OPTICAL GENERATION OF MAGNONS BY DIRECT SPIN-MAGNON RELAXATION IN MnF2 : Er3+ G.J. Jongerden, A.J. Kil, J.I. Dijkhuis, A.F.M. Arts et H.W. de Wijn J. Phys. Colloques, 46 C7 (1985) C7-241-C7-245 DOI: 10.1051/jphyscol:1985744