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The composite hydrogels are widely used in various research directions. How to improve the mechanical properties is one of the concerns of researchers. In this work, the mechanical properties of composite hydrogels with reduced graphene oxide (rGO), kaolin (KL), montmorillonite (MMT), and attapulgite (APT) as additives were compared. The morphology of polyacrylamide (PAM) composite hydrogel was observed by electron microscope, and the hydrogen bonding between inorganic additives and PAM chain in the hydrated samples were detected by IR. The rheological data (G, G', and tan [delta]) confirmed the beneficial effect of rGO as a two-dimension (2D) material on the mechanical properties of hydrogels. In the tensile-fracture experiments, the maximum tensile strain of PAM-rGO was 568% and the maximum tensile force was 1.18 N, both of which were larger than that of the clay-based composite hydrogel with the same mass concentration. Based on these experimental data, the response behavior of rGO in the process of hydrogel deformation was elucidated by the concept of '2D flexible crosslinking point,' and the reason why PAM-rGO composite hydrogel had better mechanical strength was explained in detail. KEYWORDS 2D flexible crosslinking point, composite hydrogel, mechanical properties, reduced graphene oxide, two-dimensional materials, 1 | INTRODUCTION Hydrogels are materials composed of water and polymer matrix. Because of its excellent properties, especially good biocompatibility, hydrogels have attracted more and more attention in the fields [...]

Multidimensional coherent spectroscopy (MDCS) is a highly intriguing field for the unique capacities to unravel quantum pathways of microscopic dynamics and discern different dipole–dipole interactions. These capabilities are not simultaneously accessible through any other techniques. The foundation of MDCS lies in the stable phase and accurate time information of the multi‐pulse sequences involved. Achieving the phase stability has traditionally relied on ingenious geometric optical designs and multiple feedback control systems, albeit at the cost of complexity. In this letter, a phase stability scheme for high‐resolution MDCS is proposed by replacing traditional laser sources with two highly coherent frequency combs. By employing dual‐comb interferometry, the phase distribution across a broad spectral range and the time information of all the excitation pulses are precisely measured, even in setups that lack phase stability. In the experiment, a rephasing MDCS of rubidium atoms is obtained by applying this approach, wherein the comb resolution is utilized to differentiate the couplings of hyperfine energy levels. This scheme simplifies the structure of MDCS and holds potential for applications in other MDCS systems involving many‐body interactions and non‐absorptive resonances. [ABSTRACT FROM AUTHOR]

High-resolution optical multidimensional coherent spectroscopy (MDCS) requires frequency-stable laser sources and high-resolution heterodyne spectra. Fully phase-locked dual-comb spectroscopy (DCS) enables the achievement of high resolution, high accuracy, broad bandwidth, and a rapid multi-heterodyne spectrum, which results in the DCS's potential to replace the spectrometer and phase detection system in MDCS. We verified the phase measurement capability of the MDCS system based on fully phase-locked fiber DCS by studying phase-sensitive photon echoes and double-quantum processes. The accurate phase and frequency of linear and nonlinear signals were obtained simultaneously using a single detector without subsequent frequency drift correction. Subsequently, the acquisition of longtime quantum beat signals demonstrates the high phase coherence between excitation pulses. Additionally, the two-dimensional coherent spectrum (2DCS) with high signal-to-noise-ratio and 100 MHz resolution was obtained via the MDCS system based on fully phase-locked fiber DCS. These results exhibit that fully phase-locked fiber DCS is an effective method for high-resolution 2DCS measurement, which facilitates further research on cold atoms, higher-order nonlinear spectra, and molecular fingerprint vibrational spectroscopy. [ABSTRACT FROM AUTHOR]

This Letter presents a 0.4-5.2-µm frequency comb from a compact laser. We designed an integrated fiber device for a figure-9 laser and constructed an all-fiber laser system. The spectrum of the fiber laser was scaled to the broadband region using a chirped periodically poled lithium niobate waveguide. To use this system for gas sensing, a mid-infrared comb with a spectral range of 2.5-5.2 µm and average power of 2.1 mW was divided using an optical filter. The optical part was packaged in a 305 mm × 225 mm × 62 mm box. The comb was stabilized by locking the repetition rate and carrier-envelope offset frequency of the seed source. The system provided an ultrabroadband spectral range from 0.4 to 5.2 µm, which could be applied to spectroscopy, frequency metrology, and optical synthesizers.

We demonstrate three typical mode-locking processes of a nonlinear amplifying loop mirror (NALM) fiber laser via a general nonlinear Schrödinger equation-based (GNLSE) simulation model. First, the pulse evolutions in the NALM cavity were separately simulated under asymmetric and weakly asymmetric conditions. We found that the splitting ratio and positions of the gain fiber can result in a suitable phase bias between clockwise and counter-clockwise beams, enabling the realization of a self-starting low-threshold operating condition. To assess the roles of the splitting ratio and gain in the mode-locking process, we simulated three pulse formation processes: in the soliton, stretched-pulse, and dissipative soliton mode-locking regimes. The simulation results show that the splitting ratio, gain, and dispersion directly influence the mode-locking condition and pulse characteristics, thereby providing effective quantified guidance for high-quality pulse generation. Finally, an experimental NALM oscillation operating under stretched pulse conditions was established to investigate the impact of the splitting ratio and pump power on the pulse characteristics. The experimental results prove that the splitting ratio, gain, and dispersion can be used to manipulate the mode-locking threshold, self-starting threshold, nonlinear effects, and pulse characteristics.