The invention of Fourier Transform IR (FT-IR) spectroscopy has proven to be one of the most important advances in modern instrumentation development. Optical spectroscopy utilizing the interference of light waves has made fast, sensitive detection of molecular vibration/rotation possible due to the large throughput and multiplex advantages provided by FT instrumentation. Interestingly enough, the same technological innovations, which have made FT-IR the instrument of choice for over thirty years, have also made FT-IR instruments extremely sensitive to their operating environment. As a result, the need for thermal stability, mechanical vibration isolation and stringent optical alignment have put severe limitations on where and how an FT-IR instrument can be used, confining it, for the most part, to the laboratory environment. Current FT-IR instruments use a scanning mirror, need to be purged with nitrogen in order to avoid interference from atmospheric water vapor and carbon dioxide and use single element detectors.

Planar Array IR (PA-IR), on the other hand, uses a focal plane array (FPA) detector onto which a beam of light dispersed by a prism or grating is focused. The broad range of frequencies displayed on the pixel array simultaneously make this a multiplex technique without using the complex scanning mechanism or computational requirements (for Fourier transformation of the data) used in FT-IR instruments. Thus the no-moving parts configuration of the PA-IR instrument provide the ruggedness required to make the instrument the size of a "shoe-box" and hence portable. In addition the increased sensitivity (100-1000X over single element FTIR detectors) of the FPA allows an IR spectrum to be accumulated in as little as 10 microseconds. The only current limitation comes from the frequency range available (3400-2000 cm-1) due to the initial availability of only indium-antimonide FPAs during the development of the prototype. With the impending availability of Hg-Cd-Te (MCT) FPAs, the available bandwidth of PA-IR instruments will be increased to include the IR " fingerprint " region (1800-750 cm-1) without an appreciable loss of sensitivity and speed. Hence many new applications including on-line processing and studies in molecular/polymer dynamics will now be possible using state-of-the-art PA-IR instrumentation.