Why does a circle of light appear when I shine a laser pointer at a wire? When I point a laser at a wire , a circle of light appears on a wall behind it . why this happens.
What is the circle of light and why does it appear?
Could anyone give some tips on what I should search for or any references? 
wire have diameter 3.17 mm 
PS.I don't good at English,,, sorry

Wire perpendicular to the projection screen

Laser under on the wire Then born circle of light
 A: The wire is a cylindrical reflector. The laser light that hits the top of the wire is reflected upwards; the light that hits the side is reflected sideways. 
This is simple reflection - no need for a diffraction explanation.
A: Light has properties of waves and particles and doesn't necessarily travel in "straight lines".
There is an interesting experiment (I will look up the original scientists who did it and post that info here) where they set up basically a cardboard circle in front of a wall and then shine a flashlight at it.
Interestingly enough, there is a shadow in the shape of a circle on the wall behind the cutout, but there is a bright spot in the middle of the shadow. How did the light get there? Well, the answer is, it doesn't move in a straight line.
I think your laser is doing the same thing, but the effect is probably exacerbated by the reflective properties of the metal wire that you are shining the laser at. 
Edit
Please see the very informative comments below for more information about the experiment. It is referred to as the Arago/Fresnel/Poisson spot.
