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High-energy gain can be attained, considering the direct-drive approach (laser light illuminates directly the fuel capsule), using laser systems delivering a few magejoules (>=5 MJ) of ultraviolet light. These goals are attained with the condition of a spatial uniformity of 1% and an energy and power balance among the beams of 1%, which are the perfect conditions assumed in simulations. To attain these uniformity requirements some techniques are being developed like random phase plates (RPP) ILE Univ., Osaka, Japan; induce spatial incoherence (ISI) Naval Research, U.S.A.; and smoothing by spectral dispersion (SSD) Univ. of Rochester, U.S.A. The difficulty of arriving at those critical levels is connected to the proposition of the indirect-drive approach, where the laser light is first converted to x-ray radiation producing a very uniform illumination on the fuel capsule. The conversion efficiency of laser light to radiation is a function of laser wavelength, intensity, and converter material. Conversion efficiencies of 80% have been obtained in the 3 W Nd: glass laser OMEGA at the Univ. of Rochester, and is congruent to 70% with 3 W Nd: glass laser NOVA at Lawrence Livermore National Laboratory, with intensities of 1013 - 1014 W cm-2. Numerical simulations together with the experience gained with some last experiments (NOVA, CENTURION/HALITE) have demonstrated the possibility of obtaining convergence ratios of is congruent to 30 and energy gains of is congruent to 100 with laser energies is congruent to 10 MJ in the indirect-drive option. With direct or indirect approaches, if the laser technology is able to arrive at a repetition rate of a few pulses per second, a real alternative to producing electric power in large plants >=1000 MWe can be envisioned. Indirect drive is less demanding in laser technology but more costly in the minimum drive energy needed for high gain.
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