Oxygen-doped NiCoP derived from Ni-MOFs for high performance asymmetric supercapacitor.

Oxygen doping strategy is one of the most effective methods to improve the electrochemical properties of nickel-cobalt phosphide (NiCoP)-based capacitors by adjusting its inherent electronic structure. In this paper, O-doped NiCoP microspheres derived from porous nanostructured nickel metal-organic frameworks (Ni-MOFs) were constructed through solvothermal method followed by phosphorization treatment. The O-doping concentration has a siginificant influence on the rate performance and cycle stability. The optimized O-doped NiCoP electrode material shows a specific capacitance of 632.4 F-g-1at 1 A-g-1and a high retention rate of 56.9% at 20 A g-1. The corresponding NiCoP-based asymmetric supercapacitor exhibits a high energy density of 30.1 Wh kg-1when the power density is 800.9 W kg-1, and can still maintain 82.1% of the initial capacity after 10 000 cycles at 5 A g-1.

Nickel-vanadium layered double hydroxide for a mid-infrared 2 µm Tm:YAG ceramic ultrafast laser.

In this study, a nickel-vanadium layered double hydroxide (NiV-LDH) nanosheet was prepared as a saturable absorber (SA) by liquid phase exfoliation and a drop-coating method. The microstructure and optical transmission properties of the obtained NiV-LDH nanosheet were then systematically studied. An "X"-type fold cavity was designed to evaluate the ultrafast laser modulation performance of the NiV-LDH nanosheet with a Tm:YAG ceramic gain medium. A stable passively Q-switched mode-locked (QML) pulse centered at 2011.6 nm has successfully been realized, with a repetition frequency of 145 MHz and a pulse duration of 320 ps. To the best of our knowledge, this is the first time that the LDH has been used as an SA in a mid-infrared range ultrafast laser.

Exciton-induced mid-infrared optical nonlinearity of wide bandgap hexagon boron nitride.

In this Letter, an exciton absorption assumption is made to explain the mid-infrared saturable absorption performance of the 2D h-BN nanosheet. The exciton binding energy of ∼0.4 eV corresponds to the light wavelength around 3 µm, matching well with the experimental results. Experimentally, the h-BN saturable absorber (SA) shows a modulation depth of 5.3% in the wavelength region of 3 µm. By employing the h-BN SA in an Er:Lu2O3 laser, laser pulses with a pulse duration of 252 ns are realized at a repetition rate of 169 kHz, corresponding to a pulse energy of 3.55 µJ and peak power of 14 W. The exciton absorption assumption will help obtain a better understanding of the nonlinear optical dynamics in 2D materials from a new perspective.

Nickel-vanadium layered double hydroxide nanosheets as the saturable absorber for a passively Q-switched 2 µm solid-state laser.

Nickel-vanadium (NiV)-layered double hydroxide (LDH) was fabricated into a novel saturable absorber (SA) by the liquid phase exfoliation method and utilized as the laser modulator for the first time, to our best knowledge. We investigated a passive Q-switched Tm:YAG ceramic laser at 2 µm with the NiV-LDH SA. Under an absorbed pump power of 7.2 W, the shortest pulse width of 398 ns was obtained with an average output power of 263 mW and a pulse repetition frequency of 101.8 kHz, corresponding to a single pulse energy at 2.30 µJ. The results indicate that the NiV-LDH SA has great research potential in the field of laser modulation.

Solidly mounted resonator sensor for biomolecule detections.

We report the fabrication of a solidly mounted resonator (SMR) that can also function as a sensor for biological molecules. The SMR, consisting of a Au electrode, aluminum nitride (AlN) piezoelectric thin film and Bragg acoustic reflector, was fabricated on a Si substrate by radio frequency (RF) magnetron sputtering. The Bragg acoustic reflector, made entirely of metal, has small internal stress and good heat conduction. Human immunoglobulin G (IgG) antibody was immobilized on the modified (by self-assembled monolayer method) Au electrode surface of the SMR and goat anti-human IgG antigen was captured through the specificity of bond between the antibody and antigen on the electrode surface. We found a linear relationship between the resonant frequency shift and the concentration of goat anti-human IgG antigen for concentrations smaller than 0.4 mg ml-1 and a relatively constant frequency shift for concentrations greater than 0.5 mg ml-1. A series of interference experiments can prove that the selectivity of the sensor is satisfactory. Our findings suggest that the SMR sensor is an attractive alternative for biomolecule detection.

Image quality and spectral performance evaluations of a polarization imaging spectrometer based on a Savart polariscope.

The modulation transfer function (MTF) and signal-to-noise ratio (SNR) are the key parameters to evaluate quantitatively the image quality and spectral performance in a polarization imaging spectrometer based on a Savart polariscope. In order to evaluate the image quality and reflect the detecting ability of the imaging spectrometer, calibration experiments on the MTF, SNR, and spectral resolution were carried out and some important conclusions were obtained. For incident radiance values 4.464, 3.119, and 0.523 w/m2·sr, the average SNRs of the interferogram were 500, 400, and 200 dB, respectively, and the MTF is 0.24. During the spectral resolution calibration, the maximum optical path difference was set as 57.08 µm, and the measured value is greater than the theoretical value, which is mainly caused by the structural design of the polarization imaging spectrometer. For the wavelength range of [500 nm, 600 nm], the SNR of the spectrum is lower and about 50 dB, while the SNR is obviously higher in a range of λ∈[600 nm, 960 nm]. This study provides a theoretical and practical guidance for improving the image quality and judging the spectral performance of the polarization imaging spectrometer.

Passively Q-switched Ho,Pr:LiLuF4 laser with graphitic carbon nitride nanosheet film.

A few-layer graphitic carbon nitride (g-CN) nanosheet film on an yttrium aluminum garnet substrate was fabricated and employed as saturable absorber for a passively Q-switched Ho,Pr:LiLuF4 laser at 2.95 µm. Under an absorbed pump power of 3.89 W at a pump wavelength of 1.15 µm, a maximum average output power of 101 mW was realized with a pulse duration of 420 ns and a repetition rate of 93 kHz. Even shorter pulse durations of 385 ns were obtained at a reduced output coupler transmission.

Diode-end-pumped Ho, Pr:LiLuF4 bulk laser at 2.95 µm.

A diode-end-pumped continuous-wave (CW) and passively Q-switched Ho, Pr:LiLuF4 (Ho, Pr:LLF) laser operation at 2.95 µm was demonstrated for the first time, to the best of our knowledge. The maximum CW output power was 172 mW. By using a monolayer graphene as the saturable absorber, the passively Q-switched operation was realized, in which regimes with the highest output power, the shortest pulse duration, and the maximum repetition rate were determined to be 88 mW, 937.5 ns, and 55.7 kHz, respectively. The laser beam quality factor M2 at the maximum CW output power were measured to be Mx2=1.48 and My2=1.47.

[Application Progress of Holographic Lithgraphy in Fabrication of Micro-Nano Photonic Structures].

Micro-nano photonic structures are developing vigorously based on the progress of photonics, semiconductor physics and microfabrication technology. A series of results are achieved in structure characterization, theory, and fabrication of them. Most high quality photonic structures are man-made ones; however, there are still some challenges in fabricating artificial large-area and high-quality photon materials. With the advantages of photonic structure processing technology, holographic lithography, a low-cost, time-saving and high-efficiency microfabrication method, performs superior application potentials in making metamaterials as well as photonic crystal templates. In this article, we introduced the principles of holographic lithography and described the applications in fabricating various micro-nano photonic structures, such as three dimensional face-center-cubic, wood-pile, diamond-like photonic crystals, as well as quasi-crystalline structure, chiral metamaterials and periodic defect-mode structures. Moreover, the applications of some structures in solar cell and optical fiber sensing are discussed. The success of fabricating micro-nano photonic structures by holographic lithography would pave the way for more applications of these structures in wide fields.

Efficient dual-wavelength Nd:LuLiF4 laser.

We report an efficient continuous-wave (CW) and passively Q-switched dual-wavelength Nd:LuLiF4 laser at 1314 and 1321 nm for the first time. Maximum CW output power of 6.08 W is obtained, giving an optical-to-optical conversion efficiency of 30.2% and a slope efficiency of 32.1%. Even using high doping V3+:YAG as the saturable absorber to passively Q-switch the laser, stable dual-wavelength operation remains. Maximum pulse energy extracted from the resonator is 108.7 µJ at 17.2 kHz pulse-repetition rate, and maximum peak power is 885 W.

Efficient Ho:LuLiF4 laser diode-pumped at 1.15 µm.

We report the first laser operation based on Ho(3+)-doped LuLiF(4) single crystal, which is directly pumped with 1.15-µm laser diode (LD). Based on the numerical model, it is found that the "two-for-one" effect induced by the cross-relaxation plays an important role for the laser efficiency. The maximum continuous wave (CW) output power of 1.4 W is produced with a beam propagation factor of M(2) ~2 at the lasing wavelength of 2.066 µm. The slope efficiency of 29% with respect to absorbed power is obtained.

Tm:YLF laser-pumped periodically poled MgO-doped congruent LiNbO3 crystal optical parametric oscillators.

At room temperature, highly efficient, doubly resonant periodically poled MgO-doped congruent LiNbO3 crystal optical parametric oscillators (OPO) pumped at 1.9 µm have been realized for the first time to our knowledge. A 2.9 W, 2 kHz acousto-optic Q-switched homemade Tm:YLF laser served as a pump source. A 900 mW mid-infrared emission generated from an OPO is illustrated. The overall mid-infrared generation conversion efficiency reached 31%, whereas the slope efficiency was up to 70%.

Continuous wave and passively Q-switched Nd:Lu xY1-x VO4 laser at 1.34 µm with V3+:YAG as the saturable absorber.

We demonstrated a diode-pumped continuous wave and passively Q-switched Nd:Lu(x)Y(1-x)VO4 laser at 1.34 µm with V3+:YAG as the saturable absorber. The crystal Nd:Lu(x)Y(1-x)VO4 with equal ionic ratio (x = 0.5) shows better laser performance. The maximum continuous wave output power of 1.45 W was obtained with the optical efficiency of 20.1% and the slope efficiency of 24.5%. For the pulsed operation, the minimum pulse width achieved was 42 ns with the pulse repetition frequency of 142 kHz, and the single pulse energy and the peak power were estimated to be 6.62 µJ and 157.6 W, respectively.

Efficient Q-switched Tm:YAG ceramic slab laser.

Characteristics of Tm:YAG ceramic for high efficient 2-µm lasers are analyzed. Efficient diode end-pumped continuous-wave and Q-switched Tm:YAG ceramic lasers are demonstrated. At the absorbed pump power of 53.2W, the maximum continuous wave (cw) output power of 17.2 W around 2016 nm was obtained with the output transmission of 5%. The optical conversion efficiency is 32.3%, corresponding to a slope efficiency of 36.5%. For Q-switched operation, the shortest width of 69 ns was achieved with the pulse repetition frequency of 500 Hz and single pulse energy of 20.4 mJ, which indicates excellent energy storage capability of the Tm:YAG ceramic.

High-power diode-end-pumped Tm:LiLuF4 slab lasers.

Diode-end-pumped continuous-wave and acousto-optics Q-switched Tm:LiLuF(4) slab lasers were demonstrated. The a-cut Tm:LiLuF(4) slab with doping concentrations of 2 at.% was pumped by fast-axis collimated laser diodes at room temperature. The maximum continuous-wave output power of 10.4 W was obtained while the absorbed pump power was 31.6 W and the cavity length was 30 mm. For Q-switched operation, we got the maximum pulse energy of 8 mJ with pulse width of 315.2 ns at 1 KHz pulse repetition frequency.