Speckle fields generated with binary diffusers and synthetic pupils implemented on a spatial light modulator.

Digitally controllable Gaussian speckle fields were experimentally generated by implementing binary diffusers and synthetic pupils on a liquid crystal spatial light modulator. The synthetic pupil comprises a Ronchi phase mask and a proper filtering of its diffraction orders. The binary diffuser is displayed inside an aperture defined onto the Ronchi phase mask. We demonstrated that this implementation replaces the need of using a ground glass and a physical pupil. In this way, the average speckle size, the statistical independence among the generated speckle patterns, and the average intensity distribution can be dynamically controlled.

Generation of optical vortices by using binary vortex producing lenses.

Experimental high-quality optical vortices of different topological charges are generated by using a vortex producing lens with two phase levels. In our setup, the lens is displayed on a liquid-crystal spatial light modulator that only attains phase modulation of around 1.2π. This achievement opens the real possibility of creating high-quality optical vortices with devices of very low phase modulation capacity. The experimental setup is fully described, and the considerations to set the optimal parameters to obtain high-quality optical vortices are discussed and experimentally established. The phase and intensity of the optical vortices are recovered. The phase is obtained through a phase-shifting method that is directly programmed onto the modulator avoiding any class of mechanical displacement.

High-quality optical vortex-beam generation by using a multilevel vortex-producing lens.

In the present work, we propose a method to generate high-quality optical vortices with a reduced number of phase levels by using multilevel vortex-producing lenses (VPLs). The VPL is implemented in a liquid-crystal spatial light modulator with limited capacity to project phase levels. The proposed method significantly improves the quality of the optical vortex obtained by employing spiral phase plates with the same number of phase levels. Simulations and experimental results confirming the effectiveness of the method are presented.

Three-dimensional clustered speckle fields: theory, simulations and experimental verification.

Clustered speckle patterns are a particular type of speckles that appear when a coherently illuminated diffuser is imaged through a multiple aperture pupil mask attached to a lens. The cluster formation is the result of the complex speckle modulations of the multiple interferences produced by the apertures. In this paper, a three-dimensional analytical approach to simulate cluster speckles everywhere after the lens is presented. This approach has the possibility of including multiple aperture masks at the lens and at the diffuser, in contrast to previous works which were also limited to the description of the patterns only at the image plane. This model contributes to the development of tailor made speckle patterns that can be used in diverse optical applications, including those lying in the focus region. The approach is validated under different conditions by comparing experimental results with simulations on a statistical basis. Some aspects of possible uses of these clusters are briefly revised, such as optical trapping, manipulation and metrology.

Modulated speckle simulations based on the random-walk model.

The random-walk model is employed to simulate modulated speckle patterns. We demonstrate that the geometrical image approximation fails to describe the modulated speckle pattern. A new approach to analyzing this phenomenon is proposed. The validity of the approximations employed is verified by comparison of the simulation with the experimental results. Speckle metrological applications and phase measurement techniques could be improved by taking advantage of this model.