Plasma Density Gratings Research Articles

Formation and properties of spatially inhomogeneous plasma density gratings.

Volume plasma density gratings receive increasing interest since, compared to solid-state optical media, they posses significantly higher damage thresholds. The gratings are produced by counterpropagating laser pulses in underdense plasma. When analyzing their optical properties, usually they are assumed to be homogeneous in space. The latter assumption, however, breaks down, especially when the gratings are produced by short high-power laser pump pulses. Then, generically the plasma grating posses an inhomogeneous envelope which results from the superposition of the pump pulses envelopes. The present paper discusses the effect of grating inhomogeneity on reflection and transmission of probe pulses. A Gaussian plasma density grating becomes an apodized grating which offers significant improvement over homogeneous gratings due to side-lobe suppression while maintaining reflectivity and a narrow bandwidth. On the other hand, the reflected probe pulses receive a chirp which depends on the spatial scale. For a Gaussian grating a cubic spectral phase appears. Numerical particle-in-cell simulations are supported by theoretical analysis based on coupled mode equationsas well as an effective medium approach.

Depolarization of intense laser beams by dynamic plasma density gratings

Abstract As a typical plasma-based optical element that can sustain ultra-high light intensity, plasma density gratings driven by intense laser pulses have been extensively studied for wide applications. Here, we show that the plasma density grating driven by two intersecting driver laser pulses is not only nonuniform in space but also varies over time. Consequently, the probe laser pulse that passes through such a dynamic plasma density grating will be depolarized, that is, its polarization becomes spatially and temporally variable. More importantly, the laser depolarization may spontaneously take place for crossed laser beams if their polarization angles are arranged properly. The laser depolarization by a dynamic plasma density grating may find application in mitigating parametric instabilities in laser-driven inertial confinement fusion.

Growth, saturation, and collapse of laser-driven plasma density gratings

The plasma density grating induced by intersecting intense laser pulses can be utilized as optical compressors, polarizers, waveplates, and photonic crystals for the manipulation of ultra-high-power laser pulses. However, the formation and evolution of plasma density grating are still not fully understood as linear models are adopted to describe them usually. In this paper, two theoretical models are presented to study the formation process of plasma density grating in the nonlinear stages. In the first model, an implicit analytical solution based on the fluid equations is presented, while in the second model, a particle-mesh method is adopted. It is found that both models can describe the plasma density grating formation at different stages, well beyond the linear growth stage. More importantly, the second model can reproduce the phenomenon of ion “wave-breaking” of plasma density grating, which eventually induces the saturation and collapse of plasma density grating. Using the second model, the saturation time and maximum achievable peak density of plasma density grating are obtained as functions of laser intensity and plasma density, which can be applied to estimate the lifetime and capability of plasma density grating in experiments. The results from these two newly developed models are verified using particle-in-cell simulations.

Plasma volume holograms for focusing and mode conversion of ultraintense laser pulses.

Beating of a broad laser reference beam with a quite general focused object beam inside a plasma volume generates a dynamic plasma hologram. Both beams may be of moderate intensity. The volume hologram can be read out by an ultraintense main beam (of similar structure as the reference beam) producing an object beam replica. For the latter, intensity in the focus may become extremely large. As an application, the possibility of a read-out focused Gaussian laser pulse with intensity of several 10^{19}W/cm^{2} in focus is shown by three-dimensional numerical simulations. Besides the focusing possibility, the hologram may also act as a mode converter for high-intensity laser pulses. Generating a plasma hologram with a focused Laguerre-Gaussian object beam results in a staggered plasma density grating, allowing the production of high-intensity vortex beam replica.

Laser-driven plasma photonic crystals for high-power lasers

Laser-driven plasma density gratings in underdense plasma are shown to act as photonic crystals for high power lasers. The gratings are created by counterpropagating laser beams that trap electrons, followed by ballistic ion motion. This leads to strong periodic plasma density modulations with a lifetime on the order of picoseconds. The grating structure is interpreted as a plasma photonic crystal time-dependent property, e.g., the photonic band gap width. In Maxwell–Vlasov and particle-in-cell simulations it is demonstrated that the photonic crystals may act as a frequency filter and mirror for ultra-short high-power laser pulses.

Investigation of plasma density gratings in current carrying plasmas by particle in cell method

Plasma density gratings induced in current carrying plasmas are investigated through the particle in cell method. Simulation results show that the electron phase space holes can be formed at the saturation time which confirms the counter-streaming in these plasmas. It is found that the generation of grating-like pattern strongly depends on the saturation time and velocity of electrons and positrons. Moreover, in the presence of delta distribution function the grating-like pattern is obvious, compared to the Maxwellian distribution. Finally, using the fluid model, it is demonstrated that increasing the velocity of electrons and positrons causes to increase the maximum amount of growth rate of instability which is in good agreement with those obtained using the simulation model.

Formation of a Plasma Photonic Crystal by Self-Induced Quasi Periodic Plasma Density Grating

In the present paper, we first show that the plasma injected into the interaction region forms a periodical distribution of the plasma density that is called self-induced density grating and exerts a periodic perturbation on the dielectric constant under two strong counterpropagating waves modulation. In succession, we demonstrate that the self-induced quasi periodic plasma density grating formed by the self-induced distributed feedback possesses the properties of plasma photonic crystal (PPC). Therefore, the formation of PPC by the self-induced quasi periodic plasma density grating is a feasible fabrication scenario for PPC. Based on an equivalent model of the plasma density grating, a dispersion relation is derived, and a simple case is calculated and discussed.

Femtosecond laser induced plasma diffraction gratings in air as photonic devices for high intensity laser applications

The creation of volume plasma density gratings in air by temporally overlapped high-intensity IR femtosecond laser pulses is demonstrated experimentally. Through the diffraction of various probe beams the plasma grating properties are recovered including its thickness and refractive index modulation, as well as its decay dynamics. The diffraction properties of these plasma photonic devices suggest that they can be used in applications involving high intensity lasers, such as filamentation, where no physical objects can be placed in the path of the laser beams.

Plasma density gratings induced by intersecting laser pulses in underdense plasmas

Electron and ion density gratings induced by two intersecting ultrashort laser pulses at intensities of 1016 W/cm2 or lower are investigated. The ponderomotive force generated by the inhomogeneous intensity distribution in the intersecting region of the interfering pulses produces deep electron and ion density modulations at a wavelength less than a laser wavelength in vacuum. Dependence of the density modulation on the plasma densities, temperatures, and the ion mass, as well as the laser pulse parameters are studied analytically and by particle-in-cell simulations. It is found that the density peaks of such gratings can be a few times that of the initial plasma density and last as long as a few picoseconds. It is also demonstrated that the scattering of signal pulses by such a bulk density grating results in high-harmonic generation. The density gratings may be incorporated into ion-ripple lasers [K.R. Chen and J.M. Dawson, Phys. Rev. Lett. 68, 29 (1992)] to generate ultrashort X-ray pulses of a few angstroms by using electron beams at only a few tens of MeV only.

Study of open cavity filled with plasma density grating

The dielectric open cavity filled with the plasma is studied. The plasma density grating formed by the slow wave modulation influences the resonant parameters. Based on an equivalent model of the plasma density grating, a dispersion relation is derived and the resonant frequency, the diffraction Q value, and the field function are calculated. The field magnitude in the slow-wave region increases greatly as the plasma density increases, which can help to explain the enhancement of the beam-wave interaction efficiency.