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We report experimental studies of the spectral linewidth and chirp characteristics of the mm-wave rf radiation of the Israeli Electrostatic-Accelerator free electron laser (EA-FEL), along with theory and numerical simulations. The simulations, matching the experimental data, were carried out using a space-frequency-domain model. EA-FELs have the capacity to generate long pulses of tens microseconds and more, that in principle can be elongated indefinitely (cw operation). Since a cold beam FEL is by nature a “homogeneously broadened laser,” EA-FEL can operate, unlike other kinds of FELs, at a single longitudinal mode (single frequency). This allows the generation of very coherent radiation. The current status of the Israeli Tandem Electrostatic-Accelerator FEL, which is based on an electrostatic Van de Graaff accelerator, allows the generation of pulses of tens microseconds duration. It has been operated recently past saturation, and produced single-mode coherent radiation of record narrow inherent relative linewidth ∼Δf/f=10^-6 at frequencies near 100 GHz. A frequency chirp was observed during the pulses of tens of microseconds (0.3–0.5  MHz/ms). This is essentially a drifting “frequency-pulling effect,” associated with the accelerator voltage drop during the pulse. Additionally, damped relaxation of the FEL oscillator was experimentally measured at the beginning and the end of the lasing pulse, in good correspondence to our theory and numerical simulations. We propose using the chirped signal of the pulsed EA-FEL for single pulse sweep spectroscopy of very fine resolution. The characteristics of this application are analyzed based on the experimental data.

The slow-wave cyclotron-resonance master (CRM) oscillator experiment presented in this paper produces output signals that correspond to normal and anomalous Doppler shifts. The table-top low-voltage (<10 kV) CRM device consists of a double stripline waveguide. The metal strips are loaded by dielectric slabs; thus the waveguide supports slow waves with different phase velocities in odd and even quasi-TEM modes. The suppression of axial electric-field components in this waveguide eliminates the Cherenkov interaction as a parasitic effect to the slow-wave CRM. Oscillations are observed in the frequency range 3–15 GHz. Doppler shifts of 30% down and 150% up are measured with respect to the electron cyclotron frequency. These agree with the normal and anomalous tuning conditions, respectively. The dielectric-loaded stripline scheme is discussed for practical slow-wave CRM devices.