Optically Induced Magnetization in Ruby

Abstract

The magnetization of ruby in a magnetic field at 300°K is changed when the ruby is optically pumped with linearly polarized radiation from a $Q$-switched ruby laser. With a magnetic field parallel to the trigonal axis, laser light polarized parallel to this axis induces transitions from the spin ±½ levels of the ${}_{}{}^4{}_{}{}^{}A_2^{}{}_{}{}^{}$ ground state to the levels of the $\overline{E}\left({}_{}{}^2{}_{}{}^{}E\right)$ excited state. The change in $M_z$ is linearly proportional to $H$ except near the anticrossing points of the ${}_{}{}^4{}_{}{}^{}A_2^{}{}_{}{}^{}$ spin levels at 2.07 and 4.14 kG. At these field strengths, there is an enhancement of the magnetization caused by state mixing of the ${}_{}{}^4{}_{}{}^{}A_2^{}{}_{}{}^{}$ wave functions. When $H$ has a small component perpendicular to the $z$ axis, a magnetization is detected parallel to this component in the vicinity of 4.14 kG. The effect requires a long ground-state relaxation time. In a separate experiment, the relaxation of $M_z$ was found to vary from 0.13 μsec in zero magnetic field to a constant value of 0.57 μsec for fields above 60 G.