Study On Nonlinear Absorption Characteristics Of Low-Dimensional Nanomaterials By Z-Scan

The development of nanotechnology has provided new impetus for the advancement of laser technology.Many new nanomaterials with nonlinear optical effects are emerging.These new nanomaterials have potential applications in many fields.such as optical devices,optical modulators,optional switches and some other electronic functional devices.In terms of optical properties,the non-selective absorption characteristics of nanomaterials make it a popular choice for laser saturable absorbers.In this paper,we study two typical new low-dimensional nanomaterial single-walled carbon nanotubes and CdSe/ZnS quantum dots.We have experimentally analyzed the nonlinear absorption properties of these two materials.For single-walled carbon nanotubes(SWCNTs).It was treated with SDS and a new nonionic surfactant DDA,respectively,to obtain common SWCNTs solution and semiconducting SWCNTs(s-SWCNTs)solution,and to perform Raman spectroscopy on the two solutions.The absorption spectra were studied and the nonlinear absorption characteristics of the two solutions were compared by Z-scan technique.For CdSe/ZnS quantum dots,we prepared a polymer of CdSe/ZnS quantum dots and PMMA,then transferred the polymer onto a glass substrate,and dried it to obtain a CdSe/ZnS quantum dot film,which was studied by Z-scan.It saturates the absorption performance and uses it as a saturable absorber in an all-solid-state 1 micron laser,achieving stable operation of the pulsed laser.(a)We briefly analyzed the application prospects of SWCNTs and introduced the preparation methods of SWCNTs and the purification principle of s-SWCNTs.The pure s-SWCNTs solution was obtained by adding DDA.We obtained the saturated light intensity and TPA coefficient of two solutions by Z-scan technique.Among them,the saturated light intensity of s-SWCNTs solution is 0.213GW/cm2,the TPA coefficient is 0.29cm/GW,the saturated light intensity of common SWCNTs is 0.295GW/cm,and the TPA coefficient is 0.52cm/GW.In addition,the unsaturated loss and modulation depth of s-SWCNTs solution were determined by experiments to be 14%and 8.6%.The unsaturated loss and modulation depth of common SWCNTs were 12%and 5.2%.The results show that s-SWCNTs have lower saturation intensity and larger modulation depth.As a saturated absorber,s-SWCNTs will be more conducive to the generation of ultrashort pulses.(b)We introduce the application prospects of CdSe/ZnS quantum dots.We prepared CdSe/ZnS quantum dot films and characterized the microstructure and optical properties of CdSe/ZnS quantum dots.The nonlinear absorption characteristics of CdSe/ZnS quantum dots were studied by Z-scan technique.The results show that CdSe/ZnS quantum dots It has strong saturable absorption characteristics in the 1 micron band.We used a thin film as a saturable absorber to achieve a passive Q-switching of an all-solid-state Nd:GdV04 laser,and obtained a pulse sequence with a shortest pulse width of 233 ns and a repetition rate of 556.2 kHz.The experimental results confirmed the potential of CdSe/ZnS quantum dots as saturable absorbers.