Jari Turunen

Simulation of light propagation by local spherical interface approximation

A new local elementary interface approximation is introduced for the modeling of wave propagation through interfaces between homogeneous media. The incident wave and the surface profile are approximated locally by a spherical wave and a spherical surface, respectively. The wave field travels through the modulated structure according to the laws of geometrical optics, being refracted by the surface and propagating to the output plane locally as a geometric spherical wave. Diffraction theory is applied to propagate the field from the output plane onwards. We provide comparisons of the method with the thin-element approximation, the local plane-wave and interface approach, and rigorous diffraction theory using a sinusoidal surface-relief grating as an example. We illustrate the power of the new method by applying it to the analysis of a diffractive beam splitter.

Degree of coherence and electromagnetic resonators

Electromagnetic theory of open laser resonators is formulated in the domain of partially coherent optics. The theory is then used to find out the electromagnetic degree of coherence of the field in various situations. It is shown that if only one transverse mode is present in the steady-state condition, then the field is necessarily completely coherent in view of the recently introduced degree of coherence for electromagnetic fields [Opt. Express. 11, 1137 (2003)].

Electromagnetic models for the analysis and design of complex diffractive microstructures

A review of electromagnetic models for the analysis of complex microstructures for controlling optical fields is provided. An overview of the most useful rigorous approaches and indications of their computational complexity as well as their domain of applicability is first presented. Then two types of approximate electromagnetic approaches are discusses: local interface techniques and local perturbation methods. These are compared to rigorous methods with a view on computational complexity and domain of applicability.

Broadband diffractive elements with high efficiency

We introduce a method for designing high-efficiency paraxial-domain diffractive elements working over a broad frequency range. The design method is based on the theory of dielectric polarization gratings, in which the local state of polarization is controlled by means of form-birefringent diffractive structures. We show that any scalar transmission function can be easily converted to a corresponding broadband design.

Rigorous and approximate analysis of metallic gratings in soft X-ray and EUV regions

Diffractive components in X-ray and UV regions have several attractive applications, but analysis in those regions has not been thoroughly investigated. Besides, in the X-ray and UV regions the complex refractive indices of metals differ substantially from the values in the visible region of the spectrum. The consequences of this phenomenon are analyzed for metallic structures illuminated by wavelengths ranging from infrared to soft X-rays. The rigorous diffraction theory and the thin element approximation is applied to study the behavior of both wire-grid polarizers and inductive grid filters. Single layer film theory is used to enhance the reliability of the thin element approximation.

Local spherical interface approximation in the analysis of field propagation through modulated interfaces

Local Spherical Interface Approximation (LSIA) for modelling the propagation of electromagnetic wave fields through analog interfaces is introduced. The method belongs to a class of Local Elementary Interface Approximation (LEIA) in which the propagation is modelled by decomposing the field into local elementary fields. In the method introduced here both the phase-distribution of the field and the boundary of discontinuity are assumed to be locally spherical, which enables the use of Coddingtons equations in the determination of the reflected and transmitted fields. The amplitude reflection and transmission is treated with the help of the intensity law of geometrical optics and the energy conservation law. Convergence comparison between LSIA and Local Plane Interface Approximation (LPIA) is performed for a sinusoidal diffraction grating. The accuracy of the method is illustrated with a numerical example.

Polarization modulation by subwavelength-structured space-variant dielectric interfaces

Intensity transformation by using paraxial-domain polarization-modulating diffractive elements is discussed. It is shown that taking the electromagnetic nature of light into account may lead to a dramatic increase in the diffraction efficiency also in the paraxial domain, in which the vectorial nature of light is usually ignored. Examples are given for signals for which the full 100% conversion efficiency is possible.

Fabrication of inductive grid filters for rejection of infrared radiation

Inductive grid filters are analyzed and designed with the aim to reject infrared radiation with wavelength larger than one micrometer and to transmit shorter wavelengths. Experimental results on nickel and gold grids are presented. The grids are fabricated by a process involving electron beam lithography, reactive ion etching, and electroplating. Optical characterization results were compared to the calculations.

Paraxial diffractive optics with vector fields

We consider the shaping of electromagnetic beams with spatially variable form-birefringent diffractive elements, showing that diffraction efficiencies exceeding Wyrowskis upper bounds for scalar fields are possible. Non-trivial designs with 100% efficiency are presented.

Fascination and challenge of subwavelength-structured interfaces

We consider an interesting domain of diffractive optics, namely the physics and technology of optical interface with subwavelength-structured features. Such interfaces act as effective media, which may, e.g., simulate the operation of multilayer film stacks and often feature anisotropic optical properties. The principles of the analysis and design of these interfaces are covered, and several prominent fields of application are described. The challenge of fabricating subwavelength-structured interface by low-voltage electron beam nanolithography is considered.