UC Berkeley

This thesis will detail four projects aimed at understanding and applying the principles of optics and optoelectronics.

In Chapter 1, we describe phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS), a nonlinear optical technique that can probe the molecular structure of the top few monolayers of a liquid-vapor interface. We use this technique to investigate the air-water interface, using a number of water samples with different dissolved salts. The information is used to draw inferences about the surface propensity of these salt ions—information that can shed light on both atmospheric chemistry and water solvation theory. We also give a detailed description of the experimental methodology for PS-SFVS, its rationale, and the issues that can arise.

PS-SFVS measurements, such as those described in Chapter 1, can be fruitfully used by comparing them with the signal predicted by molecular simulation. However, the relationship between a molecular configuration and its nonlinear optical signal is not thoroughly understood in the theoretical chemistry community. In particular, the procedures used in the literature to predict an PS-SFVS signal within a molecular simulation have been ambiguous, depending on arbitrary parameters. In Chapter 2, we review PS-SFVS theory at a fundamental level, then map it to modern simulation methods, thereby explaining the ambiguities as consequences of improper truncation of a multipole expansion. A molecular-dynamics simulation of the water-air interface is used as an example, illustrating the consequences of different simulation methods and suggesting which ones should be most accurate.

Chapter 3 explores a different aspect of nonlinear optics: The compression and characterization of ultrafast pulses of light. These pulses have been explored for a variety of scientific and technological applications. Ideally, an optical pulse can be reduced in duration up to the limit imposed by its spectral bandwidth via the uncertainty principle. However, the presence of "nonlinear chirp" (different frequencies arriving at different times in a nonlinear fashion), which is especially common in mode-locked fiber lasers, can be a major factor preventing the shortening of a pulse. We describe a new technology, a type of patterned glass phase plate, that promises to reduce nonlinear chirp in a convenient, adjustable, inexpensive, and high-throughput manner. After showing simulations, we describe how we made the plate, and then how we used frequency-resolved optical gating (FROG) to watch the plate change the duration and shape of a pulse from a fiber laser.

Finally, Chapter 4 discusses a new architecture for solar cells that uses the field effect, rather than the traditional p-n junction, to separate charge. This could be advantageous for semiconductor materials that are difficult to dope to both p- and n-type, such as oxides, sulfides, and nanoparticles. We discuss the underlying physics and rule-of-thumb design principles, along with both finite element simulations and experimental verifications.