Creating localized plasma waves by ionization of doped semiconductors

Localized plasma waves can be generated by suddenly ionizing extrinsic semiconductors with spatially periodic dopant densities. The built-in electrostatic potentials at the metallurgical junctions, combined with electron density ripples, offer the exact initial condition for exciting long-lasting plasma waves upon ionization. This method can create plasma waves with a frequency between a few terahertz to subpetahertz without substantial damping. The lingering plasma waves can seed backward Raman amplification in a wide range of resonance frequencies up to the extreme ultraviolet regime. Chirped wave vectors and curved wave fronts allow focusing the amplified beam in both longitudinal and transverse dimensions. The main limitation to this method appears to be obtaining sufficiently low plasma density from solid-state materials to avoid collisional damping.

Figure 1

Schematics for generation of a plasma wave by suddenly ionizing periodically aligned $p\text{−}n$ junctions and its implementation in backward Raman amplification. The curved shape of the $p\text{−}n$ junctions demonstrates manipulation of the plasma wave front can create a prefocused backscattered pulse.

Figure 2

Generation and evolution of plasma waves by ionization of periodically doped semiconductors with (a) homogeneous ion density and an initial electrostatic field, (b) ion density of 20% nonhomogeneity and an initial electrostatic field, and (c) materials having alternating electron density and no initial electrostatic fields. The density axes are normalized to $n_e=1.12\times {10}^{25}{\mathrm{m}}^{-3}$, and the fields are normalized to $1\times {10}^8\mathrm{V}/\mathrm{m}$. The black curves in (c) show the amplitude evolution of the sinusoidal field. Here, $\lambda =0.5\mu \mathrm{m}$ is the plasma wave wavelength, and $T_p$ is the period of plasma oscillation.