What theoretical concept described by Einstein in 1917 is foundational to the laser?
Answer
Stimulated emission
Einstein provided the theoretical description for stimulated emission in 1917, a mechanism essential for a laser to produce coherent light through controlled energy transitions in atoms.

Related Questions
In what year was the Special Theory of Relativity published?For which achievement did Einstein secure the 1921 Nobel Prize in Physics?What does the General Theory of Relativity posit about gravity?What did Einstein propose light consists of when explaining the photoelectric effect?What is the most frequently cited tangible invention patented by Einstein?Why must Einstein's equations be factored into Global Positioning System (GPS) operation?Approximately when did Einstein and Leo Szilard patent the absorption refrigerator design?What theoretical concept described by Einstein in 1917 is foundational to the laser?By what year was the General Theory of Relativity completed?When did Einstein begin working in the Swiss patent office in Bern?