激光器产生激光的充分必要条件是什么? What is the necessary and sufficient condition for laser to produce laser?
A.
受激物质和自发辐射 Stimulated substances and spontaneous radiation
B.
受激物质的粒子数反转分布和光学谐振腔 Inversion Distribution of Particle Number of Excited Matter and Optical Resonator
C.
受激吸收和光学谐振腔 Stimulated Absorption and Optical Resonator
D.
自发辐射和受激吸收 Spontaneous Radiation and Stimulated Absorption