A X-ray free-electron laser (XFEL) facility is based on RF superconducting accelerator at China Academy of Engineering Physics (CAEP) has been planed. The facility will be designed in a radiation range of 0.3-4 angstrom and the electron beam energy will be 12GeV. The main work focuses on the optimization of different parameters through physical analysis such as the undulator peak field strength and electron beam energy selected. A detailed simulation of start up and statistical properties of the radiation from a SASE FEL operating has been performed by time dependent FEL code.
KEYWORDS: Terahertz radiation, Free electron lasers, Resonators, Electron beams, Optical resonators, Mirrors, Computer simulations, High power lasers, Medium wave, Waveguides
A high power China Academy of Engineering Physics(CAEP) THz free electron laser (FEL) is designed and optimized in a radiation frequency range of 1~3 THz and average output power of about 10 W. The main work focuses on the optimization of different schemes through physical analysis. The wiggler peak field strength and electron beam energy have been selected with eleven frequencies ranging from 1 THz to 3 THz. It is found that the values of the gain and output power of the cavity are largest at 2.6 THz. So we can test the facility at this frequency. While the value of the output power is less than the design goal at the lower frequency region of about 1.0 THz due to the serious slippage between the electron bunch and radiation pulse. To increase the output power at the lower frequency region, the scheme of elliptical hole-coupling optical resonator is proposed to solve this problem. The simulation results show that the elliptical hole-coupling output is effective and applicable for the THz FEL and the output power can be increased by more than 30%.
KEYWORDS: Chemical oxygen iodine lasers, Chemical lasers, 3D modeling, Fluid dynamics, Resonators, Chemical reactions, Near field optics, Optical simulations, Gases, Iodine
The chemical oxygen-iodine laser (COIL) is the shortest wavelength and high-power chemical laser demonstrated. To
model the complete COIL lasing interaction, a three-dimensional formulation of the fluid dynamics, species continuity
and radiation transport equations is necessary. The computational effort to calculate the flow field over the entire nozzle
bank with a grid fine enough to resolve the injection holes is so large as to preclude doing the calculation. The approach
to modeling chemical lasers then has been to reduce the complexity of the model to correspond to the available
computational capability, adding details as computing power increased. The modeling of lasing in COIL is proposed,
which is coupling with the effects induced by transverse injection of secondary gases, non-equilibrium chemical
reactions, nozzle tail flow and boundary layer. The coupled steady solutions of the fluid dynamics and optics in a COIL
complex three dimensional cavity flow field are obtained following the proposal. The modeling results show that these
effects have some influence on the lasing properties. A feasible methodology and a theoretical tool are offered to predict
the beam quality for the large scale COIL devices.
KEYWORDS: Resonators, Chemical oxygen iodine lasers, Iodine, Chemical lasers, Laser resonators, Resonance energy transfer, Oxygen, Chemical analysis, Gas lasers, Thermal effects
The factors of Chemical Oxygen-Iodine Laser (COIL) resonator expanding angle design are analyzed in this paper. It is
shown that the primary factor is the rate of the releasing heat from the near resonant energy transfer reaction between
O2(1Δ) and I at the resonator entrance with the laser extracting. It is a characteristic of COIL that the rate of the releasing
heat with lasing is bigger than without lasing. A slightly bigger resonator expanding angle than that of constant pressure
operating condition is sufficient to avoid the shock wave appearance.
The gain optical guide effects in a COIL are found and studied for the first time. The non-uniform distribution of gain in one transverse direction is assumed to be caused by non-uniform injection of the secondary flow. Our calculations who that the gain and optical guide effects have an important influence on the transverse shape of the optical field, which results in some effects such as the reduce of the output power and the offset of the optical beam, which have been observed in the experiments made in China Academy of Engineering Physics.
We propose a method to improve the quality of a hole-coupled resonator for a free-electron laser oscillator. A mesh or grating with a reflectivity of 50 - 70%, which is quite easy to be produced, can be used to cover the hole. Both the extraction and diffraction losses can be reduced effectively and the optical cavity Q value can be improved to obtain higher net gain which allows the FEL oscillator to be operated in worse conditions. These advantages and properties are confirmed by numerical simulations using a three-dimension code with the parameters of a compact far-infrared FEL oscillator built in China Academy of Engineering Physics (CAEP). Furthermore, it can be used as an electron transparent mirror to make the FEL device more compact and less expensive.
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