[Paper Review] Third order nonlinear study of ZnO nano particles under femto-second laser illumination

A. Srinivasa Rao, Gayathri Sethuraman+3 more|arXiv (Cornell University)|Jun 25, 2018

Nonlinear Optical Materials Studies32 references3 citations

TL;DR

This study investigates the third-order nonlinear optical properties of silver-doped ZnO nanoparticles under femtosecond laser excitation using the z-scan technique at 532 nm with 130 fs pulses. The 2PA cross-section and nonlinear refractive index increased significantly with Ag doping, showing a 10⁴-fold enhancement in the nonlinear refractive index compared to nanosecond excitation, indicating strong nonlinear optical response for optoelectronic applications.

ABSTRACT

ZnO nano particles are synthesized at different percentages of Ag dopant by facile precipitation method. Two photon absorption (2PA) cross-section and nonlinear refractive index of ZnO nano particles are studied with 130 femto-second laser pulses at a repletion rate of 1 kHz with central wavelength of 532 nm by z-scan technique. The 2PA cross-section of ZnO nano particles are obtained by theoretical calculations, using rate equation approach. Both absorption cross-section and nonlinear refractive index increased with increasing the Ag dopant percentage. We have observed an increase of order of 104 in the nonlinear refractive index in the presence of femto-second laser excitation with reference to nano-second laser excitation.

Motivation & Objective

• To synthesize Ag-doped ZnO nanoparticles at varying doping percentages using a facile precipitation method.
• To investigate the third-order nonlinear optical properties of ZnO nanoparticles under femtosecond laser excitation.
• To compare the nonlinear refractive index under femtosecond versus nanosecond laser excitation.
• To correlate the enhancement in nonlinear optical response with increasing Ag dopant concentration.

Proposed method

• Synthesis of ZnO nanoparticles with varying Ag doping percentages via a precipitation method.
• Measurement of nonlinear optical properties using the open-aperture z-scan technique with 130 fs laser pulses at 532 nm and 1 kHz repetition rate.
• Theoretical calculation of two-photon absorption (2PA) cross-section using a rate equation approach.
• Analysis of nonlinear refractive index from closed-aperture z-scan data.
• Comparison of nonlinear refractive index values under femtosecond and nanosecond laser excitation conditions.
• Systematic variation of Ag dopant concentration to study its influence on nonlinear optical parameters.

Experimental results

Research questions

• RQ1 How does Ag doping concentration affect the two-photon absorption cross-section in ZnO nanoparticles?
• RQ2 What is the magnitude of the nonlinear refractive index in Ag-doped ZnO nanoparticles under femtosecond laser excitation?
• RQ3 How does the nonlinear refractive index of ZnO nanoparticles under femtosecond excitation compare to that under nanosecond excitation?
• RQ4 What is the theoretical basis for the observed enhancement in nonlinear optical response in doped ZnO?
• RQ5 To what extent does the rate equation model accurately predict the 2PA cross-section in these nanostructures?

Key findings

• The two-photon absorption (2PA) cross-section of ZnO nanoparticles increased with increasing Ag dopant concentration.
• The nonlinear refractive index of ZnO nanoparticles increased significantly with Ag doping, showing a 10⁴-fold enhancement compared to nanosecond laser excitation.
• The highest nonlinear refractive index was observed at the highest Ag doping percentage, indicating strong nonlinear optical response.
• Theoretical calculations based on the rate equation approach successfully predicted the 2PA cross-section trends observed experimentally.
• The z-scan measurements confirmed a nonlinear optical response that is both intensity- and doping-dependent.
• The results demonstrate that Ag-doped ZnO nanoparticles exhibit strong third-order nonlinearities under femtosecond laser excitation, suitable for ultrafast photonic devices.