Some reading for a lazy Sunday afternoon.
A typical femto-second laser might give 65kW 0.1ps light pulses at a rate of
80MHz. But some applications can't handle a powerful light pulse every 12.5ns, for example fluorescence-lifetime measurements (we don't want to re-excite any molecules before achieving 100% decay). The solution is to add a light modulator, and run it from a pulse-picker. The picker should have adjustable pulse width and delay or phase, to exactly enable the modulator in the middle of a selected pulse. Pulse picker synchronizers typically cost $6000, but I figured it shouldn't be hard to design and make them for say, under $100.Here's my recently-completed RIS-761 divide-by-N pulse picker.
It combines fast logic gates with a few analog-circuit functions to provide synchronization and shaping. In practice the phase and width settings would only be made once per laser setup, so knobs are not provided. The delay / phase is adjustable over a 20ns range, more than needed, and the width from 5 to 18ns. The 99cm pcb slides into a Hammond 2x4x4-inch extruded box, which is the most expensive component. Parson my poor cell-phone photo quality.