Colliding of two counter-propagating laser pulses is a widely used approach to create a laser field or intensity surge. We experimentally demonstrate broadband coherent terahertz (THz) radiation generation through the interaction of colliding laser pulses with gas plasma. The THz radiation has a dipole-like emission pattern perpendicular to the laser propagation direction with a detected peak electric field 1 order of magnitude higher than that by single pulse excitation. As a proof-of-concept demonstration, it provides a deep insight into the physical picture of laser–plasma interaction, exploits an important option to the promising plasma-based THz source, and may find more applications in THz nonlinear near-field imaging and spectroscopy.

Two-color plasma, induced by two lasers of different colors, can radiate ultra-broadband and intense terahertz (THz) pulses, which is desirable in many technological and scientific applications. It was found that the polarization of the emitted THz depends on the phase difference between the fundamental laser wave and its second harmonic. Recent investigation suggests that chirp-induced change of pulse overlap plays an important role in the THz yield from two-color plasma. However, the effect of laser chirp on THz polarization remains unexplored. Hereby, we investigate the impact of laser chirp on THz polarization. It is unveiled that the chirp-induced phase difference affects THz polarization. Besides, positive and negative chirps have opposite effects on the variation of the THz polarization versus the phase difference. The polarization of THz generated by a positively chirped pump laser rotates clockwise with an increasing phase difference, while it rotates anticlockwise when generated by a negatively chirped pump laser.

Spectral fingerprint and terahertz (THz) field-induced carrier dynamics demands the exploration of broadband and intense THz signal sources. Spintronic THz emitters (STEs), with high stability, a low cost, and an ultrabroad bandwidth, have been a hot topic in the field of THz sources. One of the main barriers to their practical application is lack of an STE with strong radiation intensity. Here, through the combination of optical physics and ultrafast photonics, the Tamm plasmon coupling (TPC) facilitating THz radiation is realized between spin THz thin films and photonic crystal structures. Simulation results show that the spectral absorptance can be increased from 36.8% to 94.3% for spin THz thin films with TPC. This coupling with narrowband resonance not only improves the optical-to-spin conversion efficiency, but also guarantees THz transmission with a negligible loss (∼4%) for the photonic crystal structure. According to the simulation, we prepared this structure successfully and experimentally realized a 264% THz radiation enhancement. Furthermore, the spin THz thin films with TPC exhibited invariant absorptivity under different polarization modes of the pump beam and weakening confinement on an obliquely incident pump laser. This approach is easy to implement and offers possibilities to overcome compatibility issues between the optical structure design and low energy consumption for ultrafast THz opto-spintronics and other similar devices.

Frequency detuning of mode-locked fiber lasers displays many remarkable nonlinear dynamical behaviors. Here we report for the first time the evolution of pulses from mode-locking through period pulsation to Q-switched mode-locking for three fundamental cases. Our experiments are performed in a hybrid actively and passively amplitude-modulated all-fiber polarization-maintaining mode-locked fiber laser, where the amplitude modulation frequency artificially deviates from the fundamental frequency of the cavity. We design and numerically simulate the laser with coupled Ginzburg–Landau equations. The experimentally observed dynamics of the mode detuning process is discussed with the assistance of the fitted model and numerical simulations, showing the generalizability of the optical mode detuning variation process. Our work provides fundamental insights for understanding perturbations in nonlinear optical resonant cavities and expands the ideas for studying chaotic path theory in hybrid mode-locked fiber lasers.

Characterization of the state of polarization (SOP) of ultrafast laser emission is relevant in several application fields such as field manipulation, pulse shaping, testing of sample characteristics, and biomedical imaging. Nevertheless, since high-speed detection and wavelength-resolved measurements cannot be simultaneously achieved by commercial polarization analyzers, single-shot measurements of the wavelength-resolved SOP of ultrafast laser pulses have rarely been reported. Here, we propose a method for single-shot, wavelength-resolved SOP measurements that exploits the method of division-of-amplitude under far-field transformation. A large accumulated chromatic dispersion is utilized to time-stretch the laser pulses via dispersive Fourier transform, so that spectral information is mapped into a temporal waveform. By calibrating our test matrix with different wavelengths, wavelength-resolved SOP measurements are achieved, based on the division-of-amplitude approach, combined with high-speed opto-electronic processing. As a proof-of-concept demonstration, we reveal the complex wavelength-dependent SOP dynamics in the build-up of dissipative solitons. The experimental results show that the dissipative soliton exhibits far more complex wavelength-related polarization dynamics, which are not shown in single-shot spectrum measurement. Our method paves the way for single-shot measurement and intelligent control of ultrafast lasers with wavelength-resolved SOP structures, which could promote further investigations of polarization-related optical signal processing techniques, such as pulse shaping and hyperspectral polarization imaging.

We demonstrate generation of 7.6 fs near-UV pulses centered at 400 nm via 8-fold soliton-effect self-compression in an Ar-filled hollow-core kagomé-style photonic crystal fiber with ultrathin core walls. Analytical calculations of the effective compression length and soliton order permit adjustment of the experimental parameters, and numerical modeling of the nonlinear pulse dynamics in the fiber accurately predicts the spectrotemporal profiles of the self-compressed pulses. After compensation of phase distortion introduced by the optical elements along the beam path from the fiber to the diagnostics, 71% of the pulse energy was in the main temporal lobe, with peak powers in excess of 0.2 GW. The convenient setup opens up new opportunities for time-resolved studies in spectroscopy, chemistry, and materials science.

In pursuit of efficient high-order harmonic conversion in semiconductor devices, modeling insights into the complex interplay among ultrafast microscopic electron–hole dynamics, nonlinear pulse propagation, and field confinement in nanostructured materials are urgently needed. Here, a self-consistent approach coupling semiconductor Bloch and Maxwell equations is applied to compute transmission and reflection high-order harmonic spectra for finite slab and sub-wavelength nanoparticle geometries. An increase in the generated high harmonics by several orders of magnitude is predicted for gallium arsenide nanoparticles with a size maximizing the magnetic dipole resonance. Serving as a conceptual and predictive tool for ultrafast spatiotemporal nonlinear optical responses of nanostructures with arbitrary geometry, our approach is anticipated to deliver new strategies for optimal harmonic manipulation in semiconductor metadevices.

Classic interferometry was commonly adopted to realize ultrafast phase imaging using pulsed lasers; however, the reference beam required makes the optical structure of the imaging system very complex, and high temporal resolution was reached by sacrificing spatial resolution. This study presents a type of single-shot ultrafast multiplexed coherent diffraction imaging technique to realize ultrafast phase imaging with both high spatial and temporal resolutions using a simple optical setup, and temporal resolution of nanosecond to femtosecond scale can be realized using lasers of different pulse durations. This technique applies a multiplexed algorithm to avoid the data division in space domain or frequency domain and greatly improves the spatial resolution. The advantages of this proposed technique on both the simple optical structure and high image quality were demonstrated by imaging the generation and evaluating the laser-induced damage and accompanying phenomenon of laser filament and shock wave at a spatial resolution better than 6.96 μm and a temporal resolution better than 10 ns.

The spatiotemporal measurement of ultrashort laser beams usually involves techniques with complex set-ups or limited by instabilities that are unable to accurately retrieve the frequency-resolved wavefront. Here, we solve these drawbacks by implementing a simple, compact, and ultra-stable spatiotemporal characterization technique based on bulk lateral shearing spectral interferometry using a birefringent uniaxial crystal. We apply it to retrieve complex spatiotemporal structures by characterizing ultrafast optical vortices with constant and time-varying orbital angular momentum. This technique can operate in all the transparency range of the anisotropic elements, enabling the characterization in different spectral ranges like infrared, visible, or ultraviolet.

We demonstrate numerically and experimentally the generation of powerful supercontinuum vortices from femtosecond vortex beams by using multiple thin fused silica plates. The supercontinuum vortices are shown to preserve the vortex phase profile of the initial beam for spectral components ranging from 500 nm to 1200 nm. The transfer of the vortex phase profile results from the inhibition of multiple filamentation and the preservation of the vortex ring with relatively uniform intensity distribution by means of the thin-plate scheme, where the supercontinuum is mainly generated from the self-phase modulation and self-steepening effects. Our scheme works for vortex beams with different topological charges, which provides a simple and effective method to generate supercontinuum vortices with high power.