# Confusion on standing wave

I learn the property of standing wave in undergraduate project some times ago. From my text, two opposite propagating waves add up to a wave with node staying in place my amplitude is oscillating in time as

$$\cos(kx + \omega t) + \cos(-kx + \omega t) = 2\cos(\omega t)\cos(kx)$$

I saw an experiment with using an string with one end is oscillating at finite frequency ($\omega/2\pi \sim 100 \ \text{Hz}$), it is clear to see the standing wave.

And I read a material about using two counter-propagating laser to create the standing wave in space. If that is implemented, will we really see the standing wave or not. It is confusing me because the frequency of laser is very high, the term for oscillating term $\cos(\omega t)$ is averaged to be zero at that high frequency. So how can we really create standing wave with laser as stated in some literature?