This here E3Z-D61K is a Omron photoelectric sensor with the amplifier built right in. Uses an infrared LED at 860 nm, which means the beam is invisible but won't get confused by overhead fluorescents or sun shining through a dirty window. It's diffuse reflective – shoots out a beam and watches for it to bounce back. The sensing range is 5 to 100 mm with a wide view, so you've got a generous cone to catch parts that aren't perfectly aligned.
How it sits next to its kin
The E3Z-D61K-M3J is the same sensor but with an M8 4-pin connector on a 0.3 m pigtail instead of the long cable. If you're swapping a panel that expected the M8 version, this D61K will mount in the same hole and sense the same – you'll just have to strip and terminate the 2 m cable instead of plugging into a prefab harness.
Out on the route
Pre-wired 2 m cable; draws 30 mA max.