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Optical and visual metrics
Published in Pablo Artal, Handbook of Visual Optics, 2017
The Strehl ratio (SR) is defined as the ratio of the intensity value at the center of the image with and without aberrations for the same pupil size: SR=PSF(0,0)PSFd−1(0,0)
Flight Optomechanical Assembly
Published in Hamid Hemmati, Near-Earth Laser Communications, 2020
The Strehl ratio is a measure of the wavefront quality and is defined by ratio of ideal on-axis irradiance for a perfectly unaberrated beam vs. actual on-axis irradiance for an aberrated beam transmittance/reflectance (throughput) of each optical component in the system which determines the overall system losses [6]. Highest wavefront quality (highest Strehl, approaching 1.0) is required to minimize the losses. The system wavefront quality is calculated by root mean squaring (RMSing) the wavefront contributions of individual optical elements in a given path. The example in Table 5.2 demonstrates the influence of individual optical elements wavefront contributions. Highest throughput is accomplished by utilizing lowest loss optical coatings.
Optical Systems for Laser Scanners
Published in Gerald F. Marshall, Glenn E. Stutz, Handbook of Optical and Laser Scanning, 2018
A real lens with aberrations will spread the energy of an imaged spot beyond the Airy disc. This redistribution of energy reduces the irradiance in the center of the point-spread function. A measure of that redistribution is the Strehl ratio, the ratio of the spot peak intensity relative to the diffraction limit. The Strehl ratio is a convenient measure of the lens image quality during the design process (along with RMS wavefront error) and it is useful in calibrating normalized point-spread function calculations when evaluating a lens over several field angles.
Zernike coefficients of a circular Gaussian pupil
Published in Journal of Modern Optics, 2020
Cosmas Mafusire, Tjaart P. J. Krüger
There are two practical problems that can be solved using orthonormal polynomials. The first is that, in diffraction-limited systems, the Strehl ratio can be calculated from a simple formula based on the wavefront variance. The second is that most devices on the market capable of measuring phase are designed to use ZC polynomials. In both cases, it is necessary to convert the acquired ZC coefficients into ZGC coefficients so that the advantages of orthonormality can be restored. This is akin to changing the basis from the ZC set, in which the amplitude plays no part, to the ZGC set for the same amplitude and phase distribution. ZC polynomials belong to a special class of polynomials referred to as orthonormal Zernike-based (OZ) polynomials that are orthonormal in a general non-circular, non-uniform pupil in which the unit circle is a special, trivial case [5,6]. A generalized model that can be used to acquire such polynomials from the ZC-polynomial set using the Gram-Schmidt procedure has been in the literature for a while. These polynomials can be fitted directly onto the wavefront to generate a set of non-orthonormal coefficients. The same coefficients can also be acquired by fitting the ZC polynomials to get the respective ZC coefficients, which are then converted to orthonormal coefficients without acquiring OZ polynomials first, a method that was used in a previous study to acquire Zernike coefficients in a scaled pupil [13]. To achieve this, a matrix approach was created and is based on deriving a positive semi-definite matrix, which is created by calculating its elements through integrating the product of any two ZC polynomials in the general pupil [14]. Using the Cholesky method, the matrix is then decomposed into a product of a lower triangular matrix and its transpose. The rest of the calculations follow from this result. This matrix approach has proved suitable for creating numerical models which are normally implemented using computers [15,16].