Deformable Mirror Assembly

September 2002

The assembly of deformable mirrors is a joint project between LLE and Lawrence Livermore National Laboratory (LLNL). LLNL has transferred the assembly technology to LLE, who will produce 186 deformable mirrors for use on the National Ignition Facility (NIF). To achieve optimal results from an inertial confinement fusion (ICF) experiment, all laser beams must be free of aberrations (i.e., the beam must be smooth and have uniform energy throughout). Deformable mirrors are part of the NIF wavefront control system, which is designed to correct optical aberrations in individual laser beams before they reach the target. Most aberrations are caused by temperature variations, imperfectly manufactured components, gravity, and coating stress from previously encountered optics.

Each deformable mirror includes 39 actuators sandwiched between a coated glass faceplate and a metal reaction block. As the wavefront control system detects beam aberrations, information is sent to the metal reaction block. The actuators push against the reaction block to move the faceplate mirror surface and correct errors in the beam.

LLE is performing the coating, assembly, and acceptance testing for the NIF deformable mirrors. The Optics Manufacturing Group has optimized a low-stress, high-reflectance coating process for the deformable mirror faceplate and has developed an aluminum sputtering capability to coat the posts on the rear side of the optic. The coating on the faceplate aids in beam reflection, while the aluminum coating protects the epoxied post and transducer joint from flash-lamp radiation.

Prior to assembly, the deformable mirror mechanical assembly is aligned on an interferometer. An optical faceplate is also given a high-reflectance coating before assembly begins.

The deformable mirror block is loaded prior to final assembly.

The block is then placed in the deformable mirror assembly chamber. After the mirror is assembled, this chamber will be closed and a constant environment will be maintained while the epoxies cure.

The mirror block must be free of contamination. Each part is cleaned by hand and then inspected.

Epoxy is applied to the surface of each actuator (post) and then inspected for contamination.

A view of the mirror assembly after the mid-shield has been loaded.

The mirror is loaded, completing assembly. Temperature probes are then attached to the mirror mount and subassemblies.

A view of the final deformable mirror assembly, ready for the cure cycle. The final assembly step bonds the optical and mechanical subassemblies in a seven-day cure cycle.

Closing the deformable mirror assembly chamber. The chamber maintains a level, temperature- and humidity-controlled environment while the epoxy cures.

A completed deformable mirror. The green color is due to the high-reflectance coating on the optic.