Break Through The Diffraction Limit Of The Photon Bunching Effect

In conventional optics, the focal size of a beam is ultimately limited by diffraction.Many efforts are concentrated into make a focused spot surpassing the diffraction limit,since it is important for optical lithography, mass optical memory, integrated circuit design,and high resolution imaging, etc…In the last decade, theoretical and experiment studiesdemonstrated that a thermal light source can play a role similar to that of the entangledtwo-photon source in quantum imaging such as ghost interference, ghost imaging andsubwavelength interference. The effects are referred to spatial intensity correlation ofthermal light. Among these effects, the subwavelength double-slit interference can showthe potential to surpass the classical diffraction limit. At the early experiment with thermallight, the subwavelength interference pattern can be observed only when the two detectorsare separately scanned in opposite directions. However, both the visibility and resolutionof subwavelength interference patterns can be improved with higher-order intensitycorrelation measurement. Unlike an entangled two-photon source, such a scheme cannotbe applied to two-photon lithography technology, because the two detectors are apart.Recently, we proposed an experimental scheme which may realize two-photon lithographywith a thermal light source. The key in this scheme is that the wavefronts of one beam isspatially reversed and then superposed with the other beam.The diffraction limit of N-photon system is N times as that of a classic photon.Therefore, compared to classical scheme, we can obtain more elaborate spots with thecorrelation effect of N-photon system. In this paper, the bunching effect of N-photonsystems is adopted to improve the precision of optical systems. In theory, according to theconjugate relation of the thermal light correlation, we design the theoretical model,analysis the system of multiphoton, and explore the best proposal of N-photon bunchingeffect. In the experiment, a new kind of thermal light is designed, and tworight-angle-mirror devices reverse the beam wavefronts horizontally and vertically,respectively. At the output port, the light field is superposed and received by a detector. Onthe basis of this interferometer we will research the distribution in the detection planewhen the optical source is large diameter. To our knowledge, using binary optical elementsand superlense can also surpass the classical diffraction limit. But these methods are dependent on well-designed elements made of particular materials. Our experiment do notuse these elements. Since the conjugate effect of thermal light correlation, the secondaryphase factors of mutual-correlation light field cancel out each other, and there is a spot inthe detect plane whether the near field or the far field in the paraxial approximation. Wewill analysis the relationship between spot and the focus of a lens by theoretical-experimental method.This kind of incoherent interferometer can get subwavelengthinterference fringes so that it can apply to two-photon lithography. We can also get thenext conclusion: the farther the distance, the greater the spot. In the higher ordercorrelation measurements the results show that the higher the order number, the figure willbe more clear, and the resolution of the pattern get improved greatly.