This dissertation reports a series of experiments directed towards nonlinear material characterization. A series of organic molecules, semiconductors, liquid crystals and inorganic clusters are investigated with Z-Scan and excite-probe measurements in order to determine the magnitude and dynamics of their nonlinear absorption and refraction. Much of this work is motivated by our search for a better optical limiter. The nonlinear absorption mechanism leading to optical limiting is investigated and its physical parameters are determined. The reverse saturable absorption (RSA) spectrum of several organic dyes is obtained in the visible in a single measurement by using an ultrafast nonlinear spectrometer. This system is based on a pump-probe experiment using an ultrashort continuum white-light pulse as probe. The continuum pulses are obtained by focusing millijoule 150 fs pulses at 850 nm into a water cell. The 850 nm wavelength pulses are produced from a Ti:Sapphire oscillator amplified by a Cr+3:LiSAF based regenerative amplifier. By varying the time-delay between the pump and the continuum probe, we have obtained the time evolution of the nonlinear spectra. Purely refractive two-beam coupling is demonstrated in transparent Kerr liquids using frequency chirped picosecond pulses with different polarization combinations. Theoretical modeling and experimental results are consistent with energy transfer from transient refractive gratings that are due to stimulated Rayleigh-wing scattering. The signals measured are sensitive to response times considerably shorter than the pulse width. Using a lock-in amplifier detection technique which enables us to measure normalized changes in probe beam energy as low as 10-5 with 100 fs pulses, we demonstrate the possibility of measuring sub-femtosecond Debye-type relaxation times for the nonlinear refractive index. Far away from the Raman resonance we can obtain a Debye-type relaxation equation which, when applied to the two-beam coupling theory yields sub-femtosecond quasiresponse times. The signals obtained in dielectrics such as Si 0 2 and PbF2 are, however, consistent with the Raman gain because the frequency difference between the pump and probe beams in these particular experiments is large enough to excite vibrational motion of the nuclei. We use the two-beam coupling signal to obtain the low frequency Raman spectrum for SiO2 and PbF2 for detunings from 0 up to 10 THz (approximately 300 cm-1). We also demonstrate that, by knowing the response time in the case of a Debye relaxation process or the low frequency Raman gain spectrum in the case of a nuclear nonlinearity, we can determine the chirp of the laser pulses.
Doctor of Philosophy (Ph.D.)
College of Arts and Sciences
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Masters Thesis (Open Access)
Arts and Sciences -- Dissertations, Academic; Dissertations, Academic -- Arts and Sciences
Dogariu, Arthur, "Spectral and temporal response of optical nonlinearities" (1997). Retrospective Theses and Dissertations. 2646.