Collimated transmission

When measuring the collimated transmission, the unscattered portion of the light is detected from a collimated illuminated sample. The extinction coefficient can be determined directly from this measured quantity according to the Lambert-Beer law. The extinction coefficient is the sum of the absorption and scatteringcoefficient. The measuring apparatus must be designed in such a way that light scattered in the sample in the forward direction is not detected. This can be achieved by a large distance between the sample and detector or a Fourier

optic in front of the detector. With a standard photometer, which does not take this into account, incorrect values are measured for scattering samples, i.e. not the extinction coefficient. The samples used must have a small optical thickness so that the unscattered portion can be measured. By measuring polystyrene spheres of known diameter, the measurement could be successfully verified with Mie theory calculations.


  • Direct determination of the extinction coefficient using the Lambert-Beer law
  • Measurement of the unscattered light through a sample layer
  • Special measuring arrangement for avoiding the detection of forward scattered light
  • Method successfully validated



Dr. Florian Foschum

Group Leader Calibration-Free Sensors

Tel: +49 (0)731 / 1429 779
Prof. Dr. Alwin Kienle

Prof. Dr. Alwin Kienle

Director Materials Optics & Imaging

Tel: +49 (0)731 / 1429 224

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