Ultrafast laser inscription (ULI) inside semiconductors offers new perspectives for 3D monolithic structures to be fabricated and new functionalities to be added in electronic and photonic microdevices. However, important challenges remain because of nonlinear effects such as strong plasma generation that distort the energy delivery at the focal point when exposing these materials to intense infrared light. Up to now, the successful technological demonstrations have primarily concentrated on silicon (Si). In this paper, we target at another important semiconductor: gallium arsenide (GaAs). With nonlinearities higher than those of Si, 3D-machining of GaAs with femtosecond pulses becomes even harder. However, we show that the difficulty can be circumvented by burst-mode irradiation. We generate and apply trains of pulses at terahertz repetition rates for efficient pulse-to-pulse accumulation of laser-induced free carriers in the focal region, while avoiding an overdose of prefocal excitations. The superior performance of burst-mode irradiation is confirmed by a comparative study conducted with infrared luminescence microscopy. The results indicate a successful reduction of the plasma density in the prefocal region so that higher pulse energy reaches the focal spot. The same method is applied to identify optimum irradiation conditions considering particular cases such as asymmetric pulse trains and aberrated beams. With 64-pulse trains, we successfully manage to cross the writing threshold providing a solution for ULI inside GaAs. The application potential is finally illustrated with a stealth dicing demonstration by taking benefit of the burst mode. The irradiation method opens wide possibilities for 3D structuring inside GaAs by ULI.

传统的16QAM（16进制正交幅度调制）相干光系统的相位估计算法主要采用QPSK（正交相移键控）分圈法，然而受放大器ASE（自发辐射）噪声的影响，星座点的径向移动将对相位恢复的准确度造成严重影响。文章针对星座点受噪声影响程度的不同，对QPSK分圈法中的分类幅值阈值进行详细分析，并引入不同权重。蒙特卡罗仿真结果表明，该改进方法不仅能有效提高16QAM的相位恢复精度，而且具有更低的误码率。