Laser assisted hatching is a technique done in the laboratory with the use of laser, where the zona is drilled and a gap is made in the zona (zona is the shell of the embryo).
This is done before embryo transfer, the idea is that a small part of the trophectoderm starts protruding out so as to help the embryo attach to the endometrial tissue
Some studies show that laser assisted hatching does improve the success rate of IVF by improving the implantation rate. Some studies also say that laser assisted hatching also improves the implantation rate of frozen embryos
(study 1: http://humrep.oxfordjournals.org/content/21/8/2136.full )
Risk of laser assisted hatching is that the embryo might get damaged. It is also possible that if more than one hatched embryo is transferred it will lead to multiple pregnancies.
Few studies also say that the thinner the zona better are the chances of implantation of that embryo. This means that assisted hatching will help the embryos with a thicker zona to hatch and implant.
The video link bellow shows the way laser assisted hatching is done :