Figure | Radiation intensity distribution behind a diatom frustule-like structure. (IMAGE)

Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, CAS

Figure | Radiation intensity distribution behind a diatom frustule-like structure.

Caption

Figure | Radiation intensity distribution behind a diatom frustule-like structure. Radiation intensity distribution behind a diatom frustule-like structure. Top: schematic representation of the continuous-wave THz raster- scanning imaging system. Middle: longitudinal map of the normalised radiation intensity recorded along the optical axis behind the structure at a wavelength of 911 μm; electromagnetic radiation propagates from left to right. Bottom: transverse intensity distributions measured perpendicular to the propagation direction at three selected planes (A–A, B–B, and C–C), located at distances of 1.02 mm, 4.60 mm, and 5.35 mm from the structure plane, respectively. The colour scale represents the normalised radiation intensity.The map reveals a clear modulation of the transmitted field with a Talbot period of approximately 10 millimetres, in agreement with the analytical estimate and with simulations performed using the Fourier modal method. The three positions marked along the propagation axis correspond to the transverse cross-sections A-A, B-B, and C-C, located at distances of 1.02, 4.60, and 5.35 millimetres from the structure plane. (c), transverse intensity distributions measured perpendicular to the propagation direction at planes A-A, B-B, and C-C. At the shortest distance (A-A) the diffraction pattern reflects the combined contribution of different structural layers of the frustule-like geometry. At the intermediate plane (B-B) the intensity redistributes into a set of well-defined localised maxima that reproduce the periodicity of the foramen layer; the peak intensity at these focal spots reaches approximately half of the incident beam intensity. Beyond this plane (C-C) the focal spots become broader and less pronounced, confirming that the focusing is a local near-field phenomenon sensitive to the propagation distance. The colour scale represents the normalised radiation intensity.

Credit

Julijana Cvjetinovic et al.

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