Control of beam patterns in a helium–neon laser using a spatially filtered feedback

Localized Control of Spatiotemporal Chaos

“…Similarly, feedback can be applied by changing the boundary conditions at one (or both) of the boundaries (e.g., heat flux through the boundary in RBC [42,77]) or by applying an integrated disturbance (e.g., volumetric heating of the fluid in Marangoni-Bénard convection [74] or superimposition of the electromagnetic field with its filtered and time-delayed version in a He-Ne laser [53]). Since the closed-loop system is translationally invariant in the extended directions, the eigenfunctions of the reduced order model are given by either Fourier modes (for spatially uniform) or by Bloch-Floquet waves (for plane wave target states).…”

“…So far, systems for which both sensing and actuation can be done optically represent the only exception. For instance, all-optical analog feedback loops have proved effective for control of pattern formation in nonlinear optical systems [43,53,55,64], while the applicability of thermalized optical perturbations for control of thin film flows has been demonstrated by Semwogerere and Schatz [74] and Garnier et al [22].…”