Multimode metal-lined capillaries for Raman collection and sensing

Buric, Michael; Chen, Kevin P.; Falk, Joel; Woodruff, Steven D.

doi:10.1364/josab.27.002612

Cited by 25 publications

(17 citation statements)

References 26 publications

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“…The terms σ and ρ represent the Raman crosssection and molecular density of the gas species of interest [5].…”

Section: Discussionmentioning

confidence: 99%

“…With mode losses determined, the Raman power propagated through the waveguide as a function of the collection angle and the waveguide's length can be predicted. There are significant differences in propagation losses predicted by previously established theory (accurate only for low-order modes) [3,4] and new calculations of actual waveguide losses (accurate for all modes) [5]. Raman power predictions were experimentally examined with a series of Raman power measurements where the waveguide is repeatedly cut back in length.…”

Section: Introductionmentioning

confidence: 99%

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Angular output of hollow, metal-lined, waveguide Raman sensors

et al. 2012

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Hollow, metal-lined waveguides used as gas sensors based on spontaneous Raman scattering are capable of large angular collection. The collection of light from a large solid angle implies the collection of a large number of waveguide modes. An accurate estimation of the propagation losses for these modes is required to predict the total collected Raman power. We report a theory/experimental comparison of the Raman power collected as a function of the solid angle and waveguide length. New theoretical observations are compared with previous theory appropriate only for low-order modes. A cutback experiment is demonstrated to verify the validity of either theory. The angular distribution of Raman light is measured using aluminum and silver-lined waveguides of varying lengths.

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“…The terms σ and ρ represent the Raman crosssection and molecular density of the gas species of interest [5].…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Angular output of hollow, metal-lined, waveguide Raman sensors

et al. 2012

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“…Herein we will not attempt to account for additional internal coatings, although they have been studied previously [3,4,5]. In recent work we showed how to calculate the modes that can propagate in such a waveguide [6]. To determine the propagating waveguide modes, we write general expressions for the fields in the core and in the metal cladding and equate the tangential components of electric and magnetic fields at each side of the boundary at r = a.…”

Section: Discussionmentioning

confidence: 99%

“…Finally, we observe that for all propagating modes in commercially available silver or aluminum lined capillaries 1 | | << em im k k and consequently we can ignore all terms containing powers of em im k k that are greater than 1. These assumptions are more fully discussed in [6] and produce a simplified characteristic equation:…”

Section: Discussionmentioning

confidence: 99%

Optical efficiency in metal-lined capillary waveguide Raman sensors

et al. 2011

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Researchers have long sought to improve collection efficiencies in scattered-light sensing applications. Herein, we demonstrate efficient collection of Raman scattered light from gaseous samples. This enables the accurate, real-time, simultaneous measurement of otherwise difficult to distinguish molecular gasses or hydrocarbons. Hollow capillary waveguides, lined with a metal and dielectric over-coating, have often been used to deliver IR laser light to a target. We show that these waveguides can be used as both a sample holder for Raman gasses and as a laser-pumped optical cell which can collect Raman scattered light from these gasses. We extend existing low mode-order capillary waveguide analysis to treat higher order modes. This extension allows a robust computer simulation to accurately predict the spontaneous Raman scattering power that can be collected by the waveguide. We verify our new theoretical models with experimental measurements of Raman signals from a nitrogen filled waveguide. We demonstrate a cutback experiment which verifies our new theoretical predictions of the variation of scattering collection efficiency with guide dimensions. The prediction accuracy of our simulations allows us to design spectrometers and detectors to maximize Raman-light throughput in a high-sensitivity gas detection system.

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“…Even the most intricately designed multi-pass gas cells can usually only achieve an equivalent optical integration path length increase of 100X or so, with the added difficulties associated with transport of the large volume of gas inside a multipass cell. The NETL RGA was designed and constructed explicitly to utilize the characteristics of hollow capillary waveguides to advantage in a fast gas measurement configuration [4].…”

Section: Introductionmentioning

confidence: 99%

Fuel flexibility via real-time Raman fuel-gas analysis for turbine system control

et al. 2015

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The modern energy production base in the U.S. is increasingly incorporating opportunity fuels such as biogas, coalbed methane, coal syngas, solar-derived hydrogen, and others. In many cases, suppliers operate turbine-based generation systems to efficiently utilize these diverse fuels. Unfortunately, turbine engines are difficult to control given the varying energy content of these fuels, combined with the need for a backup natural gas supply to provide continuous operation. Here, we study the use of a specially designed Raman Gas Analyzer based on capillary waveguide technology with sub-second response time for turbine control applications. The NETL Raman Gas Analyzer utilizes a low-power visible pump laser, and a capillary waveguide gas-cell to integrate large spontaneous Raman signals, and fast gas-transfer piping to facilitate quick measurements of fuel-gas components. A U.S. Department of Energy turbine facility known as HYPER (hybrid performance system) serves as a platform for apriori fuel composition measurements for turbine speed or power control.A fuel-dilution system is used to simulate a compositional upset while simultaneously measuring the resultant fuel composition and turbine response functions in real-time. The feasibility and efficacy of system control using the spontaneous Raman-based measurement system is then explored with the goal of illustrating the ability to control a turbine system using available fuel composition as an input process variable.

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Multimode metal-lined capillaries for Raman collection and sensing

Cited by 25 publications

References 26 publications

Angular output of hollow, metal-lined, waveguide Raman sensors

Angular output of hollow, metal-lined, waveguide Raman sensors

Optical efficiency in metal-lined capillary waveguide Raman sensors

Fuel flexibility via real-time Raman fuel-gas analysis for turbine system control

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