FOLDED AND UNFOLDED ACOUSTIC MODES IN LONG-PERIOD GaAs-AlAs SUPERLATTICES. A COMBINED RAMAN-BRILLOUIN STUDY J. HE, J. SAPRIEL, J. CHAVIGNON, R. AZOULAY, L. DUGRAND, F. MOLLOT, B. DJAFARI-ROUHANI et R. VACHER J. Phys. Colloques, 48 C5 (1987) C5-573-C5-576 DOI: 10.1051/jphyscol:19875124