OPTA was responsible for many French language publications in the 20th century. Mainly mystery and Science Fiction.
 

Both hardcover-books contain two SF-novels, and these are number 19 (Van Vogt) and 20 (Clarcke) from the series Club du livre d’antipation, both published in 1969.

Alfred Elton Van Vogt: Au-delà du néant / Destination univers
   

Arthur Charles Clarcke: Les Enfants d'Icare / La Cité et les astres