Development of An All Optical Laser-Plasma Accelerators

• Main Authors: Wei-Ting Chen, 陳威廷
• Other Authors: 易富國
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/51121668231037387920

碩士 === 國立臺灣大學 === 物理學研究所 === 92 === In laser-plasma accelerators, the electrons are accelerated by the plasma wave generated by the laser pulses. For its large accelerating gradient, Laser-plasma accelerators have potential to be the next generation accelerators. For example, an accelerating gradient of 100 GeV/m can be sustained for 10^{18} cm^{-3} plasma density. Such an accelerating gradient is three orders of magnitude larger than radio frequency linear accelerators. The concept of laser-plasma accelerators is first prposed by Tajima and Dawson in 1979. The technology at that time could not produce laser pulses with short duration and high intensity and only plsma beat wave accelerator can be studied through its lower requirement of pulse duration and intensity. The invention of chirp pulse amplification technic in 1980''s allow people to produce pulses with duration of severel tens femto second and peak power of multi-terawatt. With such pulses, we are able to study laser-plasma accelerators in depth. There are two main part in this thesis. In the first part, I will give a brief history of the development and some background knowledge of laser-plasma accelerators. In the second part, I will show the experimental results. We measured the properties of the accelerated electron beam. The electron beam divergence angle is 1.8 degree and the estimated transverse emittance is less than 0.1 pi-mm-mrad which is better than the state-of-the-art electron gun. Electron energy of 45 MeV was observed, and the accelerating gradient is 2.2 GeV/cm which is almost 2000 times larger than conventional accelerators. Furthermore, we introduced a copropagating prepulse in our experiment. We were able to control the electron injection and therefore we can control the electron number and electron beam divergence by changing the prepulse timing. This is demonstration of laser-inject-laser-accelerator. Also, we indentified that the seed plasma wave of Raman forward scattering comes mainly from ionization induced plasma wave from the dependence of Raman signal on prepulse timing and experimentally demonstrated cross-modulated laser wakefield accelerator.