CW laser-induced fluorescence of toluene for time-resolved imaging of gaseous flows

A laser-induced fluorescence diagnostic is presented for high-speed measurements in gaseous flows. The technique employs a toluene tracer excited at 266 nm by a cavity-doubled 532 nm diode-pumped 5.5 W CW laser. The high power (600 mW) of UV light produced by cavity doubling, together with the high fluorescence yield of toluene, yields strong signal levels needed for high-speed recording. Fluctuation detection limits for tracer mole fraction were investigated by applying the diagnostic to an atmospheric temperature and pressure nitrogen jet. For single-point measurements with a photomultiplier tube, the detection limit for fluctuations in the toluene mole fraction was 0.028%, achieved with 430 mW of laser power and 8.5 kHz bandwidth for a 1×0.4×0.4 mm collection volume. Line (1-D) imaging with a kinetic-readout camera (512 pixels/row) achieved a detection limit of 0.23% with 440 mW of laser power, 9.7 kHz frame rate, and 0.3×0.2×0.4 mm collection volume per pixel, while planar (2-D) imaging with a 512×512 pixel intensified camera achieved a detection limit of 0.88% with 205 mW of laser power, 100 μs exposure time, and 0.4×0.4×0.4 mm volume per pixel. Line and planar imaging were applied to a turbulent jet with Re of about 10000.     

Continuous 100 Hz planar laser-induced fluorescence applied to the study of combustion processes

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.     

Flame turbulences recorded at 1 kHz using planar laser induced fluorescence upon hot band excitation of OH radicals

Laser-induced fluorescence (LIF) in flames is excited by a diode-pumped all-solid-state disk laser system which operates at a pulse repetition rate of 1 kHz and a tunable wavelength around 1030 nm. The laser fundamental is converted to 343 nm and used to excite into the hot band transition of OH radicals in H₂/O₂ diffusion flames of an industrial burner and in the premixed flame of a microburner. The OH radical emission around 308 nm is resolved spectrally and spatially using a light-sheet technique. Imaging of the planar LIF (PLIF) by a gated camera visualizes the turbulent flame behavior on the millisecond time scale without averaging. To our knowledge this is the first time that an all-solid-state laser providing at the same time a kHz repetition rate as well as pulse energies of up to 5.5 mJ is available for PLIF observation of OH radicals. PACS 33.50.-j; 42.55.Xi; 82.33.Vx     

Hydroxyl radical imaging at kHz rates using a frequency-quadrupled Nd:YLF laser

Laser-induced fluorescence imaging of hydroxyl radicals has been an important tool in combustion research for more than twenty years. More recently, high frame rate imaging of hydroxyl radicals has been demonstrated using Nd:YAG-pumped dye laser systems. This work describes how a high repetition rate frequency-quadrupled Nd:YLF laser emitting at 263 nm can be used for laser-induced fluorescence imaging of hydroxyl radicals with less complexity. Hydroxyl radicals are excited in the A–X (2,0) band and redshifted fluorescence emission is detected with an image intensified CMOS camera at kHz frame rates. Furthermore, a strategy for high-speed temperature imaging is described.     

Laser cutting of silicon with the liquid jet guided laser using a chlorine-containing jet media

In this paper results for liquid media are presented, which are used the first time as liquid jet for cutting of silicon with laser chemical processing (LCP). The liquids contain a perfluoro-carbon compound as solvent and elemental chlorine as etching agent for silicon. Experiments were performed to investigate its influence on groove form and maximum achieved groove depth. It is shown that with the addition of low-concentration chlorine, the groove depth can already be significantly increased. The groove shape could be changed from a V-profile to a U-profile. Furthermore, an about four times greater groove depth was achieved by applying a saturated chlorine solution compared to groove depths without using chlorine. Finally, a theory is given and discussed to describe the phenomena observed.     

Simultaneous flow field and fuel concentration imaging at 4.8 kHz in an operating engine

High-speed particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) techniques are combined to acquire flow field and fuel concentration in a spray-guided spark-ignited direct-injection (SG-SIDI) engine under motored and fired operation. This is a crucial step to enable studies that seek correlations between marginal engine operation (misfires or partial burns) and local, instantaneous mixture and flow conditions. Correlated flow and fuel data are extracted from a 4 mm×4 mm sub-region directly downstream the spark plug to characterize the in-cylinder conditions next to the spark plug during the spray and ignition event. Values of equivalence ratio, velocity magnitude, shear strain rate, and vorticity all increase during the spray event and decrease an order of magnitude during the duration of the spark event.     

Spectroscopic analysis of a laser-induced NaCl–water plasma. The influence of self-absorption

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%.     

On the Stability of a Quantum Dynamics of a Bose-Einstein Condensate Trapped in a One-Dimensional Toroidal Geometry

We rigorously analyze the stability of the “quasi-classical” dynamics of a Bose-Einstein condensate with repulsive and attractive interactions, trapped in an effective 1D toroidal geometry. The “classical” dynamics, which corresponds to the Gross-Pitaevskii mean field theory, is stable in the case of repulsive interaction, and unstable (under some conditions) in the case of attractive interaction. The corresponding quantum dynamics for observables is described by using a closed system of linear partial differential equations. In both cases of stable and unstable quasi-classical dynamics the quantum effects represent a singular perturbation to the quasi-classical solutions, and are described by the terms in these equations which consist of a small quasi-classical parameter which multiplies high-order “spatial” derivatives. We demonstrate that as a result of the quantum singularity for observables a convergence of quantum solutions to the corresponding classical solutions exists only for limited times, and estimate the characteristic time-scales of the convergence.     

Pressure and composition dependences of acetone laser-induced fluorescence with excitation at 248, 266, and 308 nm

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     

Quantum Dynamics of a Harmonic Oscillator in a Deformed Bath

The dissipative quantum dynamics of a harmonic oscillator in the presence of a deformed bath is investigated. The deformed bath is modelled by a collection of deformed quantum harmonic oscillators as a generalization of Hopfield model. The transition probabilities between energy levels of the oscillator are obtained perturbatively and discussed.     

Radiation Laws of a Kerr Nonlinear Blackbody in a Moving Frame of Reference

A Kerr nonlinear blackbody (KNB) is a new kind of blackbody in which bare photons with opposite wave vectors and helicities are bound into pairs and unpaired photons are transformed into nonpolaritons. In the present paper, the radiation of a KNB is considered from the viewpoint of an observer in arbitrary uniform motion with respect to a rest frame of reference of the radiation. It is found that the radiation laws, which include the distribution of nonpolaritons and so forth, are modified due to the motion. Moreover, under a special condition, we notice that the only effect of the motion is to introduce an angle-dependent directional temperature, which replaces the rest-frame temperature of the cavity. Besides, we try to extend the model of a KNB to the whole Universe and apply the modified radiation laws to the question of 2.7 K cosmic microwave background radiation (CMBR).     

Simultaneous 36 kHz PLIF/chemiluminescence imaging of fuel,CH2O and combustion in a PPC engine

The requirements on high efficiency and low emissions of internal combustion engines (ICEs) raise the research focus on advanced combustion concepts, e.g., premixed-charge compression ignition (PCCI), partially premixed compression ignition (PPCI), reactivity controlled compression ignition (RCCI), partially premixed combustion (PPC), gasoline compression ignition (GCI) etc. In the present study, an optically accessible engine is operated in PPC mode, featuring compression ignition of a diluted, stratified charge of gasoline-like fuel injected directly into the cylinder. A high-speed, high-power burst-mode laser system in combination with a high-speed CMOS camera is employed for diagnostics of the autoignition process which is critical for the combustion phasing and efficiency of the engine. To the authors’ best knowledge, this work demonstrates for the first time the application of the burst-system for simultaneous fuel tracer planar laser induced fluorescence (PLIF) and chemiluminescence imaging in an optical engine, at 36?kHz repetition rate. In addition, high-speed formaldehyde PLIF and chemiluminescence imaging are employed for investigation of autoignition events with a high temporal resolution (5 frames/CAD). The development of autoignition together with fuel or CH₂O distribution are simultaneously visualized using a large number of consecutive images. Prior to the onset of combustion the majority of both fuel and CH₂O are located in the recirculation zone, where the first autoignition also occurs. The ability to record, in excess of 100 PLIF images, in a single cycle brings unique possibilities to follow the in-cylinder processes without the averaging effects caused by cycle-to-cycle variations.     

Representation of Quantum States as Points in a Probability Simplex Associated to a SIC-POVM

The quantum state of a d-dimensional system can be represented by a probability distribution over the d ² outcomes of a Symmetric Informationally Complete Positive Operator Valued Measure (SIC-POVM), and then this probability distribution can be represented by a vector of \mathbb R^d2-1\mathbb {R}^{d^{2}-1} in a (d ²−1)-dimensional simplex, we will call this set of vectors Q\mathcal{Q}. Other way of represent a d-dimensional system is by the corresponding Bloch vector also in \mathbb R^d2-1\mathbb {R}^{d^{2}-1}, we will call this set of vectors B\mathcal{B}. In this paper it is proved that with the adequate scaling B=Q\mathcal{B}=\mathcal{Q}. Also we indicate some features of the shape of Q\mathcal{Q}.     

Propagation of general-type of phase-locked beam array in a turbulent atmosphere

The propagation of a general-type of phase-locked beam array in a turbulent atmosphere is studied, in which four practical issues, i.e., apertured, conformal, partially coherent, and flattened beam array is taken into consideration for accurate modeling of beam array in power beaming applications. The average intensity distribution in the receiving plane is deduced analytically based on extended Huygens–Fresnel principle. The influence of beam order, transverse coherence length, and truncation ratio is briefly discussed.     

On azimuthal anisotropy in fragmentation of a classical relativistic string

A fragmenting relativistic string is widely used for modeling particle production via quark–gluon strings formed in hadronic and nuclear inelastic interactions at high energies. In this note we focus on motion and fragmentation of a relativistic string with non-zero transverse separation of its ends and study this scenario as a possible mechanism for bringing anisotropy into the azimuthal angle distribution of produced particles in inelastic interactions of hadrons.     

Dark periods in the resonance fluorescence of a single Λ system

We use the quantum jump method to study the photon statistics of a single laser-driven atom in the configuration where both lower levels are strongly coupled to the common upper level. Under certain conditions we show that, for almost degenerate lower levels, light and dark periods occur which are similar to those of the well-known Dehmelt V system. Analytic results for their mean lengths and other statistical properties are given. For large separation of the lower levels we prove an interesting bunching property by the photons in the resonance fluorescence near the dark resonance. We propose a realistic system for which these effects may be observed.     

Analysis of generation of cumulative second harmonics of Lamb modes in a layered planar structure

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Inequivalent Quantization in the Field of a Ferromagnetic Wire

We argue that it is possible to bind neutral atom (NA) to the ferromagnetic wire (FW) by inequivalent quantization of the Hamiltonian. We follow the well known von Neumann’s method of self-adjoint extensions (SAE) to get this inequivalent quantization, which is characterized by a parameter Σ∈ℝ(mod2π). There exists a single bound state for the coupling constant η ²∈[0,1). Although this bound state should not occur due to the existence of classical scale symmetry in the problem. But since quantization procedure breaks this classical symmetry, bound state comes out as a scale in the problem leading to scaling anomaly. We also discuss the strong coupling region η ²<0, which supports bound state making the problem re-normalizable.