Exceptional Points as Lasing Prethresholds

The genesis of lasing, as an evolution the laser hybrid eigenstates comprised electromagnetic modes and atomic polarization, is considered. It shown that start coherent generation at threshold preceded by formation a special state lasing prethreshold. This characterized enhanced coupling among excited atoms modes. leads to increase in rate stimulated emission and, ultimately, lasing. At prethreshold, transformation has features exceptional point (EP) observed non-Hermitian systems. formed when eigenfrequencies two states coalesce or come close each other. Below lifetimes all grow with increasing pump rate. When crosses resonance trapping occurs lifetime continuing while other begin decrease. Consequently, latter do not participate Thus, above transitions into single-mode regime.