The resonant radiation wavelength. Due to the bandwidth of time-dependent simulation SASE simulations do not require a very precise value for XLAMDS.
The input power of the radiation field. For SASE simulation PRAD0 should be set to zero value or at least well below the shot noise level.
The Rayleigh length of the seeding radiation field. ZRAYL is defined as w02/XLAMDS where w0 is the radius of the optical beam waist. The Rayleigh length is a measure for the diffraction w(z)2 = w02(1 + (z - ZWAIST)2/ZRAYL2) and is needed to calculate the size and divergence/convergence of the seeding field at the undulator entrance. Because the field size can determine the grid size it is strongly recommended to supply reasonable numbers for ZRAYL and ZWAIST even for simulation starting from noise.
Position of the waist of the seeding radiation field with respect to the undulator entrance. ZWAIST is needed in combination with ZRAYL to calculate the initial radiation field. Note that a waist position within the undulator (ZWAIST > 0) is only used to determine the initial convergence. The FEL interaction might significantly change the beam size and diffraction of the radiation field (gain guiding).
Enables the calculation of harmonics up to the one, specified by NHARM. Note that the number of NBINS has to be at least twice as large as NHARM to allow for the correct representation of the harmonics. Note also that this parameter does not enable automatically the output. For that the corresponding bit in LOUT has to be set as well.
As a default setting only the fundamental and the harmonic, defined by NHARM are calculated. Setting the value to a non-zero value will also include all harmonics between. This option will be set automaticaly when the harmonics are calculated self-consistently.
Typically the harmonics are driven by the non-linear dynamics on the fundamental and the feed back of the harmonics on the electron beam can be neglected for the sake of faster calculation. However setting IHARMSC to a non-zero value includes the coupling of the harmonic radiation back to the electron beam for a self-consistent model of harmonics. Enabling this feature will automatically include all harmonics by setting IALLHARM to one.