Quasi-monolithic saturable optical element.
An element has an axis along which the beam is propagated and comprises an undoped substrate relatively transparent to the beam and having front and rear faces at a predetermined apex angle with respect to each other. On the rear face there is a dielectric coating that reflects the beam while on the front face there is a saturable absorber platelet having a front surface disposed at Brewster's angle to the optical axis. Retroreflection is provided by the dielectric coating, polarisation by the orientation of the element relative to the optical axis, and saturable absorption by the platelet. Pref. the host material of the platelet is a single crystal of garnet or a glassy material doped with Cr4+ to a predetermined optical density of LiF, and the dielectric coating is multiple layers of silicon dioxide with titanium dioxide or zirconium dioxide. There may be a stack of platelets secured to each other and to the substrate by optically transparent cement.