Study On Time Evolution And Beam Profile Of Capillary Discharge46.9nm Laser Pulse

Researchers have been committed to extending the laser wavelength to the X-rayband. At present, the capillary discharge-pumped desktop X-ray laser has made a seriesof improvements. X-ray laser amplification is obtained from the fast pulse currentflowing through the plasma column. Therefore the study on laser pulse characteristics isimportant. This paper aims to study the capillary discharge46.9nm laser pulse timeevolution and beam profile. Understanding of the time evolution can help distinguishthe smallest time scale which the laser pulse can estimate and determine what kind ofprocess can be resolved using this laser. The beam profile may help in the opticalapplications such as focusing、collimation and transformation utilized in microscopy、machining and so on.As for the time evolution, we calculated the electron impact excitation andde-excitation coefficient. The rate equations with a electron impact excitation andde-excitation coefficient were established. The time dependent curve of populations and46.9nm laser photon number was calculated therefore the pulse shape was obtained. Therelationship between the pulse duration and the plasma parameters is discussed.Experimentally the capillary discharge46.9nm X-ray laser source was connected to themonochromator and vacuum photomultiplier tube. The time evolution was detected.The calcution and the experiment conforms well.As for the beam profile, according to the gain-guided model, the intensitydistribution was calculated theoretically. The model is derived applicable to the slitscanning method. The intensity distribution of slit scanning method were calculated.The beam divergence with respect to the radius of the plasma and the electron density isobtained. We also utilized the flat-field spectrometer which has the spatial resolution inone-dimension to detect the beam profile.These studies may help to research the X-ray laser light-emitting physicalprocesses and the state of the plasma. These studies will also contribute to achieve abetter pulse or a pulse with unque characteristic which can be useful in the applications.