Cobalt enhanced nonlinear optical properties and optical limiting of zinc oxide irradiated by femtosecond laser pulses
Abdullah Shehata, Wael Z. Tawfik, Tarek Mohamed
Abstract
In this paper the nonlinear optical properties of Co-doped ZnO and pure ZnO thin films were measured. The films were irradiated with 100 femtosecond laser pulses at 950 nm and at different input intensities ranging from 9 to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>14</mml:mn> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">G</mml:mi> <mml:mi mathvariant="normal">W</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> . We observed that two-photon absorption induced a reverse saturable absorption and saturable absorption in Co-doped ZnO, while the three-photon absorption was observed to induce saturable absorption in pure ZnO. The nonlinear absorption coefficient <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>β</mml:mi> </mml:math> and nonlinear refractive index <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi>n</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> of Co-doped ZnO were found to be intensity dependent. An enhancement of 100 times in the nonlinear refractive index was observed for the Co-doped ZnO thin films compared to pure ZnO thin films. This reveal a strong optical limiting behavior for the Co-doped ZnO in comparison to pure ZnO thin films.