Absorption,quenching,and enhancement by tracer in acetone/toluene laser-induced fluorescence

To measure the equivalent ratio distribution of the two-stage lean premixed(DLP)flame,we propose using acetone/toluene planar laser-induced fluorescence(PLIF)technology to simultaneously measure the concentrations of the two components.Appropriate excitation laser wavelength and filters are used to assess the influence of acetone and toluene on each other’s fluorescence signal at room temperature.Experimental results show that acetone has a strong absorption effect on toluene’s fluorescence signal,the effective absorption cross-section is 5.77×10-20 cm-2.Acetone has an obvious quenching effect on the toluene fluorescence signal,and the Stern–Volmer coefficient is 0.50 kPa-1.The collisions between the molecules of toluene and acetone will lead to the enhancement of the fluorescence signal of acetone,and the enhancement coefficient is exponential with the acetone’s concentration.The quantitative relationship between the fluorescence intensity and the concentrations of the two tracers is obtained by establishing the photophysical model of toluene and acetone’s fluorescence signals.

Flame features and oscillation characteristics in near-blowout swirl-stabilized flames using high-speed OH-PLIF and mode decomposition methods

Flame features and dynamics are important to the explanation and prediction of a lean blowout(LBO)phenomenon.In this paper,recognition of near-LBO flame features and oscillation characterization methods were proposed based on flame spectroscopic images.High-speed planar laser-induced fluorescence measurements of OH were used to capture unique dynamic features such as the local extinction and reignition feature and entrained reactant pockets.The Zernike moment demonstrated a good performance in recognition of stability and near-LBO conditions,though the geometric moment had more advantages to characterize frequency characteristics.Low-frequency oscillations,especially at the obvious self-excited oscillation frequency around 200 Hz,were found when approaching an LBO condition,which can be expected to be used as a novel prediction characteristic parameter of the flameout limit.Proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD)were used to conduct dynamic analysis of near-LBO flames.POD modes spectra showed the unique frequency characteristics of stable and near-LBO flames,which were basically in line with those at the heat-release frequency.The primary POD modes demonstrated that the radial vibration mode dominated in a stable flame,while the rotation mode was found to exist in a near-LBO flame.Analysis of modal decomposition showed that flame shedding and agminated entrained reactant pockets were responsible for generating self-excited flame oscillations.

Atomic structures and carrier dynamics of defects in a ZnGeP_(2) crystal

ZnGeP_(2)[ZGP] crystals have attracted tremendous attention for their applications as frequency conversion devices.Nevertheless,the existence of native point defects,including at the surface and in the bulk,lowers their laser-induced damage threshold by increasing their absorption and forming starting points of the damage,limiting their applications.Here,native point defects in a ZGP crystal are fully studied by the combination of high angle annular dark-field scanning transmission electron microscopy[HAADF-STEM] and optical measurements.The atomic structures of the native point defects of the Zn vacancy,P vacancy,and Ge-Zn antisite were directly obtained through an HAADF-STEM,and proved by photoluminescence[PL] spectra at 77 K.The carrier dynamics of these defects are further studied by ultrafast pump-probe spectroscopy,and the decay lifetimes of 180.49,346.73,and 322.82 ps are attributed to the donor V_(p)^(+)→valence band maximum[VBM] recombination,donor Ge^(+)_(Zn)→VBM recombination,and donor–acceptor pair recombination of V_(p)^(+)→V^(-)_(Zn),respectively,which further confirms the assignment of the electron transitions.The diagrams for the energy bands and excited electron dynamics are established based on these ultrahigh spatial and temporal results.Our work is helpful for understanding the interaction mechanism between a ZGP crystal and ultrafast laser,doing good to the ZGP crystal growth and device fabrication.