Animated-beam measurement of the photodetachment cross section of ${\mathrm{H}}^{-}$

The photodetachment cross section of ${\mathrm{H}}^{-}$ was measured using the animated-crossed-beam technique in the 700- to 1064-nm range. The laser beam was repeatedly swept across the ion beam by tilting a fused silica plate in order to eliminate the need for beam profile measurements. After integration of the signal, the cross section was expressed in terms of easily measurable quantities, e.g., the laser power and the ion beam current. The present results are in excellent agreement with previous experiments and compelling theoretical works.

Figure 1

Experimental setup. D: diaphragm; FC: Faraday cup; Q: quadrupolar deflector; CEM: channel electron multiplier; L: lens; RP: rotating fused silica plate; PM: powermeter. The laser beam propagates along the $z$ direction and its polarization is along the $y$ axis.

Figure 2

Laser beam passing through a glass plate. Refraction within the plate yields an output beam displaced along the vertical axis.

Figure 3

Current (pA) measured by the Faraday cups FC1 and FC2 with respect to the polarization voltage (V) applied to the guard electrode of the cup. A polarization voltage of $-100$ V is applied to each cup throughout the experiment. The offset at negative voltages is the leakage current on FC1.

Figure 4

Counting rate of the channel electron multiplier for different vertical displacements of the laser beam. The counts have been corrected for the ${\mathrm{H}}^{-}$ current and the laser power.

Figure 5

Experimental photodetachment cross section $\left({10}^{-21}{\mathrm{m}}^2\right)$ as a function of the photon energy (eV). The empty circles and triangles are, respectively, the present work and the work of Vandevraye et al. [22]. The full squares are from Popp and Kruse [19] and the disks are the relative measurement of Smith and Burch [18] set on an absolute scale using the calculation of Venuti and Decleva [10] (shown by the full line). The wavelength integrated measurements of Branscomb and Smith [17] lie within $\pm 10\%$ of the calculation of Chandrasekhar [3] multiplied by 1.01 (dashed line), as depicted by the shaded area.

Figure 6

Photodetachment cross section $\left({10}^{-21}{\mathrm{m}}^2\right)$ as a function of the photon energy (eV). The empty circles are the present work. The curves are theoretical values from Park et al. [15] in the length (dashed) and acceleration (densely dotted) gauges, Venuti and Decleva [10] (full thick), Stewart [5] (full thin), Wishart [6] (long dash-dotted), Saha [7] (dash-dotted), Broad and Reinhardt [8] (dash-doubly dotted), Ajmera and Chung [9] (dotted), and Chandrasekhar [3] (doubly dotted).