We have a bunch of light curtains at work, and I'm pretty sure they are all LED, not Laser. It cycles through each LED on the transmitter side, while reading *all* the sensors on the receiver side each time. This gives a sort of mesh of sensing lines, instead of just the individual rows. The LEDs need to have a wide enough angle to reach all of the sensors. The good ones in my experience are from Omron, formerly STI. I have also used Banner and Keyence. These all follow serious safety requirements, and they are not cheap. But I have never considered building my own. This is one I'll leave to the experts!

Yes indeed, and the rapid scanning in sequence at the same time looking at the matching detector, is not at all simple. They do work very well but they are by no means simple. And the TS wants to build it themselves, so simple is important. And probably they also want cheap, and that much logic will not be cheap, as it is far beyond an arduino sized system.

 

The red LASER , CdS option looks attractive if object is not traveling too fast.

 

"Laser 66" is a source that I have used in the past, but the last time I contacted them they did not respond to a request for pricing and delivery for 50 laser assemblies. So evidently they do not check email inquiries.