人类在实验室可实现的激光强度极限是强场量子电动力学（QED）的重要问题。在非理想真空条件下，极端超强激光与残留的电子相互作用触发伽马光子辐射与正负电子对产生的QED级联效应，从而显著消耗激光能量，大幅降低可实现的激光峰值强度。考虑到QED级联效应与激光偏振、焦斑尺寸、脉宽长度有着密切的关系，基于囊括QED过程的粒子网格模拟方法（Particle-in-cell, PIC）对上述参数的效应进行分析，同时构建了激光场演化的自洽方程来进行解释，二者结果基本保持一致，获得的强度极限在考虑的参数范围内为10²⁶～10²⁷ W/cm⁻²。结果表明，同等情形下，圆偏振激光可激发更强的QED级联，使得激光强度上限略低于线偏振。此外，紧聚焦激光由于QED级联发生的时空间尺度更小，从而激光的吸收效应被显著抑制，进而可以实现更强的聚焦强度。对于更长脉宽的激光，由于正负电子对吸收的能量区域更加弥散，使得可实现的激光强度上限阈值有所提升。但对于超短脉宽情形（如单周期），由于QED级联的种子源电子束不能很好地被约束在激光区域，理论分析耗散的激光能量偏高。此外，在高真空度的情形下，残余电子的随机性也会对可实现激光强度产生一定的影响。研究结果可为后续开展极端强场QED实验和数100 PW级超强超短激光装置建设提供指导。

The attainable upper limit of the laser intensity is a key concern in strong-field quantum electrodynamics (QED). For non-ideal vacuum conditions, the extreme laser fields interacting with the residual electrons could trigger QED cascade—the processes of gamma-photon emission and electron-positron pair production. It leads to strong depletion of the laser pulse hence limits the attainable laser intensity. Since the QED cascade is affected by the polarization, beam waist and duration of the laser pulse, we investigate the effects of these parameters based on particle-in-cell (PIC) simulations incorporating the QED modules. We also develop self-consistent dynamics equations to describe the laser depletion process, which agree well with the PIC simulations. According to the analysis, the upper limit of attainable intensity is about 10²⁶-10²⁷ W/cm^-2 in the considered parameter range. Specifically, the circularly polarized pulses drive stronger QED cascade than in the linearly polarized case under the same circumstances, resulting lower upper limit threshold of intensity. In addition, tightly focused lasers correspond to smaller cascade durations and interaction volumes. Thus, the absorption of laser energy is inhibited, i.e., higher peak intensity can be achieved. Regarding the effect of pulse duration, the depletion energy will be dispersed along larger absorption volume so that the attainable intensity will be enhanced. It should be noted that for extremely short pulses (single cycle), the seeded particles of QED cascade (i.e., electrons and positrons) cannot be efficiently trapped in the laser field, and the analytical model tends to overrate the absorption of laser energy. Regarding the extreme low purity case (i.e., the low electron residual density), the stochastic position of the residual electrons will strongly affect the upper limit of the intensity. Overall, these results offer a guideline for further experiment setups of exploring strong field QED processes and construction of the state-of-art hundred-petawatt laser facilities.