Ateneo Photonics Laboratory develops bored helical optical beams

by Dr. Nathaniel Hermosa (Imprints of Philippine Science)

Bored and twisted.

Don’t think that these adjectives can refer only to people. Recently, researchers proved that they too can be used to describe optical beams.

Fig. 1.  Changing the bore radius changes the pattern. Courtesy of S. Baluyot. Click to view animation.
Researchers from the Ateneo de Manila University, modified a helical (twisted) phase by boring a hole at the center.

Nathaniel Hermosa II and Stein Alec Baluyot called this Bored Helical (BH) beam, which possesses a variety of interesting properties different from those shown by a beam with only a helical phase. Foremost to these is the appearance of intense arms when the radius of the bore is increased.  At small bore radius, the transverse intensity profiles approximate that of a beam with a helical phase.  With increased bore radius, the intense extensions become similar to arms.  During transition, these intense arms are encapsulated by a ring.  The intensity pattern can be controlled by simply changing the number of twists (topological charge) and the bore radius of the phase.

Another interesting property of the BH beam is the seeming rotation of the intensity pattern as it travels in space.  This rotation also depends on the number of twists and on the bore.  It is observed that a beam with a smaller bore rotates more quickly than a beam with a larger cavity radius.  A beam with a lower number of twists, on the other hand, turns faster than that with a higher number.

Intensity patterns of the BH beams are easier to generate compared to patterns obtained when Helical Beams of different waists and/or of different topological charges are interfered. The former requires only a change in the hologram while the latter needs extra optical equipment and a more delicate alignment. The distinctive intensity patterns and propagation dynamics of BH beams may find potential applications in the field of optical trapping and micromanipulation, and in fabricating micrometer sized 3D structures in parallel.

The researchers also analytically calculated the angular momentum that these beams can impart to particles.

The paper was published in Optics Express through a grant from the Philippine Council for Advanced Science and Technology Research and Development (PCASTRD).

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-18-16244

A follow up paper was published in Applied Optics.

http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-49-4-673

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About ateneophysicsnews
Physics News and Features from Ateneo de Manila University

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