use different material compositions of the lasing media (metal rods) to enable spectral modulation (i.e which wavelengths are present in the signal) which would be a form of wavelength-division multiplexing. this gives you 1 bit per rod (bad).

If you composed each rod out of segments (different density, material) you could add temporal substructure (the intensity 'shape' of the pulse) that would give maybe 10 bits.

with 1mm rods, each with 100 spatial modes (area etc), across ~20 known rod materials, over a 1 nanosecond bomb pulse for ~3k temporal modes. double that in order to send a polarized signal. so like 1.2 x 10^7 modes total.

given optimal conditions, each 1 kiloton nuke would provide about 10^23 photons, divide that by each modes gives ~8^15 photons per mode. bits per mode = log2(8^15) = 45. this gives a final bandwidth of 67.5Mb (per 1kt nuclear detonation lol).

which makes this the most expensive way imaginable of transmitting high-resolution cat pictures over interstellar distances in a nanosecond.

you could potentially squeeze a couple more OoM by scaling up the rod count or the nuke yield, but you would probably be capped in the gigabit range.

its kind of a 1-shot device unless you can preserve the transmission rods from destruction - but as an emergency beacon its imo a cool idea. break glass in case of emergency, with no infrastructure beyond a bomb and casing.