We observed the light emitted along a direction 45° from the beam axis when a Nd-glass laser (frequency ${\omega }_0$) was focused on a solid target. Quite intense lines were found with frequencies $2{\omega }_0$, $\frac{3}{2}{\omega }_0$, $\frac{1}{2}{\omega }_0$. The lines at $2{\omega }_0$ and $\frac{3}{2}{\omega }_0$ are broadened on the low-frequency side only. Their occurence and broadening may be related to parametric excitation of waves.

• Received 30 January 1973

DOI:https://doi.org/10.1103/PhysRevLett.30.594