A gas analyzer for the absorption-spectroscopic in-situ determination of at least one chemical and/or physical parameter of a gaseous measurement medium, wherein the gas analyzer includes a first housing; at least one laser as a radiation source, which laser is arranged in the first housing; at least one first process window for coupling the radiation emitted by the laser into a measurement medium; and at least one detector by which, following interaction with the measurement medium, the radiation is detected. The first process window can be configured as an afocal meniscus lens having a convex surface and a concave surface.