page_title: DU spectrophotometer
section_title: Model D (limited production)
hierarchical_section_title: DU spectrophotometer / Development / Model D (limited production)
caption_attribution_description: Original photograph used for Figure 6. Quartz photoelectric spectrophotometer from Original photograph used for Figure 6. Quartz photoelectric spectrophotometer from Cary, H. H.; Beckman, Arnold O. (1941). "A Quartz Photoelectric Spectrophotometer". Journal of the Optical Society of America. 31 (11): p. 687. doi:10.1364/JOSA.31.000682. No copyright renewal for the journal (first renewal appears for 1951). No copyright renewal for the paper. No copyright renewal for the photograph (checked 1968, 1969).
context_page_description: The DU spectrophotometer or Beckman DU, introduced in 1941, was the first commercially viable scientific instrument for measuring the amount of ultraviolet light absorbed by a substance. This model of spectrophotometer enabled scientists to easily examine and identify a given substance based on its absorption spectrum, the pattern of light absorbed at different wavelengths. Arnold O. Beckman's National Technical Laboratories developed three in-house prototype models and one limited distribution model before moving to full commercial production with the DU. Approximately 30,000 DU spectrophotometers were manufactured and sold between 1941 and 1976.
  Sometimes referred to as a UV–Vis spectrophotometer because it measured both the ultraviolet and visible spectra, the DU spectrophotometer is credited as being a truly revolutionary technology. It yielded more accurate results than previous methods for determining the chemical composition of a complex substance, and substantially reduced the time needed for an accurate analysis from weeks or hours to minutes.
context_section_description: The A, B, and C prototype models all coupled an external Beckman pH meter to the optical component to obtain readouts. In developing the Model D, Beckman took the direct-coupled amplifier circuit from the pH meter and combined the optical and electronic components in a single housing, making it more economical.
  Moving from a prototype to production of the Model D involved challenges. 
  Beckman originally approached Bausch and Lomb about making quartz prisms for the spectrophotometer. When they turned down the opportunity, National Technical Laboratories designed its own optical system, including both a control mechanism and a quartz prism. Large, high optical quality quartz suitable for creating prisms was difficult to obtain. It came from Brazil, and was in demand for wartime radio oscillators. Beckman had to obtain a wartime priority listing for the spectrophotometer to get access to suitable quartz supplies.
  Beckman had previously attempted to find a source of reliable hydrogen lamps, seeking better sensitivity to wavelengths in the ultraviolet range than was possible with tungsten. As described in July 1941, the Beckman spectrophotomter could use a "hot cathode hydrogen discharge tube" or a tungsten light source interchangeably. However, Beckman was still unsatisfied with the available hydrogen lamps. National Technical Laboratories designed its own hydrogen lamp, an anode enclosed in a thin blown-glass window. By December 1941, the in-house design was being used in production of the Model D.
  The instrument's design also required a more sensitive phototube than was commercially available at that time. Beckman was able to obtain small batches of an experimental phototube from RCA for the first Model D instruments.
  The Model D spectrophotometer, using the experimental RCA phototube, was shown at MIT's Summer Conference on Spectroscopy in July 1941. The paper that Cary and Beckman presented there was published in the Journal of the Optical Society of America. In it, Cary and Beckman compared designs for a modified self-collimating quartz Fery prism, a mirror-collimated quartz Littrow prism, and various gratings. The Littrow prism was a half-prism, which had a mirrored face. Use of a tungsten light source with the quartz Littrow prism as a monochromator was reported to minimize light scattering within the instrument.
  The Model D was the first model to enter actual production. A small number of Model D instruments were sold, beginning in July 1941, before it was superseded by the DU.
caption: Quartz photoelectric spectrophotometer, Cary & Beckman, 1941[26]:687
exif: {"Image ImageWidth": "2738", "Image ImageLength": "3500", "Image BitsPerSample": "[8, 8, 8]", "Image PhotometricInterpretation": "2", "Image ImageDescription": "HyperFocal: 0", "Image Make": "Phase One", "Image Model": "IQ3 80MP", "Image Orientation": "Horizontal (normal)", "Image SamplesPerPixel": "3", "Image XResolution": "300", "Image YResolution": "300", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS5.1 Macintosh", "Image DateTime": "2016:09:19 11:31:15", "Image ExifOffset": "304", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "662", "Thumbnail JPEGInterchangeFormatLength": "4199", "EXIF DateTime": "2016:09:16 09:30:27", "EXIF ExposureTime": "40370/2422199", "EXIF ExposureProgram": "Manual", "EXIF ISOSpeedRatings": "50", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2016:09:16 09:30:27", "EXIF DateTimeDigitized": "2016:09:16 09:30:27", "EXIF ShutterSpeedValue": "590689/100000", "EXIF LightSource": "other light source", "EXIF ColorSpace": "Uncalibrated", "EXIF ExifImageWidth": "2199", "EXIF ExifImageLength": "1520", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed"}