Glan Laser Polarizer is designed specifically for high energy laser. It is made of two same birefringence material prisms that are assembled with an air space. The polarizer with two escape windows allows the rejected beam to escape out of the polarizer which makes it suitable for high power laser.
Glan-Laser polarizers are designed as polarizer elements that remove the reflected ordinary polarization component of a beam.  A significant amount of reflected light escapes the polarizers through the side port, including all of the ordinary ray and some of the extraordinary ray. As such, the escape beam is not fully polarized, and only the transmitted extraordinary ray should be used for applications that require a high-quality, polarized beam.
They are only designed to work with well collimated light beams; converging and diverging input beams will not exhibit proper polarization and incidence angle at the internal interface.