Abstract

Lasing without population inversion was studied in a three-level solid state medium of ruby. The two closely-spaced lower levels are the Zeeman split sublevels of the ground state 4A₂ of ruby, corresponding to M=−3/2 and M=+l/2. The transition between the lower levels is the electric dipole-forbidden. When the angle between the constant magnetic field and C-axis of ruby is 90°, the transition matrix element of the electric dipole-forbidden transition is quite large.¹ A strong microwave field which operates at K-band coherently couples the two lower levels.² Changing the constant magnetic field intensity or adjusting the frequency of the pumping microwave field, the exact resonant excitation can be established. The upper level of the lasing process is the Zeeman split sub-level M=−l/2 of 2E state. The ruby crystal, with about 0.05% chromium concentration, is placed at the center of a cylindrical cavity and cooled by liquid helium. With 500 Gauss magnetic field, the coupling microwave frequency is 13.1 Ghz and the required power is around 100 W/cm².

© 1993 Optical Society of America