Controlled generation of array beams of higher order orbital angular momentum and study of their frequency-doubling characteristics

Abstract

We report on a simple and compact experimental scheme to generate high-power, ultrafast, higher-order vortex-array beams. Simply by using a dielectric microlens-array (MLA) and a plano-convex lens, we have generated array-beams carrying the spatial property of the input beam. Considering the MLA as a 2D sinusoidal phase-grating, we have numerically calculated the intensity pattern of the array-beams in close agreement with the experimental results. Using vortex beams of order as high as l = 6, we have generated vortex array-beam with individual vortices of orders up to l = 6. We have also theoretically derived the parameters controlling the intensity pattern, size, and the array-pitch and verified experimentally. The single-pass frequency-doubling of vortex-array at 1064 nm in a 1.2 mm long BiBO crystal produced green vortex-array of order, l sh = 12, twice the order of pump beam. Using lenses of different focal lengths, we have observed the vortex-arrays of all orders to follow a focusing dependent conversion similar to the Gaussian beam. The maximum power of the green vortex-array is measured to be 138 mW at a single-pass efficiency as high as ~3.65%. This generic experimental scheme can be used to generate the array beams of desired spatial intensity profile across a wide wavelength range by simply changing the spatial profile of the input beam.

Analysis of multi-photon absorption: z-scan using ultra-short Gaussian vortex beam

“…The nonlinear optical phenom ena are intensitydependent and the efficiency of the nonlin ear process decreases with decreasing the excitation intensity. In recent years, it has been shown that the efficiency of the second harmonic process decreases with increasing the vortex order (l) of the Gaussian vortex beam [46,47]. In a similar way, we have observed that the depth of zscan transmittance in 2PA as well as in 3PA decreased with increasing the vortex order (l) due to the decrease of peak intensity of the vortex beam as we discussed in figure 1.…”

Optical vortex lattice mode generation from a diode-pumped Pr3+:LiYF4 laser

“…In addition to conventional optical vortices, multiple vortex modes with an array of spatially separated individual vortices [5] and optical vortex lattice (OVL) modes with multiple phase singularities on their wavefronts [6] have been proposed. OVL modes carry multiple OAM states and multiple dark cores can be used, allowing a significant increase in data capacity in communication systems [7] and the simultaneous trapping and manipulation of multiple particles [8].…”

All-optically phase-induced polarization modulation by means of holographic method

“…TC represents the number of 2π phase cycles when the optical phase circles once the beam axis. The transverse cross-sections of the optical vortices are associated with helical phase wavefront 14,15 . In many cases, there is no connection between the polarization and phase vortex of light.…”