共查询到20条相似文献,搜索用时 15 毫秒
1.
J. Delhay P. Desgroux E. Therssen H. Bladh P.-E. Bengtsson H. H?nen J. D. Black I. Vallet 《Applied physics. B, Lasers and optics》2009,95(4):825-838
Control and reduction of soot particle emissions from aeronautic turbines requires a monitoring system suitable for quantification
of these emissions. Currently, such emissions are estimated using the technique of smoke number. This is an extractive method,
which is not sensitive enough for the low emission levels of modern gas turbines. Within a recent European project, AEROTEST,
part of the project aimed at investigating an alternative soot monitoring technique, laser-induced incandescence (LII) as
an in-situ optical diagnostic for quantification of soot emissions. For aero-engine applications, especially those involving
large-scale turbines, it is necessary to perform the measurements at long distance from the turbine. The LII technique is
favourable in this respect as it provides for non-intrusive measurements and, by detecting the isotropic LII signal along
the same axis as the incoming laser beam (so called backward LII), both the laser and the detector can be built inside one
system located several meters from the turbine. The concept was initiated in the previous European projects, AEROJET I and
II. This paper describes the modified version of the system and the procedure developed to achieve reliable and quantitative
soot volume fraction measurements in the exhausts of aero-engines. Application of the backward LII technique is demonstrated
in the exhaust of a military turbojet engine for different engine speeds. 相似文献
2.
Y. Matsuo M. Kurata-Nishimura T. Kobayashi T. Kato Y. Okamura-Oho T. Sano Y. Hayashizaki J. Kawai 《Applied Physics A: Materials Science & Processing》2008,92(4):993-997
We have observed the motion of Sm+ ions as well as Sm atoms produced by femtosecond laser ablation of a solidified samarium solution sample on substrates by
using a planar laser-induced fluorescence method. Kinetic energies of both Sm+ ions and Sm atoms increase as the electrical conductivity of the substrate decreases, which suggests the effect of surface
charging. The kinetic energy of Sm+ ions is larger than that of Sm atoms for a variety of substrates due to the further electrical acceleration by the surface
charge. The knowledge of ion motion will be the key information for the optimization of femtosecond laser simultaneous atomization
and ionization of organic and inorganic samples on substrates. 相似文献
3.
The Lamb dip of CO rovibrational transition is detected by a room temperature extracavity RF optogalvanic cell and employed
to stabilize the frequency of a CO laser. The S/N ratio of optogalvanic signal is about 2000
at optical power < 1 W. The relative depth of Lamb dip is 2.3%. The S/N ratios of first and third harmonic demodulated saturation
signals are about 40
and 10
, respectively. The CO laser is stabilized using the first harmonic demodulated signal, and the frequency stability is better
than 300 kHz.
Concurrently, the influences of operational parameters, which include the coil current, partial pressures of gas mixture,
are investigated. A simple model for the influence of coil current is presented, and further improvements are addressed as
well. 相似文献
4.
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
5.
M. Galiová J. Kaiser K. Novotný J. Novotný T. Vaculovič M. Liška R. Malina K. Stejskal V. Adam R. Kizek 《Applied Physics A: Materials Science & Processing》2008,93(4):917-922
Single-pulse Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation Inductively Coupled Plasma Mass-Spectrometry (LA-ICP-MS)
were applied for mapping the silver and copper distribution in Helianthus Annuus L. samples treated with contaminant in controlled conditions. For Ag and Cu detection the 328.07 nm Ag(I) and 324.75 nm Cu(I)
lines were used, respectively. The LIBS experimental conditions (mainly the laser energy and the observation window) were
optimized in order to avoid self-absorption effect in the measured spectra. In the LA-ICP-MS analysis the Ag 107 and Cu 63
isotopes were detected. The capability of these two analytical techniques for high-resolution mapping of selected trace chemical
elements was demonstrated. 相似文献
6.
S. González-Pérez I. R. Martín F. Lahoz P. Haro-González J. Herreros 《Applied Physics A: Materials Science & Processing》2008,93(4):983-986
Local crystalline formation in erbium doped oxyfluoride glass has been obtained under a cw Argon laser irradiation up to 1.8
W pumping power. By exciting at 514 nm, the emission from 800 nm and 850 nm corresponding to the 4S3/2(2H11/2)→4I13/2 electronic transitions have been analyzed both inside and outside the irradiated area. The changes in the emission spectra
indicate that the high power Ar laser irradiation has resulted in a localized desvitrification process. The temperature dependence
of the fluorescence intensity ratio of the 800 nm and 850 nm emission bands has been used to determine the temperature of
the irradiated zone. Moreover, the average lifetime of the 4S3/2(2H11/2) thermalized levels have been measured as a function of the excitation spot position. An important decrease is observed at
the irradiated area. These results confirm that a localized cristalline phase has been created by the laser action. 相似文献
7.
Absorption of an acoustic wave in a colloidal solution via two mechanisms: due to viscous friction in the liquid and due to energy dissipation on nanoparticles is studied. The dependence of the imaginary part of the wave vector on the frequency is estimated in both cases. It is shown that in typical colloidal solutions, the first absorption mechanism dominates at low frequencies, and the second one, at higher, ultrasonic frequencies. 相似文献
8.
A numerical software has been developed to simulate heating, enthalpy-based phase changes and ablation of silicon during pulsed or continuous-wave laser irradiation. The unsteady heat transfer equation is solved by finite differences in two or three dimensions with full resolution of the thin liquid layer. An intelligent adaptive grid refinement and a semi-analytic treatment of the surface elements have been implemented to simulate laser cuts with lots of laser pulses in moderate computing time. The code has been successfully verified by comparisons with an analytic solution and with experimental data. Details of the mathematical model, the implementation in Matlab®and comparisons with experimental laser cuts are presented in this paper. 相似文献
9.
High-resolution infrared polarization spectroscopy (IR-PS) and degenerate four wave mixing (IR-DFWM) spectroscopy of methane
using a diode-seeded modeless laser (DSML) system are reported. Mid-infrared radiation around 3.3 μm is generated by difference
frequency mixing of the single-mode output of the DSML around 0.634 μm with the frequency-doubled output of a single-mode
Nd:YAG pump laser at 0.532 μm. Polarization spectroscopy signals in the forward geometry were generated in methane at around
5 Torr pressure. IR-PS spectra were recorded with a typical signal-to-noise ratio of 150:1 with methane pressures of at least
1 Torr. The line shape of the IR-PS signals was analysed to measure pressure broadening induced by nitrogen buffer gas yielding
a value of 6.3±1.5 MHz Torr−1. IR-DFWM spectra of methane were generated in the counter-propagating pump geometry yielding Doppler-free signals with signal-to-noise
ratios of typically 650:1. Signals were obtained at methane pressures down to less than 10 mTorr. A comparison of IR-PS and
IR-DFWM is made indicating that IR-DFWM has some advantages over IR-PS in this spectral region in terms of sensitivity, signal-to-noise
ratio and ease of use. The results illustrate the utility of the DSML for high-resolution nonlinear spectroscopy in the mid
infrared. 相似文献
10.
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
11.
We report on monitoring of nitric oxide (NO) traces in human breath via infrared cavity leak-out spectroscopy. Using a CO
sideband laser near 5 μm wavelength and an optical cavity with two high-reflectivity mirrors (R=99.98%), the minimum detectable absorption is 2×10−10 cm−1 Hz1/2. This allows for spectroscopic analysis of rare NO isotopologues with unprecedented sensitivity. Application to simultaneous
online detection of 14NO and 15NO in breath samples collected in the nasal cavity is described for the first time. We achieved a noise-equivalent detection
limit of 7 parts per trillion for nasal 15NO (integration time: 70 s). 相似文献
12.
N. Sanner O. Utéza B. Bussiere G. Coustillier A. Leray T. Itina M. Sentis 《Applied Physics A: Materials Science & Processing》2009,94(4):889-897
The paper is focused on the importance of accurate determination of surface damage/ablation threshold of a dielectric material
irradiated with femtosecond laser pulses. We show that different damage characterization techniques and data treatment procedures
from a single experiment provide complementary physical results characterizing laser–matter interaction. We thus compare and
discuss two regression techniques, well adapted to the measurement of laser ablation threshold, and a statistical approach
giving the laser damage threshold and further information concerning the deterministic character of femtosecond damage. These
two measurements are crucial for laser micromachining processes and high peak-power laser technology in general. 相似文献
13.
P. Dubé A. A. Madej J. E. Bernard L. Marmet A. D. Shiner 《Applied physics. B, Lasers and optics》2009,95(1):43-54
In this paper, we describe in detail a narrow linewidth and frequency-stable laser source used to probe the 5s
2
S
1/2–4d
2
D
5/2 clock transition of the 88Sr+ optical frequency standard. The performance of the laser system is investigated with studies of its frequency drift rates
and with high resolution spectra of the 88Sr+ clock transition. The observed short-term drift rates are typically in the range of 10 to 23 mHz/s, and the current long-term
drift rate is 13.9(3) mHz/s. The laser stability, after subtraction of linear drifts, reaches 5×10−16 at an averaging time of 3000 s. This high level of stability is attributed for the most part to stabilization of the reference
cavity at the temperature where the coefficient of linear thermal expansion crosses zero. An upper bound for the laser linewidth
is given by the observation of a Fourier-transform limited resonance of 4.3 Hz (Δν/ν=1×10−14) on the 88Sr+ clock transition. The effective averaging time during the linewidth measurements was about 100 s. 相似文献
14.
P. Haro-González I. R. Martin F. Lahoz S. González-Pérez N. E. Capuj D. Jaque 《Applied Physics A: Materials Science & Processing》2008,93(4):977-981
Localized desvitrifiation in strontium barium niobate glass doped with Er3+ under laser irradiation has been carried out. The samples of this study have been fabricated by the melt quenching method
and doped with 5% mol of Er3+. A 1.5-W cw Ar laser was focused on the sample to obtain desvitrifiation of the glass. Evidence of the changes induced by
the Ar laser has been observed through the analysis of the photoluminescence of the Er3+ ions. The transitions corresponding to 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 have been studied to analyze structure changes. Microluminescence measurements have been carried out to spatially select
positions inside and outside the irradiated area. We have observed changes in the emission bands corresponding to these transitions.
The emission bands from Er3+ ions in the irradiated zone show a resolved structure while they are broadened outside that area. These changes in the optical
properties of the Er3+ ions indicate that the Ar-laser irradiation has produced a change in the local structure of the material. These results show
that a localized desvitrifiation has been produced after the laser action and the transition from glass to glass ceramic has
been completed. 相似文献
15.
N. Petra J. Zweck A. A. Kosterev S. E. Minkoff D. Thomazy 《Applied physics. B, Lasers and optics》2009,94(4):673-680
Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors are based on a recent approach to photoacoustic detection which
employs a quartz tuning fork as an acoustic transducer. These sensors enable detection of trace gases for air quality monitoring,
industrial process control, and medical diagnostics. To detect a trace gas, modulated laser radiation is directed between
the tines of a tuning fork. The optical energy absorbed by the gas results in a periodic thermal expansion which gives rise
to a weak acoustic pressure wave. This pressure wave excites a resonant vibration of the tuning fork thereby generating an
electrical signal via the piezoelectric effect. This paper describes a theoretical model of a QEPAS sensor. By deriving analytical
solutions for the partial differential equations in the model, we obtain a formula for the piezoelectric current in terms
of the optical, mechanical, and electrical parameters of the system. We use the model to calculate the optimal position of
the laser beam with respect to the tuning fork and the phase of the piezoelectric current. We also show that a QEPAS transducer
with a particular 32.8 kHz tuning fork is 2–3 times as sensitive as one with a 4.25 kHz tuning fork. These simulation results
closely match experimental data. 相似文献
16.
Rok Petkovšek Aleš Babnik Janez Diaci Janez Možina 《Applied Physics A: Materials Science & Processing》2008,93(1):141-145
We present a new method for monitoring of the laser micro-drilling process. The method is based on detection of acoustic waves
in air above the processed sample using a laser beam deflection probe (LBDP). We present an augmentation of the experimental
set-up by means of a digital micrographic system which enables the acquisition of images of the plasma plume and of the hole
cross-section during a drilling sequence. Comparing the acquired images with the detected LBDP signals, we examine the drilling
process from a new perspective. 相似文献
17.
A. H. Bhuiyan D. R. Richardson S. V. Naik R. P. Lucht 《Applied physics. B, Lasers and optics》2009,94(4):559-567
An injection-seeded optical parametric generator (OPG), coupled with three pulsed dye amplification (PDA) stages, was shown
to produce tunable, narrow linewidth laser radiation. The OPG was composed of a pair of beta barium borate (β-BBO) crystals and pumped by the third harmonic (355 nm) output of a seeded Nd:YAG laser. The OPG was injection-seeded at
the idler wavelength (824 nm) using an external cavity diode laser (ECDL) with a mode-hop-free tuning range of 20 GHz. Using
the PDA stages, the OPG output signal (624 nm) was amplified to 19 mJ/pulse, while maintaining a spectral linewidth of approximately
160 MHz at full-width-half-maximum (FWHM) which was within a factor of 2 of the Fourier limit. A system of lenses and apertures
was used to minimize amplified spontaneous emission (ASE) in the PDA stages. Using the OPG/PDA system, two-photon laser-induced
fluorescence measurements of atomic oxygen were performed by sum-frequency-mixing the 624-nm beam with the third harmonic
output of the seeded Nd:YAG laser to generate approximately 1 mJ/pulse of ultraviolet radiation near 226 nm. Voigt line shapes
were found to be in good agreement with oxygen atom spectra in atmospheric-pressure, laminar, counter-flow flames; the magnitude
of Doppler and collisional broadening was approximately the same. The measured O-atom concentration profile was found to compare
well with that calculated using an opposed-flow flame code. 相似文献
18.
Atsushi Yamaguchi Yoichiroh Hosokawa Guillaume Louit Tsuyoshi Asahi Chisa Shukunami Yuji Hiraki Hiroshi Masuhara 《Applied Physics A: Materials Science & Processing》2008,93(1):39-43
An impulsive force, which was generated by focusing tightly a femtosecond laser into a cell culture medium, was applied to
inject nanoparticles into local areas of a single mouse fibroblast NIH3T3 cell. When the impulsive force was induced near
the cell, the nanoparticles adhering on the cell membrane were introduced, which was directly confirmed by confocal fluorescence
microscopy. 相似文献
19.
E. E. Eyler D. E. Chieda M. C. Stowe M. J. Thorpe T. R. Schibli J. Ye 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):43-55
We analyze several possibilities for precisely measuring electronic transitions in
atomic helium by the direct use of phase-stabilized femtosecond frequency combs. Because the comb
is self-calibrating and can be shifted into the ultraviolet spectral region via harmonic
generation, it offers the prospect of greatly improved accuracy for UV and far-UV transitions. To
take advantage of this accuracy an ultracold helium sample is needed. For measurements of the
triplet spectrum a magneto-optical trap (MOT) can be used to cool and trap metastable 23S
state atoms. We analyze schemes for measuring the two-photon 23S →43S interval, and for resonant two-photon excitation to high Rydberg states, 23S →33P →n3S, D. We also analyze experiments on the singlet-state spectrum. To accomplish this we propose schemes for producing and trapping
ultracold helium in the 11S or 21S state via intercombination transitions. A particularly intriguing scenario is the possibility of measuring the 11S →21S transition with extremely high accuracy by use of two-photon excitation in a magic wavelength trap that operates identically
for both states. We predict a “triple magic wavelength” at 412 nm that could facilitate numerous experiments on trapped helium
atoms, because here the polarizabilities of the 11S, 21S and 23S states are all similar, small, and positive. 相似文献
20.
Y.-G. Han 《Applied physics. B, Lasers and optics》2009,95(2):383-387
We propose a novel and simple scheme for a temperature-insensitive strain measurement by using a birefringent interferometer
configured by a polarization-maintaining photonic crystal fiber (PM-PCF). The wavelength-dependent periodic transmission in
a birefringent interferometer can be achieved by using a PM-PCF between two linear polarizers. Since the PM-PCF is composed
of a single material, such as silica, the peak wavelength shift with temperature variation can be negligible because of the
small amount of the birefringence change of the PM-PCF with temperature change. The measured temperature sensitivity is −0.3 pm/°C.
However, the peak wavelength can be changed by strain because the peak wavelength shift is directly proportion to strain change.
The strain sensitivity is measured to be 1.3 pm/με in a strain range from 0 to 1600 με. The measurement resolution of the
strain is estimated to be 2.1 με. The proposed scheme has advantages of simple structure and low loss without a Sagnac loop,
temperature insensitivity, ease installation, and short length of a sensing probe compared with a conventional PMF-based Sagnac
loop interferometer. 相似文献