Laser Fluorescence Spectroscopy by Two-Photon Excitation for Detection of Hydrogen Atoms in a Periphery Region of High Temperature Plasmas

Abstract

For measurements of atomic hydrogen density in the periphery region or hign temperature plasmas, laser fluorescence spectroscopy (LFS) by two-photon excitation (1s-3s, 3d) was developed.
Based upon the theoretical estimates for laser source requirements, which indicated the laser energy and spectral width to be more than 10mJ (assuming the pulse duration of 10ns) and several tens of picometers around the wavelength of 205.1nm, respectively, the first Stokes generation in deuterium gas of ArF laser output was adopted and shown to have the necessary performance.
Through the LFS experiment employing the laser source, the minimum detectable limit of atomic hydrogen, normalized by a laser power and an observing solid angle, was demonstrated to be 1x 10¹⁴ [m^-3 · MW · sr], which is usually sufficient for the above purpose, and the accuracy of the density determination was shown to be within a factor 2.