Cluster hopping effects and frequency instabilities prevent a wide use of d
oubly-resonant optical parametric oscillators (DROPOs) in the field of opti
cal diagnostics, especially in the nanosecond regime. By using a two-cavity
device, we demonstrate here that stable single-mode output can be obtained
, provided that the length of each cavity is carefully chosen. (C) 2000 Aca
demie des sciences/Editions scientifiques et medicales Elsevier SAS.