Specifications and control of spatial frequency errors of components in two-beam laser static holographic exposure for pulse compression grating fabrication

The large-aperture pulse compression grating(PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser;however, the size of the PCG manufactured by transmission holographic exposure is limited to large-scale high-quality materials. The reflective method is a potential way for solving the size limitation, but there is still no successful precedent due to the lack of scientific specifications and advanced processing technology of exposure mirrors. In this paper, an analytical model is developed to clarify the specifications of components, and advanced processing technology is adopted to control the spatial frequency errors. Hereafter, we have successfully fabricated a multilayer dielectric grating of 200 mm × 150 mm by using an off-axis reflective exposure system with Φ300 mm. This demonstration proves that PCGs can be manufactured by using the reflection holographic exposure method and shows the potential for manufacturing the meter-level gratings used in 100 petawatt class high-power lasers.

Fine-tuning growth in gold nanostructures from achiral 2D to chiral 3D geometries

Enriching the library of chiral plasmonic structures is of significant importance in advancing their applicability across diverse domains such as biosensing,nanophotonics,and catalysis.Here,employing triangle nanoplates as growth seeds,we synthesized a novel class of chiral-shaped plasmonic nanostructures through a wet chemical strategy with dipeptide as chiral inducers,including chiral tri-blade boomerangs,concave rhombic dodecahedrons,and nanoflowers.The structural diversity in chiral plasmonic nanostructures was elucidated through their continuous morphological evolution from two-dimensional to threedimensional architectures.The fine-tuning of chiroptical properties was achieved by precisely manipulating crucial synthetic parameters such as the amount of chiral molecules,seeds,and gold precursor that significantly influenced chiral structure formation.The findings provide a promising avenue for enriching chiral materials with highly sophisticated structures,facilitating a fundamental understanding of the relationship between structural nuances and chiroptical properties.

Arsenic hyperaccumulator Pteris Vittata L. and its arsenic accumulation

An arsenic hyperaccumulator Pteris vittata L. (Chinese brake) was first discovered in China by means of field survey and greenhouse cultivation. Field survey showed that Chinese brake had large accumulating capacity to arsenic; the orders of arsenic content in different parts of the fern were as follows: leaves】leafstalks】roots, which is totally different from that of ordinary plants; bioaccumulation coefficients of the above ground parts of the fern decreased as a power function of soil arsenic contents. In the control of pot trials with normal unpolluted soil containing 9mg/kg of arsenic, the bioaccumulation coefficients of the above ground parts and rhizoids of Chinese brake were as high as 71 and 80 respectively. Greenhouse cultivation in the contaminated soil from mining areas has shown that more than 1 times greater arsenic can be accumulated in the leaves of the fern than that of field samples with the largest content of 5070 mg/kg As on a dry matter basis. During greenhouse cultivation, arsenic

Effect of phosphorus on arsenic accumulation in As-hyperaccumulator Pteris vittata L. and its implication

Pot experiment was conducted to understand the effect of phosphorus on arsenic accumulation in As-hyperaccumulator Chinese brake (Pteris vittata L.). It is shown that arsenic concentrations in the fronds and rhizoids, the arsenic bioaccumulation factor, and the total arsenic in the fronds were not influenced significantly under low levels of phosphorus (≤400 mg/kg) and increased sharply under high levels of phosphorus (】400 mg/ kg). The discovery implies that the efficiency of arsenic removal in phytoremedia-tion using the hyperaccumulating plant can be greatly elevated by the phosphorus addition at high rates. The interaction between the accumulation of phosphorus and that of arsenic in plant was stimulated mutually. The result represents that Chinese brake is a good material for plant physiologist to conduct comparative and mechanism studies on the uptake behaviors of phosphorus and arsenic, and phosphorus is also a potential accelerator for phytoremediation of arsenic-contaminated soils.

Development of high-power laser coatings

Laser resistance and stress-free mirrors,windows,polarizers,and beam splitters up to 400 mm×400 mm are required for the construction of the series SG facilities.In order to improve the coating quality,a program has been in place for the last ten years.For the small-aperture pick-off mirror,the laser-induced damage threshold(LIDT)is above 60 J/cm2(1064 nm,3 ns),and the reflected wavefront is less thanλ/4(λ=633 nm).The Brewster-angle polarizing beam splitter(Φ50×10 mm)shows the best LIDT result,up to 29.8 J cm 2(1064 nm,10 ns)for a p-polarized wave in the 2012damage competition of the XLIV Annual Boulder Damage Symposium.For the larger-aperture mirror and polarizer,the LIDT is above 23 J cm 2(1064 nm,3 ns)and 14 J cm 2(1064 nm,3 ns),respectively.The reflected wavefront is less thanλ/3(λ=633 nm)at the used angle.

Numerical model and experimental demonstration of high precision ablation of pulse CO_2 laser

To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was developed under pulsed CO2laser irradiation. The model employed various heat transfer and hydrodynamic boundary and thermomechanical properties for assisting the understanding of the contributions of Marangoni convention,gravitational force, vaporization recoil pressure, and capillary force in the process of laser ablation and better prediction of laser processing. Simulation results indicated that the vaporization recoil pressure dominated the formation of the final ablation profile. The ablation depth increased exponentially with pulse duration and linearly with laser energy after homogenous evaporation. The model was validated by experimental data of pulse CO2laser ablation of fused silica. To further investigate laser beam figuring, local ablation by varying the overlap rate and laser energy was conducted, achieving down to 4 nm homogenous ablation depth.

Laser-based defect characterization and removal process for manufacturing fused silica optic with high ultraviolet laser damage threshold

Residual processing defects during the contact processing processes greatly reduce the anti-ultraviolet(UV)laser damage performance of fused silica optics,which significantly limited development of high-energy laser systems.In this study,we demonstrate the manufacturing of fused silica optics with a high damage threshold using a CO_(2)laser process chain.Based on theoretical and experimental studies,the proposed uniform layer-by-layer laser ablation technique can be used to characterize the subsurface mechanical damage in three-dimensional full aperture.Longitudinal ablation resolutions ranging from nanometers to micrometers can be realized;the minimum longitudinal resolution is<5 nm.This technique can also be used as a crack-free grinding tool to completely remove subsurface mechanical damage,and as a cleaning tool to effectively clean surface/subsurface contamination.Through effective control of defects in the entire chain,the laser-induced damage thresholds of samples fabricated by the CO_(2)laser process chain were 41%(0%probability)and 65.7%(100%probability)higher than those of samples fabricated using the conventional process chain.This laser-based defect characterization and removal process provides a new tool to guide optimization of the conventional finishing process and represents a new direction for fabrication of highly damage-resistant fused silica optics for high-energy laser applications.