Processor Controlled Multichannel Microdensitometry for Gas Electron Diffraction Patterns

Abstract

The design of a novel type of densitometer for evaluating photographic plates from gas electron diffraction is described. A commercially available linear diode array has been interfaced to a PDP-11/23 minicomputer via the DRV11 parallel interface. The diffraction pattern from a photographic plate is optically focused onto a solid state linear photodiode array. The position of each diode in the array provides the radial location information and the radial intensity of each diode is digitized with 14-bit resolution. Software development provides for control over the scan parameters for the array as well as for on-line manipulation of the collected data. The new instrument thus retains the advantages of digital data filtering described in a previous procedure, but allows for faster data recording since the total pattern is determined in one scanning measurement without the mechanical stepping process which is needed in single channel instruments to move the diffraction pattern through the measuring beam. Rapid acquisition of data with on-line transgeneration should prove to be valuable in the application of the new procedure as a real time data acquisition system for gas phase electron diffraction without photographic intensity recording.