Multi-octave high-dynamic range optical spectrometer for single-pulse diagnostic applications

TL;DR

This paper introduces an ultra-broadband optical spectrometer capable of measuring multi-octave spectral intensities of single femtosecond pulses with high dynamic range, enabling detailed characterization of electron bunches in accelerator physics.

Contribution

The paper presents a novel multi-octave spectrometer design that covers 250nm to 11.35μm, with a dynamic range of 8 orders of magnitude, optimized for single-pulse measurements.

Findings

Successfully characterized the spectrometer's wavelength and sensitivity.

Demonstrated measurement of CTR spectra from laser wakefield accelerated electrons.

Enabled high-resolution temporal structure analysis of electron bunches.

Abstract

We present design and realization of an ultra-broadband optical spectrometer capable of measuring the spectral intensity of multi-octave-spanning light sources on a single-pulse basis with a dynamic range of up to 8 orders of magnitude. The instrument is optimized for the characterization of the temporal structure of femtosecond long electron bunches by analyzing the emitted coherent transition radiation (CTR) spectra. The spectrometer operates within the spectral range of 250nm to 11.35$\mu$m, corresponding to 5.5 optical octaves. This is achieved by dividing the signal beam into three spectral groups, each analyzed by a dedicated spectrometer and detector unit. The complete instrument was characterized with regard to wavelength, relative spectral sensitivity, and absolute photo-metric sensitivity, always accounting for the light polarization and comparing different calibration methods. Finally, the capability of the spectrometer is demonstrated with a CTR measurement of a laser wakefield accelerated electron bunch, enabling to determine temporal pulse structures at unprecedented resolution.