Liquid Crystals as High Repetition Rate Targets for Ultra Intense Laser Systems

摘要

This thesis presents the development of and first experiments on freely suspended liquid crystal film targets for intense laser-matter experimentation. Liquid crystals exhibit additional phases between solid and liquid which are characterized by different levels of molecular ordering. One of these, the smectic phase, entails molecular orientational order and positional order such that the constituent molecules arrange into layers of set thickness. The surface tension inherent to this smectic phase allows a liquid crystal film to be formed within an aperture in a rigid frame; control over the parameters of film formation (temperature, volume, wiper speed, etc.) allows the number of layers comprising this freely suspended film to be modified on-demand. The result is a variable thickness target with planar geometry that is robust to target chamber vacuum environments and is also inexpensive due to the low volume used per film.;Initial ion acceleration experiments will be discussed, where the variable thickness of liquid crystal films is uniquely capable of characterizing the regions of dominance of various acceleration mechanisms. These experiments were performed on the Scarlet laser facility at the Ohio State University, which is a 400 TW, 12 J, 30 fs Ti:sapphire laser system that produces focused intensities in excess of 10 21 W/cm2. The upgrade of this facility to these specifications including damage testing measurements on the new optics is also discussed.;Additionally, a device for the rapid insertion in-vacuo of these liquid crystal films into the target plane will be presented. This apparatus takes advantage of techniques developed for film formation in a single shot capacity but increases the repetition rate possible to the 0.1 Hz scale. Films formed with the device are done so within 2 mum of the same position each time, which is critical for high repetition rate insertion where no time for target alignment is available.