Study on the imaging characteristics of far-field superlens

The optical transfer function of the far-field superlens imaging system is established in this thesis to make it easy to describe the corresponding relation between the far-field angular spectrum and the near-field object superresolution information. We utilized the established optical transfer function to make detailed research on the imaging characteristics of the far-field superresolution, also reconstruct the near-field nano-information through the far-field angular spectrum, which proves that the resolution of the far-field superlens with structure coupled with metal grating can reach 50 nm, and provides a helpful reference for the study of the new optical microscope imaging of superresolution.     

辐射场的起伏对囚禁离子的量子相干性的影响

研究了囚禁离子与一随机相位的驻波场相互作用时的量子动力学行为,讨论了辐射场的起伏对囚禁离子的量子崩塌-回复特性的影响.对于相位扩散模型获得了这个问题的解析解.     

Optical transfer function of an optical system with a vortex phase mask in the presence of primary aberrations

The impact of primary aberrations on the optical transfer function of an optical system with a vortex phase mask has been investigated in detail. The optical transfer function of such a system becomes negative in a certain frequency range even in the absence of aberrations, a feature different from the case of an optical system in which center of the point spread function is bright.     

Phase-matched second-harmonic generation due to thermal expansion of TlGaSe2 layered crystal

Second-harmonic generation effects have been investigated in TlGaSe₂ layered crystal over a temperature range where ferroelectric phase exists. Pronounced periodical changes of the second-harmonic signal with temperature have been discovered. The observed effect is explained within the phase synchronism condition which changes with the temperature. The main mechanism of the thermal expansion of the sample in the observed phenomenon is explained.     

Transverse correlation vanishing due to phase aberrations

The concept of transverse correlation vanishing, between the fraction of power contained in the centre and wings of a probe beam, recently introduced [Opt. Commun. 282 (2009) 3854-3858] is important to be considered when measuring the effective focal length of any refractive index profile. When the latter is not parabolic it is shown that the transverse correlation could vanish, and this represents a potential source of error when measuring any lensing effect. We propose a low cost set-up (two photodiodes, a pinhole and a stop) able to reveal if the probe beam has monitored a pure or an aberrated lensing effect especially when it is time-dependent.     

Wideband optical phase modulator half-wave voltage measurement technique based on phase modulation optical link

We measured the half-wave voltage V_π of LiNbO₃ phase modulators in the broadband frequency range by analyzing the gain of phase modulation interference demodulation optical link. This is a new high practical value measurement method for half-wave voltage of LiNbO₃ phase modulators in wideband frequency range, and can accurately predict the nonlinear frequency characteristics of phase modulation optical link.     

银层超透镜光学传递函数的研究

银层超透镜对基于表面等离子体激元的超分辨光刻、 成像和生物传感有着重要作用.利用银层超透镜的光学传递函数详 细研究了银板的表面等离子体激元共振和成像特性, 并利用时域有限差分法计算模拟了银层超透镜的成像过程, 得到与理论推导公式相符合的结果, 证明了光学传递函数的可靠性, 为基于表面等离子体激元的传感器件、 超分辨成像以及辅助增强干涉光刻提供了快速参数优化方法.     

扩大光学系统焦深范围的光学成象新技术研究

如何增大非相干光学系统的焦深已成为一项有意义的研究主题.对于普通光学系统,其焦深与光学系统的相对孔径平方成反比.为了增大焦深,通常的做法是缩小相对孔径,但这种做法有其缺点:会降低光学系统的光通量及调制传递函数(MTF)和分辨率.本文提出了一种新方法,通过在光学系统光路中加入一特殊设计的非球面掩模板,并用图象处理技术对相位掩模板编码后的图象进行解码得到清晰图象.保证了光学系统在维持原有相对孔径的同时扩大其焦深范围,使光学系统在离焦范围内有好的成象质量.     

Performance degradation due to cross-phase modulation in optical fdm ask coherent detection systems

The performance degradation due to cross-phase modulation in optical FDM ASK coherent detection systems has been investigated in this paper. The effect of modulation statistics and phase tracking of the receivers is taken into account. Based on the theoretical treatment, power penalty and allowable launched power per channel have been estimated.     

Measurement of sub-surface delaminations in carbon fibre composites using high-speed phase-shifted speckle interferometry and temporal phase unwrapping

A high-speed phase-shifted speckle interferometer has been developed recently for studying dynamic events. Speckle interferograms are continuously recorded by a CCD camera operating at 1 kHz with temporal phase shifting carried out by a Pockels cell running at the same frequency. Temporal phase unwrapping through sequences of more than 1000 frames allows the determination of time-varying absolute displacement maps. This paper presents the application of this speckle interferometry system to the detection and measurement of sub-surface delamination defects in carbon fibre specimens. The influence of re-referencing the temporal phase unwrapping algorithm after different time intervals is analysed to reduce the random phase errors produced by speckle decorrelation and vibration. The performance of several phase-shifting algorithms to minimize the influence of the vibration noise caused by the vacuum pump used to load the specimen is also investigated.     

天光背景下混浊大气中成像质量的分析方法

调制传递函数(MTF)定量描述混浊介质对图像质量的影响,它是混浊介质的固有光学特性,利用等效原理可以获得MTF从低频到高频的完整特征.在实际应用中,混浊介质中的图像质量不仅取决于介质的MTF,还与图像的背景辐射密切相关.本文从混浊大气中图像退化机理出发,理论分析了空间频域中天光背景下图像质量的退化过程.参考等效原理,提出了一种考虑天光背景的表观MTF,得到了表观MTF与介质MTF和天光背景的定量关系,从而得到了一种分析背景辐射下混浊介质中图像质量的有效便捷方法.针对图像质量优化方法,从空间频域的角度提出了一种评价原则.     

Linear phase slope in pulse design: application to coherence transfer

Using optimal control methods, robust broadband excitation pulses can be designed with a defined linear phase dispersion. Applications include increased bandwidth for a given pulse length compared to equivalent pulses requiring no phase correction, selective pulses, and pulses that mitigate the effects of relaxation. This also makes it possible to create pulses that are equivalent to ideal hard pulses followed by an effective evolution period. For example, in applications, where the excitation pulse is followed by a constant delay, e.g. for the evolution of heteronuclear couplings, part of the pulse duration can be absorbed in existing delays, significantly reducing the time overhead of long, highly robust pulses. We refer to the class of such excitation pulses with a defined linear phase dispersion as ICEBERG pulses (Inherent Coherence Evolution optimized Broadband Excitation Resulting in constant phase Gradients). A systematic study of the dependence of the excitation efficiency on the phase dispersion of the excitation pulses is presented, which reveals surprising opportunities for improved pulse sequence performance.     

Light scattering by some nematic liquid crystals due to phase transitions

New computer modelling of light scattering and its propagation through liquid crystal has been presented using T-matrix method in the structural phase transition regions. Numerical aspects of light scattering process, which are based on numerically solving Maxwell's equations, were calculated for some nematic liquid crystals. Firstly, we described in detail T-matrix method for computing light scattering from nematic liquid crystals and presented results of benchmark computations for the considered model. We reported results of extensive calculations for polydisperse, randomly oriented rod-like multilayered systems (nematic liquid crystals). Our results are associated with light scattering by ferroelectric and ferroelastic materials.     

Information verification and encryption based on phase retrieval with sparsity constraints and optical inference

A novel optical information verification and encryption method is proposed based on inference principle and phase retrieval with sparsity constraints. In this method, a target image is encrypted into two phase-only masks (POMs), which comprise sparse phase data used for verification. Both of the two POMs need to be authenticated before being applied for decrypting. The target image can be optically reconstructed when the two authenticated POMs are Fourier transformed and convolved by the correct decryption key, which is also generated in encryption process. No holographic scheme is involved in the proposed optical verification and encryption system and there is also no problem of information disclosure in the two authenticable POMs. Numerical simulation results demonstrate the validity and good performance of this new proposed method.     

Nonlinear dynamics of an optical phase locked loop in presence of additional loop time delay

The dynamics of an optical phase locked loop (OPLL) with first order loop filter having inherent loop time delay is investigated. In the presence of delay, the system is modeled as a third order autonomous system. In the out of lock condition or during the process of locking, the dynamics of the system is highly nonlinear and different nonlinear phenomena, like limit cycle oscillation, period doubling, chaotic oscillations etc., may be observed with the variation of design parameters. Applying the techniques of the nonlinear dynamics, we have calculated the effects of the inherent loop time delay in determining the state of the loop. The analytical results predicting the parameter values for stable and unstable region of operation are obtained using the quasi-linear Routh–Hurwitz method. The parameter range required for the onset of chaotic oscillations is estimated by Melnikov's global perturbation method. The predicted results are in agreement with those obtained by numerical integration of system equations.     

Fisher information due to a phase noisy laser under non-Markovian environment

More recently, K. Berrada [Annals of Physics 340 (2014) 60-69] [1] studied the geometric phase of a two-level atom system driven by a phase noise laser under non-Markovian dynamics in terms of different parameters involved in the whole system, and collapse and revival phenomena were found for large class of states. In this paper, using this noise effect, we study the quantum fisher information (QFI) for a two-level atom system driven by a phase noise laser under non-Markovian dynamics. A new quantity, called QFI flow is used to characterize the damping effect and unveil a fundamental connection between non-Markovian behavior and dynamics of system–environment correlations under phase noise laser. It is shown that QFI flow has disappeared suddenly followed by a sudden birth depending on the kind of the environment damping. QFI flow provides an indicator to characterize the dissipative quantum system’s decoherence by analyzing the behavior of the dynamical non-Markovian coefficients.     

Extreme wave formation in unidirectional sea due to stochastic wave phase dynamics

The authors consider a stochastic model based on the interaction and phase coupling amongst wave components that are modified envelope soliton solutions to the nonlinear Schrödinger equation. A probabilistic study is carried out and the resulting findings are compared with ocean wave field observations and laboratory experimental results. The wave height probability distribution obtained from the model is found to match well with prior data in the large wave height region. From the eigenvalue spectrum obtained through the Inverse Scattering Transform, it is revealed that the deep-water wave groups move at a speed different from the linear group speed, which justifies the inclusion of phase correction to the envelope solitary wave components. It is determined that phase synchronization amongst elementary solitary wave components can be critical for the formation of extreme waves in unidirectional sea states.     

Phase contrast enhancement in microscopy using spiral phase filtering

We demonstrate two methods based on Fourier plane filtering using (a) a fractional spiral phase plate (SPP) and (b) an off-axial SPP for phase contrast enhancement in optical microscopy. In comparison to previous works, a spatially incoherent LED is used in the Köhler illumination as the light source to illuminate the biological specimen. We demonstrate that both these methods can transform the phase specimen into a relief-like view even under such illumination. The degree and orientation of enhancement can be controlled by changing the phase structure of the filter. The SPP is displayed on a phase-only spatial light modulator, and can be integrated into the optical path of standard microscopes.     

Superconducting fluctuation induced conductance corrections near a pair-breaking quantum phase transition in doubly connected ultrathin cylinders of Al

We report measurements on ultrathin,doubly connected superconducting cylinders of Al that exhibit a destructive regime,which refers to the loss of superconductivity in a doubly connected superconductor near applied half flux quanta due to the sample topology and the small size of the sample.A depairing quantum phase transition(QPT)between a superconducting and metallic state tuned by the magnetic flux enclosed in the quasi one-dimensional(1D)cylinder was found at the onset of the destructive regime.Results on magnetic flux and temperature dependent sample resistance as well as current-voltage characteristics revealed the presence of both thermally activated and quantum phase slips near the depairing QPT.On the superconducting side of the QPT,thermally activated phase slips as described by the Langer-Ambegaokar and McCumber-Halperin(LAMH)theory were found to describe the sample resistance as the system was pushed towards the QPT by a magnetic field applied along the cylinder axis.However,deviation from this behavior was found at low temperatures,signaling the presence of the quantum phase slips.Most importantly,we observed a highly unusual negative slope in the resistance versus temperature curves on the metallic side of the QPT as predicted by the diagrammatic calculation of the dc conductivities in a 1D system near a depairing QPT.Our work suggests that fluctuations from both the phase and the amplitude of the superconducting order parameter are important for the superconductor-to-metal depairing QPT.     

Photoluminescence linewidth broadening due to alloy/thickness fluctuation of CdxZn1 − xSe/ZnSe triple quantum wells

Photoluminescence (PL) linewidth broadening of Cd_xZn_{1 − x}Se/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced.