Understanding the role of sea spray aerosol (SSA) on climate and the environment is of great interest due to their high number concentration throughout the Earth's atmosphere. Despite being of fundamental importance, direct surface tension measurements of SSA relevant sub-micrometer particles are rare, largely due to their extremely small volumes. Herein, atomic force microscopy (AFM) is used to directly measure the surface tension of individual sub-micrometer SSA particle mimics at ambient temperature and varying relative humidity (RH). Specifically, we probed both atmospherically relevant and fundamentally important model systems including electrolyte salts, dicarboxylic acids, and saccharides as single components and mixtures. Our results show that the single particle surface tension depends on RH or solute mole percentage and chemical composition. Moreover, for liquid droplets at and below 100 Pa s in viscosity, or at corresponding RH, we show good agreement between the AFM single particle and the bulk solution surface tension measurements at overlapping concentration ranges. Thus, direct surface tension measurements of individual particles using AFM is shown over a wide range of chemical systems as a function of RH, solute mole percentage, and viscosity than previously reported.

Despite being identified 4 decades ago as a potentially powerful organic material for intense terahertz (THz) generation, 2-amino-5-nitrotoluene (MNA) has not been extensively used as a THz source because of challenges associated with synthesizing large single crystals of the material. We report a consistent two-step process for growing large single crystals of MNA that are suitable for high intensity terahertz (THz) generation via optical rectification of IR light. Our process includes initial sublimation growth of thin sheets or needles of MNA, followed by solution phase slow evaporation growth using the sublimated crystals as seeds. To demonstrate the usefulness of MNA as a nonlinear optical crystal, we characterize the THz generation properties of MNA and compare these results to state-of-the-art organic THz generators such as OH-1, 4-N,N-dimethylamino-4′-N′-methylstilbazolium 4-methylbenzenesulfonate (DAST), and N-benzyl-2-methyl-4-nitroaniline (BNA). We further determine the dependence of THz intensity on crystal thickness and pump wavelength, determine the THz efficiency at different pump powers, and report the THz refractive index and absorption coefficient. These results demonstrate that high-quality MNA crystals provide a useful source for high intensity THz generation.

Using 2D THz spectroscopy, we explore nonlinear energy transfer in CdWO4. Fitting power dependent THz measurements with a complex model allows us to determine nonlinear photonic and phononic parameters, and we compare with first-principles calculations.

We have improved the THz output and damage threshold of yellow organic THz generation crystals by fusing them to sapphire and using liquid crystals as index matching fluid to reduce reflective losses.

Using 2D THz spectroscopy, we quantify vibrational nonlinear energy transfer in CdWO4 by determining parameters for electronic Raman scattering and anharmonic coupling.