OU NanoLab/NSF NUE/Bumm & Johnson
Lambert’s Law of Absorption
•The intensity I0 if a beam of
light decreases exponentially as it passes though a uniform absorbing medium with the linear decay constant α.
Restatement: In a uniform absorbing medium, the intensity
of a beam of light decreases by
the same proportion for equal path lengths traveled.
•The linear decay constant α is a
characteristic of the medium. It has
units of reciprocal length. α is the path
length over which the intensity is attenuated to 1/e.
Photo:
http://www-history.mcs.st-andrews.ac.uk/history/PictDisplay/Lambert.html
α
I0
I(x)
x
Lambert
described how intensity changes with distance in an absorbing medium.
I
l
Johann Heinrich Lambert
1728-1777
The distance traveled through the medium is called the path length.