Tuesday, 12 June 2012

Helices of light: dark helices with a bright future

A laser beam can be made to form a helix, or corkscrew shape, of great light intensity. Laser beams can also be made to form dark helix shapes, dark threads embedded in a background of bright light. A study by Dr Ole Steuernagel at the University of Hertfordshire, published in Optics Express today, shows that dark helices can have considerable advantages over their bright cousins, studied so far.

Helices appear in all parts of our life; ranging in size from everyday objects like the handrail on a spiral staircase, coil springs and screw threads to microscopic features found in helical proteins or intertwined DNA doublehelices.

Helices formed from light may have fundamental and technological applications in various areas. Deployed in photo-lithography they will allow us to produce handed materials, materials containing helical imprints repeated over and over. In optical laser-tweezer setups handedness-sensitive particle trapping and manipulation may arise. In cold-atom-physics transport along helical intertwined waveguides can be implemented exploiting optical forces.

Dr Steuernagel’s study shows that dark helices are distinctive and can outperform bright helices because they are not resolution limited. Dark helices also interact less with trapped particles and so do less damage to, say, notoriously sensitive quantum systems.

In quite a few cases dark helices `can do' what bright helices are `not be able to do', Steuernagel says, which is why he hopes his theoretical investigation will soon be implemented by experimentalists.

Figure illustrates a single bright helix (red line) enveloping a single dark helix (black line).  The x- and y-axes are given in units of focal beam radius, and the z-axis in units of wavelength.

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