Serious question: could you selectively block invisible light on the way in and *visible• light on the way out? Because that to me would be an awesome window.
I don't think so, because light propagation is symmetric. If light can get in, it can get back out by reversing direction.
However, if you simply don't want to be seen by people looking in from the outside, there are still some options:
If the inside is much darker than the outside, light from inside is overwhelmed by light from outside getting reflected back (the operating principle of "one-way" mirrors).
If the window is covered with a grid that only has small gaps (e.g. window blinds), it's hard to recognize objects on the other side unless your eye is close enough to look through a single gap.
If the glass has a rough surface (i.e. frosted glass), light that makes it through is scattered in different directions, blurring objects that aren't very close to the window.
Various combinations seem possible. (Frosted glass window blinds?)
However, if you simply don't want to be seen by people looking in from the outside, there are still some options:
If the inside is much darker than the outside, light from inside is overwhelmed by light from outside getting reflected back (the operating principle of "one-way" mirrors).
If the window is covered with a grid that only has small gaps (e.g. window blinds), it's hard to recognize objects on the other side unless your eye is close enough to look through a single gap.
If the glass has a rough surface (i.e. frosted glass), light that makes it through is scattered in different directions, blurring objects that aren't very close to the window.
Various combinations seem possible. (Frosted glass window blinds?)