Effect of focal plane array cold shield aperture size on Fourier transform infrared micro-imaging spectrometer performance

Micro-imaging spectrometers incorporating focal plane array (FPA) detection require careful demarcation of cold shield aperture size for both optimal performance and prevention of errors. This study examines the effects of changing the diameter of the cold shield aperture on the intensity and spatial homogeneity of the incident radiation. A uniform polystyrene film was repeatedly imaged by using cold shields of varying aperture sizes. It is shown that a smaller than optimal aperture size leads to image edge clipping, resulting in an inefficient use of the array, lower overall signal, spectral distortions, and higher noise characteristics. Use of an aperture size larger than required causes a decrease in the effective dynamic range of measurements, resulting in higher noise levels. The advantages and necessity of optimizing imaging spectrometer performance by employing a cold shield with an appropriately sized aperture are discussed.