True Double Beam

Absorbance spectra of polystyrene (PS) with difluoroethane (DFE) contaminant gas
A) Single beam mixed spectrum of PS and DFE (top),
B) Single beam spectrum of DFE (red)
C) PAIR spectrum of PS and DFE obtained in double beam (bottom),
DFE eliminated automatically leaving a spectrum for PS.

A PA-IR spectrograph can be designed in a true double beam configuration so as to take advantage of the large number of pixels available in the focal plane array. Hence both beams of the double beam instrument can be incident on the array simultaneously providing both a "sample" and "reference" spectrum simultaneously. Since the path lengths of each of the two beams are identical, background contaminants like H2O and CO2 can be compensated for directly thereby eliminating the need for purging. Elimination of purging not only has positive implications for increasing sample throughput; it lowers operating costs by reducing the need for a constant gas supply. Also, if a solvent is placed in the reference beam, its absorbance effects may be compensated for as well, allowing for measurement of very dilute solutions. (Note that “solvent effects” on the sample may still remain but these can be easily observed once the solvent absorbance bands have been removed.) Double Beam technology also allows for excellent instrument stability.