Abstract
We experimentally demonstrate a single-shot arrival time monitor for short picosecond infrared free-electron laser (IR FEL) pulses based on balanced optical cross-correlation with a synchronized fs table-top laser. Employing this timing tool at the Fritz Haber Institute IR FEL, we observe a shot-to-shot timing jitter of only 100 fs and minute-scale timing drifts of a few picoseconds, the latter being strictly correlated with the electron beam energy of the accelerator. We acquire sum-frequency cross-correlation data with micropulse resolution, providing full access to the IR FEL pulse shape evolution within the macropulse. These measurements provide unprecedented insights into the occurrence of limit-cycle oscillations of the FEL intensity as a consequence of subpulse formation. Our experimental results are complemented by four-dimensional simulations of the nonlinear pulse dynamics in a low-gain FEL oscillator based on Maxwell-Lorentz theory.
Highlights
The availability of extremely intense, spectrally tunable coherent light pulses facilitates progress in various scientific fields due to the possibility to perform optical spectroscopy [1] and imaging [2,3] of matter on its natural time and length scales
We experimentally demonstrate a single-shot arrival time monitor for short picosecond infrared freeelectron laser (IR FEL) pulses based on balanced optical cross-correlation with a synchronized fs table-top laser
We demonstrate the balanced optical crosscorrelation (BOC) concept employing a fs table-top near-IR laser synchronized with an IR FEL at the Fritz Haber Institute (FHI) using a low-jitter radio-frequency phaselocking system
Summary
The availability of extremely intense, spectrally tunable coherent light pulses facilitates progress in various scientific fields due to the possibility to perform optical spectroscopy [1] and imaging [2,3] of matter on its natural time and length scales. Direct cross-correlation of the table-top light with the FEL radiation has been applied in the IR regime (by sum-frequency generation [9,10]) and recently to fs x-ray pulses (e.g., via induced transient changes of the optical reflectivity [11,12]). We extend these concepts of pulse arrival determination at IR FELs by utilizing balanced optical crosscorrelation (BOC) to improve the time resolution. The experimental results are compared to numerical simulations of the FEL oscillator based on Maxwell-Lorentz theory, showing qualitative agreement
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