Proceedings Article | 14 May 2019
KEYWORDS: Plasma, Infrared radiation, Photons, Long wavelength infrared, Particle beams, Light sources, Refractive index, Structural design, Pulsed laser operation, Nonlinear optics
Wakefield excited by intense lasers or charged particle beams in plasmas has made great strides recent years in demonstrating high-gradient acceleration of electron and positron beams, showing its tremendous potential in revolutionizing the design of next-generation compact light sources and colliders. In a plasma wakefield accelerator, the wakefield essentially serves as an "accelerator" for the witness beam, at the same time a "decelerator" for the driver. For a beam driver, the deceleration is simply the effect of the deceleration field. But for a laser driver, photons do not feel a deceleration field directly, instead they deplete their energy via frequency downshifting on a refractive index gradient, leading to a slowing down of their group velocity, literally behaving like “a photon decelerator”. In fact, theory and simulations suggest that such a photon decelerator with a properly designed plasma structure could serve as an ideal nonlinear optical device for the generation of intense single-cycle broadband long-wavelength infrared (IR) pulses. Here we successfully demonstrate this novel scheme in experiments. An intense single-cycle IR pulse with a central wavelength of 9.4 µm and energy of 3.4 mJ is generated using a ~580 mJ, 36 fs, 810 nm drive laser. Furthermore, the tunability of the IR wavelength in the range of 4-15µm is also successfully demonstrated through simple adjustment of the plasma structure. This relativistically intense, ultra-broadband infrared pulse opens up many opportunities for relativistic-infrared nonlinear optics, attosecond X-ray pulses via high-harmonic generation, and pump-probe experiments in the “molecular fingerprint” region.
References:
[1] Zan Nie, Chih-Hao Pai, Jianfei Hua, et al., “Relativistic single-cycle tunable infrared pulses generated from a tailored plasma density structure”, Nature Photon., 12: 489, 2018
[2] Zan Nie, et al., to be submitted
