Found in a 1967 Electronic Design, this circuit can detect pulses as narrow as 0.2 us. Active components can be replaced with modern equivalents.
This sensitive circuit was found in the June 1995 Electronics Now magazine. R1 can be from 10k to 1M...
Obviously, it is a much more didactic setup than the one with great practical effect, but the idea...
This circuit is used in magnetic tape recorders, having been found in documentation in the 1960s....