Determination of topological charges of polychromatic optical vortices

Abstract

We introduce a simple, single beam method for determination of the topological charge of polychromatic optical vortices. It is based on astigmatic transformation of singular optical beams, where the intensity pattern of a vortex beam acquires a form of dark stripes in the focal plane of a cylindrical lens. The number of the dark stripes is equal to the modulus of the vortex topological charge, while the stripe tilt indicates the charge sign. We demonstrate experimentally the effectiveness of this technique by revealing complex topological structure of polychromatic singular beams.

Efficient beam converter for the generation of high-power femtosecond vortices

“…Figure 2 shows the experimental setup used to determine the topological charge of the generated femtosecond vortices. This simple non-interferometric technique was earlier used for cw beams [13]. Here we show that it can also be applied for analysis of femtosecond pulses.…”

Experimental determination of the azimuthal and radial mode orders of a partially coherent LGpl beam (Invited Paper)

“…The phase term expðilφÞ (l and φ are the topological charge and azimuthal angle, respectively) in a vortex beam imposes orbital angular momentum (OAM) on the beam, and each photon of such a beam has an OAM of lℏ [6] . Up to now, many methods based on the measurement of the intensity distribution, diffraction, or interference pattern of a vortex beam were proposed to measure the OAM or l [7][8][9][10] .…”

Generation of intense femtosecond optical vortex pulses with blazed-phase grating in chirped-pulse amplification system of Ti:sapphire laser

“…Using this method, we verify the topological charges for the generated OV pulses, as shown in Fig. 8c, e, and g. Though it is sufficient to determine the topological charge using a cylindrical lens [32], one more cylindrical lens can also be employed to compensate the astigmatism induced by the first cylindrical lens to generate a well-defined Hermite-Gaussian mode [33]. Thus, the topological charge of the OV can be clearly determined using the relations ℓ = m − n, and p = min(m, n), where m and n are the transverse indices of the Hermite-Gaussian mode and p is the radial index of the OV [33].…”

“…8b, d, and f displays the beam profiles for ℓ = 0, ℓ = 1, and ℓ = 2, respectively. To confirm the topological charge, we adopted the astigmatic transformation, which is a simple technique commonly used for determining ℓ for multichromatic OVs [32]. In the technique, the OVs are converted through a cylindrical lens with a focal length of f cyl to obtain their Fourier-transformed images at the focal plane of the cylindrical lens (z = f cyl ), as schematically illustrated in Fig.…”