Formation of off-axis beams in an axially pumped solid-state laser

I show that an axially pumped solid-state laser is able to support off-axis beams in a plane-concave cavity when the cavity length is adjusted within a region close to the hemispherical resonator configuration. These beams are characterized by the fact that even if an object is placed inside the cavity on axis in front of the concave mirror they can still oscillate off-axially in a V-shape path. One can further select and manipulate the desired off-axis beam by inserting a mask into the cavity. Experimental observations of cavity-length-dependent behavior of an Nd: YVO(4) laser at different pump power show that the gain-assisted self-image property in the vicinity of the hemispherical resonator configuration is responsible for the formation of these beams.