Takac S, Stojanović S
Zavod za sudsku medicinu, Medicinski fakultet, Novi Sad.
Med Pregl. 1999 Jan-Feb;52(1-2):29-34.
Laser is one of the greatest technical discoveries of the 20th century. It is important in basic sciences, but particularly in diagnosis and therapy of various pathologic conditions of human organism. It is electromagnetic radiation, not X-irradiation and, as such, it is not expected to produce new generation of iatrogenic malignancies. Laser falls between infrared and ultraviolet on the spectrum mainly in the visible light spectrum. Properties of laser light are: monochromacity (the same color), coherence (all of the light waves are in phase both spatially and temporally), collimation (all rays are parallel to each other and do not diverge significantly even over long distances). Lasers were first conceived by Einstein in 1917 when he wrote his "Zur Quantum Theorie der Strahlung" (the quantum theory of radiation) which enumerated concepts of stimulated and spontaneous emission and absorption. Drs. Arthur Schawlow and Charles Townes, in 1956, extended lasers into the optical frequency range and Maiman, in 1960, operated the first laser using ruby as the active medium (ruby laser). Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. To understand the acronym, it is necessary to understand the basic physics of the atom. However, if the atom that is in the excited state is struck by another photon of energy before it returns to the ground state, two photons of equal frequency and energy, travelling in the same direction and in perfect spatial and temporal harmony, are produced. This phenomenon is termed stimulated emission of radiation. An external power source hyperexcites the atoms in the laser medium so that the number of atoms possessing upper energy levels exceeds the number of atoms in a power energy level, a condition termed a population inversion. This "pumping system" which imparts additional energy to the atoms may be optical, mechanical, or chemical. These atoms in a hyperexcited state spontaneously emit photons of light. The laser chamber or optical cavity contains an active lasing medium which usually determines the name of each laser. There are four types of lasing material commonly employed. Solid state lasers use a solid matrix material such as a ruby crystal. Gas lasers use a gas or mixture of gases such as helium, argon, and CO2. Dye lasers employ a complex organic dye in liquid solution or suspension such as rhodamine. Semiconductor lasers use two layers of semiconductor substances such as gallium arsenide.
激光是20世纪最伟大的技术发现之一。它在基础科学中很重要，但在人体各种病理状况的诊断和治疗中尤为重要。它是电磁辐射，而非X射线，因此预计不会产生新一代医源性恶性肿瘤。激光在光谱上介于红外线和紫外线之间，主要处于可见光光谱范围内。激光的特性包括：单色性（颜色相同）、相干性（所有光波在空间和时间上均同相）、准直性（所有光线相互平行，即使在长距离传播时也不会显著发散）。激光最初由爱因斯坦在1917年提出，当时他撰写了《Zur Quantum Theorie der Strahlung》（辐射量子理论），其中列举了受激辐射、自发辐射和吸收的概念。1956年，阿瑟·肖洛博士和查尔斯·汤斯博士将激光扩展到光频范围，1960年，梅曼使用红宝石作为激活介质操作了第一台激光器（红宝石激光器）。激光是“受激辐射光放大”（Light Amplification by Stimulated Emission of Radiation）的首字母缩写。要理解这个首字母缩写，有必要了解原子的基本物理学原理。然而，如果处于激发态的原子在回到基态之前被另一个能量光子撞击，就会产生两个频率和能量相等、沿相同方向传播且在空间和时间上完美协调的光子。这种现象被称为受激辐射。外部电源使激光介质中的原子过度激发，使得拥有高能级的原子数量超过低能级的原子数量，这种状态被称为粒子数反转。这个给原子赋予额外能量的“泵浦系统”可以是光学的、机械的或化学的。这些处于过度激发态的原子会自发发射光子。激光腔或光学腔包含一种激活激光介质，通常根据这种介质来为每种激光器命名。通常使用四种类型的激光材料。固体激光器使用固体基质材料，如红宝石晶体。气体激光器使用气体或气体混合物，如氦气、氩气和二氧化碳。染料激光器在液体溶液或悬浮液中使用复杂的有机染料，如罗丹明。半导体激光器使用两层半导体物质，如砷化镓。
