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.

High-order femtosecond vortices converted from a tunable high-order Hermite–Gaussian Yb:CALGO laser

“…After the mode converter, LG modes were formed. The converted LG modes were incidentally projected on the common path radial shear interferometer to examine the phase singularity [25]. Aspheric lens L 5 and L 6 with the focal length of 120 mm and 50 mm, respectively.…”

“…Our research group fabricated a single-mode fiber-coupled laser diode (LD) offaxis pumped Brewster cut Yb:QX laser to generate femtosecond HG modes, the slope efficiencies of HG 00 , HG 10 , and HG 20 are 19.8%, 14.7%, and 11.9%. The mode locking thresholds of HG 00 , HG 10 , and HG 20 are 19.4 mW, 26.2 mW, and 37.2 mW, with the pump powers of 210 mW, 370 mW, and 580 mW, the pulse duration was about 190 fs [25]. Zhao et al push forwarded the advancement of femtosecond laser vortices into the 2 µm spectral region, the LG 0,±1 modes were generated in the femtosecond regime [26].…”

Production of orbital angular momentum states of optical vortex beams using a vortex half-wave retarder with double-pass configuration

“…The interference and diffraction characteristics of optical vortices have been utilized for measurements of the OAMs of light. The interferometric techniques involving a shearing interferometer and an inverted field interferometer were shown to determine the properties of ultrafast vortices 39 , 40 . An improved multipoint interferometer was manifested to probe the vortex beams with high OAM charge 41 .…”

The Spatial Mapping of Interconversion Between Laguerre-Gaussian and Hermite-Gaussian Beams Array With an Astigmatism Phase

“…The OAM of the light is generally characterized by detecting the magnitude and sign of the l, and many methods have been proposed, such as interference methods [7][8][9][10] and diffraction methods [11][12][13]. Most of the interference methods require a reference beam, and diffraction methods usually require special optical element and strict beam alignment.…”