Liquid deformable mirror for high-order wavefront correction

Electrowetting-actuated optofluidic phase modulator

In this paper, an optofluidic phase modulator based on electrowetting is presented. The modulator consists of an inner and outer chamber. Two immiscible liquids are filled into the chambers, and a transparent sheet is fixed between the liquid-liquid interface to obtain a flat interface. By applying different voltages to the modulator, the flat interface moves up and down leading to the change of optical path length. Consequently, the variation of the optical path in the proposed modulator exploits the ability to alter the optical phase. To prove the concept, a prototype of the phase modulator is fabricated in experiment, and the ability of phase modulation is detected. Our proposed modulator performs optical phase shift up to ∼6.68 π driven with 150 V. Widespread applications of such an optofluidic phase modulator is foreseeable.

Closed-loop adaptive optical system with a liquid mirror

A deformable mirror based on internal reflection from an electrostatically deformable liquid-air interface is proposed and investigated. A differential equation describing the static behavior of such a mirror is analyzed and solved numerically. Stable closed-loop operation of an adaptive optical system with a liquid deformable mirror is demonstrated, including forming and the correction of low-order aberrations described by Zernike polynomials and the real-time correction of dynamically changing aberrations.

Dynamic response of ferrofluidic deformable mirrors

Ferrofluids can be used to make deformable mirrors having highly interesting characteristics (e.g., extremely large strokes and low costs). Until recently, such mirrors were thought to be restricted to corrections of frequencies lower than 10 Hz, thus limiting their usefulness. We present counterintuitive results that demonstrate that the limiting operational frequency can be increased by increasing the viscosity of the ferrofluid. We tested the response of ferrofluids having viscosities as high as 494 cP, finding that they could allow an adaptive optics correction frequency as high as 900 Hz. We also demonstrate that we can counter the amplitude loss due to the high viscosity by overdriving the actuators. The overdriving technique combines high current, short duration pulses with ordinary driving step functions to deform the mirror. The integration of a FDM in a complete closed-loop adaptive optics system running at about 500 Hz thus appears to be a realistic goal in the near future.

Adaptive optics in microscopy

The imaging properties of optical microscopes are often compromised by aberrations that reduce image resolution and contrast. Adaptive optics technology has been employed in various systems to correct these aberrations and restore performance. This has required various departures from the traditional adaptive optics schemes that are used in astronomy. This review discusses the sources of aberrations, their effects and their correction with adaptive optics, particularly in confocal and two-photon microscopes. Different methods of wavefront sensing, indirect aberration measurement and aberration correction devices are discussed. Applications of adaptive optics in the related areas of optical data storage, optical tweezers and micro/nanofabrication are also reviewed.