Abstract
Laguerre-Gaussian (LG) beams have been extensively studied due to their unique structure, characterized by a phase singularity at the center of the beam. Common methods for generating such beams include the use of diffractive optical elements and spatial light modulators, which although offering excellent versatility, suffers from several drawbacks, including in many cases a low power damage threshold as well as complexity and expense. This paper presents a simple, low cost method for the generation of high-fidelity LG beams using rapid prototyping techniques. Our approach is based on a fluidic-hologram concept, whereby the properties of the LG beam can be finely controlled by varying the refractive-index of the fluid that flows through the hologram. This simple approach, while optimized here for LG beam generation, is also expected to find applications in the production of tunable fluidic optical trains.
Highlights
The Laguerre-Gaussian (LG) family of optical beams has been studied extensively over the past 15 years in both theoretical and experimental contexts
LG beams are generally characterized by a helical phase structure containing a phase singularity, commonly referred to as an optical vortex, which propagates along the centre of the beam
The cross-sectional intensity profiles of the LG beams that have been studied posses a well-defined central null, due to the phase-singularity, surrounded by an integer number of concentric rings. This particular spatial distribution has led to a number of applications, including the trapping of low-refractive-index particles and emulsions [7,8,9,10], the observation of improved efficiency in the optical trapping of high index particles [11], applications in atom optics [12,13], in situ vortex beam generation [14], and single-cell nanosurgery [15]
Summary
The Laguerre-Gaussian (LG) family of optical beams has been studied extensively over the past 15 years in both theoretical and experimental contexts. The l index has been treated as an integer [17,18], with the interpretation that the orbital angular momentum associated with the resultant electromagnetic field is quantized in discrete units of lħ per photon This view has been reconsidered [17,19,20,21] and LG beams with fractional helical phases have been experimentally demonstrated. Spatial Light Modulators (SLMs) are extremely versatile dynamic devices that allow the user to shape with high precision the phase front of a monochromatic optical beam As such, they are well suited to the generation of vortex beams with selectable phase structure [22,23,24,25]. The beam profile in (c) was taken using the setup displayed in Fig. 5(a), where the slight asymmetry between the x and y directions is due to the linear polarization axis being aligned to the y axis
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