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Lens system inspection with HASO R-Flex - VIS NIR optical metrology Application Notes

Lens system inspection with HASO R-Flex - VIS NIR optical metrology Application Notes
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Lens system inspection with HASO R-Flex - VIS NIR optical metrology Application Notes - 1

Lens system inspection with HASO R-Flex Imagine Optic, 18 rue Charles de Gaulle, 91400 Orsay, France contact@imagine-optic.com Introduction During the development of an optical system, it is necessary to characterize aberration of single components as well as complete systems. The classical technique for evaluating optical components is interferometry. An interferometer gives interference fringes of a reference and the test beam when the sample under test is present. This technique relies on the perfection of the reference beam, which is very sensitive to vibration. Alternative technique is ShackHartmann (SH) wavefront sensing, a real-time compact and robust optical metrology tool for measuring the aberrations (imperfections) present in a light beam. The SH detection technique is well known for its high accuracy, rapidity, less sensitive to vibrations compared to interferometers. The sensor is constructed with a microlens array in front of a CCD camera. Light computation is required to derive the wavefront shape from local slopes calculated from the displacement of focal spots. By combining the SH wavefront sensor with a light source, one can guide the light to pass or reflect at the optics under interest and detect the modified wavefront. Imagine Optic pioneered a compact metrology tool, called HASO R-Flex which is based on the SH sensing technique, to facilitate the characterization of optical components or systems and alignment of a telescope. The inspecting beam can be either a collimated or divergent beam. Furthermore, the inspecting wavelength is not limited to 632.8 nm but it can be the wavelengths that the optics will be used. As a result, achromatic aberration can also be measure by injecting different wavelengths to HASO R-Flex through a FC/PC fiber connector. This application note presents how an optical system, such as a camera lens, can be easily characterized using HASO R-Flex for on-axis and off-axis wavefront aberration and modulation transfer function (MTF). Lens system inspection with HASO R-Flex N.Varkentina imagine-optic.com 5 October 2020 – Property of Imagine Optic

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Lens system inspection with HASO R-Flex - VIS NIR optical metrology Application Notes - 2

Optical setup and parasitic light was attached to the front of the HASO4 Wavefront errors of a transmissive optics can be R-Flex50 with a C-mount to give the output divergent measured by passing the light through and detected the difference of wavefront between with and without the optics. Depending on the design of the optics, a divergent input beam that corresponds to the numerical aperture would characterization results as well as for comparing with the simulation. The main instruments for the wavefront error measurements are 1) a light source at the wavelength that the optical...

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Lens system inspection with HASO R-Flex - VIS NIR optical metrology Application Notes - 3

In order to get the auto-collimation, the curvature seen by the wavefront sensor should be minimum, as well as xand y-tilts. These parameters displayed in Chief ray session in the WaveView metrology software, see Figure 2 (a). Low order aberrations should be minimized real time for the on-axis configuration with the help of Modal coefficient display as shown in Figure 2 (b). Figure 4 Wavefronts of the off-axis (a) and (c); and on-axis positions (b). The wavefront errors are 79, 72 and 70 nm RMS, from left to right. Measurement results This section presents off-axis wavefront...

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Lens system inspection with HASO R-Flex - VIS NIR optical metrology Application Notes - 4

Figure 6 Screen shot of the MTF measurement. smaller than the wavefront sensor pupil. For example MOD50-6 can be used for the optics with F/8.4. FOMFOT: not recommend – part of the optical component under test is not seen by the wavefront sensor Summary Pupil size modification Figure 7 Change of the MTF contrast as a function of diaphragm aperture in percent. How to choose objective module for HASO R-Flex There are two F-numbers involved when using an output HASO R-Flex was used for charactering a camera zoom lens to quantify the aberrations both on- and off-axis. The MTF contrast was...

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