Abstract: Complex atomic or molecular spectral signatures embedded in interfering background spectra are very rapidly recognized by a spectrometric device that employs precise sweep rate control with signal slope extraction. Very fast optics become feasible. High signal to noise ratios are attained in each of three operational modes. The first, PURGE, is frequently invoked and stores an ambient background pattern in differentiated form. The second, TARGET, stores a signature derived from a target substance placed within the invention's sensing range. The signature retains only signal derivatives that significantly depart from those encountered during PURGE. A SEEK mode employs a similar derivative extraction algorithm, and searches for matches to TARGET signatures stored in a memory bank. During SEEK, pattern correlations to stored targets are sensed, and results displayed.