2-D Light Diffraction from CCD and Intensified Reticon Multichannel Detectors Causes Spectrometer Stray Light Problems

Abstract

Intensified diode arrays and charge-coupled detectors (CCD) which are used as multichannel detectors for spectroscopy exhibit strong 2-D diffraction of light due to the micro-channel plate intensifier and the CCD surface microelectronic structures. The strong 2-D diffraction of light by the intensified diode arrays shows hexagonal symmetry due to the hexagonal packing of the hollow glass fibers of the micro-channel plate intensifier. The 2-D diffraction of light from the CCD detectors shows square symmetry due to the almost square symmetry of the individual surface microelectronic structures. Light incident on the detector surfaces is diffracted into numerous angles which depend upon the incident angle and the light wavelength. This diffracted light can be redispersed and/ or reflected and scattered by optical elements inside the spectrometer. This diffracted light can then contribute to spectrometer diffuse stray light or it can be directly reimaged onto the detector to cause spectral artifacts. Backthinned CCD detectors do not show 2-D light diffraction and thus avoid these 2-D diffraction stray light limitations.