Femtosecond Optical Nonlinearities Of Several Kinds Of Nonlinear Materials Such As Carbon Disulfide

With the development of laser technique, the ultrashort laser pulses are used in many fields. In the field of nonlinear optics, ultrashort pulses are used to investigate the nonlinear optical properties of many materials with their high peak intensity and good time resolved ability. The three typical materials of simple liquids, phthalocyanine and semiconductor have potential value in the respect of optical nonlinear application and investigation. The micromechanism of ineraction of ultrashort pulses with sample liquids can be analyzed by the investigation of response of simple liquid under the action of untrashort pulses. The electric movement, the intra-molecule movement and the inter-molecule movement can be explored in simple liquid. The investigation of nonlinear optical properties of phthalocyanine and semiconductor are helpful for guiding the synthesis of phthalocyanine and the application of semiconductor. In the paper, the nonlinear optical properties of CS₂, DMSO, phthalocyanine ZnPc(OBu)₆(NCS), and ZnSe crystal are investigated by Z-scan, optical Kerr effect and pump-probe technique with 130 fs pulses. The experimental results are anslysised and explained. The following are innovative results obtained by us.The nonlinear optical effects of CS₂ come from the third order nonlinear effect under low incident intensity. The third order and fifth order effects are appeared simultaneously when the incident intensity is larger than some threshold value. We get the third order nonlinear refraction index, the fifth order nonlinear refraction index and the threshold value for emergence of fifth order nonlinear effects. The nonlinear abosorption of CS₂ is the three photon absorption at 800 nm wavelength. The three photon absorption coefficient is obtained by theoretical fitting the experimental results. The responses of CS₂, under the action of ultrashort pulses, include the fast decay component with lifetime of 160 fs and the slow decay component with lifetime of 1.6 ps. At 400 nm wavelength, the nonlinear absorption of CS₂ includes the two photon absorption and the excited state absorption induced by two photon absorption. The two photon absorption coefficient, the excited absorption cross section and the lifetime of excited state of CS₂ are obtained. The nonlinear response of DMSO is instantaneous under the action of 130 fs pulses, which comes from the electric movement. The responses of intra-molecule and inter-molecule movement can be neglected. The measured third-order nonlinear susceptibility of DMSO is about one-quarter of that of CS₂ with the CS₂ as reference by optical kerr effect experiment. The nonlinear susceptibility of DMSO comes from the nonlinear refraction, namely the real part of third order susceptibility. Based on the instantaneous response of DMSO, DMSO can be used as nonlinear media for measurement of ultrashort pulse with optical kerr effect technique. The measured pulse width with DMSO as nonlinear media is accurate, which is certified by single shot autocorrelator and spectrum analyse. The advangtages of using DMSO as nonlinear media are that DMSO can be used in a wide spectrum, and the little broaden of pulse when the pulse propagation of pulse in the media.Under the action of ultrashort pulses, the phthalocyanine ZnPc(OBu)₆(NCS) display the saturated absorption effect and the self-focusing effect. The responses of ZnPc(OBu)₆(NCS) include three parts: the instantaneous response of electric, the fast decay component and the slow decay component. By the pump probe experiment and the three-energy level analysis, we confirm that the fast decay component come from the contribution of population stayed on high excited state, which lifetime is 850 fs. The slow decay component come from the contribution of population stayed on low excited state, which lifetime is sevel picosecond. The second hyperpolarizability of ZnPc(OBu)₆(NCS) is larger three order than that of C60.The ZnSe crystal show self-focusing effect from the bound electron under the action of 130 fs pulse at 800 nm wave length. The nonlinear absorption of ZnSe are the two photon absorption of bound electron in value band and the signle photon absorption induced by the two photon absorption. The electron stayed on the low energy state excited by two photon absorption will absorp a single photon to be excited to the high energy state. But, the single photon absorption of bound electron stayed on the low energy state is less than that of two photo absorpin. The lifetime of electron stayed on low energy state in conduction band is 250 fs measured by pump probe experiment. The Z-scan experiment can not detect the absorption and refraction of carrier because the 250 fs lifetime is longer than pulse duration.