飞秒激光-固体靶相互作用中渡越辐射的测量

 为了探索超热电子的加热机制，利用光学CCD相机和OMA光学多道分析仪，分别在靶背法线方向测量了光学渡越辐射（OTR）积分成像图案和光谱。实验在100 TW掺钛蓝宝石激光器上进行，飞秒激光与铜膜靶作用后，靶表面发光信号由空间分辨装置聚焦成像并引到CCD或OMA谱仪的狭缝上。测得的积分成像图案呈圆环状，光斑形成区域直径约为225 μm，在圆环边缘附近出现局部化明亮光信号，该现象表明，超热电子在传输的过程中存在成丝效应，其分布也不均匀。光谱在300～500 nm之间出现一系列非周期锐利尖峰，在400 nm（2ω0）附近出现的尖峰应归因于v×B加热机制产生的超热电子引起的相干渡越辐射（CTR）。

Measurement of transition radiation in femtosecond laser-solid target interaction

For rearching the acceleration mechanism of hot electron, the integrated image pattern and spectrum of optical transition radiation (OTR) were measured at the normal direction from the rear side of targets employing optical CCD camera and OMA optical multi-channel spectrometer. The experiment was carried out on the 100 TW laser. The mearured integrated image pattern presents a ring-shape of about 225 μm in diameter. In the near edge of the ring-shape there is a bright localized signal, which indicates filament effect exists during hot electron transport. The spectrum presents a series of nonperiodic sharp peaks between 300～500 nm, which is attributed to the coherent transition radiation (CTR) of hot electron generated by v×B acceleration mechanism near 400 nm(2ω0.