Fig 1 - uploaded by Javier Salinas-Luna
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͑ a ͒ Classical Ronchi ruling of 50 lines per inch, and ͑ b ͒ variable-frequency ruling with three different frequencies of 50, 86, and 133 lines per inch.
Source publication
We present a new method for testing an optical surface. It
uses the Ronchi test with variable-frequency rulings and a liquid-crystal
display. The rulings can be formed by substructuring the spacing of a
Ronchi ruling or combining several classical Ronchi rulings in a single
variable-frequency ruling. This change allows us to observe smaller defects...
Contexts in source publication
Context 1
... mm= 1 in. and the size of the image produced by the ruling 1024 pixels. Thus, the first scaling factor is obtained as follows: Accordingly, a computer program displayed on the LCD 50 clear lines and 50 opaque lines, with a spacing of ap- proximately 10 pixels between them; thus a Ronchi ruling image of 1024 768 pixels is input to the LCD. See Fig. ...
Context 2
... types of Ronchi rulings of 50, 86, and 133 lines per inch were generated digitally, following the two scaling factors described. Then, the three images were added to obtain a variable-frequency ruling image on the LCD, such as that shown in Fig. 1b. Finally, we notice that the qual- ity of the Ronchi ruling image can be improved obtaining the negative of the image by means of digital image- processing ...
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Citations
... System wavefront aberration is one of the important parameters for evaluating a lithography projection lens, and has a fundamental impact on the resolution and overlay [1]. Many methods are reported to measure system wavefront aberration, such as point diffraction interferometry, Ronchi shearing interferometry, and the Hartmann-Shack sensor [2][3][4][5][6]. Research shows that Ronchi phase-shifting lateral-shearing interferometry has great potential for improving the accuracy in system wavefront measurement [7,8]. ...
We propose a general method of designing phase-analysis algorithms for Ronchi phase-shifting lateral-shearing interferometry. Based on the expression and method, three new phase-shifting algorithms are designed to eliminate negative error effects of interference from unwanted diffraction orders, which limits the accuracy of wavefront aberration measurement. The proposed eight-, 10-, and 13-frame algorithms can eliminate the effects of the first ± 5 , ± 9 , and ± 15 multi-diffraction orders, respectively. Simulation works and experimental results verify the general expression and corresponding designed method.
... By using the arrangement presented in Fig. 8, several Ronchigrams with traditional and substructured rulings, for different wavelengths, were captured. Figure 10 shows two typical 7 bit substructured Katyl type rulings employed in this work [18], which are employed in the Ronchi test to produce narrower bands in order to obtain more information from a Ronchigram [19][20][21]. The application of these kinds of sequences to the Ronchi test is analogous to the narrow interference lines of multiple beam interferometry [18]. ...
In this work we present an experimental proposal to evaluate optical surfaces with high slopes or with infrared wavelengths based on the Ronchi test as well as on the concept of equivalent wavelength. A spatial modulator is used in the implementation of the Ronchi test, and a white LED with different color filters is employed in order to generate different wavelengths. Two Ronchigrams with incoherent light, each one for a different color, are registered and computationally processed, thus generating a third one with an equivalent wavelength. The results obtained show that it is possible to generate patterns with traditional rulings and substructured sequences of Katyl. Additionally, we discuss some of the limitations of employing different rulings. Finally, we found that appropriate image enhancing algorithms allow us to improve the visibility of the resulting fringes and thus obtain a better analysis.
In the next work an automatic fringe projection system with a mobile camera has been proposed. A set of experimental images in order to scanning all the set positions in an automated rail are obtained. In each position, four profileometric images shifted pi/2 were taken and use the phase shift of 4 steps algorithm to obtain the wrapped phase. A Radon transform analysis was applied to quantify the object move using the gray levels as scale. A qualitative process to analyze the profilometry of an object with an irregular surface is applied, getting good results.
Substructured Ronchi gratings are used to sharpen and increase the number of fringes in Ronchigrams, thereby increasing their spatial resolution and allowing greater accuracy in the evaluation of a surface under test. This work presents a simple method for generating substructured Ronchi gratings and for calculating the intensity pattern produced by this type of grating. For this, we propose the generation of this kind of grating from the linear combination of classical gratings; the pattern of irradiance produced by these Ronchi gratings will be a linear combination of the intensity patterns produced by each combined classical grating. A comparison between theoretical and experimental Ronchigrams was obtained by analyzing a parabolic mirror.
