Multigrid Approach to Predictive Wave-Front Reconstruction in Adaptive Optical Systems

2004 ◽  
Vol 43 (18) ◽  
pp. 3708 ◽  
Author(s):  
Jeffrey D. Barchers
Keyword(s):  
Wave Front ◽  
Optical Systems

Thermal Deformation Modeling of Space Optical Systems With Variable Coefficient of Thermal Expansion

2005 ◽  
Author(s):  
Jennifer Batson ◽  
Ab Hashemi
Keyword(s):  
Thermal Expansion ◽  
Temperature Gradient ◽  
Wave Front ◽  
Thermal Deformation ◽  
Coefficient Of Thermal Expansion ◽  
Optical Element ◽  
Thermal Control ◽  
Temperature Gradients ◽  
Optical Systems ◽  
Space Optical Systems

In modeling space optical systems, an important property affecting the wave front error is the coefficient of thermal expansion (CTE) of the materials. The change of deformation that an optical element experiences due to thermal loads is proportional to both the CTE and the change in temperature gradient. This deformation affects the performance of the optical system by introducing error in the wave front. The deformation can be reduced in part by using materials with low CTE. Alternatively, using high conductivity materials to minimize temperature gradients through the mirror can also reduce deformation. Usually, a combination of these approaches is used to optimize the performance and meet the requirements of the system. Even with the utmost attention to thermal control, often the temperature gradients cannot be completely avoided. Low CTE materials have been developed to reduce thermal deformation, including ULE (Ultra-low Expansion), Zerodur, and Silicon Carbide. However, the manufacturing process can result in non-uniformities throughout the optics. For optical systems requiring highly precise performance, modeling these non-uniformities becomes important. The non-uniformity in the CTE of a material in effect compounds the deformation in the same manner as introducing additional temperature gradient through the optics. This paper describes the methodology for integrated thermal/mechanical modeling to predict the deformation response of an optical element with assumed CTE variations and thermal disturbances. A mirror with an assumed CTE variation was modeled in a changing thermal environment and using IDEAS/TMG analysis tools, thermal deformations were predicted. Results show excellent agreement with engineering predictions. Clearly knowing the CTE variation of the material is a critical step for modeling. However, measuring and specifying the material CTE is out of the scope of this paper.

scholarly journals Using an Adaptive Filtration to Improve Adaptive Optical Systems Performance. Analytical Review

2019 ◽  
pp. 34-60
Author(s):  
Yu. I. Shanin
Keyword(s):  
Wave Front ◽  
Adaptive Optics ◽  
Adaptive Filtering ◽  
Input Signal ◽  
Least Square ◽  
Optical Systems ◽  
Control Algorithms ◽  
Optical Wave ◽  
Adaptive Filtration ◽  
Laser Systems

For adaptive optical systems (AOS) installed in the optical path of aircraft-based laser systems, the presence of changing input light signals is typical. A wave-front sensor processes these signals. The quality of the radiation wave-front correction depends on how well the rapidly changing input signal is received and processed. When dealing with such signals, an adaptive filtration (AF) is used, which allows automatic adaptation to the changing input signal. The adaptive filtration is used in control algorithms for adaptive optical systems.The paper gives a brief theoretical AF background as applied to the AOS. The AF with feedback can be used for the following: a) predictions, b) identification of an unknown system, c) balancing of characteristics, d) disturbance rejection. The AF main point is to control the weighting factors of the input signal, which form the output signal. Under control, the difference between the reference and output signals is minimized. Mathematically, this comes down to defining the global minimum of the objective function. Among the search methods for this minimum, the paper considers the following ones: the Newton's method, the steepest-descent method and its modified version - the least square error method, and the recursive AF algorithm using the least squares criterion. The choice requirements for an adaptive algorithm are formulated.The paper considers direct application of the AF methods in the control algorithms of the AOS used in the airborne laser systems. Analyzes both the works on improving operation of classical AOS control loops (based on the PID-controllers with time-fixed gains) by adding various adaptive devices to the circuit, and the works on direct use of the adaptive filters and their relevant control algorithms. Adaptive filtering has shown the positive results both in suppressing the multiple narrow-band vibrations inherent in the aircraft and in broadband jitter due to the turbulent atmosphere, including the aero-optical wave-front aberrations of laser radiation.For more successful application of the adaptive filtering methods for AOS control, further interpretation and research into capabilities of their practical implementation for specific applications of adaptive optics is required.

Automatic Control Systems for Adaptive Optical Systems: Analytical Review. Part 1: Adaptive Optical System Control of Onboard Laser Installations

2018 ◽  
pp. 51-68 ◽  
Author(s):  
Yu. I. Shanin ◽  
A. V. Chernykh
Keyword(s):  
Control System ◽  
Laser Beam ◽  
Automatic Control ◽  
Wave Front ◽  
Control Systems ◽  
Turbulent Atmosphere ◽  
Single Channel ◽  
Optical Systems ◽  
Automatic Control Systems ◽  
Analytical Review

The first part of the analytical review presents an introduction to automatic control systems (ACS) for the adaptive optical systems (AOS) and control of tip-tilt correctors to eliminate a laser beam jitter. Considers a composition and a purpose of the AOS basic components. Also gives the AOS schemes to be used to form the sharper object images and focus radiation on a target when propagating a laser beam in a turbulent atmosphere. Briefly discusses the general issues of the AOS control, namely single-channel and multichannel linear control, bandwidth limitations of the control system, and possible signal paths in ACS of AOS.The article in-detail describes a path of the harmonic signal through the units of the feedback control loop as applied to the plane mirror of a two-channel corrector of the wave front tip-tilt. Provides guidelines to select the minimum quantization time for a propagating digital signal.Considers the certain problems of constructing ACS to be applied to AOS of the on-board laser installations. A simulated installation model where light passes through a turbulent atmosphere allowed us to develop a linear quadratic Gaussian controller (LQG-controller). Using this controller the optimal control (i.e. minimizing the dispersion of the output signal measured) with good robustness of the tip-tilt corrector is carried out.The concluding part of the review presents the certain research results of the AOS control when compensating the laser radiation wave front perturbations caused both by an aero-optical problem, arising when radiation propagates near the walls of an aircraft and by an atmospheric turbulence of free airflow. The influence of a small time delay (within one sampling step), when transmitting a control signal, on the control system operability was under special consideration.

Dynamic wave-front generation for the characterization and testing of optical systems

1998 ◽  
Vol 23 (23) ◽  
pp. 1849 ◽  
Author(s):  
M. A. A. Neil ◽  
M. J. Booth ◽  
T. Wilson
Keyword(s):  
Wave Front ◽  
Optical Systems ◽  
Dynamic Wave

scholarly journals Laser printed flat lenses for optofluidics

2019 ◽  
Vol 215 ◽  
pp. 13002
Author(s):  
Airidas Žukauskas ◽  
Andreas R. Stilling-Andersen ◽  
Xiaolong Zhu ◽  
Anders Kristensen
Keyword(s):  
Wave Front ◽  
Three Dimensional ◽  
Diffractive Optics ◽  
Imaging Systems ◽  
Optical Systems ◽  
Optical Aberrations ◽  
Optical Elements ◽  
Printing Technique ◽  
Resonant Laser ◽  
Bio Imaging

Conventional three-dimensional optics requires curvature to control the wave front of light thus making it difficult to reduce the size of the optical systems. Furthermore, for correction of optical aberrations, complex optical systems comprising more than one lens are used. This adds additional bulk, mass and complexity to the optical systems. Recent development in diffractive optics has enabled new thin lightweight optical elements such as metalenses. We introduce resonant laser printing technique as a flexible photo-thermal technology for metalens fabrication with the ability to control the light with microscale precision. Our laser printed metalenses can be integrated in bio-sensors, bio-imaging systems, and optofluidical devices.

Atomic Resolution in Crystal Aperture Stem

1990 ◽  
Vol 48 (1) ◽  
pp. 236-237
Author(s):  
J T Fourie
Keyword(s):  
Optical System ◽  
Spherical Aberration ◽  
Three Dimensional ◽  
Transmission Function ◽  
Optical Systems ◽  
Bragg Angle ◽  
Electron Optical System ◽  
Intimate Contact ◽  
Diffraction Effects ◽  
Design Aspect

The attempts at improvement of electron optical systems to date, have largely been directed towards the design aspect of magnetic lenses and towards the establishment of ideal lens combinations. In the present work the emphasis has been placed on the utilization of a unique three-dimensional crystal objective aperture within a standard electron optical system with the aim to reduce the spherical aberration without introducing diffraction effects. A brief summary of this work together with a description of results obtained recently, will be given.The concept of utilizing a crystal as aperture in an electron optical system was introduced by Fourie who employed a {111} crystal foil as a collector aperture, by mounting the sample directly on top of the foil and in intimate contact with the foil. In the present work the sample was mounted on the bottom of the foil so that the crystal would function as an objective or probe forming aperture. The transmission function of such a crystal aperture depends on the thickness, t, and the orientation of the foil. The expression for calculating the transmission function was derived by Hashimoto, Howie and Whelan on the basis of the electron equivalent of the Borrmann anomalous absorption effect in crystals. In Fig. 1 the functions for a g220 diffraction vector and t = 0.53 and 1.0 μm are shown. Here n= Θ‒ΘB, where Θ is the angle between the incident ray and the (hkl) planes, and ΘB is the Bragg angle.

Sign in / Sign up

Export Citation Format

Share Document