>That issue of scalability in optical systems is “quite fundamental,” Lu says; this new approach offers a way to circumvent it. “We have other applications in mind,” he says, to take advantage of the device’s “optical selectivity in a 3-D bulk object.” For example, a block of material could allow only one precise angle and color of light to pass through, while all others would be blocked.
Putting my science fiction hat on, if that meant you could build a light-absorbing material you could potentially have (for instance) camouflage that reflected on a certain wavelength only known to your friendly forces. Or hidden assets that require a filter to see - hidden keypads, hidden instructions, that kind of thing.
It's already easy enough to make things that only reflect at specific angles. Filtering by exact wavelength doesn't add a lot; it leaves your message visible in sunlight and incandescent light, at the very least.
Plus camouflage isn't very useful in the first place if you have wide-spectrum cameras.
I don't understand what you mean about 'requiring a filter' to see something.
Sorry, I know you're trying to come up with fun ideas, but I think you're going in the wrong direction.
Message could be written on a background of a slightly different frequency. Multispectral light would't differentiate. Similar to a color-blindness test.
I think single mode laser efficiency would be a better science fiction win, less loss so more power will less cooling. Perhaps a 100kW beam out of a backpack laser?
Putting my science fiction hat on, if that meant you could build a light-absorbing material you could potentially have (for instance) camouflage that reflected on a certain wavelength only known to your friendly forces. Or hidden assets that require a filter to see - hidden keypads, hidden instructions, that kind of thing.