Schematic of the fast ion beam spectrometer using NICE-OHMS detection. The following abbreviations are used: Faraday isolator (FI), polarizing beam splitter (PBS), double pass acousto optic modulator (AOM), quarter wave plate (QWP), electro optic modulator (EOM), radio-frequency synthesizer (RF), voltage controlled oscillator (VCO), phase shifter (PS), and time-of-flight (TOF). Amplifiers are indicated with triangles.
A schematic of the cold cathode source and its electrical connections. Gas flows in from the right, and ions are extracted to the left. In this figure, the triangles indicate the “ground” connections of the power supplies; the polycarbonate isolation box for the discharge power supply is also indicated.
Mass spectrum of an ion beam formed from a N2 plasma, showing an :N+ ratio of ∼10:1. The inset shows the energy distribution of the ions.
Scans of red- and blue-shifted components of the Q22(14.5) line (black dots) collected at 1.985 kV beam voltage along with fits to Eq. (3) (solid curves). For clarity, only 1 in every 15 experimental points is shown. The Doppler shifted lines are 180° out of phase with one another, allowing for identification of the sign of a component's Doppler shift. The Doppler shifted components are separated by ∼8.5 cm−1 as expected from Eq. (1). See the supplementary material33 for more information about the vertical scale.
Scans of red- and blue-shifted components of the Q22(14.5) line (black dots) collected at 3.781 kV beam voltage along with fits to Eq. (3) (solid curves) where the frequency axis is calibrated with the frequency comb. For clarity, only 1 in every 15 experimental points is shown. The top two traces are scanned toward the rest frequency and the bottom are scanned away from the rest frequency. As discussed in the text, the apparent frequency shifts are artifacts of the lock-in detection. The spectra have been offset vertically for clarity.
Boltzmann diagram for observed transitions; for each transition, a separate measurement is shown for each of the red- and blue-shifted components to illustrate the reproducibility of the intensities. The calculated rotational temperature is 753 ± 45 K.
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