Rotational relaxation effects in a cw chemical laser amplifier or a line-selected oscillator are examined in terms of a simple analytical model. Three rotational levels in each vibrational level of the lasing transitionare taken to have finite rotational relaxation rates. The results.indicate the effects are likely to be significant, lowering the available power and leading to an optimum level of the line intensity for maximum power output, apart from consideration of optical losses at mirrors, windows, etc. While the model accounts for Deltaj = +/-1 transitions only, the collisional transition probability was augmented in the computations in an attempt to provide high estimates for the rotational relaxation rates, including factors such as Deltaj > 1 transitions.
To suppress the secondary electron multipactor on dielectric surfaces of a dielectric load accelerator under an electromagnetic field in TM mode, the method of adopting both groove structure and external axial magnetic field is introduced. As the electric field distribution of the TM mode is composed of both normal and tangential components, it is different from that under the condition of dielectric window in HPM. Thus, theoretical analysis and numerical simulation are employed to study the movement of electrons under different conditions: such as dielectric surface shapes, electric field strength, and magnetic field strength etc. Based on the particle-in-cell (PIC) simulation, the collision energy and transmit-duration of secondary electrons in different groove structures and axial magnetic fields are compared with one another. Results show that the magnetic field is useful for suppressing the development of secondary electron on dielectric surface, while it is not very efficient under high electric field strength. The method of introducing groove structure and certain axial magnetic field on dielectric surface at the same time is capable of affecting the movement of electrons in electric field of different strength. So it is great helpful in improving the ability of multipactor suppression, which is significant for improving the threshold of breakdown on dielectric surface and the power of cavity. However, a too high or too low magnetic field is not very useful for the suppression of multipactor. Furthermore, employing only one of the two parts of the method is also less effective in suppressing the multipactor.
Micro-Raman analyses were carried out to investigate the micro-structure of cross section for diamond films prepared by hot-filament chemical vapor deposition.The variation of Raman peak feature with position was recognized as the difference of micro-structure in the film.The presence of broad band and high background intensity near the substrate surface was attributed to the amorphous carbon synthesized in the nucleation process of diamond film.The reduction of sp3-bond structure in the amorphous carbon phase was used to account for the observation of the 1200—1600cm-1 band intensity declination as the increase of film thickness.From the Raman feature it was shown that the sp2-bond structure and the graphitic phase decreased slowly,compared with the bond structure in the growth process of the film.The micro-Raman spectroscopy obtained by scanning parallel to the surface of the film showed the structure and composition difference between the diamond grain and the grain boundary.
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