A novel laser-induced fluorescence scheme for Ar-I in a plasma

Abstract

Here we describe a novel infrared laser-induced fluorescence scheme for the 1s2 state of Ar-I using an 841.052 nm (vacuum) Sacher tunable diode laser oscillator and compare it to an established 667.913 nm (vacuum) 1s4-pumping Ar-I LIF scheme using a master oscillator power amplifier laser [A. M. Keesee et al. Rev. Sci. Instrum. 75, 4091 (2004)]. The novel scheme exhibits a significantly greater signal-to-noise ratio for a given injected laser power than the established scheme. We argue that this is caused by less intense spontaneous Ar-I radiation near the LIF emission wavelength for the 1s2 scheme as compared to the 1s4 scheme. In addition we present an updated iodine cell spectrum around the 1s4 LIF scheme pump wavelength.

Laser induced fluorescence of Ar-I metastables in the presence of a magnetic field

“…The lowest energy group of Ar-I excited states occurs when one of the outer electrons occupies the 3p 5 4s levels, and in Paschen's notation these states are referred to as 1s 5 , 1s 4 , 1s 3 , and 1s 2 in order of increasing energy. Successful techniques for measuring NVDFs from the resonant 1s 2 and 1s 4 states are accessible using relatively inexpensive diode lasers [27][28][29][30]. LIF measurements originating from these states have limited applicable pressure ranges because 1s 2 and 1s 4 are primarily populated through electron-impact collisions with atoms in metastable states 1s 3 and 1s 5 , respectively, and are only weakly populated from the ground state.…”

Measurement and reduction of Ar metastable densities by nitrogen admixing in electron beam-generated plasmas

“…LIF is widely used as a non-invasive diagnostic for a variety of measurements in plasma [23], including densities of atomic [24,25] and molecular [26][27][28] species, ion/neutral temperatures [29][30][31][32] and ion velocities [33]. The Ar metastable levels are typically used for LIF measurements of neutral velocity distribution functions [34][35][36][37][38]. The density of Ar metastables is most frequently studied by optical absorption [39][40][41][42] and emission [43] techniques.…”

Laser induced fluorescence diagnostic for velocity distribution functions: applications, physics, methods and developments

“…They are increasingly employed in basic plasma physics experiments to study sheath/presheath formation and other physical processes [11][12][13][14][15], in Hall thrusters to monitor IVDFs [16][17][18][19][20][21], in helicon devices to study ion beam driving mechanism [22][23][24][25][26][27][28][29], and in plasma processing to monitor evolution of IVDFs along the presheath [30], among other usages. The LIF diagnostic itself has advanced significantly since its invention: new LIF schemes have been discovered to expand the range of ions and neutral to be measured [7,[31][32][33][34][35], accurate evaluation of hyperfine and isotope effects [36], Zeeman split and atomic reference spectra improves LIF accuracy [37,38], the adaption of diode lasers improves costeffectiveness and operational safety [7,35,37], time-resolved techniques are formulated to observe periodic phenomena, and the physical limitations of LIF are being actively explored [28,39,40]. This review will focus on single-photon, LIF diagnostics of metastable ions and neutrals, and will briefly discuss some of the basic principles of the LIF diagnostic.…”