Optical limiting properties of surface functionalized nanodiamonds probed by the Z-scan method

Abstract

This work focuses on the optical limiting behavior of surface modified nanodiamonds (DNDs) namely, amino-terminated DNDs (DND-NH2) and hydrogen-terminated DNDs (DND-H). Their relevant nonlinear optical properties for optical limiting are compared to those of unfunctionalized DNDs. The optical limitation is characterized by means of nonlinear transmittance, Z-scan, and scattered intensity assessments when submitted to a nanosecond pulsed Nd:YAG laser operating at a wavelength of 532 nm. It is stated that the largest nonlinear attenuation is attributed to the DND-H system, whereas the exceedingly low threshold values for optical limiting for the DND-H and the DND-NH2 systems is attributed to their negative electron affinity character (NEA). Using Z-scan experiments, it is shown that nonlinear refraction combined with a significant nonlinear absorption predominates in the DND-H suspension, while the pure thermal origin of the nonlinear refractive index change is conjectured in the case of the DNDs. Besides, an amazing valley to peak profile was measured on DND - NH2indicating an unexpected positive sign of the nonlinear refraction coefficient. In addition, a stronger backscattered intensity signal is highlighted for the unfunctionalized DNDs through nonlinear scattering measurements.

Figure 1

Linear transmittance spectra of the DND, DND-H and DND-NH2 suspensions in water.

Figure 2

Experimental setup used to study the optical limiting behavior. A1 and A2, apertures (12 mm and 20 mm, respectively); BS, beam splitter;ND1 and ND2, neutral density filters; L1, L2 and L3, plano-convex lenses (focal lengths 60 mm, 100 mm and 400 mm, respectively); PD, photodiode.

Figure 3

Experimental setup used to study the polar scattering properties. B/S, beam splitter; L₁, negative focal lens, f₁ = 60 mm; L₂, positive focal lens, f₂ = 375 mm; L₃, plano-convex lens, f₃ = 200 mm.

Figure 4

Z-scan optical setup. L4, plano-convex lens, f₄ = 200 mm; NDF, neutral density filters; aperture hole, 600 µm.

Figure 5

Normalized transmittance as a function of the input energy and input fluence in a log-log scale. DND, DND-H and DND-NH2 suspensions in water at λ = 532 nm are represented.

Figure 6

Close Z-scan signatures of the DND, DND-H and DND-NH2 at an incident laser fluence of F = 40 J/cm² (I₀ = 10¹⁰ W/cm²) for the former suspension and F = 4 J/cm² (I₀ = 10⁹ W/cm²) for both latter. The solid lines denote the theoretical fits of equation (8).

Figure 7

Normalized transmittances in the open Z-scan configuration for the DND suspension at an incident laser fluence of F = 40 J/cm² (I₀ = 10¹⁰ W/cm²), and for the DND-H and DND-NH2 suspensions at F = 4 J/cm² (I₀ = 10⁹ W/cm²). The solid lines denote the theoretical fits of equation (11).

Figure 8

Semilog plot of the angular distribution of the scattered intensity for the DND, DND-H and DND-NH2 suspensions at F = 40 J/cm². The laser radiation is incident from the bottom to the top.

Figure 9

Output energy as a function of the input energy and input fluence in a log-log scale. DND, DND-H and DND-NH2 suspensions in water at λ = 532 nm are represented.