Betatron radiation from laser wakefield accelerated electrons and X-rays scattered off a counter-propagating relativistic electron bunch are collimated and hold the potential to extend the energy range to hard X-ray or gamma ray band. The peak brightness of these incoherent radiations could reach the level of the brightest synchrotron light sources in the world due to their femtosecond pulse duration and source size down to a few micrometers. In this article, the principle and properties of these radiation sources are briefly reviewed and compared. Then we present our recent progress in betatron radiation enhancement in the perspective of both photon energy and photon number. The enhancement is triggered by using a clustering gas target, arousing a second injection of a fiercely oscillating electron bunch with large charge or stimulating a resonantly enhanced oscillation of the ionization injected electrons. By adopting these methods, bright photon source with energy over 100 keV is generated which would greatly impact applications such as nuclear physics, diagnostic radiology, laboratory astrophysics and high-energy density science.

对中国科学院上海光学精密机械研究所(SIOM)即将开展的基于激光尾场加速(LWFA)电子束的自由电子激光（FEL）实验(SIOM-FEL)进行了数值模拟研究，提出利用直接外种子激光驱动的方案来获得FEL辐射。理论和仿真结果表明，采用直接外种子激光驱动模式，在束流能散为1%，发射度为0.3 mm·mrad的情况下，提高峰值电流强度到10 kA可以得到接近200倍增益的FEL辐射，而利用具有横向梯度的波荡器也可以在较低的束流强度条件下获得较高的辐射增益。