Several Techniques For Measurement Of Optical Nonlinearities Based On The Phase-object

With the rapid development of the optical communication and optical information processing technology, nonlinear optical materials research has become increasingly important. Simple and reliable measurement technique is necessary for searching the expected NLO materials. So the nonlinear measurement technique has become the key point to investigate the nonlinear optical materials. In this dissertation, by using the phase object, several measurements for investigating the nonlinear optical properties (NLO) are presented, based on the traditional Z-scan technology and 4f coherent imaging system with a phase object (NIT-PO).PO Z-scan technology is presented by using a PO introduced into the traditional Z-scan system. The PO Z-scan trace for the pure third-order nonlinear refraction is a single peak shape for the positiveγand a single valley for the negativeγ.In the PO Z-scan technique, the nonlinear phase modulation due to the change of refractive index of the sample mostly results in the amplitude change inside the PO diffraction beam, which is directly related to the transmittance of the aperture. At the position which the nonlinear phase shift is most strong, the transmittance of the aperture reaches the maximum or minimum. At the both sides of this position, the nonlinear phase shift became small. So the trace of the PO Z-scan shows a single peak/valley for the Kerr nonlinearity. The PO Z-scan trace of the transient thermal effect shows a valley-peak shape which is very different from the single valley (peak) shape of the pure negative (positive) third-order nonlinearity. So the thermal lensing effect can be observed according to the trace of the PO Z-scan directly. The characterizations of nonlinear refraction composed of third-order nonlinear refraction and transient thermal effect in solution are studied by using Z-scan technique. The top-hat beam Z-scan has higher sensitivity than the Gaussian-beam Z scan by a factor of 3.5 times when the nonlinear phase-shift of the transient thermal effect is small.We present a very simple transmittance technique with a phase object (T-PO) to investigate optical nonlinearities of the materials. In this technique, the optical configuration is very easy and the material doesn't require to move, which allows us to investigate the detail of nonlinear refraction of the thick-sample more conveniently.A new time-resolved pump-probe system with phase object, which is based on the PO Z-scan technique and the standard pump-probe system, is presented. T-PO is a single shot real-time measure technique and the nonlinear optical coefficients can be obtained from a single data, so the PO pump-probe technique can simultaneously investigate the dynamic of nonlinear absorption and refraction conveniently.We convert the standard NIT-PO to the reflected NIT-PO to characterize the nonlinear optical properties in the film prepared on the opaque substrates.On the other hand, we introduce a simple variation of the NIT-PO technique that make an enhancement of the sensitivity compared to the conventional one. This modification involves replacing the CCD at the output plane in the standard NIT-PO with a mirror which can reflects the output plane beam into the 4f system again.