Computer-generated hologram (CGH) is an important component for high-precision aspherical surface testing. This paper puts forward a manufacturing method of amplitude-type CGH by femtosecond laser direct etching, and carries out detailed analysis and demonstration. Firstly, the demand of microstructure fabrication of amplitude-type CGH was analyzed by optical diffraction theory. Furthermore, we have established the theoretical model of femtosecond laser machining amplitude-type CGH fringe. Finally, we developed basic verification experiments, and analyzed the feasibility of fabricating CGH by direct etching process based on the testing results of processing fringe characteristics.
Inductively coupled plasma processing (ICPP) is regarded as an unrivaled technique in the field of aspheric and freeform optics fabrication for its non-contact chemical etching and high efficiency. In this paper, to evaluate the obliquely incident machining behavior of removal function during inductively coupled plasma, we did some plasma beam line scanning test treatments on the fused silica surface with different obliquely incident angles in two vertical directions. Test results show that the full width at half maximum (FWHM) of the footprint of removal function increases from 13.1699 mm to 14.8368 mm with the increase of the obliquely incident angle from 0° to 30° along the X-direction line scanning processing, and that of another direction only increases from from 13.1699 mm to 14.0598 mm. Furthermore, the material removal rate in both directions reduces in a small range with the increase of the obliquely incident angle less than 10° under our processing condition. Therefore, test results demonstrate that the three-axis machining system can be effective supposing that the local slopes of the part to treat are less than about 10°. The presented conclusions can provide technical guidance for fused silica aspheric and free-form optical surface machining.