【摘要】 "理论预言激光足够强时可以从真空中产生正负电子对,但没有人知道是否可以实现".本文回顾了从真空中产生正负电子对相关的理论发展,以及理论上要求的激光条件,和目前激光达到的条件:施温格推导出当准静电场达到量子电动力学关键场E_s=me²c³/e?=1.32×10¹⁶ V/cm(对应场强I_s=4.65×10²⁹ W/cm²)时,正负电子对可以从真空中产生;单束聚焦激光产生正负电子对阈值光强约为5×10²⁷ W/cm²;两束相向传输的激光同时聚焦到同一点,对应的单束光强阈值约为10²⁶ W/cm².考虑到只要有一对正负电子产生,其在激光场作用下的级联过程将耗尽激光场能,使最高的激光场强不能高于约3×10²⁶ W/cm².目前国际上最高激光功率是由钛蓝宝石激光经过多级啁啾脉冲放大获得,为5.13 PW,对应光强在10²⁴ W/cm².国际上有几个大的激光项目,近几年目标是10¹5 PW,远期目标百拍瓦到艾瓦.远期目标获得的光强可以产生正负电子对,但是能否实现仍然未知.更多还原

【Abstract】 "Theorists say an intense enough laser field would rip photons into electron-positron pairs, dousing the beam. But no one knows whether it’s possible to reach that point." The theory about electron-positron generation from vacuum is reviewed, also the developing of laser intensity. Schwinger predicted that electron-positron pair would be produced from the vacuum when the field near the critical QED field E_s=me²c³/e?=1.32×10¹⁶ V/cm(the corresponding intensity I_s=4.65×10²⁹W/cm²). The threshold to generate electron-positron pairs is about 5×10²⁷ W/cm² for single focused laser beam, and about 10²⁶ W/cm² for a pair of colliding laser pulses. When one electron-positron pair is generated, it would induce cascade effect under such strong laser field which would deplete energy of the field, so the highest intensity would be about 3×10²⁶ W/cm². The highest power people have reached is 5.13 PW, the corresponding intensity is about 10²⁴ W/cm², which was obtained by Chirped Pulse Amplification from Ti: Sapphire laser system. There are several projects in the world to generate 10–15 PW laser in the next few years, and several hundred PW to one Exawatt in the far future which would obtain laser intensity of 10²⁶–10²⁷ W/cm². It is still not clear if the far future aim could be reached.更多还原