With the continuous development of the ultra-intense ultra-short laser, the invention of chirped pulse amplification (CPA) technology has greatly promoted the breakthrough of frontier science. The grating in compressor as the vital components for ultra-short pulse compression must meet the requirements of high efficiency, broadband width, high laser induced damage threshold (LIDT), large size and good wave-front. Therefore, the grating with high LIDT is an untiring pursuit for pulse compression grating researchers.
Recently, researchers from Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (CAS) have developed a kind of metal dielectric gratings (MDG) based on gold-SiO2 system. The results were published on Optics Letters.
In their experiment, the gratings were designed by rigorous coupled-wave analysis method. The metal layer and dielectric layer were deposited by magnetron sputtering technology and ion beam sputtering technology, respectively.
The grating structures were fabricated by dual-beams interference technique and reaction ion beam etching technique.
Their study showed the parameters of grating sampleThe measured -1st order diffraction efficiency in specific wavelength range was consistent with theoretical design.
Figure1. (a) The cross-sectional image of fabricated MDG; (b) The efficiency/reflection of designed and fabricated MDG/MDL. (Image by SIOM)
Researchers used laser induced ionization theory to study the effect of nodule defect on LIDT of MDG and predict the maximum LIDT of the perfect MDG. The nodule defects could be controlled or avoided by improving coating equipment and deposition process for obtaining the MDG with maximum LIDT of 0.60J/cm2.
This pioneering work is hopeful to pave a way for high LIDT MDG.
Figure2. (a) The nodule defects distribute in the MDG; (b) The laser induced eruption of the defect, damage fluence of 0.45J/cm2; (c) the measured size of nodule defect. (Images by SIOM)
This work is funded by National Natural Science Foundation of China (NSFC) and the Science and Technology Commission of Shanghai Municipality (STCSM).
Recently, researchers at Shanghai Institute of Optics and Fine Mechanics, by combining the real-time detection of scattering intensity and time-resolved imaging technique, have revealed the laser damage development sequence in thick fused silica throughout nanosecond laser irradiation.
Recently, a research team from the Shanghai Institute of Optics and Fine Mechanics combined chemical etching and CO2 laser polishing to process the ground fused silica. Chemical etching was used to open the subsurface defects of the ground fused silica. Subsequently, CO2 laser polishing was applied to reduce surface roughness.
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