A Prism-Grating-Prism Spectral Imaging Approach

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Publication Type:

Journal Article


Dirk, Carl W.; Druzik, James; Delgado, Monica F.; Olguin, Marco;


Studies in Conservation, Volume 54, Number 2, p.77-89 (2009)


This paper describes the development and application of a spectral imaging system based on the prism–grating–prism (PGP) line-scan concept. The system is validated against an integrating sphere spectrometer using 22 pigments. Measurements were made on several Old Master drawings and one nineteenth-century watercolour. Results are reported for a watercolour by Eugène Louis Lami to illustrate application of the system. For a square object, 23970 individual reflection spectra are captured in a single scan resulting in file sizes of typically 115 MB. Software has been created that permits direct access, by on-screen selection, to the reflection spectrum of any given pixel in an image, reconstructed from the reflection data. PGP-type spectral scanning systems offer the advantage of potentially very high spectral resolutions of <0.5 nm, though the implementation here is for 5 nm resolution. Digital resolution across a square object is 512 ×  50 for a PGP slit width of 80 ?m. Details of the basic device construction, calibration and operation are provided. The system described here was designed for relatively low spatial resolution, although higher resolution can be achieved with modifications suggested in this publication.