Alternative Light Curtains , has someone designed them?

[SiyumLeisho]

Alternative "Light Curtains", has someone designed them?

I know that light curtains are generally known as an aligned collection of light beams that stop/enable a machine when such beams are blocked by a physical object. The "light curtains" that I am thinking is a machine(s) which blocks/dims light through interference. I am wondering whether such machine exists yet (and yes, I know that curtains do the job but that is not the thing I am looking for). And if it does, where can I look for one? If it doesn't, would it be possible to make one? I am thinking of coupling an interferometer with an array of visible light lasers...

 

[Simon Bridge]

Are you thinking of using light to reduce the amount of light through an aperture (i.e. a window?)
I suppose, in principle, one could sample incoming light and project an inverted signal to reduce it's intensity in the room, a bit like how noise reducers work, but I don't think it's practical: good luck.

 

[StrayCatalyst]

If I understand correctly, he's talking about a safety system - if a person reaches through the light curtain, they block some of the light, so the machine knows there's a hazard, and stops operation. These are used with machinery, where an operator reaching into the machine would create a safety hazard if the machine continues to operate.

I've seen a few varieties of them, mostly using low power lasers. It's not all that complicated - basically an array of photosensors, each with its own light source. SiyumLeisho, what are you looking to do differently, that the basic sort of light curtain won't do the trick?

 

[Simon Bridge]

If I understand correctly, he's talking about a safety system - if a person reaches through the light curtain, they block some of the light, so the machine knows there's a hazard, and stops operation. These are used with machinery, where an operator reaching into the machine would create a safety hazard if the machine continues to operate.

That was my first thought - but OP mentions this sort of device in post #1 (1st 2 sentences) as something he is not talking about.
We await clarification... :)

 

[Windadct]

Since you refer to interference - I am thinking you are talking about the wave properties of lasers, requiring coherent light. I do not think ( i may be wrong) that typical lasers have precise enough wave generation to have stable interference between the light of 2 different lasers. The slightest difference in frequency would make it unusable - for interference experiments I have always seen this done with a single laser and beam splitting.

 

[KDLNEAL]

The question seems to be about a mechanism for creating the effect of a blockage of the light curtain in the absence of an actual obstruction. I see no obvious purpose, but if such a mechanism were to be created, one approach, as has been previously noted, would work only if the light used had a coherent source (e.g. a laser) which would be split the beam to create an out of phase stream impinging on the sensor. The only other thoght that comes to mind would be fringing effects, but that doesn't have any obvious advantage over obstruction.