87,850 research outputs found
A NOVEL SOURCE FOR INFRARED KINETIC SPECTROSCOPY
No full text A. H. Hielscher, C. E. Miller, D. C. Bayard, U. Simon, K. P. Smolka, R. F. Curl, and F. K. Tittel, J. Opt. Soc. Am. B. 9, 1962 (1992).Author Institution: Department of Chemistry and Rice Quantum Institute, Rice UniversityWe present the first transient free radical spectra recorded with a recently difference frequency generation spectrometer based on . By combining the outputs from two continuous wave, single frequency visible lasers (dye, Ti:Sapphire, and/or diode), continuously tunable infrared light has been produced at power levels of tens of microwatts between 1000 and . An absolute frequency precision of and a laser linewidth of -1.0 MHz has been achieved. This infrared source is expected to be a valuable new spectroscopic tool with sub-Doppler resolution continuously spanning a large portion of the molecular fingerprint region
Modulation Cancellation Method for Spectroscopic Measurements
No full textA novel spectroscopic technique based on modulation spectroscopy is described. We demonstrated three applications: measurement of temperature differences in a gas, detection of broadband absorbing species and isotope ratio measurement
Mid infrared sensors using periodically poled LiNbO3 for trace gas detection
No full textThe design and performance characteristics of compact mid-infrared gas sensors based on difference frequency generation (DFG) are described. These sensors use periodically-poled lithium niobate (PPLN) crystals with single or multiple grating period pumped by two single frequency solid state lasers and a thermo-electrically cooled HgCdTe infrared detectors. The spectroscopic applications of DFG sensors are demonstrated.Frank K. Tittel, David G Lancaster, Dirk Richter, and Robert F. Cur
Quartz-Enhanced Photoacoustic Spectroscopy: A Review
No full textA detailed review on the development of quartz-enhanced photoacoustic sensors (QEPAS) for the sensitive and selective quantification of molecular trace gas species with resolved spectroscopic features is reported. The basis of the QEPAS technique, the technology available to support this field in terms of key components, such as light sources and quartz-tuning forks and the recent developments in detection methods and performance limitations will be discussed. Furthermore, different experimental QEPAS methods such as: on-beam and off-beam QEPAS, quartz-enhanced evanescent wave photoacoustic detection, modulation-cancellation approach and mid-IR single mode fiber-coupled sensor systems will be reviewed and analysed. A QEPAS sensor operating in the THz range, employing a custom-made quartz-tuning fork and a THz quantum cascade laser will be also described. Finally, we evaluated data reported during the past decade and draw relevant and useful conclusions from this analysis
Ppb-level detection of nitric oxide using an external cavity quantum cascade laser based QEPAS sensor
No full textGeometrical parameters of micro-resonator for a quartz enhanced
photoacoustic spectroscopy sensor are optimized to perform sensitive and
background-free spectroscopic measurements using mid-IR quantum
cascade laser (QCL) excitation sources. Such an optimized configuration is
applied to nitric oxide (NO) detection at 1900.08 cm−1 (5.26 μm) with a
widely tunable, mode-hop-free external cavity QCL. For a selected NO
absorption line that is free from H2O and CO2 interference, a NO detection
sensitivity of 4.9 parts per billion by volume is achieved with a 1-s
averaging time and 66 mW optical excitation power. This NO detection
limit is determined at an optimal gas pressure of 210 Torr and 2.5% of
water vapor concentration. Water is added to the analyzed mixture in order
to improve the NO vibrational-translational relaxation process
Mode matching of a laser-beam to a compact high finesse bow-tie optical cavity for quartz enhanced photoacoustic gas sensing
No full textWe report on the optical characterization of a compact bow-tie cavity composed of two flat mirrors and two concave mirrors, all having a reflectance > 99.99% in the spectral range between 4.8 μm and 5.3 μm, mounted in a stainless-steel enclosure. The cavity was designed for the implementation of an intracavity-quartz enhanced photoacoustic sensor system. The propagation parameters of the intra-cavity beam were determined using the ABCD-matrix method, allowing the analytical formulation of the size of two beam waists occurring inside the cavity. A collimated mid-infrared laser beam was optically coupled and mode matched into the bow-tie cavity via a focusing lens. A cavity finesse of ∼ 2000 was measured at a pressure of 90 Torr inside the cavity, corresponding to an optical power enhancement factor of ∼ 320
Tunable mid-infrared laser-based gas sensors: new technologies and applications
No full textThis work describes the design and performance characteristics of room-temperature mid-infrared diode-pumped sensors capable of either single or multicomponent real-time trace gas detection in ambient air. The difference-frequency-generation based sensor technology employs periodically poled lithium niobate crystals with multiple grating periods pumped by two single-frequency solid-state lasers and a thermoelectrically cooled HgCdTe infrared detector.David G. Lancaster, Frank K. Tittel, Dirk Richter, K.P. Petrov and Robert F. Cur
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
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