Experimental testing of focusing properties of subwavelength photon sieves using exposure method

Abstract

An exposure method is proposed to test the focusing properties of subwavelength photon sieves. To solve the problems caused by the subwavelength photon sieves (such as short focal length and small focal spot size), a grating moire fringe phase detection technique and a microcontact sensor with lead zirconium titanate (PZT) stepping hybrid technique are used in the experimental setup. The focusing properties of the subwavelength photon sieves are tested by this setup. The results show that the focal length and the focal spot size are close to the designed value. Finally, the intensity distribution of the focal spot is proposed. This research result will be beneficial for understanding the focusing properties of subwavelength photon sieves, will help us to improve the imaging quality, and will provide a good experimental basis for practical applications in the nanolithography field. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.10.026003) With requirements for increasingly high resolution, the diameters of the outermost pinholes of photon sieves are becoming smaller and smaller, and the focal spot dimensions are even smaller than the wavelength of the incident light. It is, therefore, necessary to study the focusing properties of subwavelength photon sieves, including their focal lengths, and their focal spot dimensions and energy distributions. These parameters all have a major impact on the overall imaging quality. Many techniques that can be used to test the focusing properties of lenses have been reported, 8 and they can be classified into two types: conventional geometric optical or mechani- cal methods, and the various modern techniques based on interference or diffraction theory. The techniques that have been reported in the first category include charge coupled device (CCD) imaging, 9 knife-edge scanning, 10 and fiber scanning. 11,12 The CCD imaging method suffers from aberrations and energy distribution variations caused by amplification of the small focal spot under testing, and the measurement precision is poor. The knife-edge scanning method is suit- able for the testing of optical spots with regular shapes and symmetrical energy distributions. The