High-precision time interval measurement is a fundamental technique in many advanced applications, including time and distance metrology, particle physics, and ultra-precision machining. However, many of these applications are confined by the imprecise time interval measurement of electrical signals, restricting the performance of the ultimate system to a few picoseconds, which limits ultrahigh precision applications. Here, we demonstrate an optical means for the time interval measurement of electrical signals that can successfully achieve femtosecond (fs) level precision. The setup is established using the optical frequency comb (OFC) based linear optical sampling (LOS) technique to realize timescale-stretched measurement. We achieve a measurement precision of 82 fs for a single LOS scan measurement and 3.05 fs for the 100-times average with post-processing, which is three orders of magnitude higher than the results of older electrical methods. The high-precision time interval measurement of electrical signals can substantially improve precision measurement technologies.
2023, 11(12): 2222
Launching, tracking, and controlling picosecond acoustic (PA) pulses are fundamentally important for the construction of ultrafast hypersonic wave sources, ultrafast manipulation of matter, and spatiotemporal imaging of interfaces. Here, we show that GHz PA pulses can be all-optically generated, detected, and manipulated in a 2D layered heterostructure using femtosecond laser pump–probe. Based on an interferometric model, PA pulse signals in glass are successfully decoupled from the coexisting temperature and photocarrier relaxation and coherent acoustic phonon (CAP) oscillation signals of lattice in both time and frequency domains. Under selective interface excitations, temperature-mediated interfacial phonon scatterings can compress PA pulse widths by about 50%. By increasing the pump fluences, anharmonic CAP oscillations of lattice are initiated. As a result, the increased interatomic distance at the interface that reduces interfacial energy couplings can markedly broaden the PA pulse widths by about 150%. Our results open new avenues to obtain controllable PA pulses in 2D semiconductor/dielectric heterostructures with femtosecond laser pump–probe, which will enable many investigations and applications.
2023, 11(12): 2000
In spintronic applications, there is a constant demand for lower power consumption, high densities, and fast writing speed of data storage. All-optical switching (AOS) is a technique that uses laser pulses to switch the magnetic state of a recording medium without any external devices, offering unsurpassed recording rates and a simple structure. Despite extensive research on the mechanism of AOS, low energy consumption and fast magnetization reversing remain challenging engineering questions. In this paper, we propose a newly designed cavity-enhanced AOS in GdCo alloy, which promotes optical absorption by twofold, leading to a 50% reduction in energy consumption. Additionally, the time-resolved measurement shows that the time of reversing magnetization reduces at the same time. This new approach makes AOS an ideal solution for energy-effective and fast magnetic recording, paving the way for future developments in high-speed, low-power-consumption data recording devices.
2023, 11(11): 1870
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.
2023, 11(9): 1562
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.
2023, 11(6): 978
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 () 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.
2023, 11(6): 1057
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 -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.
2023, 11(3): 383
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.
2023, 11(1): 35
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.
2022, 10(10): 2405
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.
2022, 10(9): 2099