Physical optics

About: Physical optics is a research topic. Over the lifetime, 5342 publications have been published within this topic receiving 101388 citations. The topic is also known as: wave optics.

Removing interference-based effects from the infrared transflectance spectra of thin films on metallic substrates: a fast and wave optics conform solution

Abstract: A hybrid formalism combining elements from Kramers-Kronig based analyses and dispersion analysis was developed, which allows removing interference-based effects in the infrared spectra of layers on highly reflecting substrates. In order to enable a highly convenient application, the correction procedure is fully automatized and usually requires less than a minute with non-optimized software on a typical office PC. The formalism was tested with both synthetic and experimental spectra of poly(methyl methacrylate) on gold. The results confirmed the usefulness of the formalism: apparent peak ratios as well as the interference fringes in the original spectra were successfully corrected. Accordingly, the introduced formalism makes it possible to use inexpensive and robust highly reflecting substrates for routine infrared spectroscopic investigations of layers or films the thickness of which is limited by the imperative that reflectance absorbance must be smaller than about 1. For thicker films the formalism is still useful, but requires estimates for the optical constants.

Mode transformation using graded photonic crystals with axial asymmetry

Abstract: We propose a mode conversion method that enables transformation of the propagating mode from fundamental to higher-order modes by utilizing asymmetric graded index (A-GRIN) structures. Refractive index variations of two different asymmetric gradient profiles, i.e., exponential and Luneburg lens profiles, have been approximated by two-dimensional photonic crystals (PCs). The basic structure is composed of constant radii with different lattice sizes. The designed GRIN mode converters provide relatively high transmission efficiency in the spectral region of interest and achieve the transformation in compact configuration. Numerical approaches utilizing the finite-difference time-domain and plane wave expansion methods are used to analyze the mode conversion phenomenon of proposed GRIN PC media. Analytical formulation based on ray theory is outlined to explore both ray trajectories and the physical concept of a wavefront retardation mechanism.

Chemical Oxygen-Iodine Laser Performance Modeling

Abstract: We have developed a detailed engineering model for chemical oxygen-iodine laser (COIL) performance and design predictions. In this model, mixing between the primary oxygen and the secondary iodine injectant is treated using a two-stage/three-stream shear-layer model based on the flow characteristics of the transverse injection mixing scheme. Iodine dissociation, excited-state pumping, and quenching processes are treated using the Phillips Laboratory standard COIL kinetics package. Optical extraction from a stable resonator is described by a rooftop geometric optics model. These models have been incorporated into a two-dimensional Advanced Cavity Code for COIL (AC3). The detailed models in AC 3 have been systematically validated by comparing detailed code results reflecting a hierarchy of computational complexity with data from relevant experiments. The validity of the mixing, kinetics, and optics models has been corroborated by comparing the predictions of the code with iodine dissociation, laser small signal gain, and optical power measured in the RotoRADICL device. Selected small signal gain and output power measurements from the low pressure RotoCOIL were also reproduced by the model. Computational results showed good agreement with power measurements from the high efficiency RotoRADICL/JogRADICL experiments with different throat heights. Also, predicted results showed reasonably good agreement with the dissociation and power data obtained using the RADICL device and the baseline or Big-volume generator. Output power data obtained with Rocketdyne's closed-loop Mini-GDU device were excellently predicted by the model. The good agreement with the data obtained from various devices encompassing a broad range of experimental parameters lends credibility to this model. Without an elaborate CFD and wave optics model, the good agreement strongly suggests that the present model contains the essential physics for adequate modeling and prediction of COIL performance.

Electromagnetic backscattering from aircraft propeller blades

Abstract: This paper gives a theoretical solution to the problem of determining the electromagnetic backscattering and Doppler spectrum of an aircraft propeller as presented to a radar operating in the 8-12 GHz band. At this band for all practical aircraft propeller the electromagnetic backscattering regime is in the optical region. The solution proceeds by modeling the aircraft propeller as a set of multiple skew-plated metal fan blades in the presence of a linearly polarized EM wave. Based on the quasi-stationary method combined with physical optics and physical theory of diffraction equivalent currents techniques are used to analyse the backscattering from aircraft propeller blades. Experimental results indicated that, in the far zone, the field can be considered as harmonic and expressions for the spectral components of the field are obtained. The observed waveforms are found to be in good agreement with theoretical results.

G/T maximization of a paraboloidal reflector fed by a dipole-disk antenna with ring by using the multiple-reflection approach and the moment method

Abstract: A 1.8-m paraboloidal reflector fed by a dipole-disk antenna with a beamforming ring is optimized for high G/T at L-band by using the moment method (MM) and the multiple reflection (MR) approach. The MR approach is based on using MM to calculate the radiation and scattering patterns of the feed, using physical optics plus uniform geometrical theory of diffraction (UTD) to include the reflector, and in addition to include the mutual interaction (multiple reflections) between the reflector and the feed by using the expression for the sum of an infinite geometric series. The MR approach is shown to be equally accurate as a MM solution of the complete antenna with reflector, provided the reflector is in the far field of the feed, and the MR approach is much faster. As a result of the calculations using the MR approach, design curves are presented showing how the G/T varies as a function of antenna geometry, size, and elevation angle, all for a given noise profile of the surrounding sky and ground. The computed radiation patterns and G/Ts are compared with measurements for several elevation angles and surrounding terrain.