Provided is a transparent plastic container that may be laser-welded even though the transparent plastic container does not contain a significant quantity of laser absorber and has excellent transparency, and a method for efficiently producing the transparent plastic container. A transparent plastic container including a cover portion made of a transparent polyester resin and a main plastic container body made of a transparent polyester resin and a method for producing the transparent plastic container are characterized in that the cover portion is welded to the main plastic container body by condensed light of a long-wavelength laser having a wavelength of above or equal to 1.0 m.

A device and a method for performing and monitoring a plastic laser transmission welding process includes a processing beam source for emitting a processing radiation into a joining zone between two joining members so that a weld seam is formed, a measuring beam source for irradiating a measuring zone with a measuring radiation, a detection unit for detecting the measuring radiation reflected by an interface between the weld seam and its surroundings in the joining members, and an evaluation unit connected to the detection unit for determining the depth position of the interface in the joining members from the detected reflected measuring radiation.