共查询到20条相似文献,搜索用时 0 毫秒
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J. M. Headrick F. Goulay P. E. Schrader H. A. Michelsen 《Applied physics. B, Lasers and optics》2011,104(2):439-450
We have measured time-resolved laser-induced incandescence of flame-generated soot under high-vacuum conditions (4.1×10−6 mbar) at an excitation wavelength of 532 nm with laser fluences spanning 0.06–0.5 J/cm2. We generated soot in an ethylene/air diffusion flame, introduced it into the vacuum system with an aerodynamic lens, heated
it using a pulsed laser with a spatially homogeneous and temporally smooth laser profile, and recorded LII temporal profiles
at 685 nm. At low laser fluences LII signal decay rates are slow, and LII signals persist beyond the residence time of the
soot particles in the detection region. At these fluences, the temporal maximum of the LII signal increases nearly linearly
with increasing laser fluence until reaching a plateau at ∼0.18 J/cm2. At higher fluences, the LII signal maximum is independent of laser fluence within experimental uncertainty. At these fluences,
the LII signal decays rapidly during the laser pulse. The fluence dependence of the vacuum LII signal is qualitatively similar
to that observed under similar laser conditions in an atmospheric flame but requires higher fluences (by ∼0.03 J/cm2) for initiation. These data demonstrate the feasibility of recording vacuum LII temporal profiles of flame-generated soot
under well-characterized conditions for model validation. 相似文献
3.
H. Kleine 《The European physical journal. Special topics》2010,182(1):3-34
Essentially all processes in gasdynamics are invisible to the naked eye as they occur in a transparent medium. The task to
observe them is further complicated by the fact that most of these processes are also transient, often with characteristic
times that are considerably below the threshold of human perception. Both difficulties can be overcome by combining visualization
methods that reveal changes in the transparent medium, and high-speed photography techniques that “stop” the motion of the
flow. The traditional approach is to reconstruct a transient process from a series of single images, each taken in a different
experiment at a different instant. This approach, which is still widely used today, can only be expected to give reliable
results when the process is reproducible. Truly time-resolved visualization, which yields a sequence of flow images in a single
experiment, has been attempted for more than a century, but many of the developed camera systems were characterized by a high
level of complexity and limited quality of the results. Recent advances in digital high-speed photography have changed this
situation and have provided the tools to investigate, with relative ease and in sufficient detail, the true development of
a transient flow with characteristic time scales down to one microsecond. This paper discusses the potential and the limitations
one encounters when using density-sensitive visualization techniques in time-resolved mode. Several examples illustrate how
this approach can reveal and explain a number of previously undetected phenomena in a variety of highly transient compressible
flows. It is demonstrated that time-resolved visualization offers numerous advantages which normally outweigh its shortcomings,
mainly the often-encountered loss in resolution. Apart from the capability to track the location and/or shape of flow features
in space and time, adequate time-resolved visualization allows one to observe the development of deliberately introduced near-isentropic
perturbation wavelets. This new diagnostic tool can be used to qualitatively and quantitatively determine otherwise inaccessible
thermodynamic properties of a compressible flow. 相似文献
4.
Harald O. Jeschke Momar S. Diakhate Martin E. Garcia 《Applied Physics A: Materials Science & Processing》2009,96(1):33-42
A theoretical approach to treat laser induced femtosecond structural changes in covalently bonded nanostructures and solids
is described. Our approach consists in molecular dynamic simulations performed on the basis of time-dependent, many-body potential
energy surfaces derived from tight-binding Hamiltonians. The shape and spectral composition of the laser pulse is explicitly
taking into account in a non-perturbative way. We show a few examples of the application of this approach to describe the
laser damage and healing of defects in carbon nanotubes with different chiralities and the ultrafast nonequilibrium melting
of bulk germanium, initiated by the laser-induced softening and destabilization of transversal acoustic phonon modes. 相似文献
5.
In previous studies, acetone has been successfully applied as a tracer for planar laser-induced fluorescence (PLIF) measurements
of concentration and temperature. The desire to extend acetone PLIF capability to conditions of varying pressure and composition
has motivated studies of the effects of these quantities on fluorescence yield. The present work explores pressure and composition
effects over a 0.5 to 16 atm range for the three excitation wavelengths of greatest interest for diagnostics: 248, 266, and
308 nm. In accord with previous studies, fluorescence per acetone molecule is seen to increase with pressure, apparently towards
a high-pressure limit for each wavelength, with the most significant effect observed at short wavelengths. Bath gas composition
is also seen to affect fluorescence intensity, with an impact related to the effectiveness of the bath gas species at vibrationally
relaxing excited acetone. A model of fluorescence yield considering the relative rates of intersystem crossing and vibrational
relaxation for excited singlet acetone describes the measured pressure and composition dependences well. To explain an oxygen
fluorescence quenching effect that is observed experimentally, a term is added to the model to represent oxygen-assisted intersystem
crossing. The data and model results provide useful guidance for diagnostic applications. A key conclusion is that long excitation
wavelengths are preferable from the standpoint of minimizing pressure and composition dependences.
Received: 17 December 1998 / Revised version: 21 May 1999 / Published online: 30 July 1999 相似文献
6.
E. Angelini S. Grassini D. Mombello A. Neri M. Parvis 《Applied Physics A: Materials Science & Processing》2010,100(3):919-925
An easy-to-use and cheap diagnostic tool based on digital photography and 2D-FFT imaging processing is described that can be used to monitor the corrosion process occurring over time on the surface of metallic works of art in indoor and outdoor environments and to assess the stability of the materials employed for restoration. The proposed solution has the advantage of not requiring standard lighting and artifacts manipulation, that are not easily achievable in real applications. The imaging algorithm is capable of highlighting the changes in the surface uniformity due to the corrosion process and can be used to put in evidence the beginning of dangerous localized corrosion phenomena onto the metallic surface. Although this technique does not allow a quantitative measurement of the corrosion rate, it has proved to be an effective approach to assess the stability of protective coatings. The proposed processing has been tested in laboratory to asses the stability of SiO2—like protective coatings deposited by PECVD on a set of silver reference alloys submitted to a tarnishing test in the presence of H2S vapors. 相似文献
7.
V. Dinca A. Palla-Papavlu M. Dinescu J. Shaw?Stewart T. K. Lippert F. Di Pietrantonio D. Cannata M. Benetti E. Verona 《Applied Physics A: Materials Science & Processing》2010,101(3):559-565
This paper presents polymer pixel printing for applications in chemoselective sensors where nanosecond laser direct transfer methods, with a triazene polymer (TP) acting as a Dynamic Release Layer (DRL), are used. A systematic study of laser fluence, donor film morphology and both single- and multiple-pixel deposition were optimized with the final goal to obtain continuous pixels of sensitive polymers, polyethylenimine (PEI) and polyisobutylene (PIB), on SAW surfaces. Morphology characterization after the laser transfer has been performed by Optical Microscopy and Scanning Electron Microscopy (SEM). The responses of the coated transducers were measured after deposition with different laser fluences and it was found that a fluence under 625 mJ/cm2 was required in order to prevent damage of the interdigital transducers (IDT) of the sensor devices. The sensitivity of the polymer coated devices to acetone concentrations gives an indication that LIFT can be used for printing sensitive polymer pixels onto transducer devices. 相似文献
8.
In this paper, a 100?Hz planar laser-induced fluorescence system based on the off-shelf commercial laser and self-made intensified camera is presented, which is low cost and maintainable to be applied in practical combustion research. By using this device, 100?Hz continuously planar laser-induces fluorescence laser combustion diagnostics was conducted. To evaluate this device, both laboratorial combustors and a scramjet combustor were studied. In these experiments, the structure of flame and expansion and the oscillation process of combustion can be resolved. 相似文献
9.
Makoto Yamaguchi Shigeru Ueno Ryota Kumai Keita Kinoshita Toshiaki Murai Takuro Tomita Shigeki Matsuo Shuichi Hashimoto 《Applied Physics A: Materials Science & Processing》2010,99(1):23-27
Raman spectroscopy was performed to investigate microscopic structural changes associated with a ripple structure formation initiated by femtosecond laser irradiation on the surface of single-crystal silicon carbide. The amorphous phases of silicon carbide, silicon, and carbon were observed. The intensity ratio between amorphous silicon carbide and silicon changed discretely at the boundary between fine and coarse ripples. The physical processes responsible for the formation of the ripple structure are discussed. 相似文献
10.
S. Du L. Jiang W. Zhang W. Gong Z. Fu Z. Dai 《Applied physics. B, Lasers and optics》2011,103(4):857-861
A novel sensitivity of laser-induced upconversion (UC) fluorescence dynamics to the exciting wavelength in Er3+:YAG crystal has been observed. The sensitivities to exciting wavelength variations are only 0.02 and 0.06 nm for 2 G 9/2 and 2 P 3/2 UC luminescence, respectively. The observation of this sensitivity reveals that when a certain level is populated by more than one UC mechanisms, a precise determination of suitable exciting wavelength is crucial because the competition between different UC mechanisms has a sensitive variation with exciting wavelength in near-resonant range. 相似文献
11.
The laser-induced fluorescence excitation spectrum of the A2Σ-X2Π3/2 transition of CuO in the 540-620nm region has been studied, where the CuO molecule was produced by using the technique of dc discharge reaction under a supersonic condition. We have recorded and rotationally analysed the 0-0, 1-0, 2-0 and 3-0 bands. The rotational constants of the upper state A2Σ- were determined and vibrational constants improved. In addition, the lifetime measurement for the A2Σ- state was carried out under the collision-free condition, and the lifetimes obtained are 469±2, 456±2, 488±3 and 490±4ns for v'=0, v'=1, v'=2 and v'=3 levels, respectively. 相似文献
12.
R. Hannachi S. Boussaïdi P. Teulet G. Taieb Y. Cressault A. Gleizes Zohra Ben Lakhdar 《Applied Physics A: Materials Science & Processing》2008,92(4):933-937
A spectroscopic study of the plasma plume created by a laser beam on the surface of NaCl aqueous solution is presented. Optical
emission spectra are recorded and temporally analyzed; electron number density is determined from the Stark broadening of
the NI nitrogen line, and temperature is obtained from relative intensity of OI oxygen lines. The intensity of an atomic line
from sodium was used to quantitate its molar percentage in the Oceanic and Mediterranean sea, and calibration curves have
been constructed for concentrations ranging up to 1.5%. 相似文献
13.
Shaohua Zhang 《Journal of Molecular Spectroscopy》2008,252(1):77-80
The laser-induced fluorescence excitation spectra of jet-cooled CuS molecules have been recorded in the energy range of 17 200-19 500 cm−1. Fourteen observed vibronic bands have been assigned as three transition progressions: A2Σ− (v′ = 0-4)-X2Π3/2 (v″ = 0), A2Σ− (v′ = 0-4)-X2Π3/2 (v″ = 1), and A2Σ− (v′ = 0-3)-X2Π1/2 (v″ = 0). Spectroscopic constants of both the X2Π ground state and the A2Σ− excited state of 63CuS and 65CuS were determined by analyzing their rotationally resolved spectra. Furthermore, the lifetimes of most observed bands were measured for the first time. 相似文献
14.
Yasuyo Maezawa Yoichiroh Hosokawa Kazunori Okano Mie Matsubara Hiroshi Masuhara 《Applied Physics A: Materials Science & Processing》2010,101(1):127-131
When a stress wave generated by focusing a femtosecond laser is loaded on an animal cell adhered on a substrate, the cell
is detached from the substrate. There are two possible mechanisms for the cell detachment: (a) The cell is detached from a
scaffold coated on a glass plate, and (b) the cell is detached from the glass plate with the scaffold. In this work, we have
studied the cell-detachment mechanism by visualizing the scaffold with a fluorescence probe of quantum dots. When the cell
was detached from the substrate, fluorescence from the scaffold simultaneously disappeared from the glass plate, although
the scaffold was not irradiated by the laser. This indicates that detachment due to the stress wave is attributed to mechanism (a).
On the other hand, when the cell was detached from the substrate by a trypsin treatment, the fluorescence from the scaffold
remained, suggesting mechanism (b). By comparing both results, it is considered that physiological damage of the cell membrane
during the detachment process by femtosecond laser-induced stress wave is less than that due to the trypsin treatment. 相似文献
15.
M. Miyabe M. Oba H. Iimura K. Akaoka Y. Maruyama I. Wakaida 《Applied Physics A: Materials Science & Processing》2010,101(1):65-70
A cerium oxide sample was ablated by 2nd harmonic radiation of Nd:YAG laser at a power density of 0.1 GW/cm2. Time evolution of the ablation plume was investigated by laser absorption time-of-flight (TOF) measurement. It was found
that the ablated ionic plume in vacuum consisted of two components having different velocities whereas the ablated neutral
atoms had mainly a single component. The flow velocity perpendicular to the sample surface in vacuum was determined to be
3.5 km/s for neutral atoms, and 4.7 km/s and 9.3 km/s for singly charged ions. From the detailed plume evolution in ambient
atmosphere with several pressures we obtained some experimental conditions suitable for isotope analysis of atomic cerium. 相似文献
16.
M. B. Agranat S. I. Ashitkov S. I. Anisimov A. V. Ovchinnikov A. B. Shvartsburg D. S. Sitnikov V. E. Fortov 《Applied Physics A: Materials Science & Processing》2009,94(4):879-887
The experimental study of absorption in silicon in infrared and visible spectral ranges, where the photon energy is less or
more than the bandgap width, is performed by means of the ultrafast interferometry technique. The exactly solvable model in
the electromagnetic of heterogeneous lossy plasma layer was developed. The density of carriers, their frequency of collisions,
absorbing depth of the probing waves, real and imaginary parts of dielectric function of nonuniform layer and their spatial
gradients are determined from the reflectance data by means of this model subject to the pump fluence. The heterogeneity-induced
effects are visualized due to comparison of obtained plasma parameters with those calculated in the framework of homogeneous
plasma model It is shown that in the intensity range near thresholds of melting and ablation the absorption, occurring in
both cases mainly within a thin (∼10 nm) absorbing layer (similarly to metals), is due to free carrier intraband absorption. 相似文献
17.
The objective of this paper is to present a model for predicting clustering of aerosol particles in uniformly sheared turbulent flows laden with small heavy particles. The background of the model for predicting clustering is based on a kinetic equation for the two-point probability density function of the relative velocity distribution of two particles. The effect of clustering of particles in homogeneous turbulent shear flows is demonstrated and compared with known results of direct numerical simulations. It is shown that the universality of the clustering process can take place if the characteristic cluster size is smaller than the shear scale. 相似文献
18.
The decay of OH concentration following photolysis of room-temperature vapor-phase hydrogen peroxide is studied as a function
of photolysis fluence at 266 nm in an open air environment. The rate of decay is found to increase with increasing photolysis
fluence, i.e., with increasing number of photodissociated H2O2(g) molecules. Single-exponential functions approximate the OH concentration decay rather well, even for higher photolysis
levels, and the decay time is shown to be inversely proportional to the H2O2(g) concentration. For fluences of about 450 mJ/cm2 the difference between a single-exponential decay and measured data is becoming evident after approximately 150 μs. Calculations
based on a chemical kinetics model agree well with experimental data also for times >150 μs. By combining the model with measurements,
the actual photolysis levels used in experiments are estimated. The best fit between measured data and the model suggests
that about 1.1% of the H2O2(g) molecules are dissociated with a photolysis fluence of ∼450 mJ/cm2, in reasonable agreement with a Beer–Lambert based estimation. Excitation scans did not unfold any differences between OH
spectra recorded at different photolysis fluences. 相似文献
19.
Tadatake Sato Ryozo Kurosaki Aiko Narazaki Yoshizo Kawaguchi Hiroyuki Niino 《Applied Physics A: Materials Science & Processing》2010,101(2):319-323
The well-controlled fabrication of microtrenches including inclined features using normal incidence with gradual shifting
of the irradiated area was demonstrated. Based on the variation of trench width depending on the laser fluence, the existence
of gaps between the edge of the irradiated area and sidewall of the trench was shown. Because of these gaps, the shifted laser
pulse can stay at the bottom of the trenches in the fabrication of the inclined features. In laser-induced backside wet etching
(LIBWE), the photo-activated region generated within organic solution would act on the glass surface and results in etching.
It was indicated that the photo-activated region generated at the bottom of the trenches acted not only on the bottom of the
trench but also on the sidewalls. Based on such etching of the sidewall, fabrication of inclined features becomes possible.
In this method, the tilting angle can be changed within one deep trench. Flexible structure formation deep inside the silica
glass can be achieved. 相似文献
20.
Mohamed Nazih Rhimi Riadh El-Bahi 《International Journal of Theoretical Physics》2008,47(4):1095-1111
The Landau problem of a charged particle in a plane with a uniform perpendicular magnetic field is analysed in two oscillator
modes. The coherent states for the problem have been found out using a general definition of displaced states. The time evolution
and the associated nonadiabatic geometric phase for both initially displaced and non-displaced wave packets have been studied.
The path integral is derived in a simple way through the calculation of Gaussian integrals via the concept of coherent state
wavefunctions. 相似文献