Fluorescence polarization of helium negative-ion resonances excited by polarized electron impact

Abstract

We have investigated helium (1s3d) 3 D → (1s2p) 3 P (588 nm) fl uorescence produced by electron impact excitation in the vicinity of the (2s 2 2p) 2 P and (2s2p 2 ) 2 D negative-ion resonances at 57.2 and 58.3 eV, respectively. In contrast to previous work, we use spin-polarized incident electrons and report the relative Stokes parameters P 1 , P 2 , and P 3 in the 55-60 eV region. Our failure to see discernable resonance effects in P 2 indicates that even though the lifetime of these resonances is signifi cant (~10 fs), magnetic forces acting on the temporarily captured electron are small. Resonant structures in the values of P 1 and P 3 are observed because the polarization contributions of resonant states are generally different than those from direct excitation of the 3 3 D state.

Alignment and orientation of diatomic molecules induced by polarized electron impact

“…Our experimental apparatus has been discussed in detail elsewhere [6,7]. An unstrained Cs-O activated GaAs crystal is irradiated with 785 nm light to produce an electron beam with ∆E ∼ 0.3 eV FWHM and a typical transverse spin polarization of P e ∼ 0.25 as measured by optical polarimetry [4,8,9].…”

A cylindrically symmetric “micro-Mott” electron polarimeter

“…[17][18][19][20] Our polarization measurements of the present source using neon optical electron polarimetry 21 were consistent with the above value, and so we base our reported values of S eff on this number. Although GaAs sources of this kind can have lower polarization, typically due to multiple resistive heat-cleanings of the photocathode, 22 we consider this a conservative estimate.…”

Compact inline optical electron polarimeter

“…Comprehensive accounts of how to calibrate δ, k inc , α o , and β o also exist in the literature. 10,15,16,24 We obtained the following for our experimental setup: δ = (1.65 ± 0.01) radians, k inc = (0.971 ± 0.001), α o = (0 ± 1) • , and…”

“…Optical electron polarimeters 5,6,[8][9][10][11][12][13][14][15][16][17] have no such constraints. In these devices, polarized electrons excite an atomic target, usually a noble gas, by exchange.…”

“…It also occupies a quarter the volume. Unlike earlier helium optical electron polarimeters, [10][11][12][13][14][15] which were designed for transversely polarized particles, this model can measure the polarization of longitudinally polarized beams.…”