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I am a student and trying to design an aperture from which a light will pass will project on a sensor. I tried to find some software simulation tool for this purpose where i can draw the aperture (entrance side) and put diffuser or lens and then see the response of the light for some specific wavelength. I found one tool "Synopsys Code V" but it is very paid solution. So can anyone tell me some substitute for this. I am looking for Free simulation tools.