https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=22862
Nothing else comes to mind. Maybe something better could be cooked up if you explained how you'd use it and what you need it for.
There is one extremely complex solution. Use DETC to detect whatever you are wanting to go through then wire it up to CRAY to remove a piece of the wall. Then throw in a not gate to reclose it afterward. Then tinker around to make sure it doesn't work backward.
I think one-way mirror IRL are not really one-way, but are mostly only product of illusion.
The property of light being able to pass from any direction with similar strength makes true one-way mirror difficult to make, and TPT's light has that same property while lacking another properties that might help making true one-way mirror.
But TPT has its advantages too, we can use FILT as LBPHacker's post has suggested, which is neat,
or you could abuse make good use of the TPT physics from the findings in the save linked below.
What should you do exactly? Create a 2 px. thick wall of materials which light cannot pass through and add 2 px. thick coating of BMTL on the side you wish light can enter.
i.e. ____BBCC____
B = BMTL, C = COAL
This should work for normal speed PHOT.
It works but only 50% of the PHOT make it to the other side. This is because BMTL has a 50% chance of letting PHOT through. So either you are astronomically lucky or the BMTL is glitching out. You could make a DMND wall to reflect PHOT back though and eventually they will make it though. Also, are we talking about PHOT or another element?