We'd use regular photons or electrons to produce the interference image (assuming they would "fit" in those micro-slits), while the gravitational waves would mo

We'd use regular photons or electrons to produce the interference image (assuming they would "fit" in those micro-slits), while the gravitational waves would modulate the distance between the two slits. Your crystal lattice would be a generalization of my idea. In the two black holes example, the gravitational wave oscillates at 50 Hz. Its spatial speed is irrelevant. This means that the distance between the two micro-slits would be modulated at 50 Hz with the micro-amplitude of that gravitational wave. Let's say the distance between the two slits is L, it's modulated in the L0.9..L1.1 range at 50 Hz, the screen that captures the interference image is at 100L distance, to magnify the pattern 100x. This won't work if the modulation amplitude is L1e-60 or something on that scale, as we can't magnify the image 10^60 times.