Laser assisted hatching is a very useful technique to make embryos implant themselves into the wall of the uterus. This technique helps the embryo hatch itself from Zona Pellucida, the protective outer shell, and implant itself into the uterine wall once the embryo transfer is done.
As the embryo develops into the blastocyst stage (late day 4 onward), it needs to escape the "shell" that once protected it. The blastocyst continues to fill with fluid and weakens the shell. Eventually the blastocyst hatches out of the shell (pictured) and is ready to implant into the lining of the uterus. This is thought to happen around 7-8 days post insemination.
With LAH, the embryo is artificially hatched.