Correction of vortex laser beam in a closed-loop adaptive system with bimorph mirror

Abstract

The phase correction of a vortex laser beam is undertaken in the closed-loop adaptive system including a Hartmann-Shack wavefront sensor with singular reconstruction technique and a bimorph piezoceramic mirror. After correction the vortex doughnutlike beam is focused into a beam with bright axial spot that considerably increases the Strehl ratio and optical system resolution. Since the phase break cannot be exactly reproduced on the flexible mirror surface, off-axis vortices appear in the far field at the beam periphery.

Phase-shift interference-based wavefront characterization for orbital angular momentum modes

“…Phase measurements of singularities in a vortex beam have been reported with the latter technique [10,11]. Another method, reported recently, measures the positions of the focal spots behind an array of lenslets, resulting in a piecewise-linear approximation of the phase profile of the incoming beam with a spatial resolution determined by the lenslet size [12,13]. In this Letter, we demonstrate phase-shift interference (PSI)-based wavefront characterization of OAM modes with a azimuthal index of −2, −4, −6, and −8 [14].…”

Adaptive Optics and Optical Vortices

“…A closed-loop adaptive system intended for performance of the necessary correction of vortex wavefront is shown in Figure 20 [169]. A reference laser beam is formed using a He-Ne laser 1, a collimator 2, and a square pinhole 3, which restricts the beam aperture to a size of 10×10 mm 2 .…”

Thermomechanical design, hybrid fabrication, and testing of a MOEMS deformable mirror

“…10 In contrast, piezoelectrically activated DMs are widespread in the field of laser beam shaping. [11][12][13] From their inception, unimorph (and bimorph) DMs have been applied to the compensation for thermal lensing, 14,15 and this is still the case. These days, unimorph and bimorph DMs with customized mirror coatings, mirror substrates, and actuating designs are commercially available from different companies, e.g., Cilas, TURN, and Active Optics NightN, but their thermomechanical design is not very sophisticated; in the case of homogeneous loading, by default, the differences in thermal expansion between substrate and piezoelectric layers are minimized, thereby minimizing the bimetal effect of the active mirror and leading to an athermal mirror design.…”