Construction and Evaluation of a Visible Spectrometer Using Digital Micromirror Spatial Light Modulation

Digital micromirror devices (DMDs), also known as spatial light modulators, have been produced in a wide variety of configurations specific to their applications such as joint-transform correlator systems, optical neural networks, and high-definition televisions. The characteristics of DMD technology and flexibility of design lend themselves to a new application in optical spectrometers. Medium-resolution optical spectrometers, with a spectral bandwidth on the order of 1 nm, are widely used in instrumentation designed to record molecular absorption spectra in the ultraviolet and visible regions and are among the most widely used laboratory instruments. Modern UV-visible spectrometers usually are designed to use a multichannel detector, such as a photodiode array (PDA), in conjunction with a compact fixed-resolution spectrograph and can record spectra with reasonable speed, ∼ 30 ms. These spectrographs have no moving parts and are used for on-line detection of chromatographic eluents, for routine analytical determinations, and for industrial applications such as measurements made in process streams. However, diode array detectors are generally more expensive and are less sensitive than photomultiplier tubes (PMTs), particularly in the UV, and require cooling when a long integration time and low dark current are necessary. In addition, the diode array cannot acquire spectra fast enough for most kinetic studies to be made. A medium-resolution spectrometer which incorporates DMD technology and a PMT for detection has the potential of obtaining a spectrum on the order of a few milliseconds with high sensitivity at a lower cost than that for current PDA or charged-coupled device (CCD) spectrometers. Another advantage of the DMD spectrometer is that it possesses the capability of repetitively scanning a small portion of the spectrum without collecting the entire spectrum (random pixel access). The high sensitivity of a DMD spectrometer using a PMT also makes it ideal for fluorescence and phosphorescence detection.