Research Of Optical Characters Of A Photon Sieve

In the short spectral range such as extreme ultraviolet, soft X-ray and hard X-ray, it is difficult focusing and imaging with traditional refraction and reflection optical system because of strong absorption of optical material. The diffractive optical system can work well in these situations. Fresnel zone plate is a typical diffractive optical element, which is composed of a series of cyclic structure. The diffraction light generated by different rings superposition coherently in focal plane to produce a sharp spot. In recent years, to reach the demand of higher resolution, the requirement to diffractive optical element is stricter. But the resolution of Fresnel zone plate is determined by the characteristic dimension of its most outer ring, severely limited by the current micro-fabrication technology.In 2001, Kipp proposed the concept of “photon sieve”. The ring structure in the Fresnel zone plate is instead by number of transmission pinholes in the photon sieve. Compared with the Fresnel zone plate, the photon sieve has obvious advantages:(1) A photon sieve has a higher resolution with the same minimum feature size;(2) A photon sieve has larger design freedom so that it is able to suppress the side lobes and other diffraction orders better to reach higher imaging contrast by optimizing the diameter, location and number of pinholes.(3) There is no separation structure in a photon sieve. So the additional support structure is no longer necessary, and it is easier to realize light quantization. Because of these advantages, the photon sieve has replaced Fresnel zone plate in those areas such as array of direct-write lithography, large telescopes and x-ray imaging gradually. And now photon sieves is one of the hot topics.The optical properties of a photon sieve are studied comprehensively in this paper. The scalar and vector diffraction theory are applied to analyze the focusing properties of a low numerical and a high numerical aperture photon sieve respectively. The design methods in both cases are compared. It is confirmed the necessity of re-optimizing photon sieve structure of a high numerical aperture. Using the phase modulation characteristics both of the pinhole’s size and position, a new type of design named quasi-phase photon sieve is proposed. This new design can achieve sharper focus spot under the same processing conditions. Also the affects of light source is analyzed. Among these researches polarization characteristics are discussed in details. Typically, diffraction filed is simulated when the incident light is linearly polarized, radial polarized or angular polarized. The numerical results show that the polarization properties have significant impact to lateral distribution and the vertical distribution. Then focal depth characteristics of photon sieve are studied. Two new designs are proposed to obtain longitudinal intensity distribution and numerical simulations are displayed to confirm the idea. The aberrations of a photon sieve are studied too especially the disperse characteristics. A chromatic aberration compensation design is proposed to achieve a continuous broad spectral range and discrete multi-wavelength imaging and focusing. Also, the method to establish a wave front error equivalent model of a photon sieve is given. The influences of manufacture errors on focusing properties are discussed. In the end, a photon sieve composed of square pinholes is put forward for the applying situation of large diameter and low numerical aperture. The theoretical analysis, numerical simulation and experiment are displayed. This kind of photon sieves keeps the advantages of traditional photon sieve but is less time consuming and less costly while manufacturing.