Photon accelerator: A novel method of frequency upshifting sub-picosecond laser pulses

Anovel method of frequency upshifting subpicosecond pulses of laser light, which makes use of relativistic plasma waves, is described in this paper. This method makes use of the fact that the response of a plasma to either a short laser pulse or a short relativistic electron beam is nearly identical. Thus, the wakefields, or electric fields, that are left behind in the plasma as either of these drivers pass, are also very similar. Since electron acceleration in plasma waves can effectively be thought of as the simple superposition of wakes, this analogy brings about the interesting question of whether the superposition of short laser pulse wakes would produce “acceleration” (or equivalently, frequency upshifting) of a trailing laser pulse. We estimate the rate of frequency upshift possible, and discuss some important physical limitations.