Gaussian Beam Analysis Research Articles

Controlling asymmetric transmission in layered natural hyperbolic crystals

We explore the electromagnetic properties of a structure composed of two optically active materials—each layer contains a hyperbolic crystal with its anisotropy axis rotated with respect to the crystal surface. Through this, we can control the transmission spectra where at one frequency, light with a positive incidence angle is transmitted while it is absorbed for a negative incidence angle and the reverse occurs at a second frequency. Using a Gaussian beam analysis, we determine in which material layer the absorption occurs. In a radiating line current source study, we obtain tunable output collimated beams. From these discoveries, our structure can be applied as an efficient frequency or angle selector, demultiplexer, or filter.

Design of a dual scattering angle multi-pass Thomson scattering system with signal separation function on Heliotron J.

This paper proposes a design of dual scattering angles multi-path Thomson scattering system with a signal separation function to solve the overlapping phenomenon of scattered light signals and to increase the measurement accuracy for the investigation of anisotropic electron velocity distribution. Furthermore, an optical path design is proposed to demonstrate how overlapping scattered light signals can be separated by setting the optical path in a limited room with a compact layout, which makes the incident interval between two overlapping scattered light signals 1.7 times longer than that of our current system. The specific position of each optical component existing in the system is determined via a Gaussian beam analysis to avoid damage caused by overexpansion of spot size with the application of two cooperating image relay systems. Conversely, a polychromator is optimized by resetting the pass waveband of the interference filter combination to achieve high accuracy in electron temperature (Te) measurement corresponding to two scattering angles simultaneously.

Design of an electron cyclotron emission diagnostics suite for COMPASS Upgrade tokamak.

COMPASS Upgrade is a medium size and high field tokamak that is capable of addressing key challenges for reactor grade tokamaks, including power exhaust and advanced confinement scenarios. Electron cyclotron emission will be available among the first diagnostics to provide measurements of high spatial and temporal resolution of electron temperature profiles and electron temperature fluctuation profiles through a radial view. A separate oblique view at 12° from normal will be utilized to study non-thermal electrons. Both the radial and oblique views are envisioned to be located in a wide-angle midplane port, which has dimensions that enable simultaneous hosting of the front-end of their quasi-optical (QO) designs. Each QO design will have an in situ hot calibration source in the front-end to provide standalone and calibrated Te (R,t) measurements. The conceptual design for each QO system, the Gaussian beam analysis, and the details of the diagnostic channels are presented.

Analysis of Gaussian beam broadening and scintillation index in anisotropic plasma turbulence

In this paper, new expressions for the long-term beam spreading and scintillation index of Gaussian beams in anisotropic plasma turbulent media are derived on the basis of the anisotropic hypersonic plasma turbulent refractive index undulation power spectrum combined with the Rytov approximation theory. Considering the asymmetry of turbulent eddies in the orthogonal xy-plane throughout the path, two anisotropy factors are introduced to parameterize the anisotropy properties of turbulent cells in the horizontal and vertical directions. The spreading and scintillation index of Gaussian beams in plasma turbulence are calculated, and the propagation characteristics of Gaussian beams in anisotropic plasma turbulence are analyzed. Results show that enhancing the anisotropic properties of hypersonic plasma turbulence can significantly improve the propagation performance of Gaussian beams in hypersonic plasma turbulence. The effect of hypersonic plasma turbulence on Gaussian beam increases with the increase of the refractive index undulation variance and the decrease of the turbulent outer scale and anisotropy parameters. The results provide a theoretical basis for the further study of the propagation properties of electromagnetic waves in hypersonic plasma turbulence.

Laser Gaussian beam analysis of structure constant depends on Kolmogorov in turbulent atmosphere for a variable angle of wave propagation

Laser Gaussian beam propagation is important in optical communications; the challenges of the measured constant parameters are varied angle wave propagation, the receiver plan in the slant path of laser Gaussian beam (G) in Kolmogorov gauges, and the effect of the laser in a random medium. At this point, atmospheric turbulence is reputable based on laser Gaussian beam propagation. Moreover, the space propagation of Gaussian beam waves of higher-order Gaussian beam modes has been expanded from the effects of the scintillation index and with different zenith angles between the laser propagator and the detector (receiver) in the ramp path. Furthermore, in the Cartesian coordinate system, the scintillation index in the Kolmogorov standard is evaluated, and it employs two methods; first, Huygens–Fresnel fundamental and, second, random phase screen for work synchronization. Additionally, to analyze the contour parameters of constant construction, the intensity and receiver field is found to compute the high turbulent modes in the atmospheric deposition, which depends on propagation distances. These result in significant reserves in the matlab computation period and serve the imitation for enhancement of the link transmission; therefore, the zenith angle and scintillation index are pretentious by slant beam, and they enhance the performance that makes the comparisons found with fixed structure constant parameters C2n and the propagation distance against the scintillation index.

Modeling and analysis of sulfur hexafluoride plasma etching for silicon microcavity resonators

Silicon microcavity resonators are an important component in modern photonics. In order to optimize their performance, it is fundamental to control their final shape, in particular with respect to the involved CMOS compatible, two-step sulfur hexafluoride plasma etching fabrication process. To that end, we use a ray-tracing based pseudo-particle model to enhance a level-set topography simulator enabling us to effectively capture the characteristics of sulfur hexafluoride plasma etching in the low-voltage-bias regime. By introducing a novel and robust calibration procedure and by applying it to experimental data of a reference two-step etching process, we are able to optimize the etch times and photoresist geometry without costly reactor-scale simulations and simultaneously explore beyond conventional statistical process modeling. Through defining objective design criteria by way of Gaussian beam analysis, we analyze the plasma etching process and provide new insights into alternative processing guidelines which impact shape measurements such as cavity opening and parabolic form. By means of scale analysis, we propose that the radius of curvature of the microcavity is optimized with a reduction of the photoresist opening diameter. After simulated fabrication runs, we surmise that the cavity quality parameters are improved by increasing the duration of the first etch step by a factor of 2 and by decreasing the second etch step duration by up to in comparison to the reference two-step etching process. This results in an overall reduction of etch time of at least , allowing to significantly optimize the overall fabrication process.

Scintillation and bit error rate analysis of cylindrical-sinc Gaussian beam

This article presents point-like, aperture averaged scintillation, and bit error rate(BER) performance of cylindrical-sinc Gaussian beam (CSGB). We model atmosphere utilizing random phase screen approach to be up to the complexity of source field expression. Our results indicate that it is possible to generate resistive CSGBs against turbulence considering point-like scintillation. Aperture averaged scintillation results show that all selected beams have lower scintillation index than Gauss beam. Major benefit of CSGBs is seen in BER evaluation in optical wireless communication systems. It is possible to decrease BER times lower than Gauss beam at nearly 13 dB signal to noise ratio(SNR).

Simplified physical model of interferometric radius of curvature test using the yybar diagram

The yybar diagram for Gaussian beam optics is employed to model the behavior of an interferometer system testing very small radius parts. The model was developed to overcome the limitations and known inconsistencies of a paraxial optics representation used to evaluate a calibration method for testing cylindrical wave optics using a fiber reference test. Gaussian beam analysis inherently contains physical optics conditions, and the yybar diagram method provides both an intuitive and powerful framework to generate analytical solutions. Particularly, we show how to model an interferometric test from a Fizeau transmission sphere (TS), to a small test ball and back to the TS, and yield test ball radius limits as a function of the test wavelength and TS F / # . A computation of error estimates for measuring the radius of curvature of the test balls is also presented.

Elliptical Gaussian beam propagation in nonlinear fibres with focusing and defocusing refractive profiles

The paper shows systematic analysis of elliptical Gaussian beam (GB) propagating in self-focusing/self-defocusing media of Kerr type with focusing/defocusing linear refractive profiles. Instead of solving commonly accepted Nonlinear Schrödinger Equation (NLS) we propose equations of geometrical optics: complex eikonal equation and complex transport one. Eikonal equation let us derive immediately the ordinary differential equations for principle widths omitting this way complicated variational process and virial theory used in nonlinear optics. From the transport equation we obtain first order ordinary differential equation for complex amplitude evolution and conservation principle for energy flux in the elliptical GB cross-section. For combined effects of diffraction, nonlinear refraction and focusing/defocusing graded-index factor we observe three types of the solutions for the elliptical radius of principle beam widths: self-focusing or self-defocusing together with diffraction widening, stationary and oscillatory ones under and without collapse effect. We prove here that principle curvatures of the wave front can introduce into our description the additional ellipticity of the beam, which can effectively limit collapse effect. Moreover, we discuss the evolution of elliptical Gaussian beam in nonlinear self-defocusing fibre with focusing refractive profile presenting conditions for existence of elliptical spatial solitons. We discuss here also the influence of initial wave front curvatures on elliptical Gaussian beam evolution in nonlinear inhomogeneous fibres of Kerr-type.

Comprehensive Modeling of Multimode Fiber Sensors for Refractive Index Measurement and Experimental Validation

We propose and develop a comprehensive model for estimating the refractive index (RI) response over three potential sensing zones in a multimode fiber. The model has been developed based on a combined ray optics, Gaussian beam, and wave optics analysis coupled to the consideration of the injected interrogating lightwave characteristics and validated experimentally through the realization of three sensors with different lengths of stripped cladding sections as the sensing region. The experimental results highly corroborate and validate the simulation output from the model for the three RI sensing zones. The sensors can be employed over a very wide dynamic RI range from 1.316 to over 1.608 at a wavelength of 1550 nm, with the best resolution of 2.2406 × 10−5 RI unit (RIU) obtained in Zone II for a 1-cm sensor length.

Deeply-Etched MEMS Slotted Micromirrors With Controlled Transmittance

In this paper, we report the analysis, fabrication, and characterization of metallized slotted micromirrors for optical MEMS applications. A scalar model for the transmittance of the micromirror with a vertical slit using Gaussian beam analysis is developed and a closed-form expression is obtained. Detailed finite difference time domain simulation is carried out for the micromirror transmittance to understand the effect of polarization and bench mark the developed model for slit width-to-wavelength ratios in the range 0 to 8. A MEMS chip is designed comprising fiber grooves and variable slit micromirror controlled by a comb-drive actuator. The chip is fabricated using deep reactive ion etching of silicon-on-insulator substrate with 100-μm device layer height. The motion of the actuator is characterized using an opto-mechanical technique and the transmittance of the micromirror for different incident polarizations is extracted versus the slit width and compared with the theoretical predictions showing good agreement.

Numerical and experimental verification of a trireflector compact antenna test range in the terahertz band

ABSTRACTNumerical and measured results of the quiet zone performance of a trireflector compact antenna test range (CATR) system in the terahertz band are presented in this letter. A modular Gaussian beam (GB) analysis method, which consists of frame‐based Gabor transformation, GB reflection and a 3D GB diffraction technique, was implemented to evaluate the quiet zone performance. Compared to geometrical optics method, this method is valid in predicting the field distribution in the caustic region. Moreover, simulation results of the CATR system demonstrated a superior efficiency to the physic optics method, especially in the terahertz range. Measured results show that 70% quiet zone usage can be achieved with amplitude and phase ripples less than 1.2 dB and 15°, respectively in the central frequencies. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1686–1689, 2015

A Modular Gaussian Beam Analysis Method Based on 3-D Diffraction Technique

A modular Gaussian Beam (GB) analysis method is proposed in this letter. The analysis method consists of frame-based Gabor transformation, GB reflection, and a novel 3-D GB diffraction technique that was developed to handle the scattering from the reflector edge. This 3-D GB diffraction method gracefully extends Zogbi’s solution into practical scenarios via coordinate transformation. The proposed method can analyze not only normal quadric surfaces but also shaped reflectors. Also, modular treatment has been introduced to make this method capable of analyzing multielement systems. Simulation results of an electrically large offset reflector and a tri-reflector compact antenna testing range (CATR) system show good agreement with physic optics (PO) method. The measured result of tri-reflector CATR system demonstrates the modularization and efficiency of the proposed method.

Numerical and Experimental Verification of a 3D Quasi-Optical System

A modular and efficient Gaussian beam (GB) analysis method, incorporating frame-based Gabor transformation, GB reflection, and a 3D GB diffraction technique, was developed to analyze both the reflectors and frequency selective surface (FSS) in quasi-optical (QO) system. To validate this analysis method, a 3D dual-channel QO system operating at 183 and 325 GHz was designed and tested. The proposed QO system employs two-layer structure with a FSS of perforated hexagonal array transmitting the 325 GHz signal on the top layer while diverting the 183 GHz signal to the bottom layer. Measured results of the system demonstrate that the agreement can be achieved down to −30 dB signal level for both channels in the far field pattern. The discrepancy between the calculation and measurement is within 2 dB in the main beam region (2.5 times −3 dB beamwidth), verifying the effectiveness and accuracy of the proposed method.

Radially polarized Bessel-Gauss beams: decentered Gaussian beam analysis and experimental verification

We derive solutions for radially polarized Bessel-Gauss beams in free-space by superimposing decentered Gaussian beams with differing polarization states. We numerically show that the analytical result is applicable even for large semi-aperture angles, and we experimentally confirm the analytical expression by employing a fiber-based mode-converter.

Scintillation analysis of hypergeometric Gaussian beam via phase screen method

We give a scintillation treatment of hypergeometric Gaussian beams via the use of random phase screens. In particular, we analyse the on-axis, point-like and aperture averaged power scintillation characteristics of this beam that cannot be undertaken easily by analytic means. Within the range of examined source and propagation parameters, our evaluations show that there will be less scintillation, with increasing hollowness at small source sizes and zero topological charge. At larger source sizes or topological charges, this is reversed and decreasing hollowness will reduce scintillation. More or less the same trend is observed for aperture averaging such that at small source sizes and zero topological charge, increased hollowness will result in lower scintillation. At larger source size and topological charges, there will be a transition from the case of smaller values of hollowness giving rise to less scintillation at smaller aperture openings to the case of larger values of hollowness giving rise to less scintillation at larger aperture openings. In general nonzero topological charges will produces more scintillations, both in on-axis and aperture averaged cases.

Planar Near-Field Phase Retrieval Using GPUs for Accurate THz Far-Field Prediction

With a view to using Phase Retrieval to accurately predict Terahertz antenna far-field from near-field intensity measurements, this paper reports on three fundamental advances that achieve very low algorithmic error penalties. The first is a new Gaussian beam analysis that provides accurate initial complex aperture estimates including defocus and astigmatic phase errors, based only on first and second moment calculations. The second is a powerful noise tolerant near-field Phase Retrieval algorithm that combines Anderson's Plane-to-Plane (PTP) with Fienup's Hybrid-Input-Output (HIO) and Successive Over-Relaxation (SOR) to achieve increased accuracy at reduced scan separations. The third advance employs teraflop Graphical Processing Units (GPUs) to achieve practically real time near-field phase retrieval and to obtain the optimum aperture constraint without any a priori information.

A Compensating Anastigmatic Submillimeter Array Imaging System for STEAMR

In this paper, we present a novel technique for the removal of astigmatism in submillimeter-wave optical systems through employment of a specific combination of so-called astigmatic off-axis reflectors. This technique treats an orthogonally astigmatic beam using skew Gaussian beam analysis, from which an anastigmatic imaging network is derived. The resultant beam is considered truly stigmatic, with all Gaussian beam parameters in the orthogonal directions being matched. This is thus considered an improvement over previous techniques wherein a beam corrected for astigmatism has only the orthogonal beam amplitude radii matched, with phase shift and phase radius of curvature not considered. This technique is computationally efficient, negating the requirement for computationally intensive numerical analysis of shaped reflector surfaces. The required optical surfaces are also relatively simple to implement compared to such numerically optimized shaped surfaces. This technique is implemented in this work as part of the complete optics train for the STEAMR antenna. The STEAMR instrument is envisaged as a mutli-beam limb sounding instrument operating at submillimeter wavelengths. The antenna optics arrangement for this instrument uses multiple off-axis reflectors to control the incident radiation and couple them to their corresponding receiver feeds. An anastigmatic imaging network is successfully implemented into an optical model of this antenna, and the resultant design ensures optimal imaging of the beams to the corresponding feed horns. This example also addresses the challenges of imaging in multi-beam antenna systems.

Position detection and vibration monitoring system using quad-cell optical beam power distribution

In this paper, we study the accuracy of an optical vibration sensing system using Gaussian beam analysis. The proposed optical system uses a He–Ne laser source whose Gaussian beam impinges on a quad-cell photodetector array. The normalized optical power for each cell is obtained through numerical simulation based on the well-known Gaussian beam optics formulation, as the beam scans the plane of the photodetectors due to vibration. The system detection principle lies upon finding a relationship between the power distribution of the quad-cell and the position of the beam centroid, which allows us to identify the characteristics of the vibration applied, such as direction, frequency and strength. The aspects of practical implementation and experimental limitations on the power distribution accuracy are discussed and the discrepancies with the theoretical results are presented.

Design and evaluation of a THz time domain imaging system using standard optical design software

A terahertz (THz) time domain imaging system is analyzed and optimized with standard optical design software (ZEMAX). Special requirements to the illumination optics and imaging optics are presented. In the optimized system, off-axis parabolic mirrors and lenses are combined. The system has a numerical aperture of 0.4 and is diffraction limited for field points up to 4 mm and wavelengths down to 750 microm. ZEONEX is used as the lens material. Higher aspherical coefficients are used for correction of spherical aberration and reduction of lens thickness. The lenses were manufactured by ultraprecision machining. For optimization of the system, ray tracing and wave-optical methods were combined. We show how the ZEMAX Gaussian beam analysis tool can be used to evaluate illumination optics. The resolution of the THz system was tested with a wire and a slit target, line gratings of different period, and a Siemens star. The behavior of the temporal line spread function can be modeled with the polychromatic coherent line spread function feature in ZEMAX. The spectral and temporal resolutions of the line gratings are compared with the respective modulation transfer function of ZEMAX. For maximum resolution, the system has to be diffraction limited down to the smallest wavelength of the spectrum of the THz pulse. Then, the resolution on time domain analysis of the pulse maximum can be estimated with the spectral resolution of the center of gravity wavelength. The system resolution near the optical axis on time domain analysis of the pulse maximum is 1 line pair/mm with an intensity contrast of 0.22. The Siemens star is used for estimation of the resolution of the whole system. An eight channel electro-optic sampling system was used for detection. The resolution on time domain analysis of the pulse maximum of all eight channels could be determined with the Siemens star to be 0.7 line pairs/mm.