Single-Frame Characterization of Ultrafast Pulses with Spatiotemporal Orbital Angular Momentum

Abstract

Light carrying spatiotemporal orbital angular momentum (ST-OAM) makes possible new types of optical vortices arising from transverse OAM. ST-OAM pulses exhibit novel properties during propagation, transmission, refraction, diffraction, and nonlinear conversion, attracting growing experimental and theoretical interest and studies. However, one major challenge is the lack of a simple and straightforward method for characterizing ultrafast ST-OAM pulses. Using spatially-resolved spectral interferometry, we demonstrate a simple, stationary, single-frame method to quantitatively characterize ultrashort light pulses carrying ST-OAM. Using our method, the presence of an ST-OAM pulse, including its main characteristics such as topological charge numbers and OAM helicity, can be identified easily from the unique and unambiguous features directly seen on the raw data-without any need for a full analysis of the data. After processing and reconstructions, other exquisite features, including pulse dispersion and beam divergence, can also be fully characterized. Our fast characterization method allows high-throughput and quick feedback during the generation and optical alignment processes of ST-OAM pulses. It is straightforward to extend our method to single-shot measurement by using a high-speed camera that matches the pulse repetition rate. This new method can help advance the field of spatially and temporally structured light and its applications in advanced metrologies.

Electromagnetic Spatiotemporal Differentiation Meta‐Devices

“…Recently, researchers have exploited spatiotemporal differentiators based on metasurfaces [66][67][68] and multilayered structures, [69] which are much more compact than traditional pulse shapers [70,74,75] with indispensable spatiotemporal Fourier transform components, to generate spatiotemporal optical vortices (STOVs) with transverse OAM. In Section S2 (Supporting Information), we show that our first-order spatiotemporal differentiator can not only give rise to the spatial and temporal profiles of a single rectangular-shape pulse input but also stamps a transverse OAM with a fractal topology charge number (l = 0.58) for the output pulse.…”

Spatiotemporal Optical Vortices: Toward Tailoring Orbital Angular Momentum of Light in Full Space-Time

“…As shown in Figure 3c, the value and sign of the topological charge were reflected as the number of lobes and the stretched direction of the measured diffraction patterns in the x−y plane, respectively. Guan Gui et al 26 demonstrated that, by introducing an extra reference pulse in the diffraction method, the resulting interference fringes could be used to fully characterize ST vortices with a single frame, while also not requiring strong pulse energy (Figure 3d). Furthermore, OAMdependent transverse and longitudinal pulse shifts of the reflection and refraction of an ST vortex at a planar interface were investigated recently, 27 which may provide a potential method for characterizing ST vortices (Figure 3e).…”

“…(bottom) Corresponding three-dimensional drawing, in which the reference and ST vortex pulses ( l = 1) are shown next to the camera. Adapted with permission from ref . Copyright 2022 American Chemical Society.…”

Propagation of transverse photonic orbital angular momentum through few-mode fiber

“…The STOV pulse, therefore, can carry a transverse photonic OAM of lℏ per photon 12 – 14 Since its discovery, much research has been done in studying STOV pulse, including studying its propagation dynamics, 15 , 16 developing novel characterization approaches, 17 – 19 utilizing STOV pulse in spatiotemporal imaging, 20 and designing other types of wave packets that also carry transverse photonic OAM 21 – 25 …”