Temporal quality of post-compressed pulses at large compression factors

Post-compression of ultra-short laser pulses via self-phase modulation is routinely employed for the generation of laser pulses with optical bandwidths reaching far beyond the laser gain limitations. While high compression factors can be routinely achieved, the compressed pulses typically suffer from temporal quality degradation. We numerically and experimentally analyze the deterioration of different measures of temporal quality with increasing compression factor and show how appropriate dispersion management and cascading of the post-compression process can be employed to limit the impact of this effect. The demonstrated saturation of pulse quality degradation at large compression factors puts novel femtosecond laser architectures based on post-compressed pico- or even nanosecond laser systems in sight

Ultrafast serrodyne optical frequency translator

The serrodyne principle enables an electromagnetic signal to be frequency shifted by applying a linear phase ramp in the time domain. This phenomenon has been exploited to frequency shift signals in the radiofrequency, microwave and optical regions of the electromagnetic spectrum over ranges of up to a few gigahertz, for example, to analyse the Doppler shift of radiofrequency signals for noise suppression and frequency stabilization. Here we employ this principle to shift the centre frequency of high-power femtosecond laser pulses over a range of several terahertz with the help of a nonlinear multi-pass cell. We demonstrate our method experimentally by shifting the central wavelength of a state-of-the-art 75 W frequency comb laser from 1,030 nm to 1,060 nm and to 1,000 nm. Furthermore, we experimentally show that this wavelength-shifting technique supports coherence characteristics at the few hertz-level while improving the temporal pulse quality. The technique is generally applicable to wide parameter ranges and different laser systems, enabling efficient wavelength conversion of high-power lasers to spectral regions beyond the gain bandwidth of available laser platforms

Flexible Wavelength Shifting of Ultrafast Lasers at HighPower Levels

We present a wavelength shifting method suitable for high power lasers. We demonstrate our concept via simulations and experimentally shift an 80 W, 200 fs laser at 1030 nm by ±30 nm

Pulse post-compression via multi-pass cells for FEL pump-probe experiments at FLASH

The soft x-ray Free-Electron Laser (FEL) FLASH is a unique tool to study ultrafast processes and is mostly used for pump-probe experiments in combination with an optical laser. Within the framework of the FLASH2020+ facility upgrade, the currently operating Ti:Sapphire and OPCPA systems will be largelyreplaced by high-power Yb:YAG lasers combined with nonlinear pulse compression in multi-pass cells (MPCs). This approach offers superior compactness, efficiency and simplicity of the optical laser systems. We here present first example implementations of MPC compression-based pump-probe laser systems. In particular, we investigate pulse stability, temporal contrast and intra-burst pulse dynamics. Our results confirm the applicability of MPC-based pulse compression for pump-probe experiments including promising pulse characteristics for driving secondary frequency conversion stages

Photocathode Laser Development for Superconducting X-Ray Free Electron Lasers at DESY

Modern X-Ray Free-Electron Lasers (XFEL) are a key tool to enable a variety of scientific research. Those large-scale machines rely on robust and reliable deep ultraviolet (DUV) laser sources to drive electrons from their RF photocathode gun. In this paper we present a new photocathode laser prototype, which offers more flexibility in duration and shape of the 257.5 nm pulses for driving the CsTe Photocathodes of DESY’s superconducting burst-mode FELs. The laser matches the FEL pulse structure, which are 800 µs bursts at up to 4.5 MHz intraburst-rate with 10 Hz burst-repetition-rate. In a first version the system will offer variable DUV pulse durations, tunable from 1 ps to 20 ps to address different operational regimes of the XFEL. The laser system comprises a high-resolution spectral shaper with the option of generating flat-top DUV pulses for reducing electron-beam emittance at a later version. The laser is constructed in a hybrid Yb:fiber and Yb:YAG architecture. Our prototype delivers 180 uJ pulse energy at 1030 nm and 1 MHz intra-burst rate and we demonstrated conversion of 50µJ of the NIR beam to DUV, resulting 11.5µJ at 21ps (FWHM) and 6.15 µJ at 1.05 ps (FWHM) pulse duration

Flexible Operation Modes for EuXFEL

A major challenge in single-linac - multiple undulator setups like EuXFEL is the generation of individual shaped photon pulses, in particular, when working in a mode where a single pulse train, or cw stream, feeds all undulator lines. This work presents the experimental verification of a flexible delivery scheme producing photon pulses for each of the three undulator lines with their electron bunches individually shaped in charge, compression and optics on a single RF pulse burst

Compact 60 μ\muJ, 60 fs, MHz-rate burst-mode laser for pump-probe experiments at the FLASH FEL facility

A new burst-mode laser at the FLASH-FEL facility is presented. Multi-pass-cell spectral broadening enables compression of 900-fs pulses from Yb-amplifiers to 60-fs. Nonlinear-ellipse-rotation leads to significant pulse-contrast improvement. Excellent timing-, spectrum- and energy-stability is reported