Fig. 1. Optical path of beam quality factor M2 measurement system based on far-field coaxial holography

Fig. 2. Calculation process of beam quality factor M2

Fig. 3. Experimental setup of far-field coaxial holography

Fig. 4. Interferograms and recovered complex amplitude. (a) Single-shot interferograms taken by polarization camera; (b) recovered intensity; (c) recovered phase; (d) phase distribution at rear surface of lens L₂

Fig. 5. Curve fitting and calculation results of factor M2

Fig. 6. Time characteristic of beam quality measurement process varying with image size

Fig. 7. Experimental setup for precision verification

Fig. 8. Measurement results of factor M2for three different testing fibers