless steel tubing that serves as an electrode. The electrode is biased at a high positive potential to collect electrons. The current generated is shown to be proportional over about two orders of magnitude to the concentration of the species ionized. Visible wavelength REMPI spectroscopy is used to determine probe sensitivities of 20 ppb (benzene) and 43 ppb (toluene). Designing the probe without focusing optics specifies an achromatic ionization region constant in size and position as the laser wavelength is scanned, which simplifies data collection and reduction. Focusing achromatic systems are discussed and the potential signal improvement is estimated.

MiDAS (Micro-dot Array Sensor): toward a rapid, in-vivo, reproducible, multianalyte biosensor using inkjet printing technology

The Microdot Array Sensor (MiDAS) platform for making optical fiber-based sensors using inkjet printing technology is a paradigm shifting technology for delivering low cost, rapid, in-vivo, reproducible, multianalyte biosensors. A fast-response, reproducible, pH sensor is demonstrated. The MiDAS platform is very adaptable to new and existing indicator chemistries and can be used for detecting blood/gas and enzyme biomarkers.

Fiber optic sensor system for remote, long-term monitoring of soil and groundwater contamination

We have developed a fiber-optic chemical sensor technology for the remote monitoring of various votatile solvents. The accuracy, linearity, and sensitivity of the sensor (< 5 ppb by weight by water, determined by comparison with standard gas chromatographic measurements) are sufficient for environmental monitoring of at least trichloroethylene and chloroform. The sensor has been successfully demonstrated in a variety of remediation related activities. We will present design parameters of the sensor and field test results.