Extension of a reference spectrophotometer into the near infrared

The purpose of this paper is to document adaptation of an existing reference spectrophotometer to the near infrared. Its previous wavelength range was from approximately 200 to 800 nm. The present adaptation increases its wavelength range to 2500 nm. The hardware and software necessary to achieve this were implemented along with tests necessary to characterize the instrument when it is operated in the near infrared (800 to 2500 nm). The accuracy of the transmittance measurements ranges from approximately 0.0002 to 0.012 transmittance units depending on instrument configuration, wavelength, and the sample itself, incedental to the success of this work was conversion for a dedicated microcomputer with interface boards. Many of the latter were designed at NBS.