Backscattering of light at a black hole

[MasterD]

In my book it states that if you shine a laser beam on a black hole some of the light is backscattered; so that way you can detect black holes; why is that?

Is it because of diffraction or is it because of quantum mechanical effects?

 

[George Jones]

In my book it states that if you shine a laser beam on a black hole some of the light is backscattered; so that way you can detect black holes; why is that?

Is it because of diffraction or is it because of quantum mechanical effects?

What book?

If you send light in just the right direction, it will loop once around the black hole and come back to your eye/detector. If you send light in just the right direction, it will loop twice around the black hole and come back to your eye/detector. If you send light in just the right direction, it will loop three times around the black hole and come back to your eye/detector. ...

I'm not sure about the feasibility of using this as a method for detecting black holes.