The large and thin plane optical windows are used in large high power laser devices. Typically conventional methods such as stressed-lap polishing and small-tool pitch polishing are used to manufacture these optics. Nevertheless, the required wavefront accuracy cannot be achieved by the last smal-tool pitch polishing process which can lead to middle spatial frequency errors and high-slope errors because of the edge effect , unstable removal rate and pressure -loaded deformation. Ion Beam Figuring (IBF) technology is an optical fabrication method which can highly correct different spatial frequency errors due to the highly deterministic, highly stable, very small tools and noncontact. In this paper, IBF was employed to correct different spatial frequency errors of a large and thin plane optical windows. Before IBF, transmission wavefront error of the substrate was 0.51λ PV, 32.3nm/cm GRMS, 2.91nm PSD1, 0.27nm PSD2, 0.38nm Rq after being polished by double-sided polishing machine, and was improved to 0.07λ PV, 2.1nm/cm GRMS, 1.76nm PSD1, 0.13nmPSD2, 0.33nmRq after only two IBF(about thirty six hours processing time). All spatial frequency errors reached the required values.
The in-situ monitoring of subsurface defects and laser damages initiation using high resolution on-line microscope is performed on medium aperture fused silica optics manufactured by different procedures to investigate the specific damage precursors. The digital camera, Nomarski microscope and white light interferometer are used to characterize the subsurface defects. With shallow HF etching depth, the laser induced damages are mostly initiated on indents or invisible defects under the fluence of 8~10 J/cm2@355nm. The laser induced damages initiated on indents is gradually decreased with the increased etching depth and the laser induced damage density is also decreased. Besides, decrease of the indents by optimizing the polishing process could also make the laser induced damage density sharply decrease. These results prove that the indents are important damage precursors and the laser induced damage performance of fused silica optics could be substantially improved by decreasing the indents or deep HF etching.
HF-based etching has been an effective method to increase the laser induced damage thresholds (LIDTS) of fused silica optics. In this research, the effect of etching parameters on the surface quality and laser damage performance of fused silica with Megasonic-assisted HF acid etching has been investigated systematically. The fused silica samples (50mm in diameter and 5mm thick) were maufactured through the conventional grinding and chemical mechanical polishing process, these processed samples are etched with different etching parameters. Our results show that the frequency and distribution of megasonic field will bring great effect on the surface quality of optics. The LIDTS were measured by 1- on-1 mode, results showed that the 1.3MHz megasonic field and a certain amount of etching depth will benefit the laser damage performance of fused silica optics.
The effect of ion beam etching process on the surface quality, the surface roughness and the laser-induced damage threshold at 351nm was carried out. Research results reveal that the laser-induced damage threshold of fused silica was enhanced with the increase of etching depth when the etching depth was less than 800nm, and could be further enhanced about 30% at 800nm etching depth, however the laser-induced damage threshold began to decrease with the further increase of etching depth(more than 800nm). The test results of surface microtopography, laser damage morphology, and surface roughness reveal that the ion beam etching process can remove polishing re-deposition layer without degrading the surface condition at a smaller etching depth so as to enhance the laser-induced damage threshold of fused silica, however further ion etching which can produce impurity particle often results in a decrease rather than an increase of laser-induced damage threshold.
Subsurface damage (SSD) has been identified as a main initiator of laser-induced damage in fused silica, and the most of SSD is produced during grinding process. The distribution and morphology of SSD in fused silica samples ground with loose abrasive are investigated by magneto-rheological finishing (MRF) dimpling and buffered oxide etch (BOE) etching method. The results demonstrate that the SSD depth is most responsive to the loose abrasive size and the BOE etching is good for removing the SSD. Based on these results, an efficient grinding technique combined with BOE etching is proposed to reduce the SSD of fused silica, and the damage threshold is obviously improved by this routine as a result.
Study on fine annealing process of the large-aperture K9 glasses was carried out in the report. The process parameters of glass placed way, fan speed and design of the cavity for keeping temperature uniformity were attained. By the fine annealing experiment, the stress distribution was improved evidently. The stress changed from Irregular distribution to consistency symmetric distribution and the stress max was reduced. The surface profile accuracy of the large-aperture K9 glasses was controlled steadily during CNC polishing.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.