Measuring non-radiative relaxation time of fluorophores by intensity-modulated laser induced photoacoustic effect

2013 ◽  
Author(s):  
Behrouz Soroushian ◽  
Xinmai Yang
2017 ◽  
Vol 74 (5) ◽  
pp. 1533-1547 ◽  
Author(s):  
William J. M. Seviour ◽  
Darryn W. Waugh ◽  
Richard K. Scott

Abstract The Martian polar atmosphere is known to have a persistent local minimum in potential vorticity (PV) near the winter pole, with a region of high PV encircling it. This finding is surprising, since an isolated band of PV is barotropically unstable, a result going back to Rayleigh. Here the stability of a Mars-like annular vortex is investigated using numerical integrations of the rotating shallow-water equations. The mode of instability and its growth rate is shown to depend upon the latitude and width of the annulus. By introducing thermal relaxation toward an annular equilibrium profile with a time scale similar to that of the instability, a persistent annular vortex with similar characteristics as that observed in the Martian atmosphere can be simulated. This time scale, typically 0.5–2 sols, is similar to radiative relaxation time scales for Mars’s polar atmosphere. The persistence of an annular vortex is also shown to be robust to topographic forcing, as long as it is below a certain amplitude. It is therefore proposed that the persistence of this barotropically unstable annular vortex is permitted owing to the combination of short radiative relaxation time scales and relatively weak topographic forcing in the Martian polar atmosphere.


2016 ◽  
Vol 18 (7) ◽  
pp. 5219-5231 ◽  
Author(s):  
Mohamed El-Amine Madjet ◽  
Alexey V. Akimov ◽  
Fadwa El-Mellouhi ◽  
Golibjon R. Berdiyorov ◽  
Sahel Ashhab ◽  
...  

Non-adiabatic molecular dynamics simulations of non-radiative relaxation dynamics of charge carriers in hybrid perovskites show that the carrier relaxation time can be considerably increased by halide mixing.


2008 ◽  
Vol 6 (1) ◽  
pp. 71-76
Author(s):  
Mihailo Rabasovic ◽  
Dragan Markushev

Measuring the vibrational-to-translational relaxation time ?V-T in gases is one of the first applications of the photoacoustic effect. The spatial profile of the laser beam is crucial in these measurements because the multiphoton excitation is investigated. The multiphoton absorption is a non-linear process. Because of this, the top hat profile is preferable. It allows one to deal with nonlinearity in a simple manner. In order to reveal the real laser beam profile, we have slightly changed the theoretical profiles in such a manner that the best matching is obtained between theoretical and experimental photoacoustic signals. Still, there was a question: Is it possible to deduce the laser beam profile directly from the photoacoustic signal, thus avoiding manual changing of the laser beam profile? According to this paper, it is possible. The appropriate method has been found in another photoacoustics application: photoacoustic tomography. Thus, the method for the simultaneous determination of the spatial profile of the laser beam and vibrational-to-translational relaxation time is presented in this paper. It employs pulsed photoacoustics and an algorithm developed for photoacoustic tomography.


2009 ◽  
Vol 75 (4) ◽  
pp. 517-528
Author(s):  
K. A. P. SINGH ◽  
B. N. DWIVEDI

AbstractWe study the propagation and damping of small-amplitude prominence oscillations invoking steady flow and radiative losses due to Newton's cooling with constant relaxation time. We find that the strength of steady flow has a large influence on the propagation (e.g. period, phase velocity) of wave modes. In the presence of steady flow, the thermal mode is a propagating wave and hence it can be observed in solar prominences. The thermal mode contributes to the non-thermal line broadening in the solar atmosphere. The steady flow does not affect the damping time of the wave modes. The damping of slow and thermal modes is highly dependent on the radiative relaxation time. The thermal perturbation, in the presence of steady flow, is found to be larger in the case of the thermal mode than in the slow and fast modes. The energy flux (~300 W m−2) associated with the thermal mode is sufficient to heat the quiet regions of the Sun. The slow mode contribution to non-thermal broadening has been estimated. The non-thermal broadening is found to be large in the case of the prominence with large characteristic length. The steady flow, in the presence of Newton's cooling, breaks the symmetry between the forward and backward propagating modes. No modes with negative energy have been found. For strong flows (above 10 km s−1), the canonical backward wave propagates in the forward direction, which can play an important role in wave detection and prominence seismology.


2020 ◽  
Vol 99 (3) ◽  
pp. 73-79
Author(s):  
A.P. Sarode ◽  
◽  
O.H. Mahajan ◽  

In photoacoustic effect, the solid sample absorbs a fraction of the radiation falling upon it and excitation process occurs. The type of excitation depends on the energy of the incident radiation. The relaxation processes, which are also popularly known as non-radiative de-excitation processes generally take place. The light – matter interaction is responsible for the generation of heat within the solid sample. The temperature of the sample changes due to absorption and non-radiative relaxation by the atoms. The pressure fluctuations will be generated due to the heating and cooling of the sample. Today, crystalline solids are widely studied due to their wide scientific and industrial applications. Temperature is one of the important parameter to be studied regarding artificial preparation of large crystals. In this paper, transient translational temperature on the surface of a homogeneous isotropic cubic crystal kept in a photoacoustic cell is calculated theoretically. For a simple cubic homogeneous crystal kept in a photoacoustic cell, an airy stress function is determined based on laser interaction with surface of the crystal. By applying the finite Marchi-Fasulo integral transform method within the crystal size limitations, transient translational temperature is exactly determined.


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