Laser induced fluorescence in Ar and He plasmas with a tunable diode laser

Abstract

A diode laser based laser induced fluorescence ͑LIF͒ diagnostic that uses an inexpensive diode laser system is described. This LIF diagnostic has been developed on the hot helicon experiment ͑HELIX͒ plasma device. The same diode laser is used to alternatively pump Ar II and He I transitions to obtain argon ion and atomic helium temperatures, respectively. The 1.5 MHz bandwidth diode laser has a Littrow external cavity with a mode-hop free tuning range up to 14 GHz (Ϸ0.021 nm) and a total power output of about 12 mW. Wavelength scanning is achieved by varying the voltage on a piezoelectric controlled grating located within the laser cavity. The fluorescence radiation is monitored with a photomultiplier detector. A narrow band interference filter is used to eliminate all but the plasma radiation in the immediate vicinity of the fluorescence wavelength. Lock-in amplification is used to isolate the fluorescence signal from noise and electron-impact induced radiation. For the Ar ion, the laser tuned at 668.43 nm is used to pump the 3d 4 F 7/2 Ar II metastable level to the 4p 4 D 5/2 level. The 442.60 nm fluorescence radiation between the 4p 4 D 5/2 and the 4s 4 P 3/2 levels is captured by the photomultiplier tube. For atomic He, the laser is tuned at 667.82 nm to pump a fraction of the electron population from the 2 1 P state to the 3 1 D upper level. Although the 2 1 P level is not a metastable, the close proximity of 2 1 S metastable makes this new He I LIF scheme possible. In this scheme, a fraction of the laser-excited electrons undergo collisional excitation transfer from the 3 1 D to the 3 1 P level. In turn, the 3 1 P state decays to the metastable 2 1 S by emitting 501.57 nm fluorescence photons.

Spatial Profile of Ion Velocity Distribution Function in Helicon High-Density Plasma by Laser Induced Fluorescence Method

“…Figures 5 and 6 show the measured IVDF at z = 30 and 60 cm respectively with Gaussian distribution fitting curves. Here, Zeeman shifts for argon ions are ± 1.4 GHz/kG, 14,16) which shows a small effect on our measurements. A pulsed discharge plasma was operated with two kinds of magnetic field configurations, mentioned before.…”

“…Our LIF system adopted a three-level scheme of ion particle, 14) which is shown in Fig. 1 When a target particle have a velocity along a pumping laser axis, the excitation wave length is changed by a Doppler shift.…”

“…11,12) To demonstrate and optimize this system, it is also important to measure various plasma parameters. Laser Induced Fluorescence (LIF) method [13][14][15][16] can estimate velocity distribution functions of ions, atoms and molecules non-invasively with a high spatial resolution. It can also derive their temperatures, flow velocities and relative densities from the distribution functions.…”

Scanning internal probe for plasma particle, fluctuation, and LIF tomographic measurements

“…Ion temperatures are inferred from the Doppler broadening of the absorption line. [3][4][5] For the plasma and magnetic field parameters of LEIA, Stark broadening, Zeeman splitting, and the natural linewidth of the absorption line are ignorable.…”

Deposition of Aluminum-Doped ZnO Films by ICP-Assisted Sputtering

“…With the progress in diode laser technology, inexpensive tunable single mode diode lasers with external cavity which are also called as external cavity diode lasers (ECDLs) [54][55][56][57][58] have recently been applied for the measurements of velocity distributions of In [59], He [60], Ar discharge is also shown in Fig. 21 for comparison.…”