Mechanism Of Sub-surface Defects Induced Damage And Experimental Study

With the development of mankind society, we're facing the crisis of energy. Fortunately, the nuclear technique and high-power laser system provide us Laser Nuclear Fusion. Nowadays more and more countries research on Inertial Confinement Fusion (ICF). Additionally, many high-power solid laser systems are being built, such as National Ignition Facility (NIF). But with the development of high power laser system, the low damage resistance capability of optical components has been one serious problem, which restrains the increment of laser energy output. This has been one "hot-spot" in past 30 years.Subsurface Damage (SSD) has been becoming one concernful laser induce damage origin. There're mainly three questions to deal with. Firstly, the mechanism to induce damage, and the parameters underlying which damage is easy to come forth, must be researched thoroughly. Secondly, it's necessary to find out one way to deduce SSD, which is prospective to increase the laser induce damage threshold (LIDT). In an addition, those SSD could be detected in microscope. Thirdly, it's must be validated whether some hybrid manufacturing could remove SSD cracks or redeposition layer defects to increase LIDT. If yes, the manufacturing of big optical aperture components will arise up to one newer stage.In my postgraduate period, we've dissected the mechanism of Subsurface Damage (SSD) inducing damage, and verified several popular polishing methods, mainly including HF acid wet etch, Magnetroheological Finishing (MRF), etc. Total outcome and experience can be summarized as below.One. The origin, detect and removal of subsurface damage are introduced. Furthermore, we introduced several international popular damage mechanisms. There's one typical laser induced damage threshold (LIDT) detect facility and several microscopes. Some important manufacturing come forth, including HF etch and laser conditioning. Based on the development sequence of LLNL theoretical calculation on optical coatings in Finite Difference Time Domain (FDTD), we simulated the electromagnetic field distribution round SSD, with the establishment of scratches and defects models in Fused Silica (FS). The consequence exhibits that, 2λ-size scratches or λ-diameter defects cause the most serious modulation. Additionally, defects do more than scratches.Two. We discussed the parameters and exhibitions of SSD. In microscope and stylus profilometer, scratches are contiguous or discontinuous. Furthermore, the SSD density varies very much. Based on the numerical calculation, scratches in those parameters won't contribute to laser damage inducement, for longer scratches are much wider than .the key size 2k, and shorter ones are too shallow.Three. We also verified the removal availability of SSD in fused silica by HF acid wet etch. We experimented by shallow etch and extreme deep etch. This resulted in that small-size scratches could be eliminated by enough etching depth, but larger ones remained there. Otherwise, longer or wider ones could be de-sharpened by deep etch.Four. Magnetroheological finishing (MRF) has been introduced, which affords high flat-precision and little SSD. By the way, MRF causes low LIDT of optical components by reason of Fe2+/Fe3+. The feasibility of wet etch plus MRF to eliminate subsurface cracks and redeposition defects has been proven, which can cause LIDT increment, after the reference to LLNL hybrid techniques. With one laser threshold experiment in "XingGuang II" high-power laser system, we affirmed the bright prospect of this technique.