Radiation Frequency and Penetration Depth
Date: Winter 2012-2013
Why is it that high intensity laser radiation can have a higher penetration depth in a
medium than low intensity radiation of the same wavelength? Why can it, on the other hand, have a high intensity laser have a lower penetration
depth than a low intensity laser of the same wavelength in biological tissue?
Thanks for the question. Light penetration through a material generally follows an exponential decay law. The intensity of light that makes it through a distance "x" in a material is given by the following equation: I = A*exp(-B*x). I is the intensity of light that penetrates a distance x into the material. A is the intensity of light incident on the material. B is called the linear absorption coefficient. B tells you how much the material absorbs light. If B is larger, then more light is absorbed.
So, if the intensity of light incident on a material is higher, the A value is higher and thus the penetration depth is larger.
As mentioned in the first paragraph, the penetration depth depends on the B value. The B value depends on the wavelength of used. This explanation is my answer to your last question.
I hope this helps. Please let me know if you have any more questions.
Click here to return to the Physics Archives
Update: November 2011