Bloch oscillation and Landau Zener tunnelling in a modulated optical lattice in a photovoltaic photorefractive crystal

We theoretically study the beam dynamical behaviour in a modulated optical lattice with a quadratic potential in a photovoltaic photorefractive crystal. We find that two different Bloch oscillation patterns appear for the excitation of both broad and narrow light beams. One kind of optical Landau-Zener tunnelling also appears upon the Bloch oscillation and can be controlled by adjusting the parameter of the optical lattice. Unlike the case of linear potential, the energy radiation due to Landau-Zener tunnelling can be confined in modulated lattices of this kind. For high input intensity levels, the Landau-Zener tunnelling is suppressed by the photovoltaic photorefractive nonlinearity and a symmetry breaking of beam propagation from the modulational instability appears.

准分子激光治疗近视眼早期随访结果分析

目的:评价准分子激光屈光性角膜切削术(PRK)治疗近视眼的临床效果。方法:对276例(391眼)接受了PRK的近视及近视散光眼进行了半年的随访观察。分为三组:Ⅰ组—1.00～—6.00D,100只眼;Ⅱ组—6.25～—10.00D,145只眼;Ⅲ组—10.25～—22.00D,146只眼。结果:术后半年裸眼视力≥1.0(或≥术前最好矫正视力)者在三组分别为75.0%、44.1%和25.3%。剩余屈光度≤—1.00D在三组分别为95.0%、82.1%和47.9%。剩余屈光度的均数及标准差在三组分别为—0.33±0.38D、—0.79±0.65D、—1.29±1.04D。角膜上皮下混浊与近视度数呈一定的正相关。眼压升高率为1.8%。结论:PRK治疗近视眼安全有效,对于—10D以下、特别是—6D以下的近视眼有较好的预测性和稳定性,—10D以上的高度近视眼有较高的屈光回退率。远期效果有待继续随访。

准分子激光角膜表层屈光手术发展历程

准分子激光角膜表层屈光手术经历了30余年的发展,从最初的准分子激光角膜切削术(PRK),到逐渐出现的乙醇法准分子激光上皮瓣下角膜磨镶术(LASEK)、机械法准分子激光上皮瓣下角膜磨镶术(Epi-LASIK)及近年来兴起的经角膜上皮的激光角膜切削术(Trans PRK),表层切削手术不断发展,其安全性、有效性也越来越得到人们的认可,成为一种不可或缺的屈光手术方式。本文将就角膜表层屈光手术的发展过程、基本原理、各术式的优缺点等方面做一综述,希望对屈光手术的进一步改善提供帮助。