Note that the basic laser system is with laser head and collimating optics mounted on rail with enclosure.

Optical Enclosure
The laser heads are contained in an enclosure consisting of a tooling plate base and a hinged, interlocked cover.  An air filtration system provides a clean, positive pressure, environment for the optics, to protect against environmental dust.

The enclosure also includes optics to couple into the optical fiber, and a combination beam dump shutter/absolute power meter.

这几句话中都有enclosure，enclosure在这几句话中分别是什么意思？ 谢谢！

enclosure is noun
1 an area that is sealed off with an artificial barrier.

请问哪个网站上有英文词典，看英文解释，enclosure可能是“外壳”的意思。