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Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes

Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes
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Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes - 1

Optical metrology measurements with HASOTM Imagine Optic, 18 rue Charles de Gaulle, 91400 Orsay, France contact@imagine-optic.com Imagine Optic offers a wide range of products (hardware and software), which can be used together to accurately characterize the optical quality of a complex optical systems. For instance the wavefront sensors from HASOTM line are perfectly suited for metrological characterization. They can accurately measure distortion, field curvature, wavefront error and optical aberrations. Based on a patented Shack-Hartmann technology, HASOTM wavefront sensors by Imagine Optic contain an association of a microlens grid and a detector in order to calculate local derivatives of the wavefront and this way it can reach the accuracy of /100 RMS (Root Mean Square). This document presents an example of HASOTM wavefront sensor application to characterize the optical quality of a complex lens. Optical metrology measurements with HASO N.Varkentina www.imagine-optic.com 20 October 2020 – Property of Imagine Optic

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Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes - 2

1. Introduction This document presents the optical characterization of an imager, which was designed to introduce as little distortion as possible, with a limited amount of aberrations across its field of view. This imager, called complex lens in the following paragraphs, is made of five lenses, as it is shown in Figure 1. Figure 1. The optical layout of the imager (complex lens). We chose to use HASO3 128 GE2 in this experiment, Figure 3. Experimental setup with definition of axes. because it offers a very high spatial resolution. However, Our experimental setup (see Figure 3) has total of...

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Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes - 3

Figure 6. shows magnification measurements for different positions along zsource direction, allowing the accurate estimation of the conjugation plane location. 0.203 source position along zsource (mm) Figure 6. Magnification along zsource. Figure 4. Example of alignement parameters provided by WaveView. However, for collimated beams, the “Chief ray” panel gives Once the correct conjugation location along zsource is determined, it should remain unchanged for the rest of the measurements. useful information concerning the beam’s tilt and curvature. Those parameters, in turn, assist in precise...

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Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes - 4

local changes in magnification do not show any particular tendency, so we can conclude that distorsion is less than 1%. 5. Alignment of the microscope objective Once the correct magnification adjustement is achieved, the further optical characterization requires to accurately align the source and the HASOTM through the complex lens. After roughly positioning the light source in the complex lens center, the micro-adjusters 4 and 5 should be used in order to minimize the “(X,Y) positions” parameters inside WaveView software (see Figure 4). This procedure ensures that the image plane is...

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Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes - 5

has been measured between them. As long as its optical center is known, the comparison of the optical model for the For more information, and to find the Imagine Optic’s office or distributor nearest to you, please visit www.imagine-optic.com measurements is straightforward. Indeed, WaveView allows us to simply decompose the wavefront using Zernike polynomials, which are known to correspond to classical aberrations. A comparison between aberration’s influence across the field has been done. It is displayed as a histogram for different points in the field (see Figure 11), or directly as...

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Optical metrology measurements with HASOTM - SWIR optical metrology Application Notes - 6

Figure 12. Wavefront evolution accros the work field. Coma is significant on axis, which is characteristic of an excentricity defect. Astigmatism appears with the field and prevails at the edge of the field. Figure 13. Wavefront evolution accros the work field, without the 3rd order aberrations influence. The 5th order spherical aberration is predominant on axis, but the trefoil prevails at the edge of the work field. Optical metrology measurements with HASO Application note www.imagine-optic.com 20 October 2020 – Property of Imagine Optic

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