Abstract:We report on a simple experimental scheme to generate and control the orbital angular momentum (OAM) spectrum of the asymmetric vortex beams in a nonlinear frequency conversion process. Using a spiral phase plate (SPP) and adjusting the transverse shift of the SPP with respect to the incident Gaussian beam axis, we have transformed the symmetric (intensity distribution) optical vortex of order l into an asymmetric vortex beam of measured broad spectrum of OAM modes of orders l, l − 1, l − 2, …, 0 (Gaussian mod… Show more
“…The distance, d , of the MLA from the back focal plane of L3 modulates the pitch of the vortex array and the focal length, f of the lens L3 determines the diameter of individual vortices in the array. A 1.2 mm long and 4 × 8 mm 2 in aperture bismuth borate (BiBO) crystal 18 , cut for type-I (e + e → o) frequency doubling in optical yz-plane (Φ = 90°) with an internal angle of θ = 168.5° at normal incidence, is placed at the Fourier plane for second harmonic generation (SHG) of vortex arrays at 1064 nm into green at 532 nm. The frequency doubled vortex array is extracted from the undepleted pump using a wavelength separator, S, and imaged at the CCD camera plane using lenses, L4 and L5.Figure 1Schematic of the experimental setup to generate a vortex beam array.…”
Section: Methodsmentioning
confidence: 99%
“…/2, half-wave plate; PBS1-2, polarizing beam splitter cube; SPP1-2, spiral phase plates; /4, quarter-wave plate; L1-5, lenses; M1-2, mirrors; BiBO, nonlinear crystal for frequency doubling; MLA, microlens array; S, wavelength separator; CCD, CCD camera. A 1.2 mm long and 4 x 8 mm 2 in aperture bismuth borate (BiBO) crystal [17], cut for type-I (e + e → o) frequency doubling in optical yz-plane (Φ = 90°) with internal angle of θ = 168.5° at normal incidence, is placed at the Fourier plane for second harmonic generation (SHG) of vortex arrays at 1064 nm into green at 532 nm. The frequency doubled vortex array is extracted from the undepleted pump using a wavelength separator, S, and imaged at the CCD camera palne using lenses, L4 and L5.…”
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.
“…The distance, d , of the MLA from the back focal plane of L3 modulates the pitch of the vortex array and the focal length, f of the lens L3 determines the diameter of individual vortices in the array. A 1.2 mm long and 4 × 8 mm 2 in aperture bismuth borate (BiBO) crystal 18 , cut for type-I (e + e → o) frequency doubling in optical yz-plane (Φ = 90°) with an internal angle of θ = 168.5° at normal incidence, is placed at the Fourier plane for second harmonic generation (SHG) of vortex arrays at 1064 nm into green at 532 nm. The frequency doubled vortex array is extracted from the undepleted pump using a wavelength separator, S, and imaged at the CCD camera plane using lenses, L4 and L5.Figure 1Schematic of the experimental setup to generate a vortex beam array.…”
Section: Methodsmentioning
confidence: 99%
“…/2, half-wave plate; PBS1-2, polarizing beam splitter cube; SPP1-2, spiral phase plates; /4, quarter-wave plate; L1-5, lenses; M1-2, mirrors; BiBO, nonlinear crystal for frequency doubling; MLA, microlens array; S, wavelength separator; CCD, CCD camera. A 1.2 mm long and 4 x 8 mm 2 in aperture bismuth borate (BiBO) crystal [17], cut for type-I (e + e → o) frequency doubling in optical yz-plane (Φ = 90°) with internal angle of θ = 168.5° at normal incidence, is placed at the Fourier plane for second harmonic generation (SHG) of vortex arrays at 1064 nm into green at 532 nm. The frequency doubled vortex array is extracted from the undepleted pump using a wavelength separator, S, and imaged at the CCD camera palne using lenses, L4 and L5.…”
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.
“…3 shows the intensity profiles of the pump and idler beams without any polarization projection. As in previous reports 15,33 , one can measure the purity of the OAM mode of the vector- vortex beam through the mode projection technique 1,34,35 . However, due to a lack of suitable spatial light modulator (SLM) in our laboratory, we were not able to perform the mode purity measurement for the vector- vortex beams.…”
Vector-vortex beams, having both phase and polarization singularities, are of great interest for a variety of applications. Generally, such beams are produced through systematic control of phase and polarization of the laser beam, typically external to the source. However, efforts have been made to generate vector-vortex beams directly from the laser source. Given the operation of the laser at discrete wavelengths, vector-vortices are generated with limited or no wavelength tunability. Here, we report an experimental scheme for the direct generation of vector-vortex beams. Exploiting the orbital angular momentum conservation and the broad wavelength versatility of an optical parametric oscillator, we systematically control the polarization of the resonant beam using a pair of intracavity quarter-wave plates to generate coherent vector-vortex beam tunable across 964–990 nm, with output states represented on the higher-order Poincaré sphere. The generic experimental scheme paves the way for new sources of structured beams in any wavelength range across the optical spectrum and in all time-scales from continuous-wave to ultrafast regime.
“…Thus asymmetric beams can be also be considered as a generalized version of their symmetric counterparts. These beams have been used to generate a pair of entangled photons with broad orbital angular momentum using spontaneous parametric down-conversion [52], and also for designing optical tweezers for micro-manipulation of small sized particles [53,54].…”
We present generation of asymmetric aberration laser beams (aALBs) with controlled intensity distribution, using a diffractive optical element (DOE) involving phase asymmetry. The asymmetry in the phase distribution is introduced by shifting the coordinates in a complex plane. The results show that auto-focusing properties of aALBs remain invariant with respect to the asymmetry parameters. However, a controlled variation in the phase asymmetry allows to control the spatial intensity distribution of aALBs. In an ideal ALB containing equal intensity three bright lobes (for m = 3), by introducing asymmetry most of the intensity can be transferred to any one of single bright lobe, and forms a high-power density lobe. A precise spatial position of high-power density lobe can be controlled by the asymmetry parameter β and m, and we have determined the empirical relations for them. We have found that for the specific values of β, the intensity in the high-power density lobe can be enhanced by ∼6 times the intensity in other bright lobes. The experimental results show a good agreement with the numerical simulations. The findings can be suitable for applications such as in optical trapping and manipulation as well as material processing.
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