Diode lasers have been used for ion temperature measurements in ArII plasmas by finding new laser-induced fluorescence ͑LIF͒ schemes suited to the present range of available wavelengths. The new LIF schemes require excitation at 664, 669, and 689 nm, all near industry-standard wavelengths. Conventional LIF measurements performed by dye lasers in ArII use 611.66 nm in vacuum, shorter than any commercially available red diode laser line, and depend on the population of the 3dЈ 2 G 9/2 metastable state. The metastable state density of the conventional LIF scheme was found to be larger than the populations of the other metastable states by an order of magnitude or less. A master oscillator power amplifier diode laser was used both in a Littman-Metcalf cavity and as an optical amplifier for a low power diode laser which was in a Littman-Metcalf cavity. Both systems provided intensity of up to 500 mW, continuously tunable over 10 nm centered at 666 nm, and were used to obtain high resolution ion velocity distribution functions.

Two-dimensional ion velocity distribution functions (IVDFs) of argon plasmas have been measured with optical tomography via laser-induced fluorescence (LIF). An inductive radio-frequency (RF) coil created the plasmas, and IVDFs were measured versus RF frequency, gas pressure and location (bulk plasma or presheath of a plate). Typical gas pressure was 0.3-0.4 mTorr, RF power 25 W and magnetic field 130 G. Effective perpendicular ion temperature decreased with increasing RF frequency, and changed little with pressure. Optical tomography reveals features of the presheath IVDF that cannot be deduced from LIF scans parallel and perpendicular to the plate alone. Progress also has been made toward performing optical tomography on a commercial ion beam source (Veeco/Ion Tech 3 cm RF Ion Source, Model #201). In particular, it has been discovered that the beam energy fluctuates in a range of about 20 eV over the timescale of a few minutes.

To study the physics of energetic ions in magnetized plasma, a rf ion beam is inserted into the 1 kG, ϳ3 eV, ϳ10 12 cm Ϫ3 plasma produced by the upgraded LArge Plasma Device ͑LAPD͒. The commercial 100-1000 eV argon source normally operates in an unmagnetized microelectronics production environment. Successful operation in the LAPD requires numerous modifications, including electrical isolation of the source housing, relocation of the matching network for the rf, reduction of the gas pressure, pulsed operation to avoid overheating, and care to preserve current neutralization in the presence of a strong magnetic field. With these modifications, a ϳ500 eV, milliampere beam that propagates axially more than 6 m is obtained.

A technique for measuring ion transport using laser-induced fluorescence has been developed and tested in an argon plasma. It uses only one broadband beam thus being simpler than some previous techniques because no detection beam is required. First, a 5 s laser pulse centered on 611 nm stimulates a transition from the metastable state in Ar͑II͒ 3d 2 G 9/2 to 4 p 2 F 7/2 0 . A 4p 2 F 7/2 0 to 4s 2 D 5/2 transition rapidly results with emission at 461 nm. Upon cessation of the laser pulse, the 461 nm light in the detection volume does not return to its background level immediately because the 3d 2 G 9/2 level is partially depleted. The time history of the 461 nm signal in returning to steady-state background intensity provides a means of determining ion transport because the recovery signal is due to processes including ion excitation, diffusion, convection, and thermal motion. Measurements of the ion velocity distribution yield the contributions of thermal and convective effects to ion transport. By varying the laser beam diameter and the detection volume the plasma ion spatial diffusion coefficient D, and the time, p it takes for processes other than transport to bring the 461 nm emission back to the steady-state background level are determined. For example, in one set of plasma conditions Dϭ0.58Ϯ0.16 m 2 /s and p ϭ59Ϯ7 s were found.

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