实现γ射线激光之路  

The way to realize γ-ray lasers

作　　者：张启仁[1] 高春媛[1,2] 

机构地区：[1]北京大学物理学院,北京100871 [2]核物理与核技术国家重点实验室,北京100871

出　　处：《科学通报》2017年第30期3420-3428,共9页Chinese Science Bulletin

基　　金：国土资源部公益性行业科研专项(sino-probe0903)资助

摘　　要：分析了形成激光的诸要素,统一地理解了普通(以原子、分子或凝聚态物质为介质的)激光和自由电子激光的运作机制.由此认识了实现γ射线激光的困难和解决办法,即让带电粒子在普通激光中摆动,再配以适当的"共振"和"抽运"机制.为了进行精确可靠的分析我们建立了激光中的量子电动力学.她与真空中的量子电动力学等价,因此是当今最可靠的物理理论.由此明确得出的结论是,一束适当能量的单能直线前进的电子与一束单色平面波普通激光迎面相撞将产生γ射线激光,称为量子自由电子激光.当然,这是理想条件下的理论结论.然而协同学(synergetics)告诉我们,在实际条件逼近理想条件的过程中会有一临界点,越过这一点,诱致辐射的正反馈会导致一雪崩式的过程,电子束与普通激光碰撞产生的γ射线束遂相变为γ射线激光.Essential ingredients for generating a laser are analyzed. Unified understanding on generation mechanisms for both usual lasers （with media composed of atoms, molecules or condensed matter） and free electron lasers are shown. It makes us understand the difficulties in generating a y-ray laser. First of all, it is impossible to make a resonator in the γ-ray region by mirrors, like those made for optic instruments within or near the visible spectrum. The relation between the wavelength λr of the emitted radiation, and the wiggler period λw in a free electron laser is λr ~ λw/γ^2, in which y is the Lorentz factor of the emitting electron. Requiring λr falls into the γ-ray region, λw has to be less than 1 mm. It seems impossible to be realized in a usual free electron laser either. We therefore propose a way to realize it by letting charged particles wiggle in an usual back ground laser. A circularly polarized plane wave laser distorts the electron wave in x-y planes, periodically along the z direction, and modulates the periodicity along the z direction. It is the quantum correspondence of the classical wiggling of electrons. Since a laser is a coherent electromagnetic wave, simple and clean, it is therefore an ideal wiggler. To accurately and reliably analyze the whole process, we proposed Quantum Electrodynamics in a Laser. It is equivalent to the Quantum Electrodynamics in Vacuum, and is therefore the most reliable theory nowadays as well. Moreover we noticed that, emitted y-photons moving with emitting electrons, itself is a favorable condition to make the stimulated emission easy. Its effect in some sense like the effect of a resonator. The stimulated emissions amplify the γ-radiation and make it finally transit into a γ-ray laser under favorable conditions. In this sense, the generated γ-ray laser is a Quantum Free Electron Laser. Therefore we clearly concluded that in a head on collision between a suitable mono-energetic electron beam and a monochromatic plane wave laser, a y-ray laser should

关 键 词：激光中的量子电动力学 量子自由电子激光 γ射线激光 

分 类 号：TN24[电子电信—物理电子学]