The more recently developed laser peening process, the Toshiba LPwC process, varies in significant ways from the process described above. The LPwC process utilizes low energy, high frequency producing pulse energies of and pulse durations of , using spot sizes diameter. Because the process originally was intended to operate in large water-filled vessels, the wave frequency was doubled to halve the wavelength to 532 nm. The shorter wavelength decreases the absorption of beam energy while traveling through water to the target. Due to access constraints, no opaque overlay is applied to the target surface. This factor, combined with the small spot size, requires many shots to achieve a significant surface compressive stress and depths of 1 mm. The first layers applied produce a tensile surface stress due to surface melting, although a compressive stress is developed below the melt layer. However, as more layers are added, the increasing subsurface compressive stress "bleeds" back through the melted surface layer to produce the desired surface compressive stress. Depending on material properties and the desired compressive stresses, generally about 18 spots/mm2 to 70 spots/mm2 or greater spot densities are applied, about 100 times the spot densities of the high pulse energy process. The effects of the higher spot densities on processing times are compensated for in part by the higher pulse frequency, 60 Hz, of the low energy lasers. Newer generations of these laser systems are projected to operate at higher frequencies. This low energy process achieves compressive residual stress magnitudes and depths equivalent to the high energy process with nominal depths of . However, the smaller spot size will not permit depths deeper than this.