  The paper presents and experimentally investigates a concept of an efficient
radiation trap based on adiabatic photon confinement between curved mirrors.
Such a trap is free of restrictions typical to the Fabry-Perot cells, relating
to the confined radiation quality and accuracy and stabilization of optical
elements. Experiments have demonstrated high efficiency of confinement, which
depends mainly on the reflectivity of the mirrors and defects on their surface.
