Single-shot probing of sub-picosecond solid-to-overdense-plasma dynamics.

A single-shot near-infrared probing method has been developed to characterize the formation and evolution of the pre-plasma dynamics over sub-picosecond timescales, which is essential for the societal applications of laser-accelerated ion technologies.

Sensing and coupling of optical channels in dynamic atmospheric turbulence using OAM beamlets for improved power and data transmission.

Propagation of laser light is distorted in the presence of atmospheric turbulence. This poses an issue for sensing, free-space optical communications, and transmission of power. The presented system offers a novel solution to mitigate the effects of turbulence. By rapidly probing a turbulent volume by varying a beam's spatial and phase characteristics, the best transmission mode can be determined and updated in real time. Unlike a traditional tip-tilt system, this scheme is fully electronic, and has a scalable architecture to leverage multiple optical transmission paths simultaneously. This optical control system greatly improves power efficiency and successful recovery of data through environments with strong turbulence.

OAM-based optical wavelet using a single pixel detection system for probing dynamic environments with application to real-time measurements of strong atmospheric turbulence.

This paper presents a novel method for optical probing by generating optical fields with characteristics of wavelets. The optical wavelets form a basis of rotated asymmetric beams with scaled orbital angular momentum (OAM) and beam sizes. The probing method was used experimentally to measure the continuous wavelet transform of a turbulent propagation path, giving insight into the angular properties about a fixed radius. The wavelet transform of a three-dimensional turbulence distribution was measured; the measurements are much faster than the turbulence changes, allowing characterization of an instantaneous realization of turbulence over time. Results show highly localized regions of OAM in space through the turbulence and characteristics of the turbulence can be extracted from the wavelet transforms.

Remote sensing using a spatially and temporally controlled asymmetric perfect vortex basis generated with a 2D HOBBIT.

Orbital angular momentum (OAM) is a potential tool for remote sensing applications since amplitude/phase distributions can be decomposed into an OAM basis for analysis. We demonstrate the generation of a spatially asymmetric perfect vortex (APV) basis based on a pulsed 2D HOBBIT (Higher Order Bessel Beams Integrated in Time) system using two acousto-optic deflectors and optical coordinate transformation optics. Results are demonstrated for numerous radii and OAM charges as high as 20, with switching speeds greater than 400 kHz. The spatial APV basis is used to design different types of pulse trains for amplitude object pattern recognition and phase object wavefront sensing. Experimental results of sensing are provided for an amplitude object and a phase object to demonstrate the feasibility of the spatial APV on remote sensing tasks.

Fractional orbital angular momentum conversion in second-harmonic generation with an asymmetric perfect vortex beam.

This Letter demonstrates the nonlinear conversion of asymmetric perfect vortex (APV) beams with fractional orbital angular momentum (OAM). By controlling the amplitude and phase of the fundamental light field, we create APVs whose global OAM demonstrates a one-to-one correspondence of the charge numbers for fractional OAM values. The results show that the OAM of the second-harmonic generation fields follow the OAM conservation law. The nonlinear interactions of multiple OAM beams with the APVs are also investigated as they relate to the nonlinear frequency conversion and are shown to exhibit unique frequencies as a result of the Doppler frequency tagged OAM values.

Spatio-temporal controlled filamentation using higher order Bessel-Gaussian beams integrated in time.

We demonstrate a new method for a systematic, dynamic, high-speed, spatio-temporal control of femtosecond light filamentation in BK7 as a particular example of nonlinear medium. This method is based on using coherent conjugate asymmetric Bessel-Gaussian beams to control the far-field intensity distribution and in turn control the filamentation location. Such spatio-temporal control allows every femtosecond pulse to have a unique intensity distribution that results in the generation of structured filamentation patterns on demand. The switching speed of this technique is dependent on the rise time of the acousto-optic deflector, which can operate in the MHz range while having the ability to handle high peak power pulses that are needed for nonlinear interactions. The proposed and demonstrated spatio-temporal control of structured filaments can enable generation of large filament arrays, opto-mechanical manipulations of water droplets for fog clearing, as well as engineered radiofrequency plasma antennas.

Real-time OAM cross-correlator based on a single-pixel detector HOBBIT system.

The creation and detection of spatial modes of light with transient orbital angular momentum (OAM) properties is of critical importance in a number of applications in sensing and light matter interactions. Most methods are limited in their frequency response as a result of their modulation techniques. In this paper, a new method is introduced for the coherent detection of transient properties of OAM using a single pixel detector system for the creation of an OAM spectrogram. This technique is based on the ideas utilized in acousto-optic based optical correlators with log-polar optical elements for the creation and detection of higher order bessel beams integrated in time (HOBBIT) at MHz data rates. Results are provided for beams with time varying OAM, coherent combinations, and transient scattering by phase objects.

Experimental probing of turbulence using a continuous spectrum of asymmetric OAM beams.

Propagation of a continuous spectrum of orbital angular momentum (OAM) states through a realistic and controlled 3-dimensional turbulent condition has not been studied to date to the authors' knowledge. Using the Higher Order Bessel-gauss Beams Integrated in Time (HOBBIT) system and a 60 meter optical path Variable Turbulence Generator (VTG), we demonstrate that by changing the OAM in a continuous scan, a spectrum of OAMs provide an opportunity to take advantage of additional propagation channels within the aperture of the transmitter and optical path to the receiver. Experimental results are provided illustrating the HOBBIT system's ability to position the beam in space and time to exploit eigenchannels in the turbulent medium. This technique can be used to probe the turbulence at time scales much faster than the Greenwood frequency.

Second-harmonic generation of asymmetric Bessel-Gaussian beams carrying orbital angular momentum.

Nonlinear processes of laser beams carrying orbital angular momentum (OAM) offer a means to generate new wavelengths and to manipulate OAM charge numbers. We demonstrate the second-harmonic generation (SHG) of asymmetric Bessel-Gaussian (BG) beams carrying OAM of both integer and fractional charge numbers. Experimental results show a good one-to-one correspondence of the charge numbers and compliance with the OAM conservation law. The SHG conversion process and efficiency with different combined charge numbers are also discussed.

Generating polarization vortices by using helical beams and a Twyman Green interferometer.

A stable interferometric arrangement consisting of a polarizing beam splitter, a reflector, and a right-angle prism is designed to transform helical beams into polarization vortices. The computer-generated holograms are loaded on the liquid crystal spatial light modulator (LC-SLM) in order to generate different helical beams. Then the helical beams are transformed into polarization vortices with different kinds of intensity distribution successfully.

Measuring OAM states of light beams with gradually-changing-period gratings.

A method to measure orbital angular momentum (OAM) states of light beams by using gradually-changing-period gratings is reported. Two kinds of gradually-changing-period gratings were used for the measurement of OAM states. The OAM states of the incident beam can be measured easily from the Hermite-Gaussian-like diffraction patterns. The simulation results agree well with the experiments.

Generation of optical vortices by using spiral phase plates made of polarization dependent devices.

A method to construct spiral phase plates (SPPs) from quarter-wave plates and spatially variable half-wave plates (SVHWPs) is proposed. Optical vortices were experimentally generated by using SPPs made of polarization-dependent devices. The topological charge of the optical vortex can be also determined by the structure of the SVHWP and the polarization of the incident beam.