Laser-Driven Forbidden Transitions to High-LStates in He

Transitions, driven by a C${\mathrm{O}}_2$ laser, between the $7{}_{}{}^1{}_{}{}^{}S$ state and $n=9\mathrm{}$ manifold of states in He have been observed by monitoring the optical emission from the $7{}_{}{}^1{}_{}{}^{}S$ state. In addition to the normally expected $\Delta L=1\mathrm{}$ transition to the ${}_{}{}^1{}_{}{}^{}P$ state, clearly resolved transitions have also been observed to the even-parity states with $L=2, 4, 6, \mathrm{and} 8$. The high-$L$—state transitions are observed because of a combination of diamagnetic Zeeman and motional Stark-effect mixing. A theory has been developed which describes the line shapes of these forbidden transitions.