Abstract
We propose an effective method to measure the orbital angular momentum of a perfect optical vortex (POV) beam with a hybrid angular gradient phase grating (HAG-PG), which is a gradient grating with angular changing distribution. The HAG-PG performs the transformation from the POV to the dark stripes of the diffraction intensity patterns. From the number and the orientation of dark stripes of far-field diffraction patterns formed by the HAG-PG, the modulus of TC and sign of the incident POV beam can be determined. The high scalability of this method for being unrestricted by the Fourier plane and its adaptation for measuring the POV beams with different states are demonstrated by loading the HAG-PG hologram on a spatial light modulator. And the detection sensitivity of the POV beam can be significantly improved. The experimental results agree well with the theoretical simulations.
Highlights
A S a kind of complex structured beam, optical vortices with orbital angular momentum (OAM) have many applications in both classical and quantum fields [1]
We propose an effective method to measure the orbital angular momentum of a perfect optical vortex (POV) beam with a hybrid angular gradient phase grating (HAG-PG), which is a gradient grating with angular changing distribution
Thereafter, a 4f system consisting of lens L1 and L2 is built to modulate the size of the POV beam conveniently
Summary
A S a kind of complex structured beam, optical vortices with orbital angular momentum (OAM) have many applications in both classical and quantum fields [1]. Ma et al reported an improved method to measure the POV beam with phase shift technique [29], which can overlap and interfere exactly between the POV beam and its phase conjugate in an approximately Fourier plane This method can determine the TCs of a POV with simple and non-precise optical elements, but its energy efficiency is relatively low and it even has severe distortions of far-field intensity patterns when measuring the high-order POV beam. On this point, Pinnell et al proposed and demonstrated optical modal decomposition [32] to quantitatively measure the POV beam. The scalability of this method for being unrestricted by the Fourier plane and its adaptability for measuring the POV beams with different order are demonstrated, and the TC magnitudes and sign of the POV determined by the HAG-PG has been investigated in detail
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