Fig. 1. Schematic of the far-field external cavity feedback influence on an LD: (a) detailed external feedback structure, (b) effective internal LD structure.

Fig. 2. Relationship among P2, Reff, and R3 at different R2 values: (a) dependence of Reff on R3, (b) dependence of P2 on R3.

Fig. 3. Geometric simplification of laser beam propagation at different sample positions: (a) before the focal plane, (b) on the focal plane, (c) after the focal plane.

Fig. 4. Normalized reflected light power Preflect using geometrical and Gaussian optics.

Fig. 5. Scheme of the z-scan equipment and its improvement.

Fig. 6. Relationship among LD output power, Pnoise, and sample position z: (a) normalized Pnoise in z scan, (b) dependence of Pnoise on LD power.

Fig. 7. Detailed illustration of the effective LD output with an attenuator.

Fig. 8. Relationship of Reff2 and P2 with different attenuations in z scan when R2=0.3: (a) dependence of Reff2 on R3, (b) dependence of P2 on the z position.

Fig. 9. Comparison of feedback influence with different attenuation values.

Fig. 10. Reduction of feedback light influence on open-aperture z-scan measurement: (a) z-scan experimental setup, (b) transmittance with and without an opto-isolator unit, (c) Tz-scan/Pnoise with and without an opto-isolator unit.

Fig. 11. Reduction of feedback light influence on closed-aperture z-scan measurement: (a) transmittance with and without an opto-isolator unit, (b) Tz-scan/Pnoise with and without an opto-isolator unit.