Direct Observation of Conservation of Orbital Angular Momentum in Collinear Type-I Spontaneous Parametric Down-Conversion

Date of Award


Degree Name

M.S. in Electro-Optics


Department of Electro-Optics


Advisor: Qiwen Zhan

Second Advisor

Advisor: Roberto Ramirez


We implement a direct measurement of the spatial modes distribution generated in a collinear type I spontaneous parametric down-conversion (SPDC) process using a triggered ICCD camera. This type of experiments have been realized previously. However such those cases the measurement was an indirect one, where both photons were collected into one-pixel detectors. In this thesis, to the best or our knowledge, it is the first time that a direct two dimensional measurement of the spatial modes distribution is made. These are well described by Laguerre-Gaussian modes. In our experiments we could observe up to mode l = +-10. By exploiting the capabilities of an ICCD camera, it is possible to visualize the orbital angular momentum (OAM) conservation of the unprocessed SPDC bi-photon state. This is performed by observing the diffraction pattern by a triangular aperture. We show the results using this method for modes l =+/-1;+/-2. This conservation of OAM leads to entanglement in OAM, since one photon carries the anti-correlated topological charge with respect to the other one. Therefore, they are conditioned to the state of the other photon.


Electromagnetism, Engineering, Optics, Physics, Quantum Physics, OAM, conservation, SPDC, entaglement, Laguerre-Gaussian

Rights Statement

Copyright 2018, author