Christopher R. Stockbridge

Focusing through dynamic scattering media

We demonstrate steady-state focusing of coherent light through dynamic scattering media. The phase of an incident beam is controlled both spatially and temporally using a reflective, 1020-segment MEMS spatial light modulator, using a coordinate descent optimization technique. We achieve focal intensity enhancement of between 5 and 400 for dynamic media with speckle decorrelation time constants ranging from 0.4 seconds to 20 seconds. We show that this optimization approach combined with a fast spatial light modulator enables focusing through dynamic media. The capacity to enhance focal intensity despite transmission through dynamic scattering media could enable advancement in biological microscopy and imaging through turbid environments.

Spherical aberration correction in aplanatic solid immersion lens imaging using a MEMS deformable mirror

Aplanatic solid immersion lens (SIL) microscopy is required to achieve the highest possible resolution for next generation silicon IC backside inspection and failure analysis. However, aplanatic SILs are very susceptible to spherical aberrations introduced by substrate thickness mismatch. We correct this aberration using a MEMS deformable mirror. Good agreement between theory and experiment is achieved and spot intensity increases by a factor of two to three are demonstrated.

Polymorphic optical zoom with MEMS DMs

A prototype optical system for compact, high-speed zooming is described. The system is enabled by a pair of MEMS deformable mirrors (DMs), and is capable of high-speed optical zoom without translation of components. We describe experiments conducted with the zoom system integrated with an optical microscope, demonstrating 2.5× zoom capability. Zoom is achieved by simultaneously adjusting focal lengths of the two DMs, which are inserted between an infinity-corrected microscope objective and a tube lens. In addition to zoom, the test system is demonstrated to be capable of automated fine focus control and adaptive aberration compensation. Image quality is measured using contrast modulation, and performance of the system is quantified.

Variable zoom system with aberration correction capability

We describe experiments conducted with two deformable mirrors (DMs) at fixed locations in an optical microscope imaging system. In this configuration, the DM shapes are controlled to provide 2.5× zoom capability, to allow dynamic focus control and to compensate for aberrations of the fixed optical components. Zoom is achieved by simultaneously adjusting focal lengths of the two DMs, which are inserted between an infinity-corrected microscope objective and a tube lens. Image quality is measured using contrast modulation, and performance of the system is quantified, demonstrating an improved point spread function in the adaptively compensated system.

MEMS spatial light modulators for controlled optical transmission through nearly opaque materials

A reflective microelectromechanical mirror array was used to control the intensity distribution of a coherent beam that was propagated through a strongly scattering medium. The controller modulated phase spatially in a plane upstream of the scattering medium and monitored intensity spatially in a plane downstream of the medium. Optimization techniques were used to maximize the intensity at a single point in the downstream plane. Intensity enhancement by factors of several hundred were achieved within a few thousand iterations using a MEMS segmented deformable mirror (e.g. a spatial light modulator) with 1020 independent segments. Experimental results are reported for alternate optimization approaches and for optimization through dynamically translating scattering media.