A method for inertial confinement fusion driven by powerful long wavelength electromagnetic pulses (EMPs), such as ${\rm CO}_{2}$ laser pulses or high power microwave pulses, is proposed. Due to the high efficiency of generating such long wavelength electromagnetic pulses, this method is especially important for the future fusion electricity power Special fuel targets are designed to overcome the shortcomings of the long wavelength electromagnetic pulses.

Theoretical–computational studies of table-top laser-driven nuclear fusion of high-energy (up to 15 MeV) deuterons with ${}^{7} \mathrm{Li} $, ${}^{6} \mathrm{Li} $, and D nuclei demonstrate the attainment of high fusion yields within a source–target reaction design. This constitutes a source of Coulomb-exploding deuterium nanodroplets driven by an ultraintense femtosecond near-infrared laser and a solid hollow cylindrical target containing the second element. The source–target reaction design attains the highest table-top fusion efficiencies (up to $4\times 1{0}^{9} ~{\mathrm{J} }^{- 1} $ per laser pulse) obtained to date. The highest conversion efficiency of laser energy to nuclear energy ($1{0}^{- 2} $–$1{0}^{- 3} )$ for table-top DD fusion attained in the source–target design is comparable to that for DT fusion currently accomplished for ‘big science’ inertial fusion setups.

We will review some of the requirements for a laser that would be used with a laser fusion energy power plant, including frequency, spatial beam smoothing, bandwidth, temporal pulse shaping, efficiency, repetition rate, and reliability. The lowest risk and optimum approach uses a krypton fluoride gas laser. A diode-pumped solid-state laser is a possible contender.

It is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect. Above this upper-limit critical power, the laser pulse experiences defocusing due to expulsion of local plasma electrons by the transverse ponderomotive force. Associated with the upper-limit power, a lower-limit critical plasma density is also found for a given laser spot size, below which self-focusing does not occur for any laser power. Both the upper-limit power and the lower-limit density are derived theoretically and verified by two-dimensional particle-in-cell simulations. The present study provides new guidance for experimental designs, where self-guided propagation of lasers is essential.

The process of high power laser interaction with the large scale length corona plasma produced by the leading edge of the laser pulse has been investigated. Early experimental results are re-analyzed and conclusions drawn. In particular, studies of the close connection of unstable filamentation instability with – mainly – two-plasmon decay and – partly – stimulated Raman scattering, stimulated Brillouin scattering, and resonance absorption are carried out in this paper. The positive and negative effects of filamentation instability are also discussed.

We demonstrated experimentally the formation of monoenergetic beams of accelerated electrons by focusing femtosecond laser radiation with an intensity of $2\times 1{0}^{17} ~\mathrm{W} / {\mathrm{cm} }^{2} $ onto the edge of an aluminum foil. The electrons had energy distributions peaking in the 0.2–0.8 MeV range with energy spread less than 20%. The acceleration mechanism related to the generation of a plasma wave as a result of self-modulation instability of a laser pulse in a dense plasma formed by a prepulse (arriving 12 ns before the main pulse) is considered. One-dimensional and two-dimensional Particle in Cell (PIC) simulations of the laser–plasma interaction showed that effective excitation of a plasma wave as well as trapping and acceleration of an electron beam with an energy on the order of 1 MeV may occur in the presence of sharp gradients in plasma density and in the temporal shape of the pulse.

We demonstrate a monolithic single frequency Tm-doped fiber amplifier with output power of 51.5 W. A single frequency fiber laser at 1.97 $\mathrm {\mu} $m is amplified by a cascaded master oscillator power amplifier (MOPA) system with all-fiber configuration. The optical-to-optical conversion efficiency of the main fiber amplifier is 45%. No amplified spontaneous emission (ASE) or stimulated Brillouin scattering (SBS) effect is observed in the fiber amplifier. The output power could be further scaled by launching more pump power.

The driving mechanism of solar flares and coronal mass ejections is a topic of ongoing debate, apart from the consensus that magnetic reconnection plays a key role during the impulsive process. While present solar research mostly depends on observations and theoretical models, laboratory experiments based on high-energy density facilities provide the third method for quantitatively comparing astrophysical observations and models with data achieved in experimental settings. In this article, we show laboratory modeling of solar flares and coronal mass ejections by constructing the magnetic reconnection system with two mutually approaching laser-produced plasmas circumfused of self-generated megagauss magnetic fields. Due to the Euler similarity between the laboratory and solar plasma systems, the present experiments demonstrate the morphological reproduction of flares and coronal mass ejections in solar observations in a scaled sense, and confirm the theory and model predictions about the current-sheet-born anomalous plasmoid as the initial stage of coronal mass ejections, and the behavior of moving-away plasmoid stretching the primary reconnected field lines into a secondary current sheet conjoined with two bright ridges identified as solar flares.

An energy measurement system in a Large-aperture high power laser experiment platform is introduced. The entire measurement system includes five calorimeters, which carry out the energy measurement of the fundamental frequency before the frequency conversion unit, remaining fundamental frequency, remain second-harmonics, third harmonics, as well as the energy balance measurement after the frequency conversion unit. Combinational indirect calibration and direct calibration are employed to calibrate the sampling coefficients of the calorimeters. The analysis of the data showed that, regarding the energy balance coefficients, combinational calibration approach gives a higher precision, and leads to an energy balance with 1%; and regarding the energy sampling coefficients for the various wavelengths after the frequency conversion, the results from direct and combinational calibration are consistent. The uncertainties for all energy sampling coefficients are within 3%, which guarantees the reliability of the energy measurement for the laser facility.

Considering the time delay in different hohlraum wall positions caused by oblique incidence, the spatio-temporal optical field distribution characteristics of a hohlraum wall, especially during the rising edge of a flat-topped pulse, is simulated by a fast Fourier transform method together with chromatography. Results demonstrate that beam propagation along the hohlraum wall is a push-broom process with complex dynamic spatial–temporal evolution. In the first few picoseconds, the optical intensity of the front position increases rapidly, while that of the rear position is relatively weak. The ratio $R$ of the optical intensity during the rising edge is smaller than that of the steady state. $R$ gradually increases and finally tends to the value of the steady state with time. Calculation also shows that, with shorter total width of the rising edge, $R$ of the optical field decreases and the difference compared to the steady state becomes larger. The evolution is more severe with smaller angle of inclination.

We review the use of hollow-core photonic crystal fibre (HC-PCF) for high power laser beam delivery. A comparison of bandgap HC-PCF with Kagome-lattice HC-PCF on the geometry, guidance mechanism, and optical properties shows that the Kagome-type HC-PCF is an ideal host for high power laser beam transportation because of its large core size, low attenuation, broadband transmission, single-mode guidance, low dispersion and the ultra-low optical overlap between the core-guided modes and the silica core-surround. The power handling capability of Kagome-type HC-PCF is further experimentally demonstrated by millijoule nanosecond laser spark ignition and ${\sim }100~\mathrm{\mu} \mathrm{J} $ sub-picosecond laser pulse transportation and compression.

Beam positioning stability in a laser-driven inertial confinement fusion (ICF) facility is a vital problem that needs to be fixed. Each laser beam in the facility is transmitted in lots of optics for hundreds of meters, and then targeted in a micro-sized pellet to realize controllable fusion. Any turbulence in the environment in such long-distance propagation would affect the displacement of optics and further result in beam focusing and positioning errors. This study concluded that the errors on each of the optics contributed to the target, and it presents an efficient method of enhancing the beam stability by eliminating errors on error-sensitive optics. Optimizations of the optical system and mechanical supporting structures are also presented.

The intensity distributions of a high-power broadband laser beam passing through a nonlinear optical medium with defects and then propagating in free space are investigated based on the general nonlinear Schrödinger equation and the split-step Fourier numerical method. The influences of the bandwidth of the laser beam, the thickness of the medium, and the defects on the light intensity distribution are revealed. We find that the nonlinear optical effect can be suppressed and that the uniformity of the beam can be improved for a high-power broadband laser beam with appropriate wide bandwidth. It is also found that, under the same incident light intensity, a thicker medium will lead to a stronger self-focusing intensity, and that the influence of defects in the optical elements on the intensity is stronger for a narrowband beam than for a broadband beam.

Recent experimental results on NIF revealed a much higher stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) backscatter than expected; one possible reason was due to the coherence between incident laser beams. In our research, two laser beams (${\sim }1~\mathrm{ns} $, ${\sim }250~\mathrm{J} , 527~\mathrm{nm} $ in each one) with different coherent degrees between them from the SG-II facility were employed to irradiate an Au plate target; the backscatter of SBS and SRS in the range of the given solid angle had been measured. The results showed that it could change dramatically corresponding to the difference of the coherent degree between the two laser beams, and there was usually more intense backscatter the higher the coherent degree between the incident beams.

Recent progress on rare-earth doped polycrystalline YAG transparent ceramics has made them an alternative novel solid-state laser gain material. In this paper we present results of our research on polycrystalline RE:YAG transparent ceramics. High optical quality YAG ceramics doped with various rare-earth (RE) ions such as ${\rm Nd}^{3+}$, ${\rm Yb}^{3+}$, ${\rm Er}^{3+}$, ${\rm Tm}^{3+}$, and ${\rm Ho}^{3+}$ have been successfully fabricated using the solid-state reactive sintering method. Highly efficient laser oscillations of the fabricated ceramics are demonstrated.

Laser resistance and stress-free mirrors, windows, polarizers, and beam splitters up to $400~\mathrm{mm} \times 400~\mathrm{mm} $ are required for the construction of the series SG facilities. In order to improve the coating quality, a program has been in place for the last ten years. For the small-aperture pick-off mirror, the laser-induced damage threshold (LIDT) is above $60~\mathrm{J} / {\mathrm{cm} }^{2} $ (1064 nm, 3 ns), and the reflected wavefront is less than $\lambda / 4~(\lambda = 633~\mathrm{nm} )$. The Brewster-angle polarizing beam splitter ($\Phi 50\times 10~\mathrm{mm} $) shows the best LIDT result, up to $29. 8~\mathrm{J} ~{\mathrm{cm} }^{- 2} $ (1064 nm, 10 ns) for a p-polarized wave in the 2012 damage competition of the XLIV Annual Boulder Damage Symposium. For the larger-aperture mirror and polarizer, the LIDT is above $23~\mathrm{J} ~{\mathrm{cm} }^{- 2} $ (1064 nm, 3 ns) and $14~\mathrm{J} ~{\mathrm{cm} }^{- 2} $ (1064 nm, 3 ns), respectively. The reflected wavefront is less than $\lambda / 3~(\lambda = 633~\mathrm{nm} )$ at the used angle.

Two different pulse cleaning techniques for ultra-high contrast laser systems are comparably analysed in this work. The first pulse cleaning technique is based on noncollinear femtosecond optical-parametric amplification (NOPA) and second-harmonic generation (SHG) processes. The other is based on cross-polarized wave (XPW) generation. With a double chirped pulse amplifier (double-CPA) scheme, although temporal contrast enhancement in a high-intensity femtosecond Ti:sapphire chirped pulse amplification (CPA) laser system can be achieved based on both of the techniques, the two different pulse cleaning techniques still have their own advantages and are suitable for different contrast enhancement requirements of different laser systems.

An accelerated micro-foil is used to ignite a pre-compressed cylindrical shell containing deuterium–tritium fuel. The well-known shock wave ignition criterion and a novel criterion based on heat wave ignition are developed in this work. It is shown that for heat ignition very high impact velocities are required. It is suggested that a multi-petawatt laser can accelerate a micro-foil to relativistic velocities in a very short time duration (˜picosecond) of the laser pulse. The cylindrical geometry suggested here for the fast ignition approach has the advantage of geometrically separating the nanosecond lasers that compress the target from the picosecond laser that accelerates the foil. The present model suggests that nuclear fusion by micro-foil impact ignition could be attained with currently existing technology.

We present a recent numerical analysis of impedance mismatch technique applied to carbon equation of state measurements. We consider high-power laser pulses with a Gaussian temporal profile of different durations. We show that for the laser intensity (${\approx }1{0}^{14} ~\mathrm{W} / {\mathrm{cm} }^{2} $) and the target design considered in this paper we need to have laser pulses with rise-time less than 150 ps.