Effect of focal plane array cold shield aperture size on fourier transforminfrared micro-imaging spectrometer performance

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