This is a practical book on wavefront sensing. Emphasis is on principles and techniques, rather than detailed mathematical analysis of such systems. The goal is to provide the reader with a qualitative understanding of wavefront sensor operation.
The performance of an adaptive optical system is strongly dependent upon correctly measuring the wavefront of the arriving light. The most common wavefront measurement techniques used to date are the shearing interferometer and the Shack-Hartmann sensor. Shack-Hartmann sensors rely on the use of lenslet arrays to sample the aperture appropriately. These have traditionally been constructed using ULM or step and repeat technology, and more recently with binary optics technology. Diffractive optics fabrication methodology can be used to remove some of the limitations of the previous technologies and can allow for low-cost production of sophisticated elements. We have investigated several different specialized wavefront sensor configurations using both Shack-Hartmann and shearing interferometer principles. We have taken advantage of the arbitrary nature of these elements to match pupil shapes of detector and telescope aperture and to introduce magnification between the lenslet array and the detector. We have fabricated elements that facilitate matching the sampling to the current atmospheric conditions. The sensors were designed using a far-field diffraction model and a photolithography layout program. They were fabricated using photolithography and RIE etching. Several different designs will be presented with some experimental results from a small-scale adaptive optics brass-board.
This volume in the SPIE Tutorial Text series presents a practical approach to optical testing, with emphasis on techniques, procedures, and instrumentation rather than mathematical analysis. The author provides the reader with a basic understanding of the measurements made and the tools used to make those measurements. Detailed information is given on how to measure and characterize imaging systems, perform optical bench measurements to determine first- and third-order properties of optical systems, set up and operate a Fizeau interferometer and evaluate fringe data, conduct beam diagnostics (such as wavefront sensing), and perform radiometric calibrations.
Adaptive Optics (AO) is a technique for compensating the distortions introduced by atmospheric turbulence in astronomical imaging. To measure the distortions a wavefront sensor is needed. There are a number of fundamentally different types of wavefront sensors, one of which is the curvature wavefront sensor. At the European Southern Observatory (ESO) in Garching, Germany, several adaptive optics systems using curvature wavefront sensors are being developed for the Very Large Telescope (VLT) and the VLT interferometer (VLTI). Curvature AO-systems have traditionally used avalanche photodiodes (APDs) as detectors due to strict requirements of very short integration times (200 microsec) and very low readout noise. Advances in charge-coupled device (CCD) technology motivated an investigation of the use of a specially designed CCD as the wavefront sensor detector in a 60-element curvature AO system. A CCD has never been used before as the wavefront sensor in a low light level curvature adaptive optics system. This thesis shows that a CCD can achieve nearly the same performance as APDs at a fraction of the cost and with reduced complexity for high order wavefront correction. Moreover the CCD has higher quantum efficiency and a greater dynamic range than APDs. A readout noise of less than 1.5 electrons at 4000 frames per second was achieved. A back-illuminated thinned version of this CCD can replace APDs as the best detector for high order curvature wavefront sensing. This thesis presents the concept, the design and the evaluation of the CCD. The first frontside devices were successfully evaluated and the performance of the detector was proven in a laboratory experiment.
This work covers spatial frequency, spread function, wave aberration, and transfer function - and how these concepts are related in an optical system, how they are measured and calculated, and how they may be useful.
The use of image stabilization has grown to the point that it is now a common component of modern optical systems for imaging, communications, and remote-sensing applications. The benefits of image stabilization to astronomical research alone are so rich that it is common for astronomical telescopes, built over the last century, to be retrofitted with fast steering mirrors and tip-tilt sensors to extend their useful lifetimes. This text provides the basics of image stabilization starting with a consideration of the cause of image blurring and an introduction to the components commonly used in constructing a stabilized imaging system. With this foundation, an example image stabilized system is described and used to introduce some of the important parameters in evaluating the performance of image stabilization systems. As image stabilization systems are key components of adaptive optics systems, the more sophisticated sensing and correction devices used in this area are briefly addressed. Rather than being a mathematical, rigorous treatment of image stabilization, it provides the basic ideas in an easy-to-read format.
Provides a summary of the methods for determining the requirements of an adaptive optics system, the performance of the system, and the requirements for the components of the system. This second edition has a greatly expanded presentation of adaptive optics control system design and operation. Discussions of control models are accompanied by various recommendations for implementing the algorithms in hardware.
This open access book provides a comprehensive overview of the application of the newest laser and microscope/ophthalmoscope technology in the field of high resolution imaging in microscopy and ophthalmology. Starting by describing High-Resolution 3D Light Microscopy with STED and RESOLFT, the book goes on to cover retinal and anterior segment imaging and image-guided treatment and also discusses the development of adaptive optics in vision science and ophthalmology. Using an interdisciplinary approach, the reader will learn about the latest developments and most up to date technology in the field and how these translate to a medical setting. High Resolution Imaging in Microscopy and Ophthalmology – New Frontiers in Biomedical Optics has been written by leading experts in the field and offers insights on engineering, biology, and medicine, thus being a valuable addition for scientists, engineers, and clinicians with technical and medical interest who would like to understand the equipment, the applications and the medical/biological background. Lastly, this book is dedicated to the memory of Dr. Gerhard Zinser, co-founder of Heidelberg Engineering GmbH, a scientist, a husband, a brother, a colleague, and a friend.