JP2662780B2 - Free electron laser device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a free electron laser device. [Prior Art] A free electron laser is known as a new laser.
A free electron laser irradiates a light emitting medium with free electrons to excite the free electrons, and laser oscillation is performed in the same direction as the traveling direction of the electron beam. This is not an exception in the case of emitting light using the Cherenkov effect. That is,
The Cherenkov free electron laser irradiates free electrons in a vacuum, slows the phase velocity of light by a slow-wave structure in the vacuum, and does not perform laser oscillation in the same direction as the direction of the electrons. [Problems to be Solved by the Invention] In order to enable such laser oscillation, electrons having a speed equal to the speed of light in the luminous medium are required. Has been hindered. The present invention has been made in order to solve such a problem, and it is an object of the present invention to provide a free electron laser device in which the restriction of energy purity is solved by utilizing the property that an optical fiber confines and propagates light. Aim. [Means for Solving the Problems] A free electron laser device according to the present invention comprises an optical fiber having resonance mirrors disposed at both ends, and an electron beam source for irradiating the optical fiber with a relativistic electron beam. And irradiates the optical fiber with a relativistic electron beam having a predetermined energy level in a direction crossing the longitudinal direction of the optical fiber to emit Cherenkov light therein, thereby obtaining a laser output from an optical fiber terminal. It is characterized by the following. Further, the optical fiber is spirally arranged in an electron beam irradiation area. [Action] Cerenkov light is generated in the optical fiber by free electron irradiation. This light emission direction has a certain angle with respect to the electron beam irradiation direction, but since this direction is larger than the total reflection angle of the optical fiber, the light is propagated in the optical fiber without leaking to the outside, and stimulated radiation is generated. Induce. Therefore, laser light can be extracted from the terminal. [Principle of the Invention] First, the principle of the invention will be described. Now, as shown in FIG. 1, free electrons 2 are irradiated on the optical fiber 1 at right angles to the longitudinal direction of the optical fiber 1. When the energy of the free electrons is higher than a predetermined value, Cerenkov light is generated in the optical fiber 1. The angle θ between the emission direction of the Cherenkov light and the irradiation direction of the free electrons is θ = cos ^-1 c / v · ε where c: light velocity in vacuum v: velocity of free electrons ε: refractive index of optical fiber expressed. If v → c now, ε = 1.45 in the core 1a of the quartz optical fiber 1, so that θ ≒ 46.4 ゜. Light at this angle enters the interface between the core 1a and the clad 1b at the same angle θ, but the total reflection angle at this interface is 46 °, so that Cherenkov light propagates through the core without going out. become. Therefore, when the electron beam is irradiated in the same direction over an appropriate length, light having the same angle component is generated in the optical fiber, and as a result, stimulated emission occurs in the core 1a. In order to increase the stimulated emission, it is desirable that the optical fiber has a crystal structure such as a quartz optical fiber. Further, the optical fiber may be composed of only a core having no cladding. This is because it is sufficient that total reflection occurs on the core surface. Note that the irradiation angle of the electron beam may not be a right angle to the optical fiber but may be inclined. If the angle is inclined, θ becomes larger, so that there is no problem. Embodiment FIG. 2 is a schematic view showing an embodiment of a free electron laser device according to the present invention. The laser device according to the present invention comprises a large-diameter electron accelerator 2 for outputting a high-energy electron beam, and an optical fiber 1 arranged so as to be irradiated with a relativistic electron beam 20 emitted therefrom. The angle between the direction of the electron beam 20 and the longitudinal direction of the optical fiber 1 is a right angle. Mirrors 4 for resonance at both ends of optical fiber 1
a and 4b are deposited, so that the reflectance of one of the resonance mirrors 4b is 100% and the reflectance of the other resonance mirror 4a is slightly lower than that of the other, so that a laser beam output is obtained from the mirror 4a side. ing. The optical fiber 1 may be freely bent outside the projection area of the electron beam 20 and does not interfere with laser generation at all. Therefore, the output end may be arranged at an arbitrary position. The resonance mirror may be provided outside the optical fiber. That is, a configuration may be adopted in which light emitted from the end face of the optical fiber to the outside is received by the resonance mirror formed of a concave mirror, and then is incident again on the end face of the optical fiber. Also in this case, needless to say, the reflectance of the output side mirror is set to less than 100%. FIG. 3 is a schematic view showing another embodiment of the laser device of the present invention. The optical fiber 10 is helically arranged in a plane, and an electron beam source irradiated with a relativistic electron beam from a direction perpendicular to this plane (front and back of the drawing) is the same as that shown in FIG. It is. In such an embodiment, the electron beam emitted from the electron beam source irradiates the optical fiber 20 without waste, and the emitted light is the integral thereof, so that the energy use efficiency is high. In this embodiment, since the light emission angle at each part in the spiral circumferential direction of the optical fiber 20 is slightly different, stimulated emission, that is,
It takes time until laser oscillation. However, incoherent light is output before that, but this incoherent light is white light with high brightness,
It is useful as a high brightness point light source. [Effects] As described above, in the case of the present invention, a laser can be generated regardless of the direction of the electron beam, so that there are few restrictions on the use. When the speed of free electrons is low and the angle between the emission direction of the Cherenkov light and the irradiation direction of the free electrons is within the range of the total reflection angle of the optical fiber, the laser can be emitted without the Cherenkov light exiting the optical fiber. And the requirement for energy purity is relaxed. Further, the present invention has excellent effects such that the output light can be selected by the mode selection effect of the optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of the principle of the present invention, and FIGS. 2 and 3 are schematic views of a laser device of the present invention. 1 ... optical fiber, 3 ... electron accelerators 4a, 4b ... resonant mirror

Claims (1)

(57) [Claims] An optical fiber having a mirror for resonance on both terminals,
An electron beam source for irradiating the optical fiber with a relativistic electron beam, and irradiating the optical fiber with a relativistic electron beam having a predetermined energy level in a direction crossing the longitudinal direction thereof, thereby generating Cherenkov light therein. A free electron laser device which emits and obtains a laser output from an optical fiber terminal. 2. 2. The free electron laser device according to claim 1, wherein said optical fiber is spirally arranged in an electron beam irradiation area.