Laser pumping
（重定向自Laser pump）
![A ruby laser head. The photo on the left shows the head unassembled, revealing the pumping cavity, the rod and the flashlamps. The photo on the right shows the head assembled.](/Images/godic/202501/23/Ruby_laser_pumping_cavity_assembled_and_disassembled1958.JPG")
![Various laser pumping cavity configurations.](/Images/godic/202501/23/Various_laser_pumping_cavity_cross_section_shapes1958.JPG")
![Laser pumping lamps. The top three are xenon flashlamps while the bottom one is a krypton arc lamp](/Images/godic/202501/23/Three_xenon_flashtubes_and_a_krypton_arc_lamp1959.jpg")
![The spectral outputs for flashlamps using various gases, at a current density approaching that of greybody radiation.](/Images/godic/202501/23/Rare_gas_flashtube_spectral_outputs1959.JPG")
Laser pumping is the act of energy transfer from an external source into the gain medium of a laser. The energy is absorbed in the medium, producing excited states in its atoms. When the number of particles in one excited state exceeds the number of particles in the ground state or a less-excited state, population inversion is achieved. In this condition, the mechanism of stimulated emission can take place and the medium can act as a laser or an optical amplifier. The pump power must be higher than the lasing threshold of the laser.