system
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human
Are lasers (when viewed as radio antennas) subject to the antenna reciprocity principle?

Since lasers emit electromagnetic radiation, are they subject to the reciprocity principle? I know that the principle is only for (electromagnetically) linear antennas, but I am not sure if a laser is linear. The second question then pops up, as lasers are based on diodes, are diodes subject to the reciprocity prinicple?
gpt
The laser diode as a whole cannot be thought of as an antenna by itself, It can be thought of as an array of phased antennas made up of the excited atoms.

The individual atom harmonic structure follows reciprocity only up to the point that photon in is the same as photon out in a time reversed format, This is true for any quantum interaction.

But the device as a whole is not conservative in that respect, Firstly modern diode technology is dominated by non-radiative transitions (60% +), Meaning that emission of a photon is not always the case, more often than not it's is released as a surface wave (phonon) when the mean free-time of the electron-hole pair is less than that of the mean time to photon emission. This is somewhat helped in a laser diode as the stimulated emission increases the chance that a radiative transition will happen. (this is why laser diodes can be more efficient than a regular LED)

secondly, the diode cannot be thought of as a coupling the same as an antenna, it is more accurately thought of as the laser pump, same as the xenon flash bulb in a gas laser. It's not a reversible pathway, except to the extent that it starts acting like a photo-electric cell.

But in an idealised structure, where non-radiative recombination is nil and efficiency of 100% transmit and 100% receive conversion, it could be an analogue of reciprocity.