Femtosecond Terahertz Radiation from Femtoslicing at BESSY

Abstract

Femtosecond far-infrared radiation pulses in the THz spectral range were observed as a consequence of the energy modulation of 1.7 GeV electrons by femtosecond laser pulses in the BESSY storage ring in order to generate femtosecond x-ray pulses ("femtoslicing"). In addition to being crucial for diagnostics of the laser-electron interaction, the THz radiation itself is useful for experiments where intense ultrashort THz pulses of well-defined temporal and spectral characteristics are required.

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation

“…In both generations of the set up, HHG is driven by a femtosecond Ti:sapphire laser system with a multipass amplifier with pulse energies of up to 2.5 mJ, a repetition rate of 1 kHz, typical pulse durations of 60 fs, and a center wavelength of 790 nm. This is the same laser system as it is used for the generation of femtosecond soft x-ray pulses at the electron storage ring BESSYII at the Helmholtz-Zentrum Berlin in the so called Femtoslicing facility (80,81) and as we used it for driving an Optical Parametric Amplifier for time-resolved mid-infrared pump and soft x-ray absorption probe spectroscopy of liquid water with BESSYII (82,83).…”

Generation of subpicosecond x-ray pulses in storage rings

“…Figure 8. The spectrum of the coherent synchrotron radiation produced by the electron density modulation (solid line) and the spectrum of the 1.2 ps (rms) electron bunch coherent radiation obtained in the operation with a low momentum compaction factor (dashed line) [13]. It was found at ALS, BESSY and SLS that coherent synchrotron radiation provides an excellent THz signal clearly visible on many turns after electron bunch interaction with the laser pulse.…”

“…Therefore, it is now routinely used for an initial optimization of the laserelectron beam interaction and for a feedback control of spatial and timing drifts between laser and electron beams during data logging in experiments with sub-ps x-ray pulses. It was also empirically found at BESSY that the ratio of THz pulse intensity on the first and the second turn is extremely sensitive to the initial energy modulation of electrons [13].…”

“…The electron density modulation shown in Figure 6 gives rise to a coherent synchrotron radiation [5]. This radiation was detected at ALS [12], BESSY [13] and SLS [14]. The spectrum of the signal ) (ω F measured with liquid He-cooled Si bolometer and Martin-Puplett spectrometer [13] is shown in Figure 8.…”

“…This radiation was detected at ALS [12], BESSY [13] and SLS [14]. The spectrum of the signal ) (ω F measured with liquid He-cooled Si bolometer and Martin-Puplett spectrometer [13] is shown in Figure 8. Since ) (ω F is a Fourier transform of the 1D electron density distribution and because the shape of the dip in the electron density distribution can be accurately modeled with two Gaussians functions, one can reconstruct the original distribution from the measured spectrum using either Kramers-Kronig relation [15] or iteratively.…”