The study of femtosecond second harmonic generation in bulk crystals with large walkoff

Haifeng Wang, Purdue University

Abstract

Second harmonic generation (SHG) is a, simple and effective method to generate coherent light at short wavelengths (400nm and below). In bulk nonlinear crystals there are two kinds of SHG: type I and II. In type I SHG, the linearly-polarized fundamental field interacts with itself to generate the harmonic field. The conversion efficiency is well-known for CV plane-wave sources. But for focused and pulsed sources, the process is very complicated with the spatial walkoff and temporal walkoff between the fundamental and harmonic fields. With high conversion efficiency, the pump depletion makes it even more complicated. Here we describe a theory which for the first time predicts type I SHG efficiency with both walkoffs and pump depletion in an analytical form. We will compare the results of our theory with those of a numerical model and our experiments. The comparisons strongly support our theory. Our theory can effectively predict type I SHG efficiency and improve our understanding of the SHG process. In type II SHG, two fundamental fields with perpendicular polarizations interact with each other to generate the harmonic field. We found that it can be used to transfer a waveform from one fundamental field to the harmonic output. The harmonic waveform can be a magnified or compressed version of the fundamental waveform, depending on the configuration. We will use both theory and experiments to demonstrate this technique. It is a promising method to generate programmable waveforms in the blue and UV range, where directly programming a waveform is still challenging.

Degree

Ph.D.

Advisors

Weiner, Purdue University.

Subject Area

Optics|Electrical engineering

COinS