Anomalous retroreflection from strongly absorbing nanoporous semiconductors

Abstract

Pronounced retroreflection behavior is reported for a fishnet nanoporous strongly absorbing semiconductor material. Retroreflection features a half-cone about 0.35 rad along with diffusive specular reflection for all angles of incidence. Retroreflection is apparent by the naked eye with daylight illumination and exhibits no selectivity with respect to wavelength and polarization of incident light featuring minor depolarization of retroreflected light. The reflectance in the backward direction measures 12% with respect to a white scattering etalon. The phenomenon can be classified neither as coherent backscattering nor as Anderson localization of light. The primary model includes light scattering from strongly absorptive and refractive superwavelength clusters existing within the porous fishnet structure. A reasonable qualitative explanation is based on the fact that strict retroreflection obeys shorter paths inside absorbing medium, whereas all alternative paths will lead to stronger absorption of light.

Retroreflection of light from nanoporous InP: correlation with high absorption

“…The diffuse reflection for 1,064 nm shows angular dependence close to that typically observed in low-absorptive nanoporous materials (see, e.g., Ref. [12]). Notably, in a few cases (Figs.…”

“…The primary model [12] includes light scattering from strongly absorptive and refractive super-wavelength clusters existing within the porous fishnet structure. The typical diffusive reflection inherent in low-absorptive porous structures becomes inhibited owing to low mean free path resulting from high dissipative losses.…”

“…But all of the above phenomena necessarily imply nonabsorptive material forming desirable nanostructured media since multiple scattering and interference of scattered light waves are of principal importance. Recently, we have observed yet another unusual feature in nanoporous semiconductor material, InP, namely pronounced retroreflection for light whose wavelength corresponds to interband optical transitions in bulk InP material [12]. In this experiment, green laser light was used (531 nm, 2.33 eV) to be compared with the bandgap energy E g = 1.344 eV or bandgap wavelength 922 nm [13].…”

Anomalous retroreflection from nanoporous materials as backscattering by ‘dark’ and ‘bright’ modes

“…Anomalous retroreflection apparent by the naked eye with daylight illumination has been recently observed from a fishnet nanoporous strongly absorbing semiconductor material [9]. The retroreflection features a half-cone about 0.35 rad along with diffusive specular reflection for all angles of incidence and it measures 12% in the backward direction with respect to a white scattering etalon.…”

“…In this paper, we propose an explanation of the mechanism of anomalous retroreflection observed in [9,10] on the basis of formation of both 'dark' and 'bright' modes in a nanoporous strongly absorbing semiconductor material. The proposed model explains also the observed peculiarities of the anomalous retroreflection, namely correlation with strong absoprtion and differences for s-and p-polarizations of incident radiation.…”