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Scientists develop novel grating technology with higher laser damage threshold
Update time: 06-25-2019
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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 sample {period, duty cycle, depth, base angle} were {646nm, 0.55, 902nm, 84.7°}, respectively. The measured -1st order diffraction efficiency was greater than 90% in wavelength range of 747nm-852nm (bandwidth of 105nm), which is consistent with theoretical design, as shown in Figure 1.

Figure1. (a)The cross-sectional image of fabricated MDG; (b) The efficiency/reflection of designed and fabricated MDG/MDL. (Image by SIOM)

Moreover, LIDT of the MDG is 0.4J/cm2 on grating surface at pulse of 32fs, and the initial damages were induced by nodular defects as shown in Figure 2.
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) (Grant No. 11604352, 61875212); Science and Technology Commission of Shanghai Municipality (STCSM) (Grant No. 16JC1420600).

Article website:
Mr. Cao Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS

@ Shanghai Institute of Optics and Fine Mechanics Tel:02169918000 Shanghai ICP NO.0501538