Model calculations on the linearity behavior of combs used for optical attenuation in spectrophotometers

Part I: For a multiwedge comb placed in the beam path of the radiation source of a spectrophotometer to achieve optical attenuation, formulas can be derived which express the linearity deviation as a function of comb position, number of wedges, and geometry of the wedges. These formulas are applicable provided the irradiance existing at the comb can be stated in a quadratic form expressing the attenuation of the irradiance toward the upper and lower edges of the aperture. The attenuation in the irradiance also functionally relates the position of the comb to wavelength and temperature. Part II: For a single-wedge comb, formulas for the linearity deviation can be derived provided (1) the radiation directed across the slit width of the monochromator is nonuniform, and (2) the size of the slit width is finite in relation to the length of the comb.