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Ultra-intense femtosecond vortex pulses can provide an opportunity to investigate the new phenomena with orbital angular momentum (OAM) involved in extreme cases. This paper reports a high gain optical vortex amplifier for intense femtosecond vortex pulses generation. Traditional regeneration amplifiers can offer high gain for Gaussian mode pulses but cannot amplify optical vortex pulses while maintaining the phase singularity because of mode competition. Here, we present a regeneration amplifier with a ringshaped pump. By controlling the radius of the pump, the system can realize the motivation of LG0,1(-1) mode and the suppression of Gaussian mode. Without seeds, the amplifier has a donut-shaped output containing two opposite OAM states simultaneously, as our prediction by simulation. If seeded a pulse of a topologic charge of 1 or-1, the system will output an amplified LG0,1(-1) mode pulse with the same topologic charge as the seed. To our knowledge, this amplifier can offer the highest gain as 1.45×10 6 for optical vortex amplification. Finally, we obtain a 1.8 mJ, 51 fs compressed optical vortex seeded from a 2 nJ optical vortex.

This paper reports the experimental realization of efficiently sorting vector beams by polarization topological charge (PTC). The PTC of a vector beam can be defined as the repetition number of polarization state change along the azimuthal axis, while its sign stands for the rotating direction of the polarization. Here, a couple of liquid crystal Pancharatnam-Berry optical elements (PBOEs) have been used to introduce conjugated spatial phase modulations for two orthogonal circular polarization states. Applying these PBOEs in a 4-f optical system, our experiments show the setup can work for PTC sorting with a separation efficiency of more than 58%. This work provides an effective way to decode information from different PTCs, which may be interesting in many fields, especially in optical communication.

We report on a vortex laser chirped-pulse amplification (CPA) system that delivers pulses with a peak power of 45 TW. A focused intensity exceeding 10 19 W/cm 2 has been demonstrated for the first time by the vortex amplification scheme. Compared with other schemes of strong-field vortex generation with high energy flux but narrowband vortex converting elements at the end of the laser, an important advantage of our scheme is that we can use broadband but size-limited q-plate to realize broadband modeconverting in the front end of the CPA system, and achieve high-power amplification with a series of amplifiers. This method is low cost and can be easily implemented in an existing laser system. The results have verified the feasibility to obtain terawatt even petawatt vortex laser amplification by a CPA system, which has important potential applications in strong-field laser physics, e.g. generation of vortex particle beams with orbital angular momentum, fast ignition for inertial confinement fusion, simulation of the extreme astrophysical environment.

In the past three decades, ultrafast pulse laser technology has greatly progressed and applied widely in many subjects, such as physics, chemistry, biology, materials, and so on. Accordingly, as well as for future developments, to measure or characterize the pulses temporally in femtosecond domain is indispensable but still challenging. Based on the operation principles, the measurement techniques can be classified into three categories: correlation, spectrogram, and spectral interferometry, which operate in time-domain, time-frequency combination, and frequency-domain, respectively. Here, we present a mini-review for these techniques, including their operating principles, development status, characteristics, and challenges.