Frequency-resolved optical gating (FROG) is a novel means of measuring the fast motion of a critical density surface during relativistic laser–plasma interaction. Herein, we present a design and demonstration results for a new single-shot FROG system and optical transport system for characterizing the instantaneous intensity and phase at the LFEX (Laser for Fast Ignition Experiment) laser facility at the Institute of Laser Engineering of Osaka University. At LFEX, the laser intensity at the vacuum window is intrinsically high because of two unique properties, namely, the large F-number of the off-axis parabolic mirror and the small radius of the interaction chamber. Consequently, to obtain an accurate FROG trace, attention must be paid to spectrum modulation due to self-phase modulation. The appropriate laser intensity for FROG operation was investigated experimentally, and an optical transport system with an energy attenuator composed of reflective optics was designed to eliminate the concern of spectrum modulation from measurements. A FROG trace recorded at LFEX shot with 161 J energy was reconstructed 100 times using an iterative phase-retrieval algorithm. Despite some differences in structure, the reconstructed spectrum agrees reasonably well with the spectrum obtained by a time-integrated spectrometer. This shows that the developed FROG system and the optical transport system can measure the instantaneous intensity and phase of a laser pulse without spectrum modulation.

频率分辨光学选通（FROG）是一种在相对论性激光与等离子体相互作用过程中测量临界密度表面快速运动的新颖方法。在此，我们介绍了一种新的单次FROG系统和光学传输系统的设计和演示结果，这些系统用于表征大阪大学激光工程学院的LFEX（快速点火实验激光）激光设备的瞬时强度和相位。在LFEX，由于两个独特的特性，即离轴抛物面镜的F数大和相互作用室的半径小，真空窗口处的激光强度本质上很高。因此，为了获得准确的FROG迹线，必须注意由于自相位调制引起的频谱调制。实验研究了适合FROG操作的激光强度，设计了带有能量衰减器的光学传输系统，该能量衰减器由反射光学器件组成，以消除测量中对光谱调制的关注。使用迭代相位检索算法，将LFEX拍摄的161J能量记录的FROG迹线重建了100次。尽管结构有所不同，但重建光谱与时间积分光谱仪获得的光谱相当吻合。这表明，开发的FROG系统和光学传输系统无需光谱调制即可测量激光脉冲的瞬时强度和相位。设计了一个带有由反射光学器件组成的能量衰减器的光传输系统，以消除测量中对光谱调制的担忧。使用迭代相位检索算法，将LFEX拍摄的161J能量记录的FROG迹线重建了100次。尽管结构有所不同，但重建的光谱与时间积分光谱仪获得的光谱相当吻合。这表明，开发的FROG系统和光学传输系统无需光谱调制即可测量激光脉冲的瞬时强度和相位。设计了一个带有由反射光学器件组成的能量衰减器的光传输系统，以消除测量中对光谱调制的担忧。使用迭代相位检索算法，将LFEX拍摄的161J能量记录的FROG迹线重建了100次。尽管结构有所不同，但重建的光谱与时间积分光谱仪获得的光谱相当吻合。这表明，开发的FROG系统和光学传输系统无需光谱调制即可测量激光脉冲的瞬时强度和相位。重建后的光谱与时间积分光谱仪获得的光谱相当吻合。这表明，开发的FROG系统和光学传输系统无需光谱调制即可测量激光脉冲的瞬时强度和相位。重建后的光谱与时间积分光谱仪获得的光谱相当吻合。这表明，开发的FROG系统和光学传输系统无需光谱调制即可测量激光脉冲的瞬时强度和相位。