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	Contact: UB Physical Optics Research Group Departament de Física Aplicada i Òptica Facultat de Fisica Universitat de Barcelona Martí i Franquès, 1 08028 Barcelona optics @ ub.edu

Spatial Light Modulators and Digital Holography.

You can find up-to-date information in the following section:

Holographic optical tweezers and the lack of flatness of spatial light modulators

The calculation of holograms is based on the Scalar Theory of Diffraction. This approach is used as a way to obtain the complex values of the propagated scalar electric field from knowledge of this field in a reference plane. This process is known as wave-front design or wave-front engineering. The calculated field is encoded into a digital hologram and displayed on a spatial light modulator (SLM). The use of electronically controlled LCDs as modulators allows the information to be refreshed. A specific diffracted pattern (for instance, an optical trap array) can be dynamically modified by displaying a sequence of pre-calculated holograms on the LCD.

Fig2

The set of points on the complex plane available to a modulator is known as the operative curve. A modulator can produce different operative curves depending on (i) the polarization state of the light, (ii) the optical components in the optical setup and (iii) the SLM characteristics. In general, currently available SLMs cannot modulate large areas of the complex plane, and only a few points are accessible to the operative curve. The amplitude and the phase of the points of the operative curve are strongly connected, so it is difficult to achieve a specific configuration, such as an amplitude-only or a phase-only operation. Therefore, the modulator must be accurately characterized to obtain the most suitable operative curve. The design of a hologram takes into account the SLM performance, so holograms are calculated considering the modulation. Several algorithms have been proposed in order to obtain a feasible diffracted field as close as possible to the required one.

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