Effectiveness of absorption of radiation and the distribution of heat sources inside weakly absorbing two-layer particles of an aqueous aerosol under conditions of optical resonance

Abstract

The problem of resonances of absorption of radiation of the optical range of wavelengths in two-layer particles is almost uninvestigated. The variation of the emittance of particles of aluminum oxide with radii of 1-3 ~m in the 2.25- to 5-~m spectral interval with soot films from 0.001 to 0.04 ~m thick deposited on them has been discussed only in [i0, ii]. In the indicated spectral region a low emittance is characteristic for the aluminum oxide particles under discussion. If having maintained the outer dimension of the particles one deposits on them a thin layer of soot of the order of 0.005-0.01 ~m, the emittance of such particles is increased by several orders of magnitude. The effect of a surface layer of soot on the position of resonances on the frequency scale has not been detected in [ii]. The results of an investigation of resonances of the absorption of radiation with % = 0.6943 ~m by water drops (n~ = 1.33, <1 = 3"10 -8 ) on whose surface there is a shell of a weakly absorbing liquid of the aniline type (n2 = 1.58, K2 ~ 10 -7 ) are given below. Variations of the drop sizes and the shell thicknesses for which the conditions of a resonance of the magnetic and electric partial fields are satisfied, variation of the values of the absorption efficiency factor ka corresponding to these resonances, the halfwidth of the resonance peaksof the ka(p) dependence (where p = 2~r/% is the diffraction parameter of the particle), and the distribution of the power of the heat sources inside such two-layer drops are discussed. In view of the large number of parameters to be varied, the solution of this problem in a general formulation is practically boundless. Therefore, for a start, the specific situation is investigated in which the drop sizes vary within an interval corresponding to p: = 35-50. It was assumed that films of a liquid of a different nature with the properties indicated above and a thickness Ap = 0-4 can be formed on the drops. The discussion is carried out for a bounded interval of partial wave numbers I = 53-59 and for resonances of the first and second orders (s = i, 2). The investigations show that one can select for any radius of the aqueous core a shell thickness such that resonance of the magnetic or electric partial wave of a specified number is realized. The conditions for absorption resonance in two-layer drops are satisfied for small dimensions of the aqueous cores and even smaller outer dimensions of the particles than in the case of drops without shells. But the smaller the drop radius is~ the larger the shell thickness necessary for satisfaction of the conditions of resonant absorption (Fig. I). For example, if for a uniform water drop resonance of the first order (s = !) for the magnetic partial wave with I = 53 is observed at p = 44.409121~ a shell of the selected liquid with a thickness Ap ~ 3.21 (Fig. la) is necessary for the onset of this resonance for a drop with p~ = 35. Such an appreciable decrease in the radius of a resonating two-layer particle is explained by the fact that the real part of the refractive index of the shell is significantly higher than that of water. Due to this the mean volume refractive index of two-layer