Stationary Hadamard Transform Spectrometry.

Two novel applications of a stationary electro -optic shutter have been successfully developed for use in Hadamard transform spectrometry. The first of these combines interferometric and Hadamard transform techniques for a spectrometric instrument offering advantages over conventional spectrometers. A Hadamard transform encoding mask is incorporated into a multiple-beam Fizeau interferometer design, allowing the use of a single detector element rather than the more problematic linear detector arrays in the near-infrared region. The instrument can be made small, inexpensive, and compatible with harsh industrial environments. The second application of the stationary encoding mask is in conjunction with a Hadamard transform (HT) Raman spectrometer for use in the near-infrared spectral region. This spectral region is important to the practicing Raman spectroscopist since problems associated with fluorescence in the visible spectral region are reduced significantly. However, on going to the near-infrared region, a sacrifice is made in terms of adequate Raman signal resulting in poorer signal -to-noise ratio. As such, there is a need for multiplexing spectrometers to recover the loss associated with the near -infrared spectral region. The Hadamard transform Raman spectrometer using a stationary encoding mask offers this multiplex advantage. Both instruments share some special features such as the ability to perform spectral subtraction. However, the stationary encoding masks used in both instruments have some disadvantages (e.g. less than 100% modulation efficiency). One disadvantage associated with the electro -optic encoding masks is the finite mask response time. The finite mask response time, in addition to increasing data acquisition time, has deleterious effects on the recovered spectrum following a Hadamard transform To a large extent, the problem has been alleviated by a special correction procedure which when applied to spectral results actually compensates for the spectral error associated with the finite mask response time. The use of this correction procedure, in effect, allows the user to acquire spectral data at accelerated rates relative to conventional acquisition schemes.