Free electron laser rocker radiation relativistic electron free electron laser is a new type of laser. Unlike the conventional laser, the principle of stimulated radiation is that it is the radiation generated by the relativistic electron beam when it passes through the rocker. Compared with conventional lasers, free electron lasers have a series of advantages: continuously adjustable wavelength, wide wavelength distribution range (from centimeter wave to soft X-ray, adjustable pulse width, good beam quality, high pulse power and high energy conversion efficiency, etc. Therefore, it has a wide range of potential application prospects in the fields of scientific research, medicine, industry, military, etc. 1. Since the advent of free electron laser in the 1970s2, many international research institutions have always regarded it as a research hotspot3 and proposed There are many methods for generating free electron lasers. Among these methods, widely used and considered to be the most promising method is to let a relativistic electron beam pass through a periodically changing rocker to generate free electron lasers. Take the periodic swing magnetic field as an example to study the mechanism of free electron laser generation.
Among them, A, A 'are two resonant cavity mirrors, B, B' are wobblers composed of periodic spiral coils, the period length of the spiral coil is Xw, and the axial direction is set to the z direction. The oscillating magnetic field formed by the spiral coil is transverse, alternating in the x, y plane perpendicular to the axis of the coil, and alternates according to the period of the coil. The compositional component is expressed as: When the relativistic electrons moving in the axial direction enter the rocker, according to Lorentz's law 5 The motion of electrons satisfies the following equations: pair value, and 1 is the total electric field and total magnetic field that determine the motion behavior of electrons. Considering only the action of the magnetic field, write (2) into the component form, where vWyM are the components of the velocity on three coordinate axes: Solve equation (3, you can get the velocity component of the electron in the swing field: vx = .BwCOS (kwvzt) Further solve the equation (4, get the equation of motion of the electron: x =-BwSinz electron moves along the spiral orbit in the swing magnetic field formed by the spiral coil, and its pitch is because the electron makes a spiral movement of the pitch Xw, so the electron Xw will produce a radiation. The process of electrons generating radiation in the swing field is shown as follows: electrons generate radiation in the turbulent swing field. The electrons spiral along the z axis and generate a radiation at the A position. A spiral pitch Xw advances in the electron In the period of time, the radiation propagates a distance of 7CXw / vz. At the same time, the electron will generate a radiation at point B. When the path difference of the electromagnetic wave radiation emitted by points A, B, is equal to an integer multiple of the wavelength, that : There will be constructive interference, which will amplify the radiation emitted by the electrons. X is the wavelength of the emitted wave, 0 is the external observation angle, and C is the speed of light.
Take the squares of (4) and add them together to find the numerical relationship between vz and v.
Among them, 3w = e'Bw is a dimensionless parameter, which is only related to the parameters of the rocker. (Formula 7 is derived on the premise of 1 / Y2 >> 1. This condition is generally satisfied during the generation of free electron lasers. Substituting (formula 7 into (formula 6, and taking n = 1 to obtain radiation The wavelength of the wave is pushed (Equation 8 is considered to be very small. It can be seen that changing the period length of the swing field Xw, changing the magnetic field strength Bw or changing the energy of the incident electron beam can be changed The wavelength of the outgoing wave, so as to achieve the purpose of wavelength tuning. When 0 = 0, the moving electrons will radiate in the axis of the rocker, and the reflection through the resonator and the interaction with the rocking field meet certain phase matching conditions. , The radiation will be strengthened, so as to achieve the purpose of outputting free electron laser.
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