Pulse formation mechanisms switching in hybrid mode-locked fiber laser

Hybrid mode-locking has been widely used in enhancing pulse quality, however how the hybrid two mode-locking techniques work remains unclear. In this paper, we experimentally investigate three pulse formation mechanisms in saturable absorbers (SA) and nonlinear polarization evolution (NPE) passively hybrid mode-locked fiber laser, which are SA-dominated, NPE-dominated, and SA-NPE co-domination switching. Clarified the exists dynamic competition and cooperation among the mode-locking techniques. For the first time, the method of simulating filtered gain spectrum with customized filtering is proposed, and the switching of pulse formation mechanisms is numerically investigated using the coupled Ginzburg-Landau equations. Our results deepen the understanding of hybrid mode-locked fiber lasers and provided a foundation for multi-wavelength mode-locked lasers with different mode-locking techniques in a single cavity

Multifocal laser direct writing through spatial light modulation guided by scalable vector graphics

Multifocal laser direct writing (LDW) based on phase-only spatial light modulator (SLM) can realize flexible and parallel nanofabrication with high throughput potential. In this investigation, a novel approach of combining two-photon absorption, SLM and vector path guided by scalable vector graphics (SVG) has been developed and tested preliminarily, for fast, flexible and parallel nanofabrication. Three laser focuses are independently controlled with different paths, which are according to SVG, to optimize fabrication and promote time efficiency. The minimum structure width can be as low as 74 nm. Accompanied with a translation stage, a carp structure of 18.16 $\mu$m by 24.35 $\mu$m has been fabricated. This method shows the possibility of developing LDW techniques towards full-electrical system, and provides a potential way to efficiently engrave complex structures on nanoscales

Dual-comb mode-locked Yb:CALGO laser based on cavity-shared configuration with separated end mirrors

Dual-comb spectroscopy typically requires the utilization of two independent and phase-locked femtosecond lasers, resulting in a complex and expensive system that hinders its industrial applications. Single-cavity dual-comb lasers are considered as one of the primary solution to simplify the system. However, controlling the crucial parameter of difference in repetition rates remains challenging. In this study, we present a dual-comb mode-locked Yb:CALGO laser based on a cavity-shared configuration with separated end mirrors. We employ two pairs of end mirrors and two thin-film polarizers angled at 45 degrees to the cavity axis, leading to separating the cross-polarized laser modes. We achieve simultaneous operation of two combs at approximately 1040 nm with pulse durations of around 400 fs and an average power exceeding 1 W. The repetition rates are approximately 59 MHz and their difference can be easily tuned from zero up to the MHz range. By effectively canceling out common mode noises, we observe minimal fluctuation in the repetition rate difference with a standard deviation of about 1.9 Hz over ten minutes, while experiencing fluctuations in repetition rates as large as 90 Hz. We demonstrate the capabilities of this system by utilizing the free-running dual-comb setup for asynchronous optical sampling on a saturable absorber and measuring etalon transmission spectrum. This system allows for simple and independent control of the repetition rates and their difference during operation, facilitating the selection of optimal repetition rate difference and implementation of phase-locking loops. This advancement paves the way for the development of simple yet high-performance dual-comb laser sources

Onset of nonlinear electroosmotic flow under AC electric field

Nonlinearity of electroosmotic flows (EOFs) is ubiquitous and plays a crucial role in the mass and energy transfer in ion transport, specimen mixing, electrochemistry reaction, and electric energy storage and utilizing. When and how the transition from a linear regime to a nonlinear one is essential for understanding, prohibiting or utilizing nonlinear EOF. However, suffers the lacking of reliable experimental instruments with high spatial and temporal resolutions, the investigation of the onset of nonlinear EOF still stays in theory. Herein, we experimentally studied the velocity fluctuations of EOFs driven by AC electric field via ultra-sensitive fluorescent blinking tricks. The linear and nonlinear AC EOFs are successfully identified from both the time trace and energy spectra of velocity fluctuations. The critical electric field ($E_{A,C}$) separating the two statuses is determined and is discovered by defining a generalized scaling law with respect to the convection velocity ($U$) and AC frequency ($f_f$) as $E_{A,C}$~${f_f}^{0.48-0.027U}$. The universal control parameters are determined with surprising accuracy for governing the status of AC EOFs. We hope the current investigation could be essential in the development of both theory and applications of nonlinear EOF

Large-Scale Flow in Micro Electrokinetic Turbulent Mixer

In the present work, we studied the three-dimensional (3D) mean flow field in a micro electrokinetic (μEK) turbulence based micromixer by micro particle imaging velocimetry (μPIV) with stereoscopic method. A large-scale solenoid-type 3D mean flow field has been observed. The extraordinarily fast mixing process of the μEK turbulent mixer can be primarily attributed to two steps. First, under the strong velocity fluctuations generated by μEK mechanism, the two fluids with different conductivity are highly mixed near the entrance, primarily at the low electric conductivity sides and bias to the bottom wall. Then, the well-mixed fluid in the local region convects to the rest regions of the micromixer by the large-scale solenoid-type 3D mean flow. The mechanism of the large-scale 3D mean flow could be attributed to the unbalanced electroosmotic flows (EOFs) due to the high and low electric conductivity on both the bottom and top surface