Method of compensating for aberrations in electron holography by using a liquid-crystal spatial-light modulator

Imaging properties of scanning holographic microscopy

Scanning heterodyne holography is an alternative way of capturing three-dimensional information on a scattering or fluorescent object. We analyze the properties of the images obtained by this novel imaging process. We describe the possibility of varying the coherence of the system from a process linear in amplitude to a process linear in intensity by changing the detection mode. We illustrate numerically the properties of the three-dimensional point-spread function of the system and compare it with that of a conventional imaging system with equal numerical aperture. We describe how it is possible, by an appropriate choice of the reconstruction algorithm, to obtain an ideal transfer function equal to unity up to the cutoff frequency, even in the presence of aberrations. Some practical implementation issues are also discussed.

Object-binarized phase-only matched filtering with dual liquid-crystal spatial light modulators

A real-time optical processing system with dual liquid-crystal spatial light modulators is constructed and used as both an amplitude-input device and a multilevel phase-only filter. Fourier analysis is given to show the performance of light efficiency, signal-to-noise ratio, and discrimination capability with the binarization of gray objects. The ratio of the dc power spectrum to the power spectra for input objects is introduced to incorporate the power spectrum into discrimination-capability evaluation. A numerical calculation is performed for gray-level and binarized amplitude-phase correlations. Improvement of the performance criteria has been achieved for an amplitude in a binary mode to a phase correlator. The higher the threshold level of the binarized objects is, the better performance criteria are produced. The effect of illumination over an input object on the autocorrelation maximum is experimentally investigated. Experimental results are presented to support the calculations.

Spherical aberration correction using a liquid-crystal spatial-light modulator in off-axis electron holography

One can correct spherical aberration in a transmission electron microscope by using a newly developed aberration-correction method involving off-axis electron holography. In this method, a liquid-crystal spatial-light modulator (LC SLM) is employed during the holographic reconstruction step to compensate for spherical aberration. Application of this method to high-resolution off-axis electron holograms of fine gold particles is presented. The phase distribution of the corrected object wave is visualized by the Zernike phase-contrast method carried out with the same LC SLM.