A new look at inverse Cerenkov acceleration and vacuum laser acceleration

Two approaches for inverse Cerenkov acceleration (ICA) and laser acceleration in a vacuum are presented. The improvement of the ICA process is to use reduced gas pressure, but operate with the laser wavelength near a natural resonance of the gas, thereby maintaining the necessary index of refraction. For the vacuum laser accelerator the idea is to utilize the same optical system as used during ICA (i.e. radially polarized laser beam focused by an axicon), but without a gas. The phase slippage between the electron and light wave can be limited, thereby ensuring that the oscillatory EM wave does not cancel out any net acceleration. In both schemes, acceleration gradients of several GeV/m appear possible.<>