Einstein, masers, and lasers: Asking new questions

The link between Albert Einstein’s 1916 proposal of downward stimulated atomic transitions and the development in the 1950s and 1960s of masers and lasers using stimulated emission is often noted and the question sometimes asked: Why did it take so long? The more interesting question might be, Did Einstein think that his proposed transitions represented a linear amplification process for the stimulating light? At that time, would he have encountered an amplifier of any kind? More broadly, would he or any physicist of that era have any familiarity with the basic concept of “coherent” amplification at any frequency, much less the concepts of feedback and coherent oscillation? Vacuum tubes had just begun to be explored; radio technologies used essentially incoherent spark-gap transmitters and crystal detectors; and stereo systems were far in the future. Insights on these queries from anyone familiar with Einstein’s writing and thinking could be quite interesting.