TABLE I.
Brightness of the photoelectron pulses for different operating parameters. For a given laser pulse energy, settings of the condenser lens system (Spot size and Alpha), and condenser lens aperture number (CLA), the table lists the number of electrons per pulse in the sample plane (N), the pulse duration (Δt), the instantaneous probe current (I), the FWHM of the focused electron beam (d), the convergence semi-angle (α), and the instantaneous brightness (B). Unless otherwise noted, electron pulses are generated by illuminating the emitter. For the duration of the nanosecond electron pulses, we assume 1 ns, the duration of the cathode laser pulses.
| Laser pulse energy and duration | Spot size | Alpha | CLA | N | Δt (ps) | I (nA) | d (nm) | α (mrad) | B (A/m2 sr) |
|---|---|---|---|---|---|---|---|---|---|
| Continuous beam | 5 | 3 | 3 | … | … | 0.105 | 1.8 | 3.7 | 9.0 × 1011 |
| 30 nJ, fs | 5 | 3 | 3 | 0.026 | 0.45 | 9.3 | 7.3 | 3.7 | 5.1 × 1012 |
| 2 nJ, fs | 1 | 3 | 2 | 0.23 | 0.48 | 76 | 7.5 | 9.3 | 6.3 × 1012 |
| 10 nJ, fs | 1 | 3 | 2 | 0.79 | 0.83 | 117 | 12.8 | 9.3 | 3.3 × 1012 |
| 30 nJ, fs | 1 | 3 | 2 | 2.05 | 1.90 | 143 | 19.5 | 9.3 | 1.8 × 1012 |
| 300 nJ, ns | 1 | 3 | 2 | 219 | 1000 | 35 | 10.1 | 9.3 | 1.6 × 1012 |
| 150 nJ, ns (extractor) | 1 | 3 | 2 | 111 | 1000 | 17.7 | 133 | 9.3 | 4.7 × 109 |