![]() ![]() If the disperser is replaced by a plane mirror (or if the disperser is removed in a transmissive system), the system acts as a versatile imager, with A = 1. However, it can be used effectively with transmissive dispersers. The Littrow configuration is rarely used with reflective designs when large FOV is required because of internal vignetting and consequent light loss. Thus the camera aperture must be oversized in the dispersion direction since D 2 > D 1. The grating-to-collimator configuration may also be used at the penalty of lower R but does permit a smaller camera. This is known as the grating-to-camera configuration since the grating normal points more towards the camera than to the collimator. This implies maximizing cos β, since ψ = α − β, which results in A > 1. Practical configurations that maximize R, do so by increasing W = D 1/cos α. ![]() Which varies, depending on the choice of angles required to place the chosen wavelength on the detector using eqns and. ![]()
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