I've heard, that your civilization is able to create just 300nm "peak" of light followed by nothing, preceded by nothing, of pure sine wave.

How do you do that? You call it by Greek word meaning "atom".

You also state, that length of this peak can be altered, without changing the nature of the wave to be pure sinusoidal.

How do you create such magic?

TL;DR

Don't state you know light if you don't.

How can single "photon" have frequency if it's just one hit and it doesn't repeat?