The Research Of Spatial Light Modulation Based On Nonlinear Optics

In recent years,with the wider developments of laser machining,laser alignment,optical micromanipulation,atomic optics and optical microscopic imaging,non-diffraction beam has been widely used in those application based on its special light field distribution and propagation characteristics.Therefore,how to get an excellent non-diffraction beam easily has become an important research topic in the applications of non-diffraction beam.In this dissertation,we achieve spatial light modulation based nonlinear optical methods.The main efforts and innovations are follow:Firstly,we studied the optical limiting by using SPM pattern based on kerr effect in hot Rb atomic sample.It is found in the research that the far-field diffraction pattern can be affect by laser power,sample concentration and the sample position.However,the performance of the optical limiter was only dependent on the sample position.Therefore,we studied the performance of the optical limiter regard to the sample position in detail,and we found the minimum values of limiting threshold and clamp output were obtained at the position at 10mm.In addition,we investigated the influence of the sample position on the diffraction rings pattern.The phenomenon was explained well by the theory of SPM and z-scan,which are caused by both Kerr effect and the thermal optical nonlinear effect.This work is useful in determining the optimal position of the sample in the optical limiting and other applications based on SPM such as all-optical switching,ultracold atoms trapping and the hollow laser beam generation.Secondly,we proposed a new method using XPM caused by Kerr effect to generate Bessel beams in a hot atomic Rb vapor cell.We compared the radial intensity distribution of the generated Bessel beam with the theoretical simulation.It is seen that the experimental result is in good agreement with the theory.Both the intensity distribution and ring spacing are close to the theoretical curve.In addition,we compared the generated Bessel beam by using SPM and XPM respectively,and we found the generated Bessel beam caused by XPM is better than the generated Bessel beam caused by SPM.The generated Bessel beam using XPM is even applicable to the probe beam of low power,having more practical value than the method using SPM which needs high input beam power.In addition,it is demonstrated that the Bessel beam cause by XPM exhibits self-healing and non-diffraction.The parameters of the Bessel-like beam are found to be easily adjusted by the pump beam power and sample temperature.This work offers a new idea for the generation of Bessel beam.Thirdly,we studied SPM caused by thermal optical nonlinear effect in the organic solution.We find the diffraction rings patterns only appear from alcohols?methanol,ethanol,propanol and butanol?,not from acetone.Then,we take ethanol as an example,and study the influence of the laser power,sample concentration and sample position on the far-filed diffraction pattern.In theory,we derive the expressions the nonlinear refractive index coefficient caused thermal optical nonlinear effectn₂^{t h} and additional phase shift.Then,we study the far-field distribution pattern based on the integral formula of Fresnel-Kirchhoff diffraction.Finally,the nonlinear refractive indexes are approximated by the number of the diffraction rings,which are further confirmedby the z-scan method[-?2.53?0.03??10^-8cm² W].The notable nonlinearity?8orders higher than Kerr effect?suggests that thermal nonlinear optical effect has potentials in optical light modulation.Fourthly,we studied the generation of a Bessel beam using XPM based on the thermal nonlinear optical effect both experimentally and theoretically.The thermal nonlinear medium is shown to have the ability to vary a Gaussian beam?probe beam?into a hollow beam when the medium is illuminated with a counter propagating Gaussian beam?pump beam?.It is demonstrated that this method has no restriction to the probe beam wavelength.Moreover,we obtained the Bessel beam in the focus region by focusing the generated hollow beam.The generated Bessel beam exhibits superior non-diffraction properties during propagation and self-healing after encountering an obstruction on the beam path.The parameters of the beam can be easily adjusted by both the pump beam power and the sample concentration.The merits of variable parameters,no requirement for input beam wavelengths,simple setup,and low-cost would make this method significant in a variety of applications,especially in those areas where the parameters of the Bessel beam need to be easily adjusted without changing the setup.In addition,this work provides a foundation for the next chapter.Fifthly,we used a Bessel beam as the probe beam and study the enhancement of DFWM in hot atomic Rb vapor.The Bessel beam is generated by focusing the hollow beam generated using XPM based on the thermal nonlinear optical effect.We took either the Bessel beam or the Gaussian beam as the probe beam and compared the DFWM signal under the two cases.The results show that the DFWM signal generated by the Bessel beam is about twice as large as that generated by the Gaussian beam,thanks to the extended depth of field and tight focusing properties of the Bessel beam.A DFWM signal can be detected with the Bessel beam when it encounters an obstruction.In contrast,no DFWM signal was detected using the Gaussian beam as the probe beam.This work suggests that DFWM using a Bessel beam would be of great potential in the fields of high-fidelity communication.The innovations in this dissertation is achieving spatial light modulation based nonlinear optical methods,obtaining non-diffraction Bessel beam.The generated Bessel beam exhibits superior non-diffraction properties during propagation and self-healing after encountering an obstruction on the beam path.In addition,the parameters of the generated Bessel beam can be easily adjusted by both the pump beam power and the sample concentration.The merits of variable parameters,no requirement for input beam wavelengths,simple setup,and low-cost would make this method significant in a variety of applications,especially in those areas where the parameters of the Bessel beam need to be easily adjusted without changing the setup.What's more,we achieve the enhancement of DFWM in hot atomic Rb vapor by using Bessel beam as the probe beam.It would also shed a light on those areas where the nonlinear processes are needed enhancing in some thick media and harsh environments.