# A Interference fringes in Absorption spectra

1. Dec 20, 2017

### sounouhid

Hello every one
I deposited TiO2 thin layers on glass conductive substrate and then i took there absorption spectra.
My question is why do i see interference fringes in the absorption spectra of my samples.

2. Dec 20, 2017

### sophiecentaur

Your two faces of your thin layers constitute an interference filter. The lines in the transmission spectrum will, in all probability, be frequencies that are Reflected by the filter. An interference filter need not absorb any energy. In fact, in solids, the absorption tends to have a band structure and not a line structure - which occurs in the isolated molecules in gases.
Try observing the reflected light (with non-normal incidence) and that could well give you a line spectrum (comb) that will fit the transmitted lines. (Tilting the filter will change the actual frequencies slightly)

3. Dec 20, 2017

It is possible the thin layer of $TiO_2$ is exhibiting the Fabry-Perot effect as well as the bulk absorption spectrum that goes with it.

4. Dec 20, 2017

### sounouhid

Thank you all guys for responding me ,i really appreciate your help.

5. Dec 20, 2017

### sounouhid

Can you please give me a document that help me doing that fit.

6. Dec 20, 2017

### sophiecentaur

Look up thin film interference or Interference filters for loads of sources. Pick one to suit you.

7. Dec 21, 2017

OK thank you