Professor Kastler spent most of his research career at the Ecole Normale Supérieure in Paris where he started after the war with his student, Jean Brossel a small research group on spectroscopy.
Profesor Kastler menghabiskan sebagian besar karier penelitiannya di École Normale Supérieure, Paris di mana ia memulai kelompok riset kecil spektroskopi bersama mahasiswanya, Jean Brossel setelah perang.