Fast Efficient Photon Deceleration in Plasmas by Using Two Laser Pulses at Different Frequencies

The generation of ultrashort high-power light sources in the mid-infrared (mid-IR) to terahertz (THz) range is of interest for applications in a number of fields, from fundamental research to biology and medicine. Besides conventional laser technology, photon deceleration in plasma wakes provides an alternative approach to the generation of ultrashort mid-IR or THz pulses. Here, we present a photon deceleration scheme for the efficient generation of ultrashort mid-IR or THz pulses by using an intense driver laser pulse with a relatively short wavelength and a signal laser pulse with a relatively long wavelength. The signal pulse trails the driver pulse with an appropriate time delay such that it sits at the front of the second wake bubble that is driven by the driver pulse. Owing to its relatively long wavelength, the signal pulse will be subjected to a large gradient of the refractive index in the plasma wake bubble. Consequently, the photon deceleration in the plasma wake becomes faster and more efficient for signal pulses with longer wavelengths. This greatly enhances the capacity and efficiency of photon deceleration in the generation of ultrashort high-power light sources in the long-wavelength IR and THz spectral ranges.