How do different substances in front of each slit affect interference fringes?

[hamson]

If separate baffle around two different substances，What impact on the interference fringes？

 

[mfb]

What do you mean with "If separate baffle around two different substances"?

What impact on the interference fringes？

If you plan to add some transparent material (with different refractive index) in the slits: The fringes can shift in their location.
If you block any possibility for interference: The double-slit interference does not happen any more, you get two single-slit patterns.

 

[hamson]

What do you mean with "If separate baffle around two different substances"?

If you plan to add some transparent material (with different refractive index) in the slits: The fringes can shift in their location.
If you block any possibility for interference: The double-slit interference does not happen any more, you get two single-slit patterns.

Change the damper's own material

 

[mfb]

Which damper, which material?

Actually, I have no idea what you are asking. Can you add some context, sketch or other explanations?

 

[Double-Slit]

Change the damper's own material

You mean the screen's material.Well it doesn't matter where you project that beam,it should be a nice flat surface,thats all you need,and a coherent light source.