Nonlinear characterization of materials using the D4σ method inside a Z-scan 4f-system

Abstract

We show that direct measurement of the beam radius in Z-scan experiments using a CCD camera at the output of a 4f-imaging system allows higher sensitivity and better accuracy than Baryscan. One of the advantages is to be insensitive to pointing instability of pulsed lasers because no hard (physical) aperture is employed as in the usual Z-scan. In addition, the numerical calculations involved here and the measurement of the beam radius are simplified since we do not measure the transmittance through an aperture and it is not subject to mathematical artifacts related to a normalization process, especially when the diffracted light intensity is very low.

Filamentation of light in carbon disulfide

“…The same point is also the front focal point of L 4 , which performs the Fourier transform into the camera. A recent improvement of the technique allows us to avoid the division of the two normalized Z-scan transmittances (closed and open aperture ones) by recording the beam waist relative variations according to the second-order momentum (the D4σ method) [21]. We measure the effective third-order refraction index n 2,eff using the D4σ method, with increasing intensity, for two wavelengths λ = 532 and 1064 nm (see Fig.…”

Fifth-order nonlinear susceptibility: Effect of third-order resonances in a classical theory

“…(99) again, a natural quintic term is compared to a cascaded cubic term. In CS 2 at the wavelength λ = 532 nm, values of the nonlinear indices measured using the D4σ -Z-scan method [22] are n 2 = (1.5 ± 0.3) × 10 −18 m 2 /W; n 4 = (1.2 ± 0.3) × 10 −32 m 4 /W 2 [13], while the linear index is n 0 = 1.64. Hence 9/(8n 3 0 )(χ (3) ) 2 = 5.2 × 10 −41 m 4 /V 4 , while (2n 0 ε 0 c) 2 n 4 = 9.1 × 10 −37 m 4 /V 4 : the χ (5) term greatly dominates the (χ (3) ) 2 term.…”

Saturation of the Kerr effect in carbon disulfide

“…This closeness to resonance increases the fifth order optical susceptibility, ( ) 5 χ ∝ γ . We used the recent D4σ-4f-Z-scan method [9], together with the numerical inversion related to the analytic solution of (1) and (2) (see [8] for details). The change in transmittance of the material is observed via a cooled CCD camera (−30 • C).…”