Surface molecular structure defects and laser-induced damage threshold of fused silica during a manufacturing process

The laser-induced damage threshold (LIDT) is widely used as an index for evaluating an optical component’s resistance to laser light. However, a degradation in the performance of an optical component is also caused by continuous irradiation with laser light having an energy density below the LIDT. Therefore, here we focused on the degradation in performance of an optical component caused by continuous irradiation with femtosecond laser light having a low energy density, i.e., laser-induced degradation. We performed an in situ observation and analysis of an increase in scattering light intensity in fused silica substrates. In experiments conducted using a pulsed laser with a wavelength of 800 nm, a pulse width of 160 fs and pulse repetition rate of 1 kHz, we found that the scattered light intensity increased starting from a specific accumulated fluence, namely, that the laser-induced degradation had a threshold. We evaluated the threshold fluence F t as 6.27 J/cm2 and 9.21 J/cm2 for the fused silica substrates with surface roughnesses of 0.20 nm and 0.13 nm in R a value, respectively, showing that the threshold decreased as the surface roughness increased. In addition, we found that the reflected light spectrum changed as degradation proceeded. We analyzed the details of the degradation by measuring instantaneous reflectance changes with a pump–probe method; we observed an increase in the generation probability of photogenerated carriers in a degraded silica substrate and a damaged silica substrate and observed a Raman signal originating from a specific molecular structure of silica. From these findings, we concluded that compositional changes in the molecular structure occurred during degradation due to femtosecond laser irradiation having an energy density below the LIDT.

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Investigation of laser-induced damage threshold improvement mechanism during ion beam sputtering of fused silica

Optics Express ◽

10.1364/oe.25.029260 ◽

2017 ◽

Vol 25 (23) ◽

pp. 29260 ◽

Cited By ~ 8

Author(s):

Mingjin Xu ◽

Feng Shi ◽

Lin Zhou ◽

Yifan Dai ◽

Xiaoqiang Peng ◽

...

Keyword(s):

Ion Beam ◽

Damage Threshold ◽

Fused Silica ◽

Ion Beam Sputtering ◽

Beam Sputtering ◽

Laser Induced Damage

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Laser-Induced Point Defects in Fused Silica Irradiated by UV Laser in Vacuum

Advances in Condensed Matter Physics ◽

10.1155/2014/853764 ◽

2014 ◽

Vol 2014 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Xiaoyan Zhou ◽

Xinda Zhou ◽

Jin Huang ◽

Qiang Cheng ◽

Fengrui Wang ◽

...

Keyword(s):

Point Defects ◽

Fluorescence Spectra ◽

Uv Spectroscopy ◽

Damage Threshold ◽

Laser Pulses ◽

Fused Silica ◽

Third Harmonic ◽

Structural Modifications ◽

Laser Induced Damage ◽

Induced Defects

High-purity fused silica irradiated by third harmonic of the Nd:YAG laser in vacuum with different laser pulse parameters was studied experimentally. Laser-induced defects are investigated by UV spectroscopy, and fluorescence spectra and correlated to the structural modifications in the glass matrix through Raman spectroscopy. Results show that, for laser fluence below laser-induced damage threshold (LIDT), the absorbance and intensity of fluorescence bands increase with laser energies and/or number of laser pulses, which indicates that laser-induced defects are enhanced by laser energies and/or number of laser pulses in vacuum. The optical properties of these point defects were discussed in detail.

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Hexagonal boron nitride nanosheets incorporated antireflective silica coating with enhanced laser-induced damage threshold

High Power Laser Science and Engineering ◽

10.1017/hpl.2018.16 ◽

2018 ◽

Vol 6 ◽

Author(s):

Jing Wang ◽

Chunhong Li ◽

Wenjie Hu ◽

Wei Han ◽

Qihua Zhu ◽

...

Keyword(s):

Boron Nitride ◽

High Power ◽

Damage Threshold ◽

Fused Silica ◽

High Power Laser ◽

Power Laser ◽

Silica Substrate ◽

Laser Systems ◽

Laser Induced Damage ◽

Ar Coating

Boron nitride (BN) nanosheets incorporated silica antireflective (AR) coating was successfully prepared on fused silica substrate to improve the antilaser-damage ability of transmissive optics used in high-power laser systems. The BN nanosheets were obtained by urea assisted solid exfoliation, and then incorporated into basic-catalyzed silica sols without any further treatment. The transmission electron microscope (TEM) images indicated that the BN nanosheets generally consisted of 2–10 layers. The antireflective BN/$\text{SiO}_{2}$ coating exhibited excellent transmittance as high as 99.89% at 351 nm wavelength on fused silica substrate. The thermal conductivity $0.135~\text{W}\cdot \text{m}^{-1}\cdot \text{K}^{-1}$ of the BN/$\text{SiO}_{2}$ coating with 10% BN addition was about 23% higher than $0.11~\text{W}\cdot \text{m}^{-1}\cdot \text{K}^{-1}$ of the pure $\text{SiO}_{2}$ AR coating. The laser-induced damage threshold (LIDT) of that BN/$\text{SiO}_{2}$ coating is also 23.1% higher than that of pure $\text{SiO}_{2}$ AR coating. This research provides a potential application of BN/$\text{SiO}_{2}$ coatings in high-power laser systems.

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The Optimization of Termination in Combined Technique of Magnetorheological Finishing and HF Etching for Laser-Induced Damage Threshold High-Efficiency Improving of Fused Silica

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1027.199 ◽

2014 ◽

Vol 1027 ◽

pp. 199-202

Author(s):

Ye Tian ◽

Xiao Qiang Peng ◽

Yi Fan Dai ◽

Feng Shi ◽

Wen Wan

Keyword(s):

High Efficiency ◽

Experimental Parameter ◽

Damage Threshold ◽

Fused Silica ◽

Fdtd Simulation ◽

Structural Defects ◽

Process Time ◽

Optical Elements ◽

Laser Systems ◽

Laser Induced Damage

The developing high-power laser systems are requiring higher laser-induced damage threshold (LIDT) and fabrication efficiency of fused silica optical elements. To solve these problems, MRF polishing and HF etching have been combined utilized wiping and passivating structural defects as well as removing impurities. Furthermore, the LIDT improvement is dependent greatly on the corporation of processes. But the LIDT improving mechanism is partly ambiguous yet, that may lead to random or experimental parameter choice and ultimately generate unsatisfied results. Consequently, this paper focuses on the termination mechanism of the process. Atom Force Microscope (AFM) measurement, finite difference time-domain (FDTD) simulation and LIDT test will be utilized to analysis and validate the optimization theoretically and practically. Finally, in one side, the LIDT value of optimized-terminated sample is 16.7J/cm2, which is about the same level (even 3.7% higher) as that of the over-etched one. In another side, the etching process time could be shorted by 32% using the optimized method.

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SSD detection on LIDT tested coated Fused Silica samples

EPJ Web of Conferences ◽

10.1051/epjconf/202125503009 ◽

2021 ◽

Vol 255 ◽

pp. 03009

Author(s):

Heidi Cattaneo ◽

Daniel Schachtler ◽

Roelene Botha ◽

Oliver Fähnle

Keyword(s):

Laser Energy ◽

Substrate Surface ◽

Single Layer ◽

Damage Threshold ◽

Surface Damage ◽

Laser Pulses ◽

Fused Silica ◽

Small Surface ◽

Additional Information ◽

Laser Induced Damage

Material changes and Sub-Surface Damage (SSD) under Laser Induced Damage Threshold (LIDT) testing sites were investigated on 3 diverse single layer coated transparent fused silica samples to obtain additional information on damage precursors on these samples. As a detection method, photothermal deflection technique utilizing a resonant UV laser beam was used. The local variations in UV absorption and probe beam transmittance due to previous exposure to high fluence laser pulses were strongly dependent on the coating itself and on the laser energy used during the LIDT testing. Also the obtained LIDT values differ from coating to coating. Detected effects on the coatings and substrate surface beneath ranged from small surface dislocations to complete coating damage with material transformations. Additional absorbing damage precursors were found close to the damaged sites.

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Study on the Absorption Characteristics and Laser Damage Properties of Fused Silica Optics under Flexible Polishing and Shallow DCE Process

Micromachines ◽

10.3390/mi12101226 ◽

2021 ◽

Vol 12 (10) ◽

pp. 1226

Author(s):

Wanli Zhang ◽

Feng Shi ◽

Ci Song ◽

Ye Tian ◽

Yongxiang Shen

Keyword(s):

Chemical Etching ◽

Ion Beam ◽

Damage Threshold ◽

Fused Silica ◽

Laser Damage ◽

Damage Resistance ◽

Etching Depth ◽

Treatment Processes ◽

Laser Induced Damage ◽

Combined Technique

The enhancement of laser damage resistance of fused silica optics was a hotspot in scientific research. At present, a variety of modern processes have been produced to improve the laser induced damage threshold (LIDT) of fused silica optics. They included pre-treatment processes represented by flexible computer controlled optical surfacing (CCOS), magnetorheological finishing (MRF), ion beam finishing (IBF), and post-treatment processes represented by dynamic chemical etching (DCE). These have achieved remarkable results. However, there are still some problems that need to be solved urgently, such as excessive material removal, surface accuracy fluctuation in the DCE process, and the pollution in MRF process, etc. In view of above problems, an MRF, CCOS, IBF and shallow DCE combined technique was used to process fused silica optics. The surface morphology could be greatly controlled and chemical etching depth was reduced, while the LIDT increased steadily. After processing by this combined technique, the LIDT increased to 12.1 J/cm2 and the laser damage resistance properties of fused silica were significantly enhanced. In general, the MRF, IBF, CCOS and shallow DCE combined technique brought much help to the enhancement of laser damage resistance of fused silica, and could be used as a process route in the manufacturing process of fused silica.

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