[li]Diffraction is when a wave passesa through a gap or object, and it spreads[/li]
[li]For maximum diffraction to occur, the wavelength of the wave must equal or be roughly the same size as the gap ([lambda] = gap-size)[/li]
[li]The wavelength of laser red light is [b]630nm[/b], or 6.3[multiply]10^-7[/li]
[li]Plane wave fronts are equally spaced and travelling at the same speed[/li]
These wavefronts then become circular when they pass through a gap roughly the same size as their wavelength:
This is called [b]diffraction[/b].
In the above example, they diffract a lot.
In the below example they just reflect, as the gap isn't large enough:
In the below example the gap is a bit bigger, so not much diffraction occurs: