Directly determining orbital angular momentum of ultrashort Laguerre-Gauss pulses via autocorrelation measurement

ROSA: Reconstruction of Spectrogram Autocorrelation for Self-Amplified Spontaneous Emission Free-Electron Lasers

In recent years X-ray Free Electron Lasers (XFELs) proved to be unmatched sources of ultrashort pulses of spatially coherent quasimonochromatic X-ray radiation. Diagnostics of XFEL emission properties, in particular pulse duration, spectrum and temporal profile is extremely important in order to analyze the experimental results. In this paper we propose a cost-effective method to examine these properties of Self-Amplified Spontaneous Emission (SASE) pulses. It only requires an ensemble of measured SASE spectra and provides the temporal autocorrelation of the ensemble-averaged Wigner distributi…

Mode-locked ultrashort pulses from an 8 $μ$m wavelength semiconductor laser

Quantum cascade lasers (QCL) have revolutionized the generation of mid-infrared light. Yet, the ultrafast carrier transport in mid-infrared QCLs has so far constituted a seemingly insurmountable obstacle for the formation of ultrashort light pulses. Here, we demonstrate that careful quantum design of the gain medium and control over the intermode beat synchronization enable transform-limited picosecond pulses from QCL frequency combs. Both an interferometric radio-frequency technique and second-order autocorrelation shed light on the pulse dynamics and confirm that mode-locked operation is ach…

紫外和软X射线光谱区域超短自由电子激光脉冲的产生与测量

Generation and Measurement of Ultrashort Free Electron Laser Pulses in Ultraviolet and Soft-X-ray Spectral Regions

本文报告了外种子自由电子激光器产生和测量紫外至软X射线超短相干脉冲的新进展，重点介绍了FERMI装置上少飞秒极紫外脉冲的产生与自相关表征。

Femtosecond pulses from a mid-infrared quantum cascade laser

The quantum cascade laser (QCL) has evolved to be a compact, powerful source of coherent mid-infrared (mid-IR) light. However, its fast gain dynamics strongly restricts the formation of ultrashort pulses. As such, the shortest pulses reported so far were limited to a few picoseconds with some hundreds of milliwatts of peak power, strongly narrowing their applicability for time-resolved and nonlinear experiments. Here, we demonstrate an alternative approach capable of producing near-transform-limited sub-picosecond pulses with several watts of peak power. Starting from a frequency modulated pha…

Photon statistics of incoherent cathodoluminescence with continuous and pulsed electron beams

Photon bunching in incoherent cathodoluminescence (CL) spectroscopy originates from the fact that a single high-energy electron can generate multiple photons when interacting with a material, thus revealing key properties of electron-matter excitation. Contrary to previous works based on Monte-Carlo modelling, here we present a fully analytical model describing the amplitude and shape of the second order autocorrelation function ($g^{(2)}(τ)$) for continuous and pulsed electron beams. Moreover, we extend the analysis of photon bunching to ultrashort electron pulses, in which up to 500 electron…

Stable mode-locked pulses from mid-infrared semiconductor lasers

We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train of short pulses was generated by actively modulating the current and hence the optical gain in a small section of an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch equatio…