Tunable system for Generating Higher Order Bessel Beams

Technical Summary:

The HOBBIT optical system is made up of an acousto-optic deflector (AOD) and log-polar transformation optics. The AOD is used to add a linear phase gradient to a Gaussian input beam. The output Gaussian beam from the AOD is then elongated into an elliptical Gaussian line and propagates through the log-polar HOBBIT optics that wrap the ellipse into an asymmetric annular-distribution. The log-polar HOBBIT optics consist of two diffractive phase only optics. The first optic performs the geometric log-polar coordinate mapping that wraps the elliptical Gaussian line into a ring. The second optic corrects for the phase of the transformed beam. Overall, this results in an elliptical Gaussian beam with linear phase being wrapped into an asymmetric ring with azimuthal OAM phase. A RF signal is applied to the AOD to produce a traveling wave in the crystal. The frequency of the acoustic signal corresponds to the angle of the 1st order diffraction relative to the 0th order. The optical system is designed around this angle to produce specific OAM topological charge numbers. As the frequency of the applied signal is varied, the deflection angle of the 1st order changes accordingly. Each frequency corresponds to a specific deflection angle and therefore, a unique OAM charge number. The OAM charge numbers that can be generated are limited by the precision of the frequency of the signal applied to the AOD.