上世纪90年代以来出现了一种新型的激光束——“空心激光束”。空心激光束的特点是存在位相奇异点，在传播方向上中心光强（轴向光强）为零的环状光束，被称为“空心光束”或“暗中空光束”。空心激光束除具有激光的特点之外，还具有很多独特的物理特性，比如径向强度呈桶装分布、具有自旋与轨道角动量等。由于这些独特的性质，空心激光柬在几乎所有激光的应用领域，包括激光加工、激光医学诊断治疗、激光扫描成像、激光通信、激光武器等，有着巨大的应用价值和广阔的应用前景。另外，空心激光束还可作为光学导管和光学镊子，对微观粒子实现精确的捕捉和控制。但是，经研究发现，空心激光束在近场传播稳定性好，但在远场传播时，却具有很独特的“自聚焦”效应，即在传输一定距离后“空心”的特质消失，退化为普通的激光束。这种效应使得空心激光束在激光远距离通信等领域失去了具有一定隐蔽性的独特优势，这并不是人们所希望看到的，也必将限制其在远距离传输上的应用。针对空心激光束远距离传中出现“自聚焦”现象，为了发挥空心激光束的独特优势，本文将对空心激光柬的远距离传输控制作深入研究，具有一定的实用意义。%Since the 1990s, a new type of laser beam - hollow laser beam appeared. The characteristic of the hollow laser beam is present phase singular point. An annular beam, the center light intensity in the direction of propagation is zero, is referred to as "hollow beam" or "dark hollow beam". Hollow laser beam in addition to the characteristics of the laser, but also has a lot of unique physical characteristics, such as radial strength was bottled distribution, spin and orbital angular momentum. Because of these unique properties, hollow laser beam in almost all laser applications, including laser processing, laser medical diagnosis and treatment, laser scanning, imaging, laser communications, laser weapons, has tremendous value and broad application prospects. In addition, the hollow laser beam can also be used as optical catheter and optical tweezers, to accurate capture and control microscopic particles. However, the study found that the hollow laser beam propagation stability in the near-field, but in the far field propagation, it has a very unique "self-focusing" effect that disappear after a certain distance of the transmission characteristic of the "hollow" degenerate into common laser beam. This effect makes the unique advantage of having some hidden hollow laser beam lost in the field of laser distance scanning imaging, this is not that people want to see, and will also limit its application in the long-distance transmission. Long distance pass for hollow laser beam appeared self-focusing phenomenon; this topic will be the long-distance transmission of hollow laser beam in order to play the unique advantages of the hollow laser beam for in-depth study has some practical significance.
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