Dark field imaging of high aspect ratio structures - a simple model.

A simplified model for dark-field optical imaging of three-dimensional high aspect ratio micro- and nano- structures is proposed, to reduce the time taken to simulate object fields with in-plane scattering between different parts of the object. Primary scattering is found by assuming that illumination of Manhattan geometries generates a set of spherical edge waves, following the incremental theory of diffraction. Secondary scattering is found by assuming that primary scattering is re-scattered from nearby features. Diffraction coefficients are simplified, and the number of illuminating beams is limited to those generating waves that enter the objective lens. Images obtained using TE and TM polarizations are compared, and results are benchmarked against a vectorial finite element model. Applications lie in simulating optical inspection of structures containing vertically etched features including MEMS and NEMS.

Refractive index of solutions of human hemoglobin from the near-infrared to the ultraviolet range: Kramers-Kronig analysis.

Because direct measurements of the refractive index of hemoglobin over a large wavelength range are challenging, indirect methods deserve particular attention. Among them, the Kramers-Kronig relations are a powerful tool often used to derive the real part of a refractive index from its imaginary part. However, previous attempts to apply the relations to solutions of human hemoglobin have been somewhat controversial, resulting in disagreement between several studies. We show that this controversy can be resolved when careful attention is paid not only to the absorption of hemoglobin but also to the dispersion of the refractive index of the nonabsorbing solvent. We present a Kramers-Kroning analysis taking both contributions into account and compare the results with the data from several studies. Good agreement with experiments is found across the visible and parts of near-infrared and ultraviolet regions. These results reinstate the use of the Kramers-Kronig relations for hemoglobin solutions and provide an additional source of information about their refractive index.

Eigenanalysis of dichroic, birefringent, and degenerate polarization elements: a Jones-calculus study.

A theoretical analysis of eigenpolarizations and eigenvalues pertaining to the Jones matrices of dichroic, birefringent, and degenerate polarization elements is presented. The analysis is carried out employing a general model of a polarization element. Expressions for the corresponding polarization elements are derived and analyzed. It is shown that, despite the presence of birefringence, a polarization element can, in a general case, demonstrate a totally dichroic behavior. Moreover, it is proved that birefringence necessarily accompanies dichroic elements with orthogonal eigenpolarizations. A transition between degenerate, dichroic, and birefringent eigenvalues is studied, and examples of synthesis of polarization elements are given.

Conditions for polarization elements to be dichroic and birefringent.

The polarization of light when it passes through optical media can change as a result of change in the amplitude (dichroism) or phase shift (birefringence) of the electric vector. The anisotropic properties of media can be determined from these two optical features. We derive the conditions required for polarization elements to be dichroic and birefringent. Our derivation starts from commonly accepted assumptions for dichroism and birefringence. Our main conclusions are that (i) the generalized Jones matrix for dichroic elements has in general nonorthogonal eigenpolarizations and (ii) in the general case, the birefringent and dichroic properties of polarization elements have no direct association with the corresponding phase and dichroic polar forms derived in the polar decomposition of the polarization elements' Jones matrices.