The penetration depth is defined as the depth for the 1/e attenuation. The values you cited, match exactly the ranges for IR-C R = 0,1 mm, IR-B R = 2 mm and IR-A R = 4-5 mm. You have no uncertainty just the different ranges for the different wave lengths.

IR-C lambda = 1mm - 3000nm

IR-B lambda = 3000 - 1400 nm

IR-A lambda = 1400 nm - 780 nm

The range of 0.1 mm for IR-C is in the same depth like the horny layer.

Thats you Hanno.. For ranges..

Ya I have this wavelength besed classification from CIE..

Dear Hanno,

In fact, I completely agree with you. accurately tabulated and nicely said.

 Professor Hanno Krieger gave a very good answer & I want to give a reply for the second question : Infrared coagulation (IRC) is a non-surgical  procedure  which is used to treat small to medium sized internal hemorrhoids.This is generally not a painful procedure and recovery time is relatively short. Patients usually can return to their regular activities the same day.

I agree with  dear Dr. Nizar Matar´s comment. If you absorb infrared radiation you deposit energy in form of heat. If the irradiated tissue can´t compensate this local energetic transfer you are overheated and burnt. Thats exactly the application in cases without surgery. Because of restricted attenuation range, you are constrained to the surface layers.

BTW: This thermic effect doesn´t cause cancer like ionizing radiaton.

Thank you all @ for useful information..

In physiotherapy, we dont use IRC..

Therapeutic range which we use is between 760nm to 15000nm..