Sub Aperture Polishing of Fused Silica Aspheric Surface Using Dwell Time Approach

Tailored optical freeform lenses are required for different applications. Sub-aperture deterministic machining techniques such as plasma jet machining have shown great potential to generate freeform surfaces. However, depending on the required local slopes of the surface shape geometrical limitations occur due to the lateral tool function width. In the paper an alternative approach to fabricate freeform shapes exhibiting steep local slopes is presented. A first step involves a dwell time based fs-laser ablation process to generate the surface contour on a fused silica sample. Since the resulting roughness after laser machining lies in the range of 400 nm RMS which does not match optical requirements a subsequent plasma jet based polishing step is performed where micro-roughness is drastically reduced to values below 0.3 nm RMS.

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Study of Form Control Algorithm in Atmospheric Pressure Plasma Processing

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.620.49 ◽

2014 ◽

Vol 620 ◽

pp. 49-54

Author(s):

Duo Li ◽

Bo Wang ◽

Jun Wang ◽

Qiang Xin

Keyword(s):

Atmospheric Pressure ◽

Dwell Time ◽

Control Algorithm ◽

Removal Rate ◽

Ion Beam ◽

Plasma Processing ◽

Atmospheric Pressure Plasma ◽

Fused Silica ◽

Time Function ◽

Pressure Plasma

Atmospheric Pressure Plasma Processing (APPP) has demonstrated that it can achieve high removal rate and induce no sub-surface damage on the silica based material of optical surface. Compared with traditional mechanical polishing and ion beam figuring, APPP technology is cost effective and very promising in the optics fabrication field. In principle, Atmospheric Pressure Plasma Processing can be described by the two-dimensional convolution equation with dwell time function and plasma removal function. Thus, dwell time function can be solved theoretically by the process of de-convolution, which is the essence of form control algorithm. First, this paper compares and analyzes common de-convolution algorithms by the simulated processing. From the simulation results, the algorithm based on the principle of image restoration has good solving speed, high calculation accuracy. Therefore, we choose it as the form control algorithm for Atmospheric Pressure Plasma Processing. However, the high temperature of plasma plume results in the non-linear relationship between the removal depth and time, further affecting the stability of the algorithm. Then, using the actual experiment data, we build the nonlinear relationship function model to compensate the heat effect in the algorithm. Finally, the modified algorithm is verified by the 7um uniform removal on the fused silica using Atmospheric Pressure Plasma Processing.

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Research on the Normal Error of Large Aspheric Mirror Employed in Bonnet Polishing

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.690-693.3321 ◽

2013 ◽

Vol 690-693 ◽

pp. 3321-3324

Author(s):

Wei Yang ◽

Chun Jin Wang

Keyword(s):

Dwell Time ◽

Residual Error ◽

Aspheric Surface ◽

Action Orientation ◽

Bonnet Polishing ◽

Direction Error ◽

Axis Direction ◽

Normal Error ◽

Aspheric Mirror ◽

The Difference

The influence functions action orientation of the Bonnet Polishing (BP) process is perpendicular to the contact zone. So the normal error of the aspheric surface should be used as the residual error to calculate the dwell time. But the Z axis direction error is generally adopted as the residual error and few papers on the normal error have been reported hitherto. Its necessary to pay attention to this issue. In this paper, two algorithms which are Asphericity Subtraction (AS) algorithm and Z Axis Direction Error Transformation (ZADET) algorithm are presented to calculate the normal error of the large aspheric surface. Simulations in three different cases are organized to utilize these two algorithms, together with the comparison of them. And the comparison of the normal error and the Z axis direction error is also organized. Its found that there exists difference between AS algorithm and ZADET algorithm. Both of them can be used to calculate the normal error of the aspheric surface when the ratio value of the width to radius is small. And the difference between the normal error and Z axis direction error is considerable. So the normal error should be used as the residual error to calculate the dwell time in BP process.

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The Control Algorithm of Ultrasonic-Magnetorheological Combined Finishing for Rotary Symmetrical Aspheric Surface

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.97-101.2099 ◽

2010 ◽

Vol 97-101 ◽

pp. 2099-2102

Author(s):

Fei Hu Zhang ◽

Xing Bin Yu ◽

Yong Zhang ◽

Yong Yong Lin ◽

Dian Rong Luan

Keyword(s):

Computer Simulation ◽

Dwell Time ◽

Control Algorithm ◽

Curvature Radius ◽

Aspheric Surface ◽

Ultraprecision Machining ◽

Freeform Surfaces ◽

Aspheric Surfaces ◽

A New Technique ◽

Derivation Process

Concave aspheric surface with small curvature radius is difficult to fabricate by most of existing technologies. Ultrasonic- magnetorheological combined finishing (UMC) is a new technique for the ultraprecision machining of aspheric surfaces, especially for the ultrasmooth surfaces machining of small-radiuses concave surfaces and freeform surfaces. According to the characteristics of rotary symmetrical aspheric surface, path algorithms for UMC finishing have been developed. Propose and compare two kinds of polishing dwell time algorithms, and the derivation process and computer simulation result of the algorithms was also presented. The experiments using the control algorithm have been conducted, and the efficiency of algorithm is proved by experimental results.

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Non-linear Compensated Dwell Time for Efficient Fused Silica Surface Figuring Using Inductively Coupled Plasma

Plasma Chemistry and Plasma Processing ◽

10.1007/s11090-018-9873-7 ◽

2018 ◽

Vol 38 (2) ◽

pp. 443-459 ◽

Cited By ~ 12

Author(s):

Zuocai Dai ◽

Xuhui Xie ◽

Heng Chen ◽

Lin Zhou

Keyword(s):

Inductively Coupled Plasma ◽

Dwell Time ◽

Silica Surface ◽

Fused Silica ◽

Inductively Coupled ◽

Non Linear

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SEM analysis of DC magnetron sputtered beryllium films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106867 ◽

1988 ◽

Vol 46 ◽

pp. 960-961

Author(s):

E. F. Lindsey ◽

C. W. Price ◽

E. L. Pierce ◽

E. J. Hsieh

Keyword(s):

Fine Structure ◽

Electron Emission ◽

Secondary Electron ◽

Low Voltage ◽

Ion Beam ◽

Secondary Electron Emission ◽

Sem Analysis ◽

Fused Silica ◽

Grain Structure ◽

Silica Substrate

Columnar structures produced by DC magnetron sputtering can be altered by using RF biased sputtering or by exposing the film to nitrogen pulses during sputtering, and these techniques are being evaluated to refine the grain structure in sputtered beryllium films deposited on fused silica substrates. Beryllium is brittle, and fractures in sputtered beryllium films tend to be intergranular; therefore, a convenient technique to analyze grain structure in these films is to fracture the coated specimens and examine them in an SEM. However, fine structure in sputtered deposits is difficult to image in an SEM, and both the low density and the low secondary electron emission coefficient of beryllium seriously compound this problem. Secondary electron emission can be improved by coating beryllium with Au or Au-Pd, and coating also was required to overcome severe charging of the fused silica substrate even at low voltage. The coating structure can obliterate much of the fine structure in beryllium films, but reasonable results were obtained by using the high-resolution capability of an Hitachi S-800 SEM and either ion-beam coating with Au-Pd or carbon coating by thermal evaporation.

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