Ultrafast vortices generation at low pump power and shearing interferometer-based vortex topological detection

Abstract

A single mode fiber coupled laser diode was employed to generate a low threshold femtosecond vortex by using an off-axis pumping technique and mode converter with a pair of cylindrical lenses. In this way, the pump threshold of a laser system can be decreased and the slope efficiency can be increased. Two lateral interferometric techniques for optical vortex detection were improved using the circular common-path (CCP) geometry configuration. In the CCP interferometer, the object optical vortex was divided into two beams that transmit oppositely along the interferometer and interfere with themselves in the beam splitter. The two beams traveled along the same path through the same optical elements. These new designs omit delicate adjustment of two interference arms, and can easily manipulate the optical path difference between the two beams. The results show that the experimental results are in good agreement with the numerical simulation. These CCP interferometers are insensitive to the environment and are suitable for the measurement of topological charge of a laser source with a short coherence length, including white lasers.