A diffractive optic image spectrometer (DOIS)

Abstract

The diffractive optic imaging spectrometer, DOIS, is a high resolution, compact, economical, rugged, programmable, multi-spectral imager. The design implements a conventional CCD camera and emerging diffractive optical element (DOE) technology in an elegant configuration, adding spectroscopy capabilities to current imaging systems. One limitation of DOEs, also known as zone plate lenses, is abundant chromatic aberration. DOIS exploits this typically unwanted effect, utilizing a DOE to perform the imaging and provide the dispersion necessary to separate a multi-spectral target into separate spectral images. The CCD is stepped or scanned along the optical axis recording a series of these spectral images. This process is referred to as diffractive spectral sectioning. Under this dissertation, three-dimensional spectral/spatial DOE imaging theory was developed to describe and predict the system's performance. The theory was implemented in a software model to simulate DOIS image cubes. A visible spectrum DOIS prototype was designed, fabricated and characterized. The system's incoherent point spread function was theoretically modeled and experimentally determined. To verify the simulations, the prototype's performance was demonstrated with a variety of known targets and compared to simulated image cubes. To reconstruct the three-dimensional object cubes, various deconvolution algorithms, nearest neighbor, inverse filtering and constrained iterative deconvolution, were developed and applied to both computer generated and experimentally measured image cubes. The best results were obtained using an SVD inverse Fourier deconvolution algorithm with regularization for noise suppression. The results demonstrate a resolving power greater than 288 (lambda /Deltalambda = 577nm/2nm). Finally, three additional DOIS designs are presented as suggestions for future work, including a configuration with no moving parts which records the entire 3D image cube in one "snapshot". DOIS is a practical image spectrometer that can be built to operate at ultraviolet, visible or infrared wavelengths for applications in surveillance, remote sensing, medical imaging, law enforcement, environmental monitoring, and laser counter intelligence.