The refraction and reflection of Gaussian beam on two-dimensional photonic crystal （2DPC） slab are studied by the finite-difference time-domain （FDTD） method. It is shown that 2DPC slab enables negative refraction...The refraction and reflection of Gaussian beam on two-dimensional photonic crystal （2DPC） slab are studied by the finite-difference time-domain （FDTD） method. It is shown that 2DPC slab enables negative refraction, which is demystified by the distribution of Poynting vector directions and values inside the 2DPC. A negative Goos-Haenchen shift is also found in the simulation.展开更多
The inferior mirage from road surfaces is a common phenomenon,which can be easily seen in everyday life.It has been recognized in the literature as a light refraction phenomenon due to the refractive index gradient ca...The inferior mirage from road surfaces is a common phenomenon,which can be easily seen in everyday life.It has been recognized in the literature as a light refraction phenomenon due to the refractive index gradient caused by the temperature gradient in the air strata above the road surfaces.However,it was also suggested that the mirage is just a phenomenon of specular reflection at grazing incidence.Because of the lack of reasonable and quantitative evidence,the generally accepted light refraction theory has not yet been refuted.Here we show some mirror-like reflection images captured from a road surface stretch in Yujiashan North Road,Wuhan,China,when there was no obvious temperature gradient on or above the road,measured on a winter day in December 2009.This provided direct evidence to doubt the temperature induced light refraction mechanism of the inferior mirage.Furthermore,the critical grazing angle of about 0.2° to the road plane where the mirror-like reflection appears could not make the rough surface scatter incident light as a smooth surface according to the Rayleigh criterion.Therefore the phenomenon is a mirrorlike observation effect of scattering from the surface,which cannot be entirely explained by light refraction via air strata.The results demonstrate that the image-formation mechanism and the observer-based-analysis method shown here potentially offer a means of understanding a wide range of scattering phenomena from rough surfaces at grazing angle;for example,the superior mirages of unusual brightness occasionally observed over frozen lakes and the off-specular reflection phenomenon.展开更多
The light propagation within an absorbing medium and the reflection and refraction at the interface of two absorbing media are studied. By using the unit vectors denoting the planes of constant field amplitude and con...The light propagation within an absorbing medium and the reflection and refraction at the interface of two absorbing media are studied. By using the unit vectors denoting the planes of constant field amplitude and constant phase respectively, the light propagation and attenuation are described by the effective refractive indices which depend on both the complex refractive index of the medium and the angle between the unit vectors. With the expression for the light propagation, the corresponding Snell＇s law and the expression of Fresnel coefficients are obtained, which can be applied to describe the reflection-refraction event at the interface between an arbitrary combination of transparent and absorbing media.展开更多
基金This work was supported by the Natural Science Foundation of Jiangsu Province of China under Grant No. BK2004059.
文摘The refraction and reflection of Gaussian beam on two-dimensional photonic crystal （2DPC） slab are studied by the finite-difference time-domain （FDTD） method. It is shown that 2DPC slab enables negative refraction, which is demystified by the distribution of Poynting vector directions and values inside the 2DPC. A negative Goos-Haenchen shift is also found in the simulation.
基金supported by the National Natural Science Foundation of China(50636010,50721005)the Program of Introducing Talents of Discipline to Universities of China(B06019)
文摘The inferior mirage from road surfaces is a common phenomenon,which can be easily seen in everyday life.It has been recognized in the literature as a light refraction phenomenon due to the refractive index gradient caused by the temperature gradient in the air strata above the road surfaces.However,it was also suggested that the mirage is just a phenomenon of specular reflection at grazing incidence.Because of the lack of reasonable and quantitative evidence,the generally accepted light refraction theory has not yet been refuted.Here we show some mirror-like reflection images captured from a road surface stretch in Yujiashan North Road,Wuhan,China,when there was no obvious temperature gradient on or above the road,measured on a winter day in December 2009.This provided direct evidence to doubt the temperature induced light refraction mechanism of the inferior mirage.Furthermore,the critical grazing angle of about 0.2° to the road plane where the mirror-like reflection appears could not make the rough surface scatter incident light as a smooth surface according to the Rayleigh criterion.Therefore the phenomenon is a mirrorlike observation effect of scattering from the surface,which cannot be entirely explained by light refraction via air strata.The results demonstrate that the image-formation mechanism and the observer-based-analysis method shown here potentially offer a means of understanding a wide range of scattering phenomena from rough surfaces at grazing angle;for example,the superior mirages of unusual brightness occasionally observed over frozen lakes and the off-specular reflection phenomenon.
基金supported by the National Natural Science Foundation of China(No.50876069)the Ministry of Education of the People's Republic of China(No. 208041)the Shanghai Municipal Education Commission (No.07ZZ88)
文摘The light propagation within an absorbing medium and the reflection and refraction at the interface of two absorbing media are studied. By using the unit vectors denoting the planes of constant field amplitude and constant phase respectively, the light propagation and attenuation are described by the effective refractive indices which depend on both the complex refractive index of the medium and the angle between the unit vectors. With the expression for the light propagation, the corresponding Snell＇s law and the expression of Fresnel coefficients are obtained, which can be applied to describe the reflection-refraction event at the interface between an arbitrary combination of transparent and absorbing media.
