共查询到20条相似文献,搜索用时 93 毫秒
1.
Development of a pulsed quantum cascade laser (QCL)-based spectroscopic trace-gas sensor for sub-part-per-million detection of nitric oxide (NO) and capable of monitoring other molecular species such as CO2, H2O, and NH3 in industrial combustion exhaust systems is reported. Rapid frequency modulation is applied to the QCL to minimize the influence of fluctuating non-selective absorption. A novel method utilizes only a few laser pulses within a single wavelength scan to probe an absorption spectrum at precisely selected optical frequencies. A high-temperature gas cell was used for laboratory evaluation of the NO sensor performance. A noise-equivalent sensitivity (1) of 100 ppb × m/
at room temperature and 200 ppb × m/
at 630 K was achieved by measuring the NO R(6.5) absorption doublet at 1900.075 cm–1. 相似文献
2.
Spectroscopic concentration measurements of ammonia and ethylene were done with a pulsed, distributed feedback (DFB) quantum
cascade (QC) laser centered at 970 cm−1. An astigmatic Herriot cell with 150 m path length was employed, and we compare the results from experiments using inter-
and intrapulse techniques, respectively. The measurements include the detection of ammonia in breath with these methodologies.
In the interpulse technique, the laser was excited with short current pulses (5–10 ns), and the pulse amplitude was modulated
with an external current ramp resulting in a ∼0.3 cm−1 frequency scan. A standard amplitude demodulation technique was implemented for extracting the absorption line, thus avoiding
the need for a fast digitizer or a gated integrator. In the intrapulse technique, a linear frequency down-chirp is used for
sweeping across the absorption line. A 200 ns long current pulse was used for these measurements which resulted in a spectral
window of ∼1.74 cm−1 during the down-chirp. The use of a room temperature mercury-cadmium-telluride detector resulted in a completely cryogen
free spectrometer. We demonstrate detection limits of ∼3 ppb for ammonia and ∼5 ppb for ethylene with less than 10 s averaging
time with the intrapulse method and ∼4 ppb for ammonia and ∼7 ppb for ethylene with the interpulse technique with an integration
time of ∼5 s. 相似文献
3.
Spectroscopic sensing of gases can be performed with high sensitivity and photometric precision by cavity ringdown (CRD) absorption
spectroscopy. Our cavity ringdown spectrometer incorporates continuous-wave (cw) tunable diode lasers, fibre-optic coupling
and standard photonics and optical telecommunications components. It comprises a rapidly swept optical cavity in a single-ended
optical heterodyne transmitter–receiver configuration, enabling optical absorption of gases to be recorded either as single-frequency
scanned spectra or as simultaneous, multi-wavelength tailored spectra. By measuring weak near-infrared rovibrational spectra
of carbon dioxide gas (CO2), with high resolution in the vicinity of 1.53 μm, we have realised a noise-limited absorption sensitivity of 2.5×10-9 cm-1 Hz-1/2. Analytical sensitivity limits (both actual and projected) and prospective gas-diagnostic applications are discussed. Our
approach to cw-CRD spectroscopy offers high performance in a relatively simple, low-cost, compact instrument that is amenable
to chemical analysis of trace gases in medical, agricultural, industrial and environmental situations.
Received: 16 May 2002 / Revised version: 3 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +61-2/9850-8313, E-mail: brian.orr@mq.edu.au 相似文献
4.
J. Wang S.T. Sanders J.B. Jeffries R.K. Hanson 《Applied physics. B, Lasers and optics》2001,72(7):865-872
Measurements of oxygen concentration at high pressures (to 10.9 bar) were made using diode-laser absorption of oxygen A-band
transitions near 760 nm. The wide current-tuning frequency range (>30 cm-1) of vertical cavity surface-emitting lasers (VCSELs) was exploited to enable the first scanned-wavelength demonstration of
diode-laser absorption at high pressures; this strategy is more robust than fixed-wavelength strategies, particularly in hostile
environments. The wide tuning range and rapid frequency response of the current tuning were further exploited to demonstrate
wavelength-modulation absorption spectroscopy in a high-pressure environment. The minimum detectable absorbance demonstrated,
∼1×10-4, corresponds to ∼800 ppm-m oxygen detectivity at room temperature and is limited by etalon noise. The rapid- and wide-frequency
tunability of VCSELs should significantly expand the application domain of absorption-based sensors limited in the past by
the small current-tuning frequency range (typically <2 cm-1) of conventional edge-emitting diode lasers.
Received: 26 July 2000 / Revised version: 2 January 2001 / Published online: 20 April 2001 相似文献
5.
D. Lognoli G. Cecchi I. Mochi L. Pantani V. Raimondi R. Chiari T. Johansson P. Weibring H. Edner S. Svanberg 《Applied physics. B, Lasers and optics》2003,76(4):457-465
Extensive fluorescence multispectral imaging of the cathedral and baptistery of Parma, Italy, is reported and discussed. In
particular, the first fluorescence imaging data from protection-treated stony materials were recorded. Fluorescence spectra
were taken with a mobile lidar system scanning the monument surfaces with a frequency-tripled Nd:YAG laser beam from a distance
of about 80 m. For each pixel of the area investigated, a high-spectral-resolution spectrum in the full visible range was
acquired. The principal-component analysis technique was used to obtain thematic maps that outlined areas subject to protective
treatment and biological growth, and other features, such as different types of stones and decoration pigments.
Received: 24 July 2002 / Revised version: 16 January 2003 / Published online: 3 April 2003
RID="*"
ID="*"Corresponding author. Fax: +39-055/410-893, E-mail: g.cecchi@ifac.cnr.it 相似文献
6.
A compact, diode-based difference-frequency laser system combined with a photoacoustic detection scheme is presented for trace-gas
sensing. It features a broad, continuous tuning range (3.2–3.7 μm), a narrow line width (154 MHz), and room-temperature operation,
and thus allows numerous gas species to be measured both isolated and in mixtures of different gases. Several trace-gas species
of environmental interest were detected, and gas mixtures were analysed. The detection limits are in the low-ppmV range, e.g.
1.3 ppmV for methane, 1.8 ppmV for ethane, and 1.2 ppmV for hydrogen chloride.
Received: 10 April 2002 / Revised version: 5 June 2002 / Published online: 12 September 2002
RID="*"
ID="*"Corresponding author. Fax: +41-1/633-1077, E-mail: Sigrist@iqe.phys.ethz.ch 相似文献
7.
M.W. Todd R.A. Provencal T.G. Owano B.A. Paldus A. Kachanov K.L. Vodopyanov M. Hunter S.L. Coy J.I. Steinfeld J.T. Arnold 《Applied physics. B, Lasers and optics》2002,75(2-3):367-376
A novel instrument, based on cavity-ringdown spectroscopy (CRDS), has been developed for trace gas detection. The new instrument
utilizes a widely tunable optical parametric oscillator (OPO), which incorporates a zinc–germanium–phosphide (ZGP) crystal
that is pumped at 2.8 μm by a 25-Hz Er,Cr:YSGG laser. The resultant mid-IR beam profile is nearly Gaussian, with energies
exceeding 200 μJ/pulse between 6 and 8 μm, corresponding to a quantum conversion efficiency of approximately 35%. Vapor-phase
mid-infrared spectra of common explosives (TNT, TATP, RDX, PETN and Tetryl) were acquired using the CRDS technique. Parts-per-billion
concentration levels were readily detected with no sample preconcentration. A collection/flash-heating sequence was implemented
in order to enhance detection limits for ambient air sampling. Detection limits as low as 75 ppt for TNT are expected, with
similar concentration levels for the other explosives.
Received: 1 April 2002 / Revised version: 13 June 2002 / Published online: 12 September 2002
RID="*"
ID="*"Corresponding author. Fax: +1-408/524-0551, E-mail: mtodd@picarro.com 相似文献
8.
A pulsed optical parametric oscillator (OPO) operated in an optical cavity with a grazing-incidence grating configuration
(GIOPO) was used for sensitive photoacoustic detection of trace quantities of dinitrogen oxide (N2O). The (ν1+ν3) combination vibration band of N2O was excited with the idler beam of the GIOPO at 2.86 μm using an optical cavity optimized for the idler beam. The linewidth
of the GIOPO could be reduced to 0.4 cm-1, allowing the rotational structure of the absorption spectrum to be resolved. A concentration sensitivity (signal-to-noise
ratio=3) of 60 parts in 109 by volume (60 ppb V) N2O in synthetic air was obtained. This may be sufficient for continuous monitoring of N2O in the atmosphere.
Received: 29 April 2002 / Revised version: 4 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +49-6221/54-4255, E-mail: peter.hess@urz.uni-heidelberg.de 相似文献
9.
R. Horváth J. Vörös R. Graf G. Fricsovszky M. Textor L.R. Lindvold N.D. Spencer E. Papp 《Applied physics. B, Lasers and optics》2001,72(4):441-447
It has been found that patterns and inhomogeneities on the surface of the waveguide used for optical waveguide lightmode spectroscopy
applications can produce broadening and fine structure in the incoupled light peak spectra. During cell spreading on the waveguide,
a broadening of the incoupling peaks is observed, while regular microstructures on the incoupling grating produce shifts and
splitting of the peaks. A theoretical model, based on the zigzag wave representation of light propagation in a planar optical
waveguide has been developed in order to understand the physical background of the observed effects. Numerical results are
given for the different cases observed, and they are compared with the experimental data. Several possible applications of
these effects are considered.
Received: 10 July 2000 / Revised version: 9 October 2000 / Published online: 21 February 2001 相似文献
10.
D.D. Nelson J.H. Shorter J.B. McManus M.S. Zahniser 《Applied physics. B, Lasers and optics》2002,75(2-3):343-350
Non-cryogenic, laser-absorption spectroscopy in the mid-infrared has wide applications for practical detection of trace gases
in the atmosphere. We report measurements of nitric oxide in air with a detection limit less than 1 nmole/mole (<1 ppbv) using
a thermoelectrically cooled quantum cascade laser operated in pulsed mode at 5.26 μm and coupled to a 210-m path length multiple-pass
absorption cell at reduced pressure (50 Torr). The sensitivity of the system is enhanced by operating under pulsing conditions
which reduce the laser line width to 0.010 cm-1 (300 MHz) HWHM, and by normalizing pulse-to-pulse intensity variations with temporal gating on a single HgCdTe detector.
The system is demonstrated by detecting nitric oxide in outside air and comparing results to a conventional tunable diode
laser spectrometer sampling from a common inlet. A detection precision of 0.12 ppb Hz-1/2 is achieved with a liquid-nitrogen-cooled detector. This detection precision corresponds to an absorbance precision of 1×10-5 Hz-1/2 or an absorbance precision per unit path length of 5×10-10 cm-1 Hz-1/2. A precision of 0.3 ppb Hz-1/2 is obtained using a thermoelectrically cooled detector, which allows continuous unattended operation over extended time periods
with a totally cryogen-free instrument.
Received: 1 May 2002 / Revised version: 6 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-978/663-4918, E-mail: ddn@aerodyne.com 相似文献
11.
Emission spectra of multimode lasers are very sensitive to spectrally selective extinction in their cavity. This phenomenon
allows the quantitative measurement of absorption. The sensitivity of measurements of intracavity absorption grows with the
laser pulse duration. The ultimate sensitivity obtained with a cw laser is set by various perturbations of the light coherence,
such as quantum noise, Rayleigh scattering, four-wave mixing by population pulsations, and stimulated Brillouin scattering.
It depends on the particular laser type used, and on its operative parameters, for example pump power, cavity loss, cavity
length, and length of the gain medium. Nonlinear mode-coupling dominates the dynamics of lasers that feature a thin gain medium,
such as dye lasers, whereas Rayleigh scattering is more important in lasers with a long gain medium, such as doped fibre lasers,
or the Ti:sapphire laser. The highest sensitivity so far has been obtained with a cw dye laser. It corresponds to 70000 km
effective length of the absorption path. The ultimate spectral resolution is determined by the spectral width of mode emission,
which is 0.7 Hz in this dye laser. High sensitivity and high temporal and spectral resolution allow various practical applications
of laser intracavity spectroscopy, such as measurements and simulations of atmospheric absorption, molecular and atomic spectroscopy,
process control, isotope separation, study of free radicals and chemical reactions, combustion diagnostics, spectroscopy of
excited states and nonlinear processes, measurements of gain and of spectrally narrow light emission. Intracavity absorption
in single-mode lasers shows enhanced sensitivity as well, although not as high as in multimode lasers.
Received: 10 May 1999 / Published online: 29 July 1999 相似文献
12.
S.F. Hanna R. Barron-Jimenez T.N. Anderson R.P. Lucht J.A. Caton T. Walther 《Applied physics. B, Lasers and optics》2002,75(1):113-117
An all-solid-state continuous-wave laser system for ultraviolet absorption measurements of the nitric oxide (NO) molecule
has been developed and demonstrated. The single-mode, tunable output of a 10-mW, 395-nm external-cavity diode laser (ECDL)
is sum-frequency-mixed with the output of a 115-mW, frequency-doubled, diode-pumped Nd:YAG laser in a beta-barium-borate crystal
to produce 40 nW of tunable radiation at 226.8 nm. The wavelength of the 395-nm ECDL is then scanned over NO absorption lines
to produce fully resolved absorption spectra. Initial results from mixtures of NO in nitrogen in a room-temperature gas cell
are discussed. The estimated NO detection limit of the system for a demonstrated absorption sensitivity of 2×10-3 is 0.2 ppm per meter of path length for 300 K gas. The estimated accuracy of the measurements is ±10%.
Received: 25 February 2002 / Revised version: 31 May 2002 / Published online: 8 August 2002 相似文献
13.
D. Masiyano J. Hodgkinson S. Schilt R. P. Tatam 《Applied physics. B, Lasers and optics》2009,96(4):863-874
We report the effects of self-mixing interference on gas detection using tunable diode laser spectroscopy. For very weak feedback,
the laser diode output intensity gains a sinusoidal modulation analogous to that caused by low finesse etalons in the optical
path. Our experiments show that self-mixing interference can arise from both specular reflections (e.g. cell windows) and
diffuse reflections (e.g. Spectralon™ and retroreflective tape), potentially in a wider range of circumstances than etalon-induced interference. The form and magnitude
of the modulation is shown to agree with theory. We have quantified the effect of these spurious signals on methane detection
using wavelength modulation spectroscopy and discuss the implications for real gas detectors. 相似文献
14.
R. Wolleschensky T. Feurer R. Sauerbrey U. Simon 《Applied physics. B, Lasers and optics》1998,67(1):87-94
Received: 26 August 1997/Revised version: 2 February 1998 相似文献
15.
Towards practical quantum cryptography 总被引:5,自引:0,他引:5
S. Chiangga P. Zarda T. Jennewein H. Weinfurter 《Applied physics. B, Lasers and optics》1999,69(5-6):389-393
Quantum cryptography bases the security of quantum key exchange on the laws of quantum physics and is likely to become the
first application employing quantum effects for communication. Here we present performance tests of a new design based on
polarization encoding of attenuated, coherent light pulses. Our measurements show that this compact setup can achieve an effective
key-bit rate in the kHz range with low alignment requirements and thus offers the tools for fast and user-friendly quantum
key exchange.
Received: 27 July 1999 / Revised version: 3 September 1999 / Published online: 10 November 1999 相似文献
16.
We present the first photoacoustic spectrometer for gas sensing employing both the fundamental and the frequency-doubled radiation
of a continuously tunable high-pressure CO2 laser with room temperature operation. A quasi-phase-matched diffusion-bonded GaAs crystal is used in the system for second-harmonic
generation. A pulsed photoacoustic detection scheme with a non-resonant cell, equipped with an 80-microphone array, is employed.
The wide continuous tuning range in the fundamental (9.2–10.7 μm) and the frequency-doubled (4.6–5.35 μm) regimes, together
with the narrow linewidth of 540 MHz (0.018 cm-1) for the 10-μm region and of 1050 MHz (0.0315 cm-1) for the 5-μm region, allow the measurement of gas mixtures, individual species and isotope discrimination. This is illustrated
with measurements on NO and CO2. The measured isotope ratio 15
NO/14
NO=(3.58±0.55)×10-3 agrees well with the literature (3.700×10-3) and demonstrates the good selectivity of the system.
Received: 30 April 2002 / Revised version: 10 June 2002 / Published online: 2 September 2002
RID="*"
ID="*"Corresponding author. Fax: +41-1/633-1077, E-mail: sigrist@iqe.phys.ethz.ch 相似文献
17.
S.T. Sanders 《Applied physics. B, Lasers and optics》2002,75(6-7):799-802
A swept-wavelength source is created by connecting four elements in series: a femtosecond fiber laser at 1.56 μm, a non-linear
fiber, a dispersive fiber and a tunable spectral bandpass filter. The 1.56-μm pulses are converted to super-continuum (1.1–2.2 μm)
pulses by the non-linear fiber, and these broadband pulses are stretched and arranged into wavelength scans by the dispersive
fiber. The tunable bandpass filter is used to select a portion of the super-continuum as a scan-wavelength output. A variety
of scan characteristics are possible using this approach. As an example, an output with an effective linewidth of approximately
1 cm-1 is scanned from 1350–1550 nm every 20 ns. Compared to previous scanning benchmarks of approximately 1 nm/μs, such broad,
rapid scans offer new capabilities: a gas sensing application is demonstrated by monitoring absorption bands of H2O, CO2, C2H2 and C2H6O at a pressure of 10 bar.
Received: 5 August 2002 / Revised version: 23 September 2002 / Published online: 22 November 2002
RID="*"
ID="*"Corresponding author. Fax: +1-608/265-2316, E-mail: ssanders@engr.wisc.edu 相似文献
18.
Leleux DP Claps R Chen W Tittel FK Harman TL 《Applied physics. B, Lasers and optics》2002,74(1):85-93
A Kalman filtering technique is applied to the simultaneous detection of NH3 and CO2 with a diode-laser-based sensor operating at 1.53 μm. This technique is developed for improving the sensitivity and precision
of trace gas concentration levels based on direct overtone laser absorption spectroscopy in the presence of various sensor
noise sources. Filter performance is demonstrated to be adaptive to real-time noise and data statistics. Additionally, filter
operation is successfully performed with dynamic ranges differing by three orders of magnitude. Details of Kalman filter theory
applied to the acquired spectroscopic data are discussed. The effectiveness of this technique is evaluated by performing NH3 and CO2 concentration measurements and utilizing it to monitor varying ammonia and carbon dioxide levels in a bioreactor for water
reprocessing, located at the NASA–Johnson Space Center. Results indicate a sensitivity enhancement of six times, in terms
of improved minimum detectable absorption by the gas sensor.
Received: 13 July 2001 / Revised version: 11 October 2001 / Published online: 29 November 2001 相似文献
19.
M. Lorenc M. Ziolek R. Naskrecki J. Karolczak J. Kubicki A. Maciejewski 《Applied physics. B, Lasers and optics》2002,74(1):19-27
The paper discusses three different artifacts related to two-photon absorption (TPA), stimulated Raman amplification (SRA)
and cross-phase modulation (XPM), all intrinsic to transient absorption measurements with femtosecond time resolution. Certain
properties of these signals are analysed and shown to superimpose onto measured transient absorption spectra. Ways of reducing
the influence of the artifacts discussed are suggested. A simple correcting procedure based on the linear intensity dependence
of the artifacts discussed is proposed.
Received: 29 May 2001 / Final version: 15 October 2001 / Published online: 29 November 2001 相似文献
20.
B. Bakowski L. Corner G. Hancock R. Kotchie R. Peverall G.A.D. Ritchie 《Applied physics. B, Lasers and optics》2002,75(6-7):745-750
Cavity-enhanced absorption spectroscopy is explained in terms of the transmission function of a rapidly swept interferometer,
and the integrated transmission is shown to be proportional to the cavity ringdown time. The technique is demonstrated on
the b1Σg
+-X3Σg
- (1,0) band in molecular oxygen at 687 nm using a tunable diode laser and a relative-ly high-Q optical cavity (finesse ≈4000).
A detection limit of 3×10-8 cm-1 s1/2 is achieved for a 0.8 cm-1 scanning range.
Received: 24 June 2002 / Revised version: 5 August 2002 / Published online: 15 November 2002
RID="*"
ID="*"Corresponding author. Fax: +44-1865/275410, E-mail: peverall@physchem.ox.ac.uk 相似文献