Infrared technique


Infrared technique

In 1934, the Commission for Physical Capabilities was requested to conduct experiments with invisible rays. Since then, the laboratory has been working on infrared technology:


Background information: What is infrared?

When looking at the electromagnetic spectrum, the visual part that our eye is sensitive to is the most familiar. This part roughly corresponds to wavelengths where the solar radiation is maximal. In addition to the visual part of the spectrum, whose wavelength ranges from 0.4 to 0.7 micrometre (μm), we find other spectral areas where many optical applications have proved possible. For example, for wavelengths smaller than 0.4 μm, we find the ultraviolet that is used, among other things, for making electronic chips. For wavelengths larger than 0.7 μm the infrared. The range of 0.7 to 3.0 μm is called the near-infrared and the range above 3.0 μm is the far-infrared, which is the part of the spectrum no light source is required for observations. The object to be observed emits radiation itself based on its own temperature. The warmer the object, the more radiation it emits. This is illustrated in the following picture, in which the radiation distribution over the visual and infrared parts of the spectrum is displayed for objects with different temperatures. It is clear that the radiation increases strongly with the temperature and that the maximum of radiation distribution for higher temperatures shifts to shorter wavelengths.

Visual and infrared spectrum
Visual and infrared spectrum (zon= sun; brand= fire; kookplaat = hot plate; omgeving = environment; nabij infrarood = near infrared)

Infrared radiation was first observed by Sir William Herschel in 1800. At that time radiation was measured with a mercury thermometer.  Herschel observed during the analysis of the solar spectrum that in addition to the red wavelengths heat could also be detected in this way. He called it “invisible light”. Some other discoveries from the last two hundred years that have made the use of infrared technology possible are:

  • 1833: Nobili develops together with Melloni a thermopile of Bismuth / Antimony
  • 1840: Herschel Jr. discovers three atmospheric windows
  • 1873 and 1877: Smith, Adams and Day discover Selenium as a photoconductor and photovoltaic cell
  • 1880: Langley uses a platinum bolometer for atmospheric transmission measurements
  • 1901: Bose discovers photoelectric effects in lead sulphide
  • 1929: Kohler developed a photocathode of Ag / O / Cs that was sensitive to 1.2 μm
  • 1942: Eastman develops an infrared-sensitive film that is sensitive to 1 μm
  • 1947: Golay realises a very sensitive pneumatic detector for heat radiation
  • 1950: Shockley develops the first transistors
  • 1960: Highly sensitive InSb, Ge: Hg and HgCdTe photon detectors are being developed
  • 1970: Development of miniature chillers, including at Philips USFA in Eindhoven