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Metrology for Nanolithography
Published in Bruce W. Smith, Kazuaki Suzuki, Microlithography, 2020
The focus level is another factor affecting the determination of the line edge position in the intensity profile as well as the measurement repeatability. Usually, the focus is adjusted for optimum image quality. Attempts to accurately determine the line edge position from intensity profiles are being made through the use of theoretical calculations [42]. One starts with calculating the image intensity as a function of the lateral position across the feature. The calculated intensity profile is then fit to the experimental distribution with the desired critical dimension as an adjustable parameter. Once agreement between the theoretical and measured intensity profiles has been found, the position of the edges can be determined. The desired critical dimension is then obtained as the distance between the edges.
F
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
focal length distance from a lens or mirror at which an input family of parallel light rays will be brought to a focus. focus the position of the plane of best focus of the optical system relative to some reference plane, such as the top surface of the resist, measured along the optical axis (i.e., perpendicular to the plane of best focus). focus of attention the center of the region detected by a visual attention mechanism, which is the first stage of a pattern recognition system that is aimed to detect regions where a target object is likely to be found. focus of expansion the point in an image from which feature points appear to be diverging when the camera is moving forwards or objects are moving towards the camera.
Light, Waves, and Rays
Published in Vincent Toal, Introduction to Holography, 2011
Equation 1.17 is the lensmaker’s formula for the focal length of a lens. It tells us that a plane wavefront passing through a lens along its axis ultimately comes to a point on the axis called the focus located a distance f from the lens. There are two foci one on each side. The distance f is called the focal length. A plane containing the focus and perpendicular to the lens axis is called the focal plane. It is the plane in which infinitely distant objects are imaged since light from such objects takes the form of plane waves. Another way of saying this is that the focal plane is conjugate to an infinitely distant plane.
The ruling engines and diffraction gratings of Henry Augustus Rowland
Published in Annals of Science, 2022
The way of using a concave grating was remarkably simple. Imagine the grating at a point on the circumference of a circle, which came to be called the Rowland circle, of diameter equal to the radius of curvature of the grating. If there is a source of light at any point on the circle, the image of this source and all its diffraction spectra are brought to a focus at other points on the circumference. The word focus is misleading because the image of a point source of light is extended into a line. In practice, the source is a narrow line of light passing through a slit, and the image is extended into a longer line, but not broadened. A simple way of keeping the slit, the grating, and an eyepiece for viewing the spectra, on the circle was to mount them at the ends of three arms of equal length connected together at their other ends. One position of the arms has a particular advantage: with the eyepiece diametrically opposite the grating the spectrum is ‘normal’, so that equal distances between spectral lines represent equal changes in wavelength. Furthermore, since there were no lenses to introduce chromatic aberration, the overlapping spectra of different orders were in focus together, so that by measuring the positions of lines in different orders of spectra with a micrometer a scale of relative wavelengths could be established easily and more accurately than by any other means.
Design and implementation of CCD image-based DNA chip scanner with automatic focus calibration
Published in Systems Science & Control Engineering, 2019
The focus can be calibrated by adjusting the image distance, the object distance, or the focus of the imaging lens. Adjusting the image distance changes the back intercept of the imaging system, destroying the integrity of the CCD and the imaging lens. However, adjusting the object distance, generally by moving up and down the glass loading platform of the biochip, has two drawbacks. One is that achieving control of the platform’s up and down movement requires much more complex hardware. The other is that adjusting the object distance changes the imaging ratio and decreases the efficiency of the fluorescence collection (Xiao, Di, Zhu, Wang, & Xu, 2016). Adjusting the focus of the imaging lens only requires an additional focusing motor and a connector between the motor and the lens, but it has the advantages of low cost and little effect on the scanner, so we chose it as the focus calibration scheme in this study. Furthermore, a limit switch is used to ensure that the calibration is within the focus range (Selek, 2016).
Blind deconvolution using bilateral total variation regularization: a theoretical study and application
Published in Applicable Analysis, 2022
Idriss El Mourabit, Mohammed El Rhabi, Abdelilah Hakim
Three major types of blur [10] are addressed: motion blur, atmospheric blur, and out-of -focus blur. Out-of-focus blur is produced by the deviation of an imaging plane from the focus of an optical lens. Atmospheric blur is due to the optical turbulence of photonic media through traveling light rays, and motion blur is caused by the movement of either the observed object or of the camera during the image acquisition process. In addition, images are always corrupted by noise, which arises from several sources such as radiation scatter from the surface before the image is acquired and electrical noise in the sensor or camera.