Curvelet transform and its application in multiscale analysis of surface topography

Linfu Li

Supervisor: Min Xu, Xiangchao Zhang

Most of the surfaces are manufactured by not only one process. The resulting texture is combination of the textures due to all processes. A typical engineering surface consists of a range of spatial frequencies. The short wavelength components are referred to as roughness, the medium wavelength as waviness and long wavelength components as form. The surface topography such as roughness, waviness, form and multi-scalar features (e.g. random peaks/pits and ridges/valleys) will influence the functional behavior and optical properties of the whole system such as aberration, reflection, refraction, transmission, scattering, diffraction, etc. The highly accurate characterization of surface topography such as the extraction of multi-scalar features is a very important issue in optical precision manufacturing and detection. 

  A great deal of the ultra precision optical manufacturing workpiece failure due to surface problems.  Accurate extraction of surface features, established a connection between the characteristics and process change. If it has been machined surface morphology decomposed into different spatial and frequency band, and with a particular process, changes in processing conditions correspond, it provides a means of a through analysis of surface morphology change to monitor process. The Multiscale analysis of surface morphology provide a qualitative theory for ultra-precision optical functional surface process design. A new method for monitoring optical device processing.

参考文献:

[1]   Zeng W, Jiang X and Scott P.Metrological characteristics of dual-tree complex wavelet transform for surface analysis. 2005;16:1410-1417.

[2]   Jiang X Q, Zeng W H, Scott P, Ma J W, Blunt L. Linear feature extraction based on complex ridgelet transform. Wear. 2008; 264:428-433.

[3]   Candès E J and Donoho D L, Curvelets-a surprisingly effective nonadaptive representation for objects with edges. in Curves and Surface Fitting: Saint-Malo 1999, edited by A. Cohen, C. Rabut, and L. Schumaker Vanderbilt University Press, Nashville, 2000;105-120.

[4]   Emmanuel J. Candès and David L. Donoho. Recovering edges in ill-posed inverse problems: optimality of curvelet frames Source: Ann. Statist. 2002;30(3): 784-842.

[5]   Candès E J, Demanet L, Donoho D L, and Ying L. Fast discrete curvelet transforms. Multiscale Model. Simul. 2006;5(3):861-899.

Study of molecule formation during laser ablation of graphite in ECR Nitrogen plasma by optical emission spectroscopy

Peipei Liang

Supervisor: Jiada Wu

The expansion of the carbon plasma induced by pulsed laser ablation of graphite in the nitrogen plasma generated by electron cyclotron resonance (ECR) microwave discharge of N2 gas was studied by optical emission spectroscopy (OES). OES measurements show that in addition to the emissions emitted from the species ablated from the target and present in the reactive background, C2 and CN emissions are also observed. The C2 emission bands locate in the small regions near the target, while the emissions from CN molecules are observed at a region with larger distances. The temporal and spatial features of the C2 and CN emissions as well as those emitted from other species allow us to access the gas phase reactions for the formation of C2 and CN molecules. C2 molecules originate from gas-phase reactions mainly due to three-body effect promoted by excited nitrogen, while the presence of the CN emissions and their characteristics together with the emissions from other emitting species give a direct evidence of the gas-phase reactions between the energetic carbon species ablated from the target and the reactive nitrogen species present in the nitrogen plasma which is highly excited by the hybrid processes of ECR microwave discharge and pulsed laser ablation.

参考文献：

[1] Feng H, Sun J, Ding D, et al, Plasma Processes and Polymers, 2011, 8(12): 1146-1153.

[2] Sun J, Feng H, Gan J, et al, Diamond and Related Materials, 2012, 21: 66-72.

[3] Acquaviva S, De Giorgi M L, Journal of Physics B: Atomic, Molecular and Optical Physics, 2002, 35(4): 795.

[4] Al-Shboul K F, Harilal S S, Hassanein A, et al, Journal of Applied Physics, 2011, 109(5): 053302-053302-6.

[5] Al-Shboul K F, Harilal S S, Hassanein A , Applied Physics Letters, 2011, 99(13): 131506-131506-3.

The study of the characteristic of light through the interface of metal films

Chen Zhang

Supervisor: Liangyao Chen

Metal-based micro-structural materials play pivotal roles in modern optical and optoelectronic devices. They can be used to make, for example, new green energy devices with high-efficient photovoltaic and solar-thermal conversion abilities, high-performance optical reflectors, conductive transparent windows that would have important applications in the new flat panel display devices, stealth devices with characteristics of ultralow electromagnetic radiations, perfect optical lens for super-resolution imaging,and so on.

It is important to study and clarify how the light transfers through the interface of metal-based materials. By overcoming the extreme difficulty due to very short light penetration depth in the metal ,out team carried out a novel experiment to fabricate thin wedge-shaped film and to measure the light refraction and find out that the light refraction changes from negative to positive ,by crossing zero.And observation agrees with the prediction of the group velocity based on the dispersive feature of the phase refractive index, and give an advance understanding of the complicated light refraction phenomena occurred at the metal interface.

参考文献：

[1]V. G. Veselago. The electrodynamics of substances with simultaneously negative values of � and μ [J]. Sov. Phys. Usp., 1968, 10(4):509~514.

[2] X. Hu, Y. Shen, X. Liu, R. Fu, J. Zi. Superlensing effect in liquid surface waves [J].Phys. Rev. E, 2004, 69(3):030201

[3] X. D. Zhang and Z. Y. Liu, Negative refraction of acoustic waves in two-dimentional phononic crystals [J]. Appl. Phys. Lett., 2004, 85(2):341

[4] S. Yang, J. H. Page, Z.Y. Liu, M. L. Cowan, C. T. Chan and P. Sheng. Focusing of sound in a 3D phononic crystal [J]. Phys. Rev. Lett., 2004, 93(2):024301

[5] K.Imamura and S. Tamura. Negative refraction of phonons and acoustic lensing effect of a crystalline slab [J]. Phys. Rev. B, 2004,70(17):174308

[6] J. Li and C. T. Chan. Double-negative acoustic metamaterial [J]. Phys. Rev. E, 2004, 70(5):055602

[7] Y. Jin and S. He. Focusing by a slab of chiral medium [J]. Opt. Expr., 2005.13(13). 4974-4979

[8] C. Monzon and D. Forester. Negative refraction and focusing of circularly polarized waves in optically active media [J]. Phys. Rev. Lett., 2005, 95(12):123904

[9] J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs, Extremely low frequency plasmons in metallic mesostructures [J], Phys. Rev. Lett., 1996, 76(25): 4773-4776.

[10]  J. B. Pendry, A. J. Holden, D. J. Robbins, and W. J. Stewart, Magnetism from conductors and enhanced nonlinear phenomena [J], IEEE Trans. Microwave Theory Tech.,1999, 47(11): 2075-2084.

Study of Dynamic Photocoercivity Effect

Zhe Zhang

Supervisor: Haibin Zhao

Absolutely the magnetic storage has been the mainstream of memory and storage. However, with the rapid development of storage density, the selection of magnetic storage material becomes a very important issue. Nowadays, magnetic materials with high perpendicular magnetic anisotropy （PMA） have been extensively explored with the increased demand for high-density magnetic recording. It is because even a nanosized bit has the advantage of excellent thermal stability and reliability due to the high PMA. Ultrahigh coercivity always accompany with giant perpendicular magneto-crystalline anisotropy. Traditional control method to control coercive field is the magneto-optical storage, a type of thermal secondary storage. Photocoercivity effect, the so-called PCE, has the potential application to control the coercivity with relatively small pulse power due to a completely new mechanism. Coercivity decreases when the sample is irradiated by ultrafast pulse, and the transient thermal effects are supposed to reduce the coercive force. However the dynamics of the reverse process is still unknown, which will be of great help to reduce the threshold of Magnetization reversal.

参考文献：

[1] X. D. Liu, Z. Xu, R. X. Gao, Z. F. Chen, T. S. Lai, J. Du, and S. M. Zhou,Single laser pulse induced dynamic magnetization reversal mechanism of perpendicularly magnetized L 1 0 FePt films, Journal of Applied Physics 106, 053907 (2009);

[2] A. H. M. Reid, G. V. Astakhov, A. V. Kimel, G. M. Schott, W. Ossau, K. Brunner, A. Kirilyuk, L. W.

Molenkamp, and Th. Rasing, Single picojoule pulse switching of magnetization in ferromagnetic (Ga,Mn)As, Applied Physics Letters 97, 232503 (2010);

[3] Shufa Li, Zhifeng Chen, Chuyuan Cheng, Jiaming Li, Shiming Zhou, and Tianshu Lai, Coercivity dynamics and origin of time-delayed magneto-optical hysteresis loops in pump-probe Kerr spectroscopy, Journal of Applied Physics 113, 053913 (2013);

[4] G.V. Astakhov,* H. Hoffmann,V. L. Korenev, T. Kiessling, J. Schwittek, G. M. Schott,C. Gould, W. Ossau, K. Brunner, and L.W. Molenkamp, Nonthermal Photocoercivity Effect in a Low-Doped (Ga,Mn)As Ferromagnetic Semiconductor, PRL 102, 187401 (2009);

[5] A. Oiwa, T. Supinski, and H. Munekata, Control of magnetization reversal process by light illumination in ferromagnetic semiconductor heterostructure p -(In,Mn)As/GaSb, Applied Physics Letters 78, 518 (2001)