Design and Performance of a Biological Spectrograph

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Abstract
A spectrograph was constructed to determine biological action spectra by simultaneous analysis of spectral efficiencies. With a minimum compromise the design satisfies requirements of spectral purity, intensity, and specimen area for such photobiological responses as mutagenesis, photo-tropism, and photoreactivation. The spectrograph utilizes the lemniscate plane grating mounting with a single mirror. Light from a 14-kw high-intensity carbon arc is focused through a quartz lens on a 5 inch slit; it passes to a 20-inch front-surfaced concave mirror, and is reflected to converge upon a mosaic of two 4 X 8-inch gratings (6000 rulings/cm). In the 53 feet between grating and focal curve, a bank of filters absorbs irra-diances of the second and higher orders and only the first-order spectrum on one side of the central image is used. The spectrum extends from 2200 to 8000 A and is 19 feet wide (a nearly uniform dispersion of 1 A/mm). Magnification is 1.7, giving an 8.5 inch high spectrum. Flux at 3800 A with a 25-mm slit is 450 [mu]w/cm2 and may be increased ninefold by a Fresnel-type prism arrangement; mirror banks are also available on the focal curve to redirect the beam. Operational characteristics as a function of slit width, extra-focal positions, and specimen size are easily determined, increasing the flexibility of the system.