The excitation spectrum of a free exciton in GaSe has been measured in magnetic fields up to nearly 200 T. The measured spectrum compares favorably with a theoretical calculation done within the effective-mass approximation, consistent with a recent interpretation that the mass anisotropy is small, $\frac{{\mu }_{\parallel }}{{\mu }_{\perp }}=1\mathrm{}$.

• Received 18 October 1978

DOI:https://doi.org/10.1103/PhysRevB.23.3970