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The rigorous coupled-wave approach (RCWA) and the differential evolution algorithm (DEA) were coupled in a practicable approach to maximize absorption in optical structures with three-dimensional morphology. As a model problem, optimal values of four geometric parameters and the bandgaps of three i-layers were found for an amorphous-silicon, multiterminal, thin-film tandem solar cell comprising three p--i--n junctions with a metallic hexagonally corrugated backreflector. When the optical short-circuit current density was chosen as the figure of merit to be maximized, only the bandgap of the topmost i-layer was significant and the remaining six parameters played minor roles. While this configuration would absorb light very well, it would have poor electrical performance. This issue arises because the optimization problem allows for the thicknesses and bandgaps of the semiconductor layers to change. We therefore devised another figure of merit that takes into account bandgap changes by estimating the open-circuit voltage. The resulting configuration was found to be optimal with respect to all seven variable parameters. The RCWA + DEA optimization approach is applicable to other types of photovoltaic solar cells as well as optical absorbers, with the choice of the figure of merit being vital to a successful outcome. [ABSTRACT FROM AUTHOR]

Fingerprint analysis is a popular identification technique due to the uniqueness of fingerprints and the convenience of recording them. The quality of a latent fingerprint on a surface can depend on various conditions, such as the time of the day, temperature, and the composition of sweat. We first developed latent fingerprints on transparent and blackened glass slides by depositing 1000-nm-thick columnar thin films (CTFs) of chalcogenide glass of nominal composition Ge28Sb12Se60. Then, we used transmission-/reflection-mode multiwavelength digital holography to construct the topograms of CTF-developed fingerprints on transparent/blackened glass slides. The two wavelengths chosen were 514.5 and 457.9 nm, yielding a synthetic wavelength of 4.1624 μm, which is sufficient to resolve pores of depths 1 to 2 μm. Thus, our method can be used to measure the level-3 details that are usually difficult to observe with most other techniques applied to latent fingerprints. [ABSTRACT FROM AUTHOR]

Surface-plasmon-polariton (SPP) wave excitation in a composite structure obtained by depositing a columnar thin film (CTF) on a metal (silver) substrate decorated periodically by an array of rectangular grooves was analyzed using the rigorous coupled-wave approach. The SPP wave is excited as a Floquet harmonic of different orders by light incident from different directions, the incidence plane being the same as the grating plane. But, in some instances, the SPP wave appears to be excited as a doublet, i.e., a Floquet harmonic of the same order at two closely spaced angles of incidence, the excitation being less efficient for one angle of incidence than for the other. The characteristics of the SPP wave are affected by the vapor incidence angle chosen to deposit the CTF. [ABSTRACT FROM AUTHOR]