In UV-VIS analysis of a thin film, suppose we measure Reflectance and absorbance. Absorbance sometimes can be different in meaning. Some instruments include the reflectance in the absorbance, and some give true absorbance (after correcting the reflectance).
In an ideal setup, how does the absorbance behave? does it oscillate as a function of frequency due to interference? Or the interference in the reflectance and transmittance cancels out and we get absorbance without oscillation?
Another thing: if we have semi-reflecting barriers on the two sides of a film, does the multiple reflection within the film interfere inside to change the absorption to a pattern other than simply exponentially decaying?
There are a lot of content in this question so it would be difficult to answer everything but here are a few comments that may help your reflection:
-UV-VIS spectroscopy use white sources and monochromators so the light is not coherent and interferences phenomenon's are limited. If your sample has a simple planar geometry you should only observe peaks of reflectivity and transmissivity when your wavelength is a multiple of the film thickness.
-Even thou you don't seem to really do the confusion, a clear distinction must be made between absorbance (the property of a material) and absorption (the quantity of luminous energy absorbed). Absorbance is globally independent of intensity, and thus of interferences, whereas absorption is proportional to the flux and thus varies with interferences. Semi reflecting barriers could impact the repartition of absorbed energy in a film.
However in most cases, the intensity of those phenomenon is very low and you probably don't need to care about it. If you really need to, some simple simulation software like IMD can be used. The difficulty is that you need to input your materials parameter which are generally unknown if you need to do spectroscopy...
dear colleague
it is very complicated, if you use monochromatic light your system should be assimilated to Pérot-Fabry interferometer with suitable optiical ajustements and in reflection. Hence, you have in litterature how the circular fringes will appear. the absorbance is correlated, in intensity, with reflectance then i believe it will have same allure
regards
Some suggestions for you which should clarify all your questions:
Article The electric field standing wave effect in infrared transfle...
Article The Electric Field Standing Wave Effect in Infrared Transmis...
Article Removing interference-based effects from the infrared transf...
Article Removing interference-based effects from infrared spectra - ...
Article CaF2: An Ideal Substrate Material for Infrared Spectroscopy?
You can also have a look at my lecture notes:
Preprint Wave optics in Infrared Spectroscopy
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