Diffraction from Sub-Wavelength Features

[peter.ell]

I was wondering what occurs when a diffraction grating is produced with features smaller than a wavelength of visible light. If the pits in a CD were made to be only a few tens of nanometers wide, what would we see?

 

[DiracRules]

The minimum intensity occurs at angles given from the following law:d\sin\theta_{min}=\lambda\approx \theta_{min}=\frac{\lambda}{d}
So, if d <<\lambda, then \theta_{min} becomes great: you can't see any minimum of diffraction.

 

[Andy Resnick]

I was wondering what occurs when a diffraction grating is produced with features smaller than a wavelength of visible light. If the pits in a CD were made to be only a few tens of nanometers wide, what would we see?

It entirely depends on the details- pit spacing, etc. Subwavelength apertures produce evanesecent field modes. People have been trying to exploit that property for super-resolution imaging.