Generation of Ellipsoidal Laser Pulses with Periodic Intensity Modulation for Photoinjectors

Modern linacs are considered for generation of THz pulses with up to mJ energies at high repetition rates due to the capabilities of modern photo injectors. A Self-Amplified Spontaneous Emission (SASE) FEL is proposed for such a powerful THZ source [1]. In order to improve the Carrier-Envelope-Phase (CEP) stability of the THz SASE FEL a seeding option using temporally modulated electron bunches from the photo injector is under study. One of the methods is to generate electron beams with a sub-picosecond structure. Modern linac based FELs (like the European XFEL at DESY and LCLS at SLAC) start from photo injectors, where electron bunches are generated by laser pulses from a cathode surface. In this case, the phase space distribution of the electron bunches strongly depends on the 3D spatio-temporal intensity distribution of the photocathode laser pulses. So, it is necessary to modulate the temporal intensity distribution of the laser pulses to obtain rippled (or microbunched) electron beams. Spectral phase or spectral amplitude modulation of linearly chirped laser pulses can be used to obtain laser pulses with ∼1 ps modulation period. A spatial light modulator (SLM) placed inside the optical compressor with zero frequency dispersion is an attractive way to produce the modulation [3, 4]

Shaping Picosecond Ellipsoidal Laser Pulses with Periodic Intensity Modulation for Electron Photoinjectors

A method for shaping periodic intensity distributions of strongly chirped picosecond laser pulses in the infrared range by periodic phase modulation of the spectrum is proposed. The dependence of the time modulation period and depth on the parameters of periodic phase modulation of the spectrum is analyzed by analytical and numerical methods. It is demonstrated that the intensity distribution structure obtained at second- and fourth-harmonic generation can be retained by introducing an angular chirp. The electron bunch dynamics at the photoinjector test facility at DESY in Zeuthen (PITZ) was modeled numerically using ellipsoidal laser pulses with intensity modulation

Shaping of cylindrical and 3D ellipsoidal beams for electron photoinjector laser drivers

With the use of spatial light modulators it became possible to implement in experiments the method of con-trolling the space–time intensity distribution of femtosecond laser pulses stretched to picosecond duration.Cylindrical and quasi-ellipsoidal intensity distributions were obtained and characterized by means of a 2Dspectrograph and a cross-correlator

Production of quasi ellipsoidal laser pulses for next generation high brightness photoinjectors

The use of high brightness electron beams in Free Electron Laser (FEL) applications is of increasing importance. One of the most promising methods to generate such beams is the usage of shaped photocathode laser pulses. It has already demonstrated that temporal and transverse flat-top laser pulses can produce very low emittance beams [1]. Nevertheless, based on beam simulations further improvements can be achieved using quasi-ellipsoidal laser pulses, e.g. 30% reduction in transverse projected emittance at 1 nC bunch charge.In a collaboration between DESY, the Institute of Applied Physics of the Russian Academy of Science (IAP RAS) in Nizhny Novgorod and the Joint Institute of Nuclear Research (JINR) in Dubna such a laser system capable of producing trains of laser pulses with a quasi-ellipsoidal distribution, has been developed. The prototype of the system was installed at the Photo Injector Test facility at DESY in Zeuthen (PITZ) and is currently in the commissioning phase.In the following, the laser system will be introduced, the procedure of pulse shaping will be described and the last experimental results will be shown