不同加热机制产生的超热电子的相干渡越辐射谐波研究

Study of the harmonics of coherent transition radiation emitted by hot electrons generated in ultra-intense laser plasma interaction due to different heating mechanism

利用不同加热机制产生的超热电子所导致的相干渡越辐射(CTR)在谐波分量强度比上的不同,给出了区分飞秒激光等离子体相互作用产生超热电子过程中的主要与次要加热机制的一种可能方法.得到了加热周期不同的加热机制所产生超热电子的比例与CTR谐波分量的二倍频和一倍频的强度比之间的具体关系式.如果在实验上测到此谐波分量强度比,就可以推出不同加热机制在加热过程中所起作用的大致比例关系.另外,CTR谐波分量的强度比还与超热电子的温度、实验上所使用靶的厚度有一定依赖关系,对此作了较为详细的讨论.

Coherent transition radiation （CTR） emitted by hot electrons generated in ultra-intense laser plasma interaction presents spikes at the harmonics of the laser frequency. If the hot electrons are generated in different heating mechanisms, CTR can have different ratios of the intensities of harmonics of the laser frequency （e. g., 2ω0 to ω0 ）, from which we can infer the dominant heating process. For example, forward hot electrons are generated once in a laser circle when resonant absorption or vacuum heating takes effect, while CTR will present spikes at nω0 ; energetic electrons can be accelerated twice in a laser circle when j × B heating dominates, while CTR will give more prominence to 2 nω0 than （ 2 n - 1 ） ω0 . The latter will have higher ratio of the intensities of harmonic of 2ω0 to ω0 than the former. We deduced an equation of the relation between the ratio of the intensity of harmonic of 2ω0 to ω0 and the ratio of the number of electrons produced by different heating mechanism, by which we can study the main heating mechanism in ultra-intense laser plasma interactions. The ratio of the intensity of harmonics also depends on the temperature of the hot electrons, as well as the thickness of the target.