Passively Q-switched Nd3+ solid-state lasers with hexakis-[(trimethylsilyl)ethynyl]benzene and graphdiyne as saturable absorbers.

In this paper, two-dimensional Graphdiyne and Hexakis-[(trimethylsilyl)ethynyl]benzene nanosheets were prepared using the liquid-phase exfoliation method and were then successfully applied to 1.06 µm passively Q-Switched all-solid-state lasers. The Hexakis-[(trimethylsilyl)ethynyl]benzene was applied for the first time in passively Q-Switched all-solid-state lasers, as we know. For Graphdiyne, the Q-Switched pulse achieved a narrowest pulse width of 415 ns, a maximum repetition frequency of 244.2 kHz, a maximum pulse energy of 133.53 nJ, and peak power of 321.77 mW was obtained. While, the narrowest pulse width, maximum repetition frequency, maximum pulse energy, and peak power for Hexakis-[(trimethylsilyl)ethynyl]benzene are approximately 398.4 ns, 297.1 kHz, 89.61 nJ, and 220.39 mW respectively. The findings demonstrate the promising potential of both candidates as saturable absorbers for signal modulation in solid-state lasers.

High performance 1.9†µm passively Q-switched bulk laser with germanene as a saturable absorber.

Germanene is an analog of graphene, and its independent novel low-bending honeycomb structure gives outstanding advantages such as environmental stability and significant low-frequency optical absorbance. In this paper, the few-layer germanene was successfully prepared by the liquid phase exfoliation method. The saturable absorption characteristics of germanene in the infrared waveband were detected by the open-aperture Z-scan method. With germanene as a saturable absorber, a high-performance passively Q-switched bulk laser was realized at 1.9 µm. The shortest pulse width of 60.5 ns was obtained from continuous-wave pumping, corresponding to a single pulse energy of 6.7 µJ and peak power of 110 W. By utilizing the pulse pumping style with a repletion rate of 10 Hz, the single pulse energy and peak power increased to 45.8 µJ and 328 W, respectively, which exceeded all two-dimensional SA materials reported before. This research manifests that germanene is an excellent SA material for mid-infrared solid-state lasers.

Remarkable temperature-dependent second-harmonic-generation performance of a YCOB crystal.

For the first time, the temperature stability of second-harmonic-generation (SHG) is reported for the entire space of a YCa4O(BO3)3 (YCOB) crystal for a temperature range of -10 - 520 °C. Both theoretical calculations and experimental data indicate an optimum phase-matching (PM) direction of (θ = 149.2°, ϕ = 0°), which is located in the XZ principle plane (90° < θ < 180°). A special regression phenomenon of the PM angle was found in this direction, which further increased the SHG output at high temperature (> 200 °C). As a result, for SHG of the Nd:YAG laser, the measured temperature bandwidth of a YCOB crystal cut along the optimum PM direction is larger than 490 °C·cm. As demonstrated in this study, among all nonlinear optical crystals, this cut-type is currently the best choice when temperature-insensitive SHG is required.

Multiwalled Carbon Nanotube-Templated Nickel Porphyrin Covalent Organic Framework for Pencil-Drawn Noninvasive Respiration Sensors.

Paper-integrated configuration with miniaturized functionality represents one of the future main green electronics. In this study, a paper-based respiration sensor was prepared using a multiwalled carbon nanotube-templated nickel porphyrin covalent organic framework (MWCNTs@COFNiP-Ph) as an electrical identification component and pencil-drawn graphite electric circuits as interdigitated electrodes (IDEs). The MWCNTs@COFNiP-Ph not only inherited the high gas sensing performance of porphyrin and the aperture induction effect of COFs but also overcame the shielding effect between phases through the MWCNT template. Furthermore, it possessed highly exposed M-N4 metallic active sites and unique periodic porosity, thereby effectively addressing the key technical issue of room-temperature sensing for the respiration sensor. Meanwhile, the introduction of a pencil-drawing approach on common printing papers facilitates the inexpensive and simple manufacturing of the as-fabricated graphite IDE. Based on the above advantages, the MWCNTs@COFNiP-Ph respiration sensor had the characteristics of wide detection range (1-500 ppm), low detection limit (30 ppb), acceptable flexibility for toluene, and rapid response/recovery time (32 s/116 s). These advancements facilitated the integration of the respiration sensor into surgical masks and clothes with maximum functionality at a minimized size and weight. Moreover, the primary internal mechanism of COFNiP-Ph for this efficient toluene detection was investigated through in situ FTIR spectra, thereby directly elucidating that the chemisorption interaction of oxygen modulated the depletion layers, resulting in alterations in sensor resistance upon exposure to the target gas. The encouraging results revealed the feasibility of employing a paper-sensing system as a wearable platform in green electronics.

A corrugated epsilon-nearzero saturable absorber for a high-performance 1.3 µm solid-state bulk laser.

Epsilon-near-zero (ENZ) materials with vanishing permittivity exhibit unprecedented optical nonlinearity within subwavelength propagation lengths in the ENZ region, making them promising photoelectric materials that have achieved exciting results in ultrafast pulse laser modulations. In this study, we fabricated a novel saturable absorber (SA) based on a corrugated indium tin oxide (CITO) film with a symmetrical geometry using a low-cost self-assembly process. The strong saturable absorption of the CITO film triggered by the ENZ effect at normal incidence was comparable to that of the planar indium tin oxide (ITO) film at an optimal 60° incidence (TM polarization) at 1340 nm. In addition, the strong nonlinear optical properties of the CITO film were not limited by the incident angle and polarization state of the pump laser over a wide range of 0-20°. Benefiting from the excellent saturable absorption of CITO-based SA at normal incidence, a Q-switching operation with CITO-based SA at 1.34 µm was achieved in a Nd:YVO4 solid-state laser system, obtaining pulses of a duration of 85.6 ns, which was one order of magnitude narrower than that of the planar ITO-based SA. This study presents a new strategy for developing high-performance ENZ-based SAs and ultrafast lasers.

Porphyrin-Based Covalent Organic Framework Thin Films as Cathodic Materials for "On-Off-On" Photoelectrochemical Sensing of Lead Ions.

Currently, cathodic photoelectrochemical (PEC) sensors, which could effectively reduce background interference, are urgently required for ultrasensitive environmental monitoring. Herein, porphyrin-based covalent organic framework (TAPP-COF) thin films were fabricated via a bottom-up growth approach on the liquid/liquid interface and applied as a photocathode material to "on-off-on" PEC sensing of Pb2+. Benefitting from the unique charge channels of COFs and the good photoelectric properties of porphyrin, the as-prepared TAPP-COF thin films presented an improved photocathodic current, with a strongly enhanced "signal-on" response with low background. Then, CdSe@SiO2 quantum dots (QDs), as a quenching agent, were introduced through a hybridization chain reaction (HCR) to obtain a "signal off" PEC response. Afterward, with the introduction of target Pb2+, CdSe@SiO2 QDs were detached from TAPP-COF thin films, and the PEC response transformed into a signal-on state. Benefiting from the multiple-quenching and steric hindrance effect of CdSe@SiO2 QDs and the photocathodic property of TAPP-COFs, accurate monitoring of Pb2+ in a wide detection range from 0.05 to 1000 nM with a lower detection limit of 0.012 nM was realized based on the proposed on-off-on PEC approach. Notably, the methodology provides an efficient platform for ultrasensitive determination of heavy metal ions, which would play a significant role in environmental monitoring and public safety fields.

3D synergistical rGO/Eu(TPyP)(Pc) hybrid aerogel for high-performance NO2 gas sensor with enhanced immunity to humidity.

The prevalence of Internet of Things and portable electronics create an unprecedented demand for the high performance gas sensors. To pursuit such sensor, sandwich-type (phthalocyaninato)(porphyrinato) europium double-decker complex Eu(TPyP)(Pc) [TPyP = meso-tetra(4-pyridyl)porphyrin; Pc = phthalocyanine] was in situ self-assembled on the surface of reduced graphene oxide (rGO) driven by the π-π interaction, forming a 3D synergistical rGO/Eu(TPyP)(Pc) hybrid aerogel. The resulting aerogel not only effectively integrates the gas sensing of Eu(TPyP)(Pc) and good conductivity of rGO, but also exhibited a prominent synergy effect. Ascribed to the attractive properties, the fabricated NO2 gas sensor exhibits superior sensitivity and selectivity in the range of 0.5 to 100 ppm with an extremely low theoretical limit level of detection (80 ppb) at ambient temperature. The response and recovery time of rGO/Eu(TPyP)(Pc) hybrid aerogel based sensor to20 ppm NO2 were 172 and 828 s, respectively. Remarkably, the hydrophobic porous structure of rGO/Eu(TPyP)(Pc) hybrid aerogel endows the prepared sensor with excellent immunity to high relative humidity, which conquered the key technical issue of real application. The present sensor, simultaneously featured with high performance, low-power consumption, and good tolerance to environmental variations, is anticipated to offer the "on-site" and "on-line" measurement tool in real samples.