Photon accelerator

Abstract

A novel method of frequency upshifting short (≤1 ps) pulses of laser light, which makes use of relativistic plasma waves, is described. This method makes use of the fact that a laser pulse moving in a plasma can be thought of as a packet of photons, each possessing an effective mass of $m_{\gamma }$=ħ${\omega }_{\mathrm{pe}}$/$c^2$ and moving with the group velocity of the laser pulse. These photons experience a force acting on them when in the presence of a gradient in the plasma density. By using a relativistic plasma wave (i.e., a moving density gradient) traveling with the photons, energy of the photons (thus the frequency) can be continuously increased.