Papers by Keyword: Local Wet Etching

Abstract: Local wet etching (LWE) is a non-conventional deterministic surface figuring and finishing technique in ultra-precision optics fabrication fields. The general removal function in LWE is cylinder, so fringe of the removal function is sharp and scale of the removal function is determined by inner diameter of the nozzle head. When fabricating some specimen with high frequency figure error, ideal designed shape can’t be achieved easily. Compared with general LWE removal function, Gaussian removal function is more suitable for figuring owing to its smoother fringe and the centralization of its energy. At the same time Gaussian removal function can improve the efficiency in calculation of the dwelling time, because it’s very suitable for Fourier transform. What’s more, theoretical residual figure error can also be reduced for Gaussian removal function’s high spatial resolution. Ideal Gaussian function is difficult to obtain in LWE, so we have proposed near-Gaussian removal function by eccentric rotation of the nozzle head. Through controlling offset of the eccentric rotation, we achieve the optimal near-Gaussian removal function in LWE. Aims of the introduction of near-Gaussian removal function in LWE are to improve the fabrication efficiency and to remove the surface’s high frequency residual figure error.

Abstract: Numerically controlled local wet etching (NC-LWE) is very promising technique for deterministic figuring of ultraprecision optical devices, such as aspherical lens, photo mask substrate and X-ray or neutron focusing mirror. NC-LWE technique is non-contact removal process using chemical reaction between etchant and surface of workpiece, so this technique enables us to figure the objective shape without introduction both substrate deformation and sub-surface damage. It is essential to measure temperature and concentration of the etchant to maintain the material removal rate constant over a processing time, since the etching rate of NC-LWE strongly depends on these parameters. Hydrofluoric (HF) acid solution is used as an etchant for synthesized quartz glass. We aim to develop an in situ monitoring system of etchant concentration using Raman spectroscopy and electric conductivity measurement. Raman spectroscopy measurement result indicates that there is a good linear relationship between HF concentration and intensity ratio of two specific Raman bands.

Abstract: Numerical controlled local wet etching is a novel non-contact deterministic figuring method in ultra precision optics fabricating and functional material manufacturing fields, and the cross-sectional shape of the traditional removal spot is a simple cylinder, so the removal function has no adjustability. In order to create more practical and regular removal function, an eccentric rotation system is introduced to improve the LWE system. By controlling the eccentricity, it can achieve varied shapes removal function. When the rotary axis is controlled to a proper eccentricity, the removal function can be close to the Gaussian function. Moreover, the theoretical calculation and experimental validation are coincident and can give the research a steady foundation. The improvement not only can increase the adjustability of the removal function in LWE, but also can expand its applied field and provide reference for other ultra precision machining methods whose removal function does not have circular symmetry.

Abstract: Numerically controlled local wet etching (NC-LWE) is a novel technique to fabricate the ultraprecision optical components and/or finishing the functional materials. In this technique, a figuring is performed by controlling the dwelling time of the combination nozzle, which consists of a supply and a suction part of an etchant, on the workpiece. In this paper, we proposed fabrication process of millimeter-thick elliptical neutron focusing mirror substrate by applying NC-LWE figuring involving CeO2 slurry polishing. We fabricated a millimeter-thick elliptical neutron focusing mirror substrate with a figure error of less than 0.2 μm and obtained a surface roughness of less than 0.15 nm rms.

Abstract: Numerically controlled local wet etching is a novel figuring method for fabricating the ultraprecision optical components and/or finishing the functional materials. In this method, localized wet etching area is formed by applying the combination nozzle which consists of a supply part and a suction part of an etchant, and the removal volume at any point on the workpiece surface is determined by the dwelling time of the nozzle. In this paper, we proposed the two-step figuring process, which consists of a rough figuring process by applying a one-dimensional numerically controlled scanning using a large rectangular nozzle and a finishing process by applying two-dimensional numerically controlled scanning using a small circular nozzle, for figuring the plano-aspherical mirror. By applying the two-step figuring process, we fabricated the plano-elliptical neutron focusing mirror with the figure accuracy of less than 0.5 µm and succeeded in achieving the focusing gain of 6.

Abstract: We have developed numerically controlled local wet etching (NC-LWE) as a novel deterministic subaperture figuring and finishing technique, which is suitable for fabricating various optical components and finishing functional materials. In this technique, a chemical reaction between the etchant and the surface of the workpiece removes the surface without causing the degradation of the physical properties of the workpiece material. Furthermore, the processing properties of NC-LWE are insensitive to external disturbances, such as the vibration or thermal deformation of the machine or the workpiece, because of its noncontact removal mechanism. By applying the NC-LWE process using HF/HNO3 mixtures to etch the silicon, we corrected the thickness distribution of the bulk silicon wafer with a diameter of 200 mm and achieved the total thickness variation of less than 0.23 µm within the diameter of 190 mm.