| Author | Message | ||
     Mark (Courage) |
hello, I am interested in a model (for example Lambert Beer) which can describe the absorption of the energy trough three layers. Afterwards I want to now how much energy would be available for the third layer so that i can make an estimation of the temperature rise by a infrared light. Further more I am interested in de absorption coefficients of different polymers at a infrared wavelength of 850 -1200 nm | ||
| David W. Hopkins (Dhopkins) |
Mark, The Beer-Lambert Law gives the absorption of light of a mixture as the sum of the contributions of each absorber as if it were alone. Therefore, you may combine the first and second layers to find out how much light is absorbed and therefore available for raising the temperature of the sample. However, this will only give you an upper limit, assuming all the energy stays within the sample. If the sample is in good contact with the surroundings, the actual temperature rise may be negligible, due to heat transfer to the surroundings. Regards, Dave | ||
| hlmark |
Mark - a key question is: do the layers scatter the light or are they clear? If clear, then the absorbance (via a transmittance measurement) is the sum of the absorbances of the individual layers - you don't even have to worry about interactions. If they scatter the light, then the situation becomes much more complicated, because the illumination of the second and third layers is dependent on both the absorbance and scattering characteristics of the first layer. The general problem is unsolved, although Don Dahm has done considerable work (and written much of it up in NIR News and other places) trying to understand the effects. As for calculating the temperature rise of the third layer, there was a similar question posted recently, to which I wrote a moderately extensive discussion of the complications inherent in that attempt; unfortunately I don't recall the thread it appeared in. Howard \o/ /_\ |