He was appointed assistant professor of physics at the University of Southern California, Los Angeles, (1969-1973) and associate professor at the University of Campinas, Sao Paulo, Brazil (1974-1977). He was visiting fellow at the Joint Institute for Laboratory Astrophysics at the University of Colorado, Boulder in 1977-1978 and professor at the Georgia Institute of Technology, Atlanta from 1979 to 1984, and the University of Arkansas, Fayetteville since 1985. He has also been visiting fellow at the Center for Astrophysics | Harvard & Smithsonian, Cambridge, Massachusetts from 1993.