HADAMARD SPECTROSCOPY WITH A 2-DIMENSIONAL DETECTING ARRAY

In a conventional grating spectrograph consisting of a single entrance slit, a grating, and a multichannel (imaging) detector, considerable light throughput advantage can be realized by replacement of the singl e entrance slit with a mask. This replacement can yield a signal-to-no ise ratio increase because of increased light collection over an exten ded area of the mask when compared with a single slit. The mask produc es a spectrum on the detector, which is the convolution of the mask pa ttern and the spectral distribution of the light source. To retrieve t he spectrum, the spectrum has to be inverted. In special cases in whic h emission spectra are superimposed on weak backgrounds, the signal-to -noise advantage is preserved through the inversion process. Thus this technique is valuable in the observation of light sources that are pr oduced by atomic or molecular emissions such as aurora, airglow, some interstellar emission, or laboratory spectra. Considerable signal-to-n oise advantages can also be realized when the background noise of the imaging detector is not negligible. The spectral mixing of the light f rom the mask on the detector causes high photon fluxes on the detector , which tend to swamp the detector noise. This is a particularly impor tant advantage in the application of CCD's as detectors because they c an have significant background noise. The technique was demonstrated b y computer simulations and laboratory tests.