A high sensitivity two-color interferometer for pulsed power plasmas

Abstract

A high sensitivity, high bandwidth, two-color interferometer (1064 and 532 nm) has been tested on the Hawk pulsed power generator at the Naval Research Laboratory. The phase resolution is 10−5 waves with a rise time of 3 ns, a new capability for diagnosing plasmas, and neutrals in pulsed power experiments. The two-color feature is used to distinguish phase shifts from free (plasma) electrons and bound (neutral and ion) electrons. Simultaneous electron and neutral density measurements were demonstrated in a plasma opening switch (POS) experiment. The ability to measure small phase shifts with fast rise time were demonstrated in a plasma filled diode experiment. The high sensitivity and vibration isolation enable neutral gas distribution measurements from supersonic nozzles used in plasma radiation source experiments. Examples of these measurements and future applications are described.

Two-color interferometer for the study of laser filamentation triggered electric discharges in air

“…The other originates from the neutral-bound a) Electronic mail: guillaume.point@ensta-paristech.fr electrons, because the neutral density along the probe beam and the reference beam are not balanced. A way to separate these two contributions is to record the plasma optical index at two different wavelengths, so-called twocolor interferometry [22][23][24][25] . Using this technique, it becomes possible to isolate the free electron density, and to record neutral density as well.…”

Experimental simulation of a double return‐stroke lightning flash by lasers

“…The temporal evolution of the plasma and hot core air temperature was determined by interferometry. At the initial stage our plasma is not completely ionized [ Radziemski et al , 1983; Zel'dovich and Raizer , 1966], and consequently two‐color interferometry must be used to determine the electron density according to Weber and Fulghum [1997]: where ϕ i is the phase shift corresponding to the λ i wavelength, r e = 2.82 × 10 −13 cm is the classical radius of the electron and L the ray path inside the plasma. These measurements were made at times greater than 1–3 μs, when pressure reached atmospheric equilibrium [ Radziemski et al , 1983; Yalçin et al , 1999, Sobral et al , 2000].…”

“…[8] The temporal evolution of the plasma and hot core air temperature was determined by interferometry. At the initial stage our plasma is not completely ionized [Radziemski et al, 1983;Zel'dovich and Raizer, 1966], and consequently two-color interferometry must be used to determine the electron density according to Weber and Fulghum [1997]:…”

Interferometric measurements on a triggered plasma opening switch source

“…Interferometry is one of the most commonly used diagnostics for plasma density measurements [5], and has been successfully employed previously on pulsed power experiments [6,7]. It utilizes the fact that an electromagnetic wave propagating in a magnetized plasma with E| | | || | | |B will experience a phase shift relative to a wave in vacuum given by …”