We have been developing a compact and lightweight X-ray micropore optics for small satellite mounting. We achieved three-dimensional machining into a single flat glass substrate by femtosecond laser irradiation and wet etching. In addition to the three-dimensional machining, we applied annealing and magnetic fluid polishing to reduce surface roughness of inner walls, and coated the surface with Pt layer by ALD to improve the reflectance. In this paper, we introduce our achievement on micromachining into a single flat glass substrate. As principle verification, we achieved extremely small hole with 2μm diameter and 100μm depth, slit with 10μm width, 2500(50×50) multiple through holes in 26μm pitch and hole angle control within 0.15 degree. We will further develop manufacturing techniques and explore other applications of our micropore optics, such as fundamental research, security inspection and infrastructure inspection.
Compact and lightweight X-ray micropore optics with high quality stability have been developed utilizing our microfabrication technology. We have fabricated Schmidt type Lobster Eye Optics named Pre Bread Board Model (PreBBM). This optics has a plurality of oblique grooves having a width of 10 um formed by laser modification and wet etching in flat glass substrate. Both smoothing by annealing and Pt coating were applied on the groove surface to complete Pre-BBM. And we conducted the first X-ray irradiation test. In order to obtain high X-ray reflectivity, next challenge is to reduce surface roughness of the micropore side wall to nanometers or less. We adopted magnetic fluid polishing and glass annealing technology as a method to reduce surface roughness of the glass. We are trying to optimize the condition to achieve side wall surface roughness of 1 nm.
In this paper, we propose a new glass Micropore Optics (MPO), which forms a Wolter type-1 optical system into a single glass substrate without bending or alignment. We call this new X-ray condenser mirror as NXCM.
In recent years, lightweight and high-productivity X-ray optics have been demanded for small satellite and detector calibration. We aim to develop a high-performance X-ray MPO by applying our fine patterning and design techniques on the basis of semiconductor-based micromachining technologies.
Generally, reducing process steps and cutting out error factors make “productivity” and “resolution” better. It has been expected to form a Wolter type-1 optics directly on a base substrate. Therefore, we focused on the process technology using femtosecond laser irradiation and wet etching, which can form arbitrary fine three-dimensional structure in glass substrate, and applied this technology to MPO fabrication.
Using this technique, we successfully achieved to form the two-step oblique grooves machining of 1.7 degrees in the primary stage and 5.1 degrees in the secondary stage with groove widths of 20 μm and 40 μm to the flat glass t 0.5 mm. The groove structure was confirmed by cross-sectional image. The surface roughness of the groove side wall serving as the X-ray reflection surface is expected to be improved by the better scanning of femtosecond laser and the magnetic fluid polishing process. Based on the results, we are proceeding with the production of a condenser mirror prototype while optimizing the coating process and polishing process. In this paper, we report the simulation result of focusing performance and the achievement of the fabrication process in consideration of machining accuracy and error factors.
With this method, the higher aspect structure is achieved by stacking several substrates in the optical axis direction or the large area structure is achieved by tiling in the plane direction. The various types of optical structure can be considered with this method.