Are you sure you are exporting a true DXF. A DXF is a vector format by design. Working with lasers and turret punches on a daily basis, the quality of DXF files can vary greatly from excellent, load straight into CNC programming software, and away you go, to complete rubbish that requires a bit of work to be able to use it to generate tool paths. If you wish to do work in engineering / manufacturing environment you need to learn how to produce good DXF files to enable manufacture.
The best way to do this varies with the different design software, I have no experience with CATIA so I don't know the exact procedure with this software.If I am required to send a DXF file to anyone for parts cutting and the like, I always check the actual file I am sending to ensure there will be no problems. So I open file in cad software to check, AutoCad if you have it or you can download Draftsight, free from: which will open DXF files and check for ends of lines connected, lines on top of lines and other faults that will upset the profile cutter and add uneccesary cost to your parts.You can send me an example of the files you had problems with at and I will take a look and let you know as regards to suitability for laser cutting.
I have design in Catia and want to export that product in dwg file. File in CATIA and draft the views from the product file and convert it to a dxf.