中央研究院 原子與分子科學研究所

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.