Carbon disulfide is the most popular material for applications of nonlinear optical (NLO) liquids, and is frequently used as a reference standard for NLO measurements. Although it has been the subject of many investigations, determination of the third-order optical nonlinearity of CS 2 has been incomplete. This is in part because of several strong mechanisms for nonlinear refraction (NLR), leading to a complex pulse width dependence. We expand upon the recently developed beam deflection technique, which we apply, along with degenerate four-wave mixing and Z-scan, to quantitatively characterize (in detail) the NLO response of CS 2 , over a broad temporal range, spanning 6 orders of magnitude (∼32 fs to 17 ns). The third-order response function, consisting of both nearly instantaneous bound-electronic and noninstantaneous nuclear contributions, along with the polarization and wavelength dependence from 390 to 1550 nm, is extracted from these measurements. This paper provides a self-consistent, quantitative picture of the third-order NLO response of liquid CS 2 , establishing it as an accurate reference material over this broad temporal and spectral range. These results allow prediction of the outcome of any NLR experiment on CS 2 .

We modify the well-known photothermal beam deflection technique to study ultrafast nonlinearities. Using phase-sensitive detection we directly measure the temporal and polarization dynamics of nonlinear refraction (NLR) with sensitivity to optically induced phase changes of approximately λ/20,000. We use the relative polarization dependence of excitation and probe to separate the isotropic and reorientational components of the NLR.

We present a technique in which small solute nonlinearities may be extracted from large solvent signals by performing simultaneous Z-scans on two samples (solvent and solution). By using a dual-arm Z-scan apparatus with identical arms, fitting error in determining the solute nonlinearity is reduced because the irradiance fluctuations are correlated for both the solvent and solution measurements. To verify the sensitivity of this technique, the dispersion of nonlinear refraction of a squaraine molecule is measured. Utilizing this technique allows for the effects of the solvent n 2 to be effectively eliminated, thus overcoming a longstanding problem in nonlinear optical characterization of organic dyes.

Printing of high‐resolution three‐dimensional nanostructures utilizing two‐photon polymerization has gained significant attention recently. In particular, isopropyl thioxanthone (ITX) has been implemented as a photoinitiator due to its capability of initiating and depleting polymerization on demand, but new photoinitiating materials are still needed in order to reduce the power requirements for the high‐throughput creation of 3D structures. To address this point, a suite of new thioxanthone‐based photoinitiators were synthesized and characterized. Then two‐photon polymerization was performed using the most promising photoinitiating molecule. Importantly, one of the initiators, 2,7‐bis[(4‐(dimethylamino)phenyl ethynyl)‐9H‐thioxanthen‐9‐one] (BDAPT), showed a fivefold improvement in the writing threshold over the commonly used ITX molecule. To elucidate the fundamental mechanism, the excitation and inhibition behavior of the BDAPT molecule were evaluated using density functional theory (DFT) calculations, low‐temperature phosphorescence spectroscopy, ultra‐fast transient absorption spectroscopy, and the two‐photon Z‐scan spectroscopic technique. The improved polymerization threshold of this new photoinitiator presents a clear pathway for the modification of photoinitiators in 3D nanoprinting. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1462–1475