Elsewhere there are answers to a similar qustion about square waves which I am mostly going to ignore. The type of impulse I am interested in ideally travels at the speed of light, is very narrow in the time domain (ideally zero width) and carries (holds?) an amount of energy (ideally one Joule). The replies for square waves rush to Fourier analysis and speak of the bandwidth etc. I want to approximate my impulse with a 14 keV gamma ray (photon) emitted by iron-57 when it transitions to its base state. I'm borrowing this photon from the Pound-Rebka experiment ( see for example https://en.wikipedia.org/wiki/Pound–Rebka_experiment ). The energy of the photon is about 2.243E-15 Joules and the frequency about 3E15 Hertz. In the actual Pound-Rebka experiment they used a filter with a bandwidth of ?? 1Hz or less to detect the effect of gravitational potential. As part of the experiment the gamma rays (photons) are counted. My claim is that these photons are going to behave like impulses when looked at from our nice 1Hz to (say) 2.4 Ghz 'radio' spectrum. Any tuned circuit that gets hit by one of these gamma rays is (ideally) going to absorb the entire energy of the gamma ray and 'ring' at its natural frequency - giving rise to the claim (true or false?) that the gamma ray contained or was made up of or could be decomposed into - the natural frequency response of the tuned (or untuned) circuit that detected it. Yet the Pound-Rebka experiment was pretty conclusive that the frequency of the gamma ray was 3E15 Hertz +- less than 1 Herz. So - can we transmit an impulse through free space and is it made up of simewaves? Rider - are photons (all photons) really impulses? En masse they might not behave like impulses but is that a property of the quantity not the individual.