Date of Award
Doctor of Philosophy (PhD)
Eric G. Johnson
In this work, the manipulation including generation and detection of the asymmetric perfect vortex (APV) carrying fractional orbital angular momentum (OAM) was demonstrated and discussed. All the manipulation of the modes is in real-time which provides a perfect tool for sensing the dynamic properties of complex media. The OAM-involved nonlinear conversion, specifically the second-harmonic generation (SHG) using the APV and asymmetric Bessel-Gaussian (BG) beams was studied in detail.
The generation and detection of the APV are based on the HOBBIT concept which includes acoustic optical deflector (AOD) and log-polar coordinate transformation optics. The RF signal driving the AOD allows the real-time controlling of the OAM modes. Because of the asymmetric property of the modes, the APV beams can carry fractional OAM with a linear one-to-one correspondence of the fractional charges. The feature of the Doppler frequency shift caused by the AOD was introduced and demonstrated which was used to build a Poincaré sphere to encode and decode information. The spatial APV basis was also demonstrated by developing a pulsed 2D HOBBIT system which includes two AODs controlling both the OAM and radial dimensions. Examples using all these HOBBIT systems to sense complex media were given to show the real-time OAM spectrum measurement.
The SHG process of the APV and the asymmetric BG beams was discussed. The theoretical and experimental results show how beams with OAM-independent and OAM-dependent sizes behave in the nonlinear process. Both the two beam models gave a very good one-to-one correspondence of fractional charges which shows the potential to use the beam models for information encoding and decoding. Different parameters impacting the OAM-related nonlinear conversion were discussed. These parameters include power density, phase-matching condition, and mode overlapping. Multiple OAM modes nonlinear interaction was also studied. The reverse HOBBIT system was used to verify the multi-mode interaction theory of the APV modes. Using the nonlinear interaction theory of the APV, the 2D HOBBIT was used as the source to excite the SHG process and generate deep UV APV carrying OAM. The effects of how OAM and radial beam size affect the nonlinear interaction were illustrated.
Dai, Kunjian, "A Study on Asymmetric Perfect Vortex: Fractional Orbital Angular Momentum and Nonlinear Interaction" (2023). All Dissertations. 3338.
Author ORCID Identifier