Enhancement of Photon Number Reflected by the Relativistic Flying Mirror

Laser light reflection by a relativistically moving electron density modulation (flying mirror) in a wake wave generated in a plasma by a high intensity laser pulse is investigated experimentally. A counterpropagating laser pulse is reflected and upshifted in frequency with a multiplication factor of 37–66, corresponding to the extreme ultraviolet wavelength. The demonstrated flying mirror reflectivity (from $3\times {10}^{-6}$ to $2\times {10}^{-5}$, and from $1.3\times {10}^{-4}$ to $0.6\times {10}^{-3}$, for the photon number and pulse energy, respectively) is close to the theoretical estimate for the parameters of the experiment.

Figure 1

A schematic of the experimental setup.

Figure 2

(a) Artificially superimposed top-view plasma image from two independent shots with driver (left) and source (right) only present. The line shows the plasma density distribution measured via interferometry. The open circle shows the colliding point in this particular shot ($x_0=580\mu \mathrm{m}$). (b) Shadowgram side view of two colliding pulses. The bright spot in the center is strong emission around the laser wavelength.

Figure 3

(a) Raw CCD image obtained with the normal incidence spectrograph. (b) Spectra in the diffraction order of $m=1$ (black) and $m=-1$ (red). (c) CCD counts within the 1st diffraction order vs driver delay. The source off shots are shown for comparison, the delay is arbitrarily assigned.

Figure 4

(a) CCD counts (solid line) and He atom density (dashed line) vs the distance to the gas-jet center $x$. The best collision point $x_0$ is marked with the open circle. (b) The signal spatial position vs the driver delay ${\tau }_D$.

Figure 5

The laser pulse (a) self-focusing and the electron density (b),(c) evolution seen in the 2D PIC simulation. The self-focusing position $x_{\mathrm{sf}}$ corresponds to the collision point in Fig. 2. (d) The radiation reflected from the wake wave revealing an instantaneous pattern of the breaking wake wave (e).