In this Letter, new concepts of fluorescence phase-change materials and fluorescence phase-change multilevel recording are proposed. High-contrast fluorescence between the amorphous and crystalline states is achieved in nickel- or bismuth-doped Ge_2Sb_2Te_5 phase-change memory thin films. Opposite phase-selective fluorescence effects are observed when different doping ions are used. The fluorescence intensity is sensitive to the crystallization degree of the films. This characteristic can be applied in reconfigurable multi-state memory and other logic devices. It also has likely applications in display and data visualization.
Four different states of Si15Sb85 and Ge2Sb2Te5 phase change memory thin films are obtained by crystallization degree modulation through laser initialization at different powers or annealing at different temperatures. The polarization characteristics of these two four-level phase change recording media are analyzed systematically. A simple and effective readout scheme is then proposed, and the readout signal is numerically simulated. The results show that a high-contrast polarization readout can be obtained in an extensive wavelength range for the four-level phase change recording media using common phase change materials. This study will help in-depth understanding of the physical mechanisms and provide technical approaches to multilevel phase change recording.
A method of describing one-dimensional photonic crystals(1DPCs) based on Z-domain digital signal processing theory is presented. The analytical expression of the target band gap spectrum in the digital domain is obtained by the autocorrelation of its impulse response. The feasibility of this method is verified by reconstructing two simple 1DPC structures with a target photonic band gap obtained by the traditional transfer matrix method. This method provides an effective approach to function-guided designs of interference-based band gap structures for photonic applications.
With the development of semiconductor technology,semiconductor laser devices and semiconductor laser pump solid-state laser devices have been widely applied in z-scan experiments.However,the feedback light-induced output instability of semiconductor laser devices can negatively affect the accurate testing of the nonlinear index.In this work,the influence of feedback light on z-scan measurement is analyzed.Then the calculated formula of feedback light-induced false nonlinear z-scan curves is theoretically derived and experimentally verified.Two methods are proposed to reduce or eliminate the feedback light-induced false nonlinear effect.One is the addition of an attenuator to the z-scan optical path,and the other is the addition of an opto-isolator unit to the z-scan setup.The experimental and theoretical results indicate that the feedback light-induced false nonlinear effect is markedly reduced and can even be ignored if appropriate parameters are chosen.Thus,theoretical and experimental methods of eliminating the negative effect of feedback light on z-scan measurement are useful for accurately obtaining the nonlinear index of a sample.
In this work, TeO_(0.7)thin films were prepared by the reactive magnetron-controlling sputtering method. Complex gray-scale patterns were successfully fabricated on TeO_(0.7)thin films through the laser direct writing method.The structural origin of TeO_(0.7)thin film was investigated for gray-scale pattern formation. It is found that multiple gray-scale levels are dependent on the "virtual" bandgap energy of TeO_(0.7)thin films. The bandgap energy changes lead to refractive index and reflectivity difference. Thus, gray-scale tones can be formed. By accurately controlling laser energy, various "virtual" bandgaps can be generated in TeO_(0.7)thin films, and colorful gray-scale levels can be formed. Experimental results indicate that TeO_(0.7)thin film can be used as micro/nano image writing material.
Using a strong nonlinear saturation absorption effect is one technique for breaking through the diffraction limit. In this technique, formation of a dynamic and reversible optical pinhole channel and transient superresolution is critical. In this work, a pump–probe transient detection and observation–experimental setup is constructed to explore the formation process directly. A Ge2Sb2Te5 thin film with strong nonlinear saturation absorption is investigated. The dynamic evolution of the optical pinhole channel is detected and imaged, and the transient superresolution spot is directly captured experimentally. Results verify that the superresolution effect originates from the generation of an optical pinhole channel and that the formation of the optical pinhole channel is dynamic and reversible. A good method is provided for direct detection and observation of the transient process of the superresolution effect of nonlinear thin films.
