material that has fast light-sensitive transparency/opacity?

[wosoka]

Is there any material that if applied to or used as a film and illuminated by IR, UV beam or visible light beam or beam of specific polarization will become transparent or opaque in that spot and the opposite when not, and transition at fast rates (<= 8 ms)?

Ordinary photochromic films are quite slow with 15 second transition to one state and several minutes to the other.

[koti]

23 minutes ago, wosoka said:

Is there any material that if applied to or used as a film and illuminated by IR, UV beam or visible light beam or beam of specific polarization will become transparent or opaque in that spot and the opposite when not, and transition at fast rates (<= 8 ms)?

Ordinary photochromic films are quite slow with 15 second transition to one state and several minutes to the other.

I don’t think you could get such fast transition times without an active system like liquid crystal or similar. 8ms is good quality monitor territory so a chemically based technology wouldn’t be capable to do the job. Im not an expert but to get such times you’d have to combine triggering the dimming with electrical current with some kind of a sensor array built into the material. 

[wosoka]

An LCD matrix or anything with pixels wouldn't do. But a sheet material which requires electrical field or similar to function would work.

[koti]

7 minutes ago, wosoka said:

An LCD matrix or anything with pixels wouldn't do. But a sheet material which requires electrical field or similar to function would work.

They make dimmable windows based on some kind of liquid crystal technology which requires electrical current to trigger. There are also these sheet like display systems, all the big mobile phone players are testing these. You’d need to provide more details on what exactly you are looking to build. 

[wosoka]

2 hours ago, wosoka said:

Is there any material that if applied to or used as a film and illuminated by IR, UV beam or visible light beam or beam of specific polarization will become transparent or opaque in that spot

What you are referring to is PDLC (polymer dispersed liquid crystal), it is either all opaque or all transparent. There was some research on making a PDLC with pixels but it would have the same issue as ordinary LCD for my use case. With both I can't achieve what I quoted above, which is making an area of a film become transparent or opaque by shining a beam on it.

What I am looking for is similar to a beamsplitter used to combine beams, but in my case I need one beam to block an area of the other (bigger) beam, and beam position can change. Unlike a beamsplitter where they beams would get superimposed.

Edited April 1, 2018 by wosoka

[John Cuthber]

In the right conditions, this is very fast.

https://en.wikipedia.org/wiki/Saturable_absorption

[Chopsticks]

So, you need very fast transition, reversibility, and locality (? whatever word describes a bulk material where only one part changes). I suspect you won't find anything that can do completely clear to completely opaque; if you can't get 100%/0% what kind of percentages can you tolerate?

My first google was reversible light sensitive polymers, but couldn't find any speed information. Closest I saw was 100s each way. I guess those are the photochromic films you mentioned in the OP

I do know something that will do fast and reversible, and somewhat local (the version I know creates a interference pattern, not a single spot). Look up "optical kerr effect" and maybe "four-wave mixing" on wikipedia.  The version I worked with, you have a liquid crystal "capacitor" - crystal is in something transparent, with electrodes to apply a voltage difference to the front and back sides. Bias that with a few hundred volts - almost no current unless something blows up. Then you can do things like beamsplit a laser and recombine at the cell to get a dark interference pattern.

For what you want, I think you can just shine a single powerful laser at the cell, and the optical kerr effect will happen at that point. Now, this bends the light instead of absorbing it so you need a beam dump to one side, but that should still give you a dark spot on an image. (in some respects this is similar to a biased diode. the voltage is almost enough to switch the liquid crystal, and the light hitting a spot adds energy to push that area to switch) Reviewing, maybe not quite what you wanted. The cell wouldn't necessarily darken, but if you projected an image through the cell the same time as the laser, then the image would come out with a dark spot at the laser location.

Obligatory safety reminder: Lasers powerful enough to do something interesting can blind you or do other nasty things, even IR lasers, and any scattered light is still rather dangerous. Wear your laser safety goggles.

 

[Strange]

I don't know if it helps, but you can get liquid-crystal devices that modulate the phase of reflected light. These can be used to create holographic images, for example.

https://en.wikipedia.org/wiki/Spatial_light_modulator

[wosoka]

2 hours ago, Chopsticks said:

I suspect you won't find anything that can do completely clear to completely opaque; if you can't get 100%/0% what kind of percentages can you tolerate?

Thanks, If I can get 25% or more of the original light to pass and 90% or more of the original light to be blocked than it will do.

 

I looked up "optical kerr effect" and looks like it would mess up any other wave besides a beam so looking through it would give false image.

6 hours ago, John Cuthber said:

In the right conditions, this is very fast.

https://en.wikipedia.org/wiki/Saturable_absorption

"Saturable absorption is a property of materials where the absorption of light decreases with increasing light intensity. "

I'm not sure how such a material sheet would work here. Care to explain please?

Edited April 1, 2018 by wosoka

[John Cuthber]

If you have a sheet of coloured plastic and shine a bright enough light at it you excite all the dye molecules into some higher state.

That excited state won't be the same colour as the original dye and it will allow some colours of light through that it previously blocked.

The amount of light you need for this is likely to make it impossible, except on  a very small scale

[wosoka]

yeah, probably won't work

 

What about optically active dyes ? Anyone heard of em? Someone said there are two kinds, ones photo bleach and decompose and others that don't decompose but need constant source of light as those bleach for only few nanoseconds. Haven't heard from him yet.

Edited April 4, 2018 by wosoka