Background With the continuous advancement of photoelectric applications such as LiDAR, three-dimensional sensing, and free-space communication towards longer distances, larger fields of view, and higher precision, large-spot, nanosecond-pulse lasers are progressively emerging as a critical type of light source, owing to their advantages in far-field uniform illumination and weak signal detection.

Purpose To address the challenges of amplitude distortion and sampling difficulties in beam quality measurements of large-spot, nanosecond-pulse lasers caused by optical path shaping distortions, transient capture limitations, and coherence requirements, this paper proposes a beam quality measurement system tailored for nanosecond pulsed large-aperture lasers.

Methods The system employs a three-dimensional stepping platform combined with a photodetector to reconstruct the spatial intensity distribution of the beam, and incorporates a multi-channel peak-hold circuit to accurately latch pulse peaks, thereby ensuring transient fidelity in amplitude acquisition. To mitigate non-ideal conditions such as partial beam truncation and incomplete boundaries, a circle-fitting method is introduced as a complement to the second-moment calculation of energy, enhancing the robustness of beam size evaluation.

Results Experiments employing a typical vertical-cavity surface-emitting laser (VCSEL) were conducted through multi-position 3D axial scanning, comparing the consistency of beam size and energy distribution measured by different methods.

Conclusions  The results verify the measurement reliability and applicability of the proposed system under large-spot, nanosecond-pulse conditions, offering an effective means for laser beam quality assessment in related applications.