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Joseph T. Hodges - One of the best experts on this subject based on the ideXlab platform.

  • Quantum-noise-limited Cavity Ring-Down Spectroscopy
    Applied Physics B, 2014
    Co-Authors: David A. Long, A. J. Fleisher, S. Wójtewicz, Joseph T. Hodges
    Abstract:

    We demonstrate a heterodyne-detected Cavity Ring-Down Spectroscopy (CRDS) method that allows for a noise-equivalent absorption coefficient of 6 × 10^−14 cm^−1 Hz^−1/2, the lowest which has been reported in a CRDS measurement. It is shown that heterodyne-detected CRDS also reaches the quantum noise limit at reasonable optical powers. In addition to offering ultra-high sensitivity, this technique provides high frequency agility over a range of 2 THz in the near-infrared, which allows entire absorption bands to be recorded in minutes. As a demonstration experiment, high resolution spectra of a near-infrared carbon dioxide band have been recorded.

  • Differential Cavity Ring-Down Spectroscopy
    Journal of the Optical Society of America B, 2013
    Co-Authors: Jérémie Courtois, K. Bielska, Joseph T. Hodges
    Abstract:

    High-precision Cavity-enhanced spectroscopic measurements are commonly compromised by interferences caused by external etalons. Here, we present the differential Cavity Ring-Down Spectroscopy (D-CRDS) technique for reducing these perturbations. We discuss how etalons are caused by coupled-Cavity interactions between the primary Ring-Down Cavity and other optical elements of the experiment, and we model and experimentally verify how drift in Cavity base loss correlates with barometric pressure and laboratory temperature. D-CRDS measurements of near-infrared CO2 spectra that are insensitive to etalon-induced distortions are then presented. Based on an average of ∼100 spectra, these results yield a signal-to-noise ratio of 170,000∶1 and a minimum detectable absorption coefficient of 4×10−12  cm−1.

  • Coupled-Cavity Ring-Down Spectroscopy technique
    Optics Letters, 2012
    Co-Authors: Jeremie B. Courtois, Joseph T. Hodges
    Abstract:

    We present a technique called coupled-Cavity Ring-Down Spectroscopy (CC-RDS) for controlling the finesse of an optical resonator. Applications include extending the sensitivity and dynamic range of a Cavity-enhanced spectrometer as well as widening the useful spectral region of high-reflectivity mirrors. CC-RDS uses controlled feedback of the probe laser beam to a Ring-Down Cavity, which leads to interference between the internally circulating light and that which is fed back through a Cavity mirror port. Using a 74 cm long Ring-Down Cavity and a feedback Cavity with a finesse of 16, we demonstrate that this effect increases the decay time constant from 210 μs to 280 μs, corresponding to an increase of finesse from 2.7×105 to 3.6×105. Finally, we show that with the addition of a second feedback Cavity, we observe Ring-Down times as long as ∼0.5  ms, which is equivalent to (1−R)≈4.9×10−6, where R is the effective mirror reflectivity.

  • Frequency-stabilized Cavity Ring-Down Spectroscopy
    Chemical Physics Letters, 2012
    Co-Authors: David A. Long, Roger D. Van Zee, M. Okumura, Charles E. Miller, Agata Cygan, Daniel Lisak, Joseph T. Hodges
    Abstract:

    We describe frequency-stabilized Cavity Ring-Down Spectroscopy (FS-CRDS), an ultraprecise refinement of conventional CRDS. We review the technique and highlight some recent studies that have utilized FS-CRDS to perform precision measurements of molecular transitions in the near-infrared. We describe system enhancements that are currently under implementation, including Pound–Drever–Hall locking and optical frequency comb-stabilization, which have the potential to reduce the uncertainty in both the absorption and frequency axes of our spectra by more than an order of magnitude. Finally, we describe high impact applications of this capability that can exploit frequency axis uncertainty at the 10 kHz level and signal-to-noise ratios exceeding 200000:1.

  • Linking Molecular- and Atomic-Frequency Standards with Cavity Ring-Down Spectroscopy
    Laser Applications to Chemical Security and Environmental Analysis, 2008
    Co-Authors: Joseph T. Hodges, Piotr Masłowski, David J. Robichaud, M. Okumura, Charles E. Miller, Linda R. Brown
    Abstract:

    We report a new method for measuring absorption transition frequencies using frequency-stabilized Cavity Ring-Down Spectroscopy. We determined absolute frequencies of O2A-band transitions using saturation Spectroscopy of39K and demonstrated combined uncertainties < 1 MHz.

Hans-peter Loock - One of the best experts on this subject based on the ideXlab platform.

  • Chemical sensing using fiber Cavity Ring-Down Spectroscopy
    Sensors, 2010
    Co-Authors: Helen Waechter, Jessica Litman, Adrienne H. Cheung, Jack A. Barnes, Hans-peter Loock
    Abstract:

    Waveguide-based Cavity Ring-Down Spectroscopy (CRD) can be used for quantitative measurements of chemical concentrations in small amounts of liquid, in gases or in films. The change in Ring-Down time can be correlated to analyte concentration when using fiber optic sensing elements that change their attenuation in dependence of either sample absorption or refractive index. Two types of fiber cavities, i.e., fiber loops and fiber strands containing reflective elements, are distinguished. Both types of cavities were coupled to a variety of chemical sensor elements, which are discussed and compared.

Azer P. Yalin - One of the best experts on this subject based on the ideXlab platform.

  • Open-path Cavity Ring-Down Spectroscopy sensors for atmospheric measurements
    Conference on Lasers and Electro-Optics, 2016
    Co-Authors: Azer P. Yalin, Laura E. Mchale, Soran Shadman, Charles Rose
    Abstract:

    Open-path Cavity Ring-Down Spectroscopy provides a potential means for sensitive detection of trace gas species in compact, lightweight packages. This contribution presents studies of attainable sensitivity along with details of methane and ammonia sensors.

  • Cavity Ring-Down Spectroscopy sensor for detection of hydrogen chloride
    Atmospheric Measurement Techniques, 2014
    Co-Authors: Christopher L. Hagen, Steven S. Brown, Brian Lee, Isaiah Franka, Jordan Rath, Trevor C. Vandenboer, J. M. Roberts, Azer P. Yalin
    Abstract:

    Abstract. A laser-based Cavity Ring-Down Spectroscopy (CRDS) sensor for measurement of hydrogen chloride (HCl) has been developed and characterized. The instrument uses light from a distributed-feedback diode laser at 1742 nm coupled to a high finesse optical Cavity to make sensitive and quantifiable concentration measurements of HCl based on optical absorption. The instrument has a (1σ) limit of detection of

  • Sputter erosion sensor for anode layer-type Hall thrusters using Cavity Ring-Down Spectroscopy
    Journal of Propulsion and Power, 2010
    Co-Authors: Naoji Yamamoto, John D. Williams, Lei Tao, Binyamin Rubin, Azer P. Yalin
    Abstract:

    We report the development of a sputter erosion monitoring system to study Hall thruster lifetime and contamination. The laser-based sensor uses the continuous-wave Cavity Ring-Down Spectroscopy technique and allows for in situ measurements in near-real time. The continuous-wave Cavity Ring-Down Spectroscopy technique diagnostic allows direct probing of sputter products in their ground state, thereby providing a reliable quantitative measure of their overall number density. Combining the number density of sputtered particles with their velocity allows determination of the flux of sputtered particles and erosion rate. We perform proof of principle experiments, in which sputtered manganese atoms from the acceleration channel of an anode layer-type Hall thruster are measured. The measurement strategy is to detect the manganese atoms via an absorption line from the ground state at a wavelength of 403.076 nm (air). The measured path-integrated number density of sputtered manganese atoms is 1.7 ± 0.3 × 10 13 m -2 for an argon anode mass flow rate of 2.08 mg/s and a discharge voltage of 250 V. A finite element sputter model is used to compare the Cavity Ring-Down Spectroscopy results against validating mass loss measurements and shows good agreement.

  • Species-Specific Sputtering Measurements with Cavity Ring-Down Spectroscopy
    43rd AIAA ASME SAE ASEE Joint Propulsion Conference &amp; Exhibit, 2007
    Co-Authors: Vijay Surla, Lei Tao, Azer P. Yalin
    Abstract:

    We report sputtering studies using Cavity Ring-Down Spectroscopy (CRDS). The high sensitivity of the technique and its non-intrusive nature make it amenable to both in situ device studies as well as basic characterization studies. We provide demonstrative measurements of sputtered particles showing the ability to determine species-specific number density and velocity. We summarize a spatial-scanning approach for differential sputter yield measurements and give a measurement example based on a tantalum target. We discuss the use of CRDS for measurement of multi-component materials and provide experimental results for detection of a Fe-Mn target as well as a proposed detection scheme for boron nitride.

  • Detection of sputtered metals with Cavity Ring-Down Spectroscopy.
    Applied Optics, 2005
    Co-Authors: Azer P. Yalin, Vijay Surla, M. Butweiller, John D. Williams
    Abstract:

    We report on use of Cavity Ring-Down Spectroscopy (CRDS) as a means to detect and quantify ion sputtering of refractory metal species. CRDS measurements are made with a neodymium:YAG-pumped optical parametric oscillator laser system in the 375–400 nm region. CRDS sputtering measurements are presented for argon ions incident on iron, aluminum, molybdenum, and titanium. The measurements are based on absorption from fine-structure levels of the electronic ground-state multiplets. For each species, characteristic spectra are provided, the dependence of sputtered particle number density on the beam current is examined, measured densities are compared with a sputter model, and detection limits are determined. For iron, aluminum, and titanium we probe multiple fine-structure levels within the ground-state multiplet and obtain information on their relative populations.

Helen Waechter - One of the best experts on this subject based on the ideXlab platform.

  • Diverse industrial applications of Cavity Ring-Down Spectroscopy
    2016 Photonics North (PN), 2016
    Co-Authors: Helen Waechter, Florian Adler, Marten Beels, Ryan Matz, Brian Siller, Bill West, Yu Chen
    Abstract:

    Over the last decade, Continuous-Wave Cavity Ring-Down Spectroscopy (CW-CRDS) has gained growing acceptance and become a field-proven trace gas measurement technique widely used in industry and at major national metrology institutes. The technology has shown remarkable diversity, being used in applications ranging from ultra-clean semiconductor fabs to harsh and dirty coal-fired boilers. Here we will present our newest developments for three very different applications: 1) continuous emissions monitoring of hydrogen chloride in stack emissions of cement and coal-fired power plants with very dirty sample gas; 2) trace moisture measurement in ultra-high purity ammonia for LED and semiconductor manufacturing, a spectroscopically challenging matrix; and, 3) detection of impurities in cryogenic liquids by adapting CW-CRDS to very cold temperatures.

  • Chemical sensing using fiber Cavity Ring-Down Spectroscopy
    Sensors, 2010
    Co-Authors: Helen Waechter, Jessica Litman, Adrienne H. Cheung, Jack A. Barnes, Hans-peter Loock
    Abstract:

    Waveguide-based Cavity Ring-Down Spectroscopy (CRD) can be used for quantitative measurements of chemical concentrations in small amounts of liquid, in gases or in films. The change in Ring-Down time can be correlated to analyte concentration when using fiber optic sensing elements that change their attenuation in dependence of either sample absorption or refractive index. Two types of fiber cavities, i.e., fiber loops and fiber strands containing reflective elements, are distinguished. Both types of cavities were coupled to a variety of chemical sensor elements, which are discussed and compared.

Kevin K. Lehmann - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical detection limit of saturated absorption Cavity Ring-Down Spectroscopy (SCAR) and two-photon absorption Cavity Ring-Down Spectroscopy
    Applied Physics B, 2014
    Co-Authors: Kevin K. Lehmann
    Abstract:

    Giusfredi et al. (Phys Rev Lett 104, 110801, 2010 ), have developed a new approach to Cavity Ring-Down Spectroscopy where a saturable sample absorption is determined simultaneously with the Cavity loss, providing immunity to changes in Cavity loss, thereby allowing for lower analyte detection limit. This paper presents an error analysis that provides predictions of the ultimate sensitivity limits that can be realized with this detection method. In particular, the sensitivity is strongly dependent upon the initial degree of saturation of the sample, and optimal values for this are determined both for photon detector and shot-noise-limited detection of both inhomogeneous and homogeneous broadened spectroscopic lines. Also presented are sensitivity limits expected for two-photon absorption Spectroscopy determined by Cavity Ring-Down Spectroscopy.

  • Sensitivity limits of continuous wave Cavity Ring-Down Spectroscopy.
    The Journal of Physical Chemistry A, 2013
    Co-Authors: Haifeng Huang, Kevin K. Lehmann
    Abstract:

    An optimized nonlinear least-squares fit algorithm for data processing in Cavity Ring-Down Spectroscopy (CRDS) is discussed, which improves the calculation efficiency substantially over using a general purpose fitting package. Theoretical absorption sensitivity limits for both the detector noise and the shot noise limited situations are derived and compared with experimental results. The effect of limiting the bandwidth of detection system on Ring-Down signal is discussed and compared with real Ring-Down data. The optimal trigger level and fitting interval are obtained for continuous wave Cavity Ring-Down Spectroscopy (cw-CRDS) in both the detector noise and shot noise limits, with the resulting sensitivity in units of cm–1 per (Hz1/2) derived. Interestingly, it is found that the optimized shot noise limited sensitivity in cw-CRDS method is, in principle, comparable with the ultimate sensitivity of noise-immune Cavity-enhanced optical heterodyne molecular Spectroscopy (NICE–OHMS).

  • Single-cell detection by Cavity Ring-Down Spectroscopy
    Applied Physics Letters, 2004
    Co-Authors: Peter B. Tarsa, P. Rabinowitz, Aislyn D. Wist, Kevin K. Lehmann
    Abstract:

    The implementation of Cavity Ring-Down Spectroscopy in an optical fiber resonator extends the viability of this highly sensitive technique for label-free detection of biological species. By chemically treating the surface of discrete tapered sensing regions along the length of a physically extended optical fiber resonator, we show single-cell sensitivity arising from optical scattering of the evanescent field surrounding the fiber. The observed detection limits, based on a minimum detectable scattering cross section on the order of 10μm2, suggest a broad range of new applications in a simple, inexpensive device for real-time Cavity Ring-Down biosensing.

  • Cavity Ring‐Down Spectroscopy - An Introduction to Cavity Ring‐Down Spectroscopy
    Cavity Ring-Down Spectroscopy, 1
    Co-Authors: Kevin K. Lehmann, Giel Berden, Rah Richard Engeln
    Abstract:

    Spectroscopy, the study of the interaction of light (electromagnetic radiation) and matter, is the most ubiquitous and precise method available to the physical scientist. Especially for isolated atoms, molecules, and small clusters, it has no peer. It is used to elucidate the structure and dynamics of quantum systems from atomic nuclei to natural proteins. Essentially everything we know about the universe beyond the domain that humans and their instruments can physically touch, comes from Spectroscopy. Without it, astronomy would be no more than stamp collecting. While a mature field, Spectroscopy is periodically reborn by the development of new tools that open up new vistas, such as under-explored regions of the spectrum, dramatic improvements in resolution, or in sensitivity. Almost always, these are initially unexpected and have been developed to address some specific problem. However, truly seminal work inspires and leads to an explosion of new applica tions and with it advancement of methods. Nuclear magnetic resonance Spectroscopy is the epitome of this experience. This book is devoted to Cavity Ring-Down Spectroscopy (CRDS). Like most new methods in science, CRDS grew out of an advance in technology, in this case the dramatic improvement in the reflectivity of the best dielectric mirrors, which in turn was made possible by the development of the ion sputtering method for forming thin films.