28.02 W LD side-pumped CW laser operated at 2.8†µm in YSGG/Er:YSGG/YSGG crystal.

We demonstrated a 978 nm laser diode (LD) side-pumped YSGG/Er:YSGG/YSGG composite crystal with a size of Ф 3 mm × 65 mm and continuous-wave (CW) mode. By optimizing resonator length and output mirror transmittance, a maximum output power of 28.02 W is generated, corresponding to slope efficiency of 17.55% and optical-optical efficiency of 12.29%, respectively. The thermal focal lengths are obtained by resonator stability condition. The laser wavelength is centered near 2.8 µm. Moreover, the beam quality factors M x2/M y2 are fitted to be 8.14 and 7.35, respectively. The above results indicate that a high-performance 2.8 µm CW laser can be achieved by LD side-pumped YSGG/Er:YSGG/YSGG composite crystal with excellent heat dissipation ability, which promotes effectively the development and applications of the mid-infrared solid-state lasers.

Thermal, spectroscopy and optimized ∼3†µm CW laser properties for Ho,Pr:YAP crystal.

We demonstrate the thermal, spectroscopy and laser properties of Ho,Pr doped YAP crystal grown successfully by Cz method. The thermal expansion coefficient, thermal conductivity, absorption and emission spectra of Ho,Pr:YAP crystal are investigated in detail. Additionally, the level lifetimes suggest that Pr3+ is a suitable deactivating ion for Ho:YAP crystal. Particularly, the actual laser performance is optimized by doping active ion Ho with high concentrations and introducing deactivated Pr3+, resulting in decreased laser threshold, increased laser output power and slope efficiency. A 3.01 µm laser with output power of 502 mW, slope efficiency of 6.3% and beam quality factors of 1.42/1.43 is achieved in the Ho,Pr:YAP crystal, as far as we know this is the highest ∼3 µm CW laser power realized in Ho3+ doped oxide crystals.

Structure, spectroscopy and laser performance of an Er:YGGAG crystal.

In this work, we report on investigations of structure, spectroscopic properties and laser performances of, what we believe to be, a novel Er:YGGAG laser crystal. High crystalline quality is proved by an FWHW of XRC of 0.019°. Thermal conductivity of a 30 at.% Er:YGGAG crystal is determined as 4.98 W/(m·K). The refractive index is measured in the range of 400 to 1000 nm and fitting with Sellmeier equation is done. A broad fluorescence emission band is located at 2786∼2819 nm, suggesting that this crystal is favorable to realize tunable and ultrafast laser. Under the pump at 969 nm with a fiber-coupled diode laser, at 400 Hz repetition rate and 600 µs pulse duration, the 30 at.% Er:YGGAG delivered maximum average power of 506 mW with overall optical-to-optical efficiency of 12.4% and slope efficiency of 16.9%. The laser beam quality was characterized by M2 factors of 1.53 and 1.39 in horizontal and vertical directions, respectively.

Phase change metamaterial for tunable infrared stealth and camouflage.

In the paper, a type of phase change metamaterial for tunable infrared stealth and camouflage is proposed and numerically studied. The metamaterial combines high temperature resistant metal Mo with phase-changing material GST and can be switched between the infrared "stealthy" and "non-stealthy" states through the phase change process of the GST. At the amorphous state of GST, there is a high absorption peak at the atmospheric absorption spectral range, which can achieve infrared stealth in the atmospheric window together with good radiative heat dissipation in the non-atmospheric window. While at the crystalline state of GST, the absorption peak becomes broader and exhibits high absorption in the long-wave infrared atmospheric window, leading to a "non-stealthy" state. The relationship between the infrared stealth performance of the structure with the polarization and incident angle of the incident light is also studied in detail. The proposed infrared stealth metamaterial employs a simple multilayer structure and could be fabricated in large scale. Our work will promote the research of dynamically tunable, large scale phase change metamaterials for infrared stealth as well as energy and other applications.

13-W and 1000-Hz of a 2.7-µm laser on the 968†nm LD side-pumped Er:YAP crystal with concave end-faces.

We demonstrate a 968-nm LD side-pumped Er:YAP laser with concave end-faces and a working frequency of 50∼1000 Hz. The maximum average powers of 26.75 and 13.18 W are obtained at 250 and 1000 Hz, corresponding to the slope efficiency of 16.2% and 9.0%, respectively. The M2 factors of 7.98 and 1.49 are determined under the multi-mode and single-mode, and three laser wavelengths of 2713, 2732 and 2796 nm are observed. The results indicate that the LD side-pumped Er:YAP crystal with negative curvature end-faces is a promising candidate for the high power and high frequency mid-infrared laser device.

Homotopic Gradients of Generative Density Priors for MR Image Reconstruction.

Deep learning, particularly the generative model, has demonstrated tremendous potential to significantly speed up image reconstruction with reduced measurements recently. Rather than the existing generative models that often optimize the density priors, in this work, by taking advantage of the denoising score matching, homotopic gradients of generative density priors (HGGDP) are exploited for magnetic resonance imaging (MRI) reconstruction. More precisely, to tackle the low-dimensional manifold and low data density region issues in generative density prior, we estimate the target gradients in higher-dimensional space. We train a more powerful noise conditional score network by forming high-dimensional tensor as the network input at the training phase. More artificial noise is also injected in the embedding space. At the reconstruction stage, a homotopy method is employed to pursue the density prior, such as to boost the reconstruction performance. Experiment results implied the remarkable performance of HGGDP in terms of high reconstruction accuracy. Only 10% of the k-space data can still generate image of high quality as effectively as standard MRI reconstructions with the fully sampled data.

Comparative biochemical and transcriptome analyses in tomato and eggplant reveal their differential responses to Tuta absoluta infestation.

Tomato is more prone to Tuta absoluta invasion and damages as compared to other host plants but the mechanism behind this preference has not been elucidated. Here, two contrasting host preference plants, tomato and eggplant, were used to investigate biochemical and transcriptomic modifications induced by T. absoluta infestation. Biochemical analysis at 0-72 h post T. absoluta infestation revealed significantly reduced concentrations of amino acid, fructose, sucrose, jasmonic acid, salicylic acid, and total phenols in tomato compared to eggplant, mainly at 48 h post T. absoluta infestation. Transcriptome analysis showed higher transcript changes in infested eggplant than tomato. Signaling genes had significant contributions to mediate plant immunity against T. absoluta, specifically genes associated with salicylic acid in eggplant. Genes from PR1b1, NPR1, NPR3, MAPKs, and ANP1 families play important roles to mitigate T. absoluta infestation. Our results will facilitate the development of control strategies against T. absoluta for sustainable tomato production.

Multiband metamaterial selective absorber for infrared stealth.

Nanostructured selective absorbers have widespread applications ranging from artificial color to thermophotovoltaics and radiative cooling. In this paper, we propose a metamaterial selective absorber with a metal-insulator-metal structure for infrared stealth. It can realize multiband absorption, and one sharp peak is at 1.54 µm, which can be used to reduce the scattering signals in laser-guided missiles. The other two relatively broad absorption peaks are at 2.83 µm and 6.11 µm, which can match the atmospheric absorption band. It can reduce up to 90 % of the detected infrared signals while maintaining a relatively high level of thermal emission capability. The dependence of the spectral characteristics on the incident angle is studied. The infrared signatures of the structure could be suppressed across a wide temperature range.

Spectroscopic and laser properties of Er:LuSGG crystal for high-power ∼2.8 µm mid-infrared laser.

We demonstrate a novel Er:LuSGG active gain medium emitting laser wavelength at 2795 nm for the first time. The Er:LuSGG crystal is grown successfully by the Czochralski method with high crystalline and optical quality. The spectra properties, including absorption and fluorescence emission cross-section are presented in contrast with similar Er-doped garnet crystals. The fluorescence lifetimes of the upper (4I11/2) and lower (4I13/2) laser levels are 1.75 and 4.64 ms, respectively. Under 973 nm laser diode pumping, a maximum output power of 789 mW in continuous-wave mode, corresponding to optical-to-optical efficiency of 20.2% and slope efficiency of 24.4%, is achieved with high laser beam quality. The results show that the Er:LuSGG is a promising MIR laser material operated at 2.8 µm.

2.7 µm dual-wavelength laser performance of LD end-pumped Er:YAP crystal.

We demonstrate a laser diode (LD) end-pumped Er:YAP laser with dual-wavelength outputs of 2710 and 2728 nm. The maximum average powers of 739 and 738 mW are achieved in the continuous wave (CW) and pulse modes, which corresponds to optical-to-optical efficiencies of 10.1% and 12.3%, and the slope efficiencies of 12.1% and 13.8%, respectively. In addition, a comparison of laser performance on differently sized crystals indicates that the 1 × 1 × 5 mm3 Er:YAP crystal has a best cooling efficiency. This helps to decrease the thermal lensing effect, which contributes to improving laser efficiency and beam quality.

Laser performance of a 966 nm LD side-pumped Er,Pr:GYSGG laser crystal operated at 2.79 µm.

We demonstrate a 966 nm laser diode (LD) side-pumped Er,Pr:GYSGG laser crystal operated at 2.79 µm under a high repetition rate. The lifetimes of the upper level I11/24 and lower level I13/24 are 0.66 and 0.85 ms, respectively. The laser performance under different repetition rates and pulse widths is experimentally studied with the optimal cavity structure. A maximum output power of 8.86 W is achieved at 125 Hz and 200 µs pulse widths, corresponding to the slope efficiency of 14.8% and electrical-to-optical efficiency of 7.7%. With increasing frequency from 50 to 200 Hz, the slope efficiency varies from 24.7% to 11.7% operated at a 125 µs pulse width. Moreover, the Mx2/My2 factors of 7.52/7.59 and Θx/Θy far-field divergences of 16.1/16.5 mrad are also measured. The results indicate that a high-performance 2.79 µm laser could be realized on the Er,Pr:GYSGG radiation resistant crystal by deactivation and LD side-pumping.

Thermal analysis and laser performance of a GYSGG/Cr,Er,Pr:GYSGG composite laser crystal operated at 2.79 µm.

We demonstrate the thermal analysis and laser performance of a GYSGG/Cr,Er,Pr:GYSGG composite crystal. The lifetime ratio of lower and upper levels of Er3+ in Cr,Er,Pr:GYSGG crystal is further reduced due to the optimized doping concentrations. The thermal effect of composite crystal is lower than that of Cr,Er,Pr:GYSGG crystal. A maximum pulse energy 342.8 mJ operated at 5 Hz and 2.79 µm is obtained on the composite crystal, corresponding to electrical-to-optical efficiency of 0.86% and slope efficiency of 1.08%. Under the same condition, these values on the Cr,Er,Pr:GYSGG crystal are only 315.8 mJ, 0.79% and 1.04%, respectively. Moreover, the composite crystal has also a relative high laser beam quality, exhibiting obvious advantage in reducing thermal effects and improving laser performances.

Systematic manipulation of glutathione metabolism in Escherichia coli for improved glutathione production.

BACKGROUND: L-glutathione (GSH) is a non-protein thiol compound with important biological properties and is widely used in pharmaceutical, food, cosmetic and health products. The cellular GSH is determined by the activity and characteristic of GSH-synthesizing enzymes, energy and precursor supply, and degradation of formed GSH. RESULTS: In this study, genes encoding enzymes related to the precursor amino acid degradation and glycogen formation as well as GSH degradation were systematically manipulated in Escherichia coli strains over-expressing gshF from Actinobacillus succinogenes. The manipulation included disrupting the precursor degradation pathways (tnaA and sdaA), eliminating L-glutathione degradation (ggt and pepT), and manipulating the intracellular ATP level (disruption of glgB). However the constructed mutants showed lower levels of GshF expression. 2-D electrophoresis was performed to elucidate the reasons for this discrepancy, and the results indicated obvious changes in central metabolism and amino acid metabolism in the penta-mutant. Fed-batch culture of the penta-mutant ZJ12345 was performed where the GshF expression level was enhanced, and both the GSH production (19.10 mM) and the yield based on added L-cysteine (0.76 mmol/mmol) were significantly increased. CONCLUSION: By interrupting the degradation pathways of L-cysteine, serine and GSH and blocking glycogen formation, the GSH production efficiency was significantly improved.