Hongzhen Wang

Nonlinear properties of unfilled d shell metal porphyrins of 5,10,15,20-tetraphenyl-21H, 23H-porphine cobalt(II) et 5,10,15,20-tetrakis(4-methoxyphenyl)-21H, 23H-porphine cobalt(II) using D4 σ-Z-scan

We study the nonlinear (NL) absorption and refraction of 5,10,15,20-tetraphenyl-21H, 23H-porphin cobalt(II) (CoTPP) and 5,10,15,20-tetrakis(4-methoxyphenyl)-21H, 23H-porphin cobalt(II) (MCoTPP). The measurements were carried out in solutions prepared with chlorobenzene applying the D4σ-Z-scan technique with a laser delivering single pulses in the picosecond regime at 532nm. For each compounds, the NL coefficients were measured for three concentrations. The results show that these materials with unfilled d shell exhibit a saturable absorption (SA), where they have been compared to the basic structure tetraphenylporphyrin (TPP) and zinc tetraphenylporphyrin (ZnTPP) with filled d shell metal in order to see the influence of the central metal ion on the NL absorption (NLA) behavior.

Dark-field Z-scan technique with highly nonlinear absorbing materials: Application to porphyrins

The newly introduced imaging Dark-field Z-scan (DFZ-scan) technique is applied here to demonstrate its ability to measure the optical third-order nonlinear (NL) index coefficient in the presence of nonlinear absorption (NLA). We present our experimental results for two compounds of Porphyrin molecules, known to have relatively high NLA in the picosecond regime, at 532nm, allowing to test both cases of positive and negative nonlinear refraction (NLR). Moreover, we show that, it is possible to increase the sensitivity of the method by introducing a circular aperture in the image plane. Also, limitations are discussed to process optically a pure NL refractive signal, not subject to the influence of the NLA one, at the output of the imaging setup.

Picosecond cubic and quintic nonlinearity of lithium niobate at 532 nm

The nonlinear (NL) optical response of bulk lithium niobate (LiNbO3) was investigated at 532 nm using the second harmonic of a Nd:YAG laser delivering pulses of 12 ps. The experiments were performed using the D4σ method combined with the conventional Z-scan technique. Two- and three-photon absorption coefficients equal to 0.27 cm/GW and 2.5×10−26 m3/W2, respectively, were determined. The NL absorption processes were due to transitions from the valence to the conduction band and to free-carrier absorption. The third- and fifth-order NL refractive indices were n2=(2.5±0.6)×10−19 m2/W and n4<5.5×10−36 m4/W2. The present results give the support for previous experiments that indicate possible fifth-order processes in bulk samples and channel waveguides fabricated with LiNbO3.

Nonlinear properties of unfilled d shell metal porphyrins using the beam waist relative variation method

We study the nonlinear absorption and refraction of 5,10,15,20-tetraphenyl-21H,23H-porphin cobalt(II) (CoTPP) and 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphin cobalt(II) (MCoTPP). The measurements were carried out in solutions prepared in chlorobenzene applying the D4σ-Z-scan technique with a laser delivering single pulses in the picosecond regime at 532 nm. For each compounds, the NL coefficients were measured for three concentrations. The results show that these materials with unfilled d shell exhibit a saturable absorption (SA), where they have been compared to the basic structure tetraphenylporphyrin TPP and zinc tetraphenylporphyrin ZnTPP with filled d shell metal in order to see the influence of the central metal ion on the nonlinear absorption behavior.

Dark-field Z-scan imaging technique and application to optical nonlinear refraction measurement

We introduce an imaging technique based on a combination of Dark-field microscopy and Z-scan techniques (called Dark-field Z-scan) in order to characterize optical third-order refractive nonlinearity. The overall proprieties of this new method is presented. In particular, we show that it is possible to determine the magnitude and the sign of the induced nonlinear phase shift. Application to two porphyrin compounds showing both negative and positive NL refractive indices is performed. Advantages and inconveniences of this technique are discussed.