This is how ultrafast lasers work. You have many different frequencies that are mode locked, which basically means phase locked, to form an intense but short pulse on the order of pico- to femtoseconds. There are some built by physicists that are in the attosecond regime.

https://en.m.wikipedia.org/wiki/Ultrashort_pulse_laser

https://en.m.wikipedia.org/wiki/Mode_locking

https://en.m.wikipedia.org/wiki/Frequency_comb

https://opg.optica.org/oe/fulltext.cfm?uri=oe-18-12-13006&id=199923

There are other devices called pulse shapers that can change the phase relationships between the different frequencies in the pulse in order to shape the pulse envelope to be gaussian or to resemble a square pulse or even make two separate pulses that have a delay time similar to the duration of the original pulse.

https://en.m.wikipedia.org/wiki/Femtosecond_pulse_shaping