Transmission coefficient

See also reduce.

Transmission coefficient is a scalar multiplier for the reflectivity and can be used for several different purposes:

 * For NG-7 data is divided by the monitor.  If you set the transmission
   coefficient to the detector to monitor ratio (usually about 12) you will 
   get normalized reflectivity.
 * For sample environments with significant absorption, set the transmission
   coefficient to the attenuation you expect through the medium.
 * For back reflectivity, where the beam enters the side of the substrate
   and reflects off the back side of the film, set the transmission 
   coefficient to the absorption you expect in the substrate.

These effects are multiplicative.

If you don't know the correct value of the transmission coefficient, you can guess by looking at the data below the critical angle. There is a flat region which should be perfectly reflecting. Take the average of the values in this region and use that for the transmission coefficient. The "Guess" button in Reflred uses the maximum value of the reflectivity rather than the average value.

Please make sure the guessed value makes sense. If for example the critical edge is too low, you may not see it in the data and the guessed transmission coefficient will be too high.

2005-04-22


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