Photon deceleration in plasma wakes generates single-cycle relativistic tunable infrared pulses

Zan Nie,Yunxiao He,Hsu-Hsin Chu,Xiaonan Ning,Jyhpyng Wang,Warren B Mori,Jie Zhang,Chaojie Zhang,Shuang Liu,Yue Ma,Chih-Hao Pai,Yipeng Wu,Wei Lu,Qianqian Su,Chan Joshi,Zhi Cheng,Jianfei Hua

doi:10.1038/s41467-020-16541-w

Abstract

Availability of relativistically intense, single-cycle, tunable infrared sources will open up new areas of relativistic nonlinear optics of plasmas, impulse IR spectroscopy and pump-probe experiments in the molecular fingerprint region. However, generation of such pulses is still a challenge by current methods. Recently, it has been proposed that time dependent refractive index associated with laser-produced nonlinear wakes in a suitably designed plasma density structure rapidly frequency down-converts photons. The longest wavelength photons slip backwards relative to the evolving laser pulse to form a single-cycle pulse within the nearly evacuated wake cavity. This process is called photon deceleration. Here, we demonstrate this scheme for generating high-power (~100 GW), near single-cycle, wavelength tunable (3–20 µm), infrared pulses using an 810 nm drive laser by tuning the density profile of the plasma. We also demonstrate that these pulses can be used to in-situ probe the transient and nonlinear wakes themselves.

Highlights

Availability of relativistically intense, single-cycle, tunable infrared sources will open up new areas of relativistic nonlinear optics of plasmas, impulse IR spectroscopy and pump-probe experiments in the molecular fingerprint region
It has been proposed that a wake generated by an intense pump laser pulse in a properly designed plasma density structure can serve as a new type of nonlinear optical device for generating intense single-cycle broadband LWIR pulses[15]
The strong time-dependent plasma density gradients formed during the expulsion of the plasma electrons phase modulate the laser pulse downshifting the instantaneous frequency of the photons as explained earlier while the wavelength-dependent group velocity disperses these photons

Summary

Introduction

Availability of relativistically intense, single-cycle, tunable infrared sources will open up new areas of relativistic nonlinear optics of plasmas, impulse IR spectroscopy and pump-probe experiments in the molecular fingerprint region. It has been proposed that a wake (density disturbance) generated by an intense pump laser pulse in a properly designed plasma density structure (such as that shown in Fig. 1a) can serve as a new type of nonlinear optical device for generating intense single-cycle broadband LWIR pulses[15]. This happens because of a combination of asymmetric self-phase modulation (ASPM) that mainly produces frequency downconverted photons and group velocity dispersion (GVD) of these photons in the plasma. We experimentally demonstrate the generation of such pulses containing millijoules of energy in the 3–20 μm wavelength range by utilizing the interaction between an intense laser pulse and the nonlinear wake it generates in a specially prepared plasma density structure

Methods

Results

Conclusion