Nonlinear spectroscopy of excited atoms, molecular gases, and plasmas

Xiaobo Xie, Ting Sun

The investigation of spectroscopy of vacuum ultraviolet (VUV, 100-200 nm) and extreme ultraviolet (XUV, 10-100 nm) regions has attracted the attention of many researchers in recent years because of its promising applications in such areas as spectroscopy of highly excited states of atoms and molecules, life science, plasma physics and material science. In this paper we report the study of molecular coherent spectrum in the VUV and XUV regions through nonlinear optical processes and the determination of the rotational temperature of molecules. Because molecular gases have abundant energy levels, it can provide resonant levels to enhance the generated radiation and a wide tunibility of the spectrum in VUV and XUV regions. The determination of the rotational temperature of molecules will be very useful for the study of molecular spectroscopy and the nonlinear optical process in VUV/XUV regions.

Kōichi Shimoda, Tadao Shimizu

Aleksei M. Zheltikov, Nikolai I Koroteev

A review of the main directions of development, the most promising new techniques, and urgent applications of coherent four-photon methods of investigation of excited and ionized gas media is presented. It is demonstrated that the methods of coherent four-wave mixing (FWM) provide important spectrochronographic information on atoms and ions, allow selective studies of separate components of nonstationary gas and plasma systems with a complex composition using polarization-sensitive four-photon spectroscopy and coherent ellipsometry, and permit nonlinear-optical imaging of the spatial distribution of atoms and ions in excited gases and plasmas.

Daniel Kleppner

M. Aghigh, K. M. Grant, Rafael Haenel +8 more

Abstract Not long after metastable xenon was photoionized in a magneto-optical trap, groups in Europe and North America found that similar states of ionized gas evolved spontaneously from state-selected, high principal quantum number Rydberg gases. Studies of atomic xenon and molecular nitric oxide entrained in a supersonically cooled molecular beam subsequently showed much the same final state evolved from a sequence of prompt Penning ionization and electron-impact avalanche to plasma, well-described by coupled rate-equation simulations. But, measured over longer times, the molecular ultracold plasma was found to exhibit an anomalous combination of very long lifetime and very low apparent electron temperature. This review first summarizes early developments in the general study of ultracold plasmas formed by atomic and molecular Rydberg gases, and then turns to describe the particular properties of the nitric oxide molecular ultracold plasma that appear to call for an explanation beyond the realm of conventional plasma physics.

Wolfgang Demtröder