Speaker
Description
Charged particles passing over a metallic grating induce undulating surface currents that emit broadband Smith-Purcell radiation (SPR) at an angle-dispersed fan of wavelengths 𝜆(𝜃), where the angle 𝜃 is measured from the particle’s propagation direction [1-2]. For a bunch of N particles of longitudinal extent 𝜎z, SPR becomes coherent, and its intensity proportional to N^2, for wavelengths 𝜆 ≳ 𝜎z. Since electron bunches from laser-driven accelerators typically have durations 𝜏 of only a few fs (i.e. 𝜎z ≲ 1 µm), their SPR is fully coherent and strong over the entire THz band (10 µm < 𝜆 < 3 mm), as recent experiments [3] have confirmed. Moreover, this coherent SPR (CSPR) is perfectly synchronized with the generating electron bunch and its secondary X-rays, potentially enabling a compact, versatile and tunable THz pump/X-ray probe combination for ultrafast high-field terahertz science. Unfortunately, CSPR suffers from inherent spatiotemporal chirping due to its angular-spectral dispersion. Left uncorrected, this chirp stretches the radiation pulse in time, limiting its effectiveness for ultrafast high-field terahertz (THz) spectroscopy.
Here, aided by simulations, I will describe an optical configuration that can remove the spatial and angular chirp from a selected bandwidth of CSPR, then compress this radiation to sub-picosecond duration and focus it to field strengths of several GV/m. Such fields are strong enough e.g. to drive resonant nonlinear interactions with phonons or high-order harmonic generation in solids at any desired THz frequency. The proposed system utilizes standard components from Chirped Pulse Amplification (CPA) technology, most notably Martinez "stretcher" configurations [4] functioning as dechirpers or compressors. The simulations will assume a simple periodic planar SPR grating, but shorter THz pulses with higher field strengths and more controlled pulse shapes than simulated here can be achieved by using more complex aperiodic gratings [5]. This study will establish a pathway for generating high-intensity, compressed pulses at any desired THz frequency, significantly enhancing the utility of CSPR from femtosecond wakefield-accelerated electron bunches in ultrafast science.
References
1. S. J. Smith and E. M. Purcell, “Visible light from localized surface charges moving across a grating,” Phys. Rev. 92, 1069 (1953).
2. G. Doucas, Smith-Purcell Radiation: Basic Theory and Applications (Oxford University Press, 2025).
3. R. Rudzinsky et al., “Coherent THz Smith–Purcell radiation from few-fs LWFA bunches,” Optica 13(5), 810–821 (2026).
4. O. Martinez, “Design of high-power ultra short pulse amplifiers by expansion and recompression,” IEEE J. Quantum Electron. 23, 1385–1387 (1987).
5. R. Remez, N. Shapira, C. Roques-Carmes et al., “Spectral and spatial shaping of Smith-Purcell radiation,” Phys. Rev. A 96, 061801 (2017).
| Working group | WG6 |
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