Lens Aberrations and Ray Tracing
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چکیده
When beam quality is a concern in an optical setup, lens aberrations are an undesired side-effect. Which aberration affects a particular experiment is not always as obvious as one would like. Take for example, the simple goal to concentrate the maximum amount of optical power at a certain point using a lens. The first “obvious” requirement is that the initial beam should be well collimated, sent along the axis of the optical system, and free of spherical aberrations. However, the power may still not be as high as you might expect at the focus. If you are using white light, the various wavelengths will focus at different points along the axis (chromatic aberration). Or, if using short pulses, the central ray will reach the focus later than the marginal ray. You will learn that these two effects are in fact . . . identical. Where would spherical aberrations be an issue? Many times an experiment will require a wellcollimated beam or focusing as much energy as possible into a point, situations that mandate minimal spherical aberrations. Which lens should be used? Bi-convex or plano convex — and in the latter case, which orientation? Another case would be the common practice of using spatial filters to improve the optical quality of an illuminating system. Spherical aberrations within the spatial filter assembly can lead to uncorrectable distortion (concentric fringes). Where would chromatic aberrations be an issue? On a general level, certain applications may require color imaging without having multicolored “halos” from chromatic aberration. What are the best methods for focusing all wavelengths by the same amount? A more specific concern with chromatic aberration would be the aforementioned distortion caused by broad bandwidth ultrashort pulses. The intent of this laboratory is to study certain key aberrations, get a “feeling” for their importance, and find ways to minimize or even eliminate them.
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تاریخ انتشار 2011