Development of laser mirrors of very high reflectivity using the cavity-attenuated phase-shift method

Herbelin, John M.; McKay, James A.

doi:10.1364/ao.20.003341

Cited by 60 publications

(29 citation statements)

References 2 publications

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“…mirrors include SiC>2, Ti02, Zr02, and ThF4 (41). It was in the development and characterization of these high reflectivity mirrors that cavity approaches were first employed to measure mirror reflectivity (1)(2)(3)(4). While multilayer dielectric mirrors are more durable than metallic mirrors, and can be fabricated for any desired reflectance, the high reflectance is only realized over a narrow wavelength range.…”

Section: Mirror Mirrormentioning

confidence: 99%

Introduction to Cavity-Ringdown Spectroscopy

Busch

1999

ACS Symposium Series

122

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Cavity-ringdown spectroscopy is an alternative way of measuring small fractional absorptions down to sub-ppm levels per pass in the cavity.In this chapter, the basic principles behind cavity-ringdown spectroscopy are discussed. The areas where ultra-sensitive absorption measurements in the gas phase are important are illustrated, and existing methods of making these measurements are presented. The experimental requirements for performing cavity-ringdown spectroscopy are discussed, and an expression for the detection limit in cavity-ringdown spectroscopy is derived from statistical considerations. Finally, future prospects for the technique are discussed.Cavity-ringdown spectroscopy is an alternative way of making ultra-sensitive absorption measurements, particularly with gas-phase samples. This volume will discuss the research being conducted on cavity-ringdown spectroscopy by the leading research groups in the area. In the chapters that follow, various aspects of the cavity-ringdown experiment will be discussed and its applications described. Although the origins of the technique can be traced back to attempts to measure mirror reflectivities in the early 1980s (1-4), the spectroscopic application of the concept has only recently been reviewed (5,6) and is still not widely known to the general scientific community. Because the technique can provide the ability to measure small fractional absorptions (down to sub-ppm levels per pass), it should be of interest to broad segments of the analytical-, physical-, and engineering communities. This includes analytical chemists, spectroscopists, physical chemists doing laser spectroscopy and molecular beam work, combustion scientists, atmospheric chemists, and chemical engineers involved with process measurements-in fact, anyone involved with measuring trace components in gas-phase samples by absorption spectroscopy.This chapter will provide a basic introduction to cavity-ringdown spectroscopy for the reader who is not familiar with the technique. The intent is to show the basic principles of the technique without introducing undue mathematical complexity at the outset. However, before describing the technique, it is worthwhile to review some of the areas where sensitive gas-phase absorption measurements are important.

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Section: Mirror Mirrormentioning

confidence: 99%

Introduction to Cavity-Ringdown Spectroscopy

Busch

1999

ACS Symposium Series

122

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“…Because of the long path lengths associated with the light within the cavity, the detected wave form of the light which leaves the cavity is distorted with respect to the initial modulation. [1][2][3][4] This distortion is measured as a phase shift, which is completely comparable to measuring the time decay or "cavity ring down" ͑CRD͒. [4][5][6][7] Prior to our first report of over two years ago of a CAPS device employing a LED, 8 virtually all CAPS and CRDbased detection devices employed coherent light sources for two primary reasons.…”

Section: Introductionmentioning

confidence: 99%

Optical extinction monitor using cw cavity enhanced detection

Kebabian

Robinson

Freedman

2007

Review of Scientific Instruments

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We present details of an apparatus capable of measuring optical extinction (i.e., scattering and/or absorption) with high precision and sensitivity. The apparatus employs one variant of cavity enhanced detection, specifically cavity attenuated phase shift spectroscopy, using a near-confocal arrangement of two high reflectivity (R approximately 0.9999) mirrors in tandem with an enclosed cell 26 cm in length, a light emitting diode (LED), and a vacuum photodiode detector. The square wave modulated light from the LED passes through the absorption cell and is detected as a distorted wave form which is characterized by a phase shift with respect to the initial modulation. The amount of that phase shift is a function of fixed instrument properties-cell length, mirror reflectivity, and modulation frequency-and of the presence of a scatterer or absorber (air, particles, trace gases, etc.) within the cell. The specific implementation reported here employs a blue LED; the wavelength and spectral bandpass of the measurement are defined by the use of an interference filter centered at 440 nm with a 20 nm wide bandpass. The monitor is enclosed within a standard 19 in. rack-mounted instrumentation box, weighs 10 kg, and uses 70 W of electrical power including a vacuum pump. Measurements of the phase shift induced by Rayleigh scattering from several gases (which range in extinction coefficient from 0.4-32 Mm(-1)) exhibit a highly linear dependence (r(2)=0.999 97) when plotted as the co-tangent of the phase shift versus the expected extinction. Using heterodyne demodulation techniques, we demonstrate a detection limit of 0.04 Mm(-1) (4 x 10(-10) cm(-1)) (2sigma) in 10 s integration time and a base line drift of less than +/-0.1 Mm(-1) over a 24 h period. Detection limits decrease as the square root of integration time out to approximately 150 s.

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“…CAPS is only the first of several highly creative detection technologies, generally referred to as cavity enhanced optical absorption, which have been invented since the advent of high reflectivity (R > 99.9%) mirrors three decades ago (14,15).…”

Section: Introductionmentioning

confidence: 99%

A Practical Alternative to Chemiluminescence-Based Detection of Nitrogen Dioxide: Cavity Attenuated Phase Shift Spectroscopy

Kebabian

Wood

Herndon

et al. 2008

Environ. Sci. Technol.

117

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We present results obtained from a greatly improved version of a previously reported nitrogen dioxide monitor (Anal Chem. 2005, 77, 724-728) that utilizes cavity attenuated phase shift spectroscopy (CAPS). The sensor, which detects the optical absorption of nitrogen dioxide within a 20 nm bandpass centered at 440 nm, comprises a blue light emitting diode, an enclosed stainless steel measurement cell (26 cm length) incorporating a resonant optical cavity of near-confocal design and a vacuum photodiode detector. An analog heterodyne detection scheme is used to measure the phase shift in the waveform of the modulated light transmitted through the cell induced by the presence of nitrogen dioxide within the cell. The sensor, which operates at atmospheric pressure, fits into a 19 in.-rack-mounted instrumentation box, weighs 10 kg, and utilizes 70 W of electrical power with pump included. The sensor response to nitrogen dioxide (calculated as the cotangent of the phase shift) is demonstrated to be linear (r2 > 0.9999) within +/- 1 ppb over a range of 0-320 ppb (by volume). The device exhibits a detection limit (3sigma precision) of less than 60 parts per trillion (0.060 ppb) with 10 s integration, a value derived from measurements at NO2 concentration levels of both 0 and 20 ppb; the detection limit improves as the integration time is increased to several hundred seconds. The observed baseline drift is less than +/- 0.5 ppb overthe course of a month. An intercomparison of measurements of ambient NO2 concentrations over several days using this sensor with a quantum cascade laser-based infrared absorption spectrometer and a standard chemiluminescence-based NOx analyzer is presented. The data from the CAPS sensor are highly correlated (r2 > 0.99) with the other two instruments. The absolute agreement between the CAPS and each of the two other instruments is within the expected statistical noise associated with the infrared laser-based absorption spectrometer (+/- 0.3 ppb with 10 s sampling) and chemiluminescence analyzer (+/- 0.4 ppb with 60 s averaging). The major limitation concerning accuracy is a direct spectral interference with phototchemically produced 1,2-dicarbonyl species (e.g., glyoxal, methylglyoxal). However, this interference can be readily removed by shifting the detection band to a slightly longer wavelength and ensuring that the lower edge of the detection band is greater than 455 nm.

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Development of laser mirrors of very high reflectivity using the cavity-attenuated phase-shift method

Cited by 60 publications

References 2 publications

Introduction to Cavity-Ringdown Spectroscopy

Introduction to Cavity-Ringdown Spectroscopy

Optical extinction monitor using cw cavity enhanced detection

A Practical Alternative to Chemiluminescence-Based Detection of Nitrogen Dioxide: Cavity Attenuated Phase Shift Spectroscopy

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