Efficient method to measure the spectral distortions using periodically distributed slit in hyperspectral imager

The imaging spectrometer generally shows geometrical asymmetric distortions known as the keystone and smile that are different from the regular imaging optical system. The conventional method of measuring such distortions requires a precision movement control stage and specialized optical setup. Moreover, it is even harder to measure other characteristics such as the wave front error (WFE) simultaneously and to repeat the measurements since an accumulated vast number of statistical data is required to calculate the keystone and smile. To overcome these disadvantages, a new and simple method is proposed. The newly proposed method takes images separated in fields and wavelengths utilizing a simple tool called the field identifier (FI). Then, the keystone and the smile are calculated fast and repeatedly from a single measurement image while measuring the WFE with the Shack-Hartmann sensor with the minimum change of the measurement setup. With this method, hyperspectral imager is aligned and its geometrical distortions are measured.