Binning Spectral Images in a Charge-Coupled Device

A charge-coupled device (CCD) can selectively combine photogenerated charge from several detector elements into a single charge packet via a special charge readout mode called binning. This article focuses on the use of charge binning in a two-dimensional CCD for increasing the sensitivity and dynamic range of spectroscopic measurements. Binning allows the effective detector element size to be matched to the size of the slit image. Equations describing the signal-to-nolse ratio and dynamic range of the binned readout of spectral lines are developed. Results of binning to increase the sensitivity of atomic emission and molecular fluorescence measurements are presented. An intraspectral dynamic range of 500 000 is achieved by mixing binned and normal readout modes of a Hg atomic emission spectrum. Practical factors related to binning spectral images including spectral line orientation, readout speed, and blooming are discussed.