Minimal Absorption Coefficient Research Articles

A simulation approach for optimization of optical absorption in amorphous silicon solar cell

One of the major drawbacks of thin-film silicon solar cells is their limited optical absorptance due to the thin absorber layer and the minimal absorption coefficient. The mechanism of using surface textured interface in layered structure is widely accepted to scatter light and enhance the optical path length, which in turn enhances the optical absorption and improves the solar cell efficiency. A textured amorphous silicon solar cell is designed in order to observe the impact of scattering layers on optical absorption and efficiency. A pyramid, cylindrical and micro lenses array structure has been simulated using simulation tool used to obtain the optimum absorption at a particular wave length. A max Power conversion efficiency of 0.0992 is obtained at Voc of 0.9218 V. In this regard, the impact of scattering layers and different geometrical structure on V-I characteristics solar cell were observed. The maximum value obtained for refractive index is 2.0 for optimized a-Si solar cell.

Isosbestic Point in Optical Mapping; Theoretical and Experimental Determination With Di-4-ANBDQPQ Transmembrane Voltage Sensitive Dye.

Optical mapping methods utilize fluorescence dyes to measure dynamic response of cardiac tissue such as changes in transmembrane potential (Vm). For the commonly used Vm sensitive dyes, a dye absorption and emission spectra shift as Vm changes. Signals relevant to Vm are calculated as a relative fluorescence change with respect to the fluorescence baseline. The amplitude of the change depends on the long-pass (LP) filter cut-on wavelength, placed on the sensor side, and the excitation wavelength. An excitation wavelength near the absorption peak, termed the isosbestic point, results in minimal absorption coefficient change as absorption spectra shifts. Consequentially the fluorescence intensity virtually does not change, when fluorescence across the entire emission spectra is measured, irrelevant of Vm changes. In this study we experimentally determined the isosbestic point for a near infrared dye Di-4-ANBDQPQ. We then present a theoretical study examining the dye linear or non-linear response as the fractional fluorescence change of Vm change, due to emission spectra shift and amplitude change, over a range of excitation wavelengths and LP filters. Linear "optical" response is important to quantify certain aspects of cardiac dynamics such as the action potential (AP) shape and duration, especially when studying drug effects and dynamical substrates for arrhythmia development.

Effect of charged particles’ flow velocity on THz absorption characteristic of dusty plasma

In this paper, on the basis of considering the influence of charged particles’ (electrons and ions) flow velocity, the absorption characteristic of dusty plasma in THz region is studied. Firstly, based on the model of conductivity which has considered the effect of flow velocity, the absorption coefficient is deduced. And then, the dependence of absorption coefficient on the flow velocity is discussed, which manifests that the absorption coefficient has a turning point (minimum) in the relation. In particular, it is found that the minimal absorption coefficient does not appear when the flow velocity is comparable to the thermal velocity, which is different from that of the complex conductivity. Finally, the condition where the minimal absorption coefficient appears is theoretically deduced.

Pulsed-laser excitation of acoustic modes in open high-Q photoacoustic resonators for trace gas monitoring: results for C_2H_4

The pulsed excitation of acoustic resonances was studied with a continuously monitoring photoacoustic detector system. Acoustic waves were generated in C(2)H(4)/N(2) gas mixtures by light absorption of the pulses from a transversely excited atmospheric CO(2) laser. The photoacoustic part consisted of high-Q cylindrical resonators (Q factor 820 for the first radial mode in N(2)) and two adjoining variable acoustic filter systems. The time-resolved signal was Fourier transformed to a frequency spectrum of high resolution. For the first radial mode a Lorentzian profile was fitted to the measured data. The outside noise suppression and the signal-to-noise ratio were investigated in a normal laboratory environment in the flow-through mode. The acoustic and electric filter system combined with the averaging of the photoacoustic signal in the time domain suppressed the outside noise by a factor of 4500 (73 dB). The detection limit for trace gas analysis of ethylene in pure N(2) was 2.0 parts in 10(9) by volume (ppbV) (minimal absorption coefficient α(min) = 6.1 × 10(-8) cm(-1), pulse energy 20 mJ, 1-bar N(2)), and in environmental air, in which the absorption of other gas components produces a high background signal, we can detect C(2)H(4) to ~180 ppbV. In addition, an alternative experimental technique, in which the maximum signal of the second azimuthal mode was monitored, was tested. To synchronize the sampling rate at the resonance frequency, a resonance tracking system was applied. The detection limit for ethylene measurements was α(min) = 9.1 × 10(-8) cm(-1) for this system.