have the potential for use in underwater communications because seawater is quite transparent in this range of wavelengths. Common argon and krypton lasers are capable of emitting continuous-wave (CW) output of several milliwatts to tens of watts. Their tubes are usually made from nickel end bells, kovar metal-to-ceramic seals, beryllium oxide ceramics, or tungsten disks mounted on a copper heat spreader in a ceramic liner. The earliest tubes were simple quartz, then followed by quartz with graphite disks. In comparison with the helium–neon lasers, which require just a few milliamperes of input current, the current used for pumping the argon laser is several amperes, since the gas has to be ionized. The ion laser tube produces much waste heat, and such lasers require active cooling. The typical noble-gas ion-laser plasma consists of a high-current-density glow discharge in a noble gas in the presence of a magnetic field. Typical continuous-wave plasma conditions are current densities of 100 to 2000 A/cm2, tube diameters of 1.0 to 10 mm, filling pressures of 0.1 to 1.0 Torr (0.0019 to 0.019 psi), and an axial magnetic field of the order of 1000 gauss. William R. Bennett, a co-inventor of the first gas laser (the helium–neon laser), was the first to observe spectral hole burning effects in gas lasers, and he created the theory of "hole burning" effects in laser oscillation. He was co-discoverer of lasers using electron-impact excitation in each of the noble gases, dissociative excitation transfer in the neon–oxygen laser (the first chemical laser), and collision excitation in several metal-vapor lasers. Other commercially available types Ar/Kr: A mix of argon and krypton can result in a laser with output wavelengths that appear as white light. Helium–cadmium: blue laser emission at 442 nm and ultraviolet at 325 nm. Copper vapor: yellow and green emission at 578 nm and 510 nm. Experimental Xenon Iodine Oxygen Applications Confocal laser scanning microscopy Surgical Laser medicine High speed typesetters Laser light shows DNA sequencers Spectroscopy experiments Pumping dye lasers Semiconductor wafer inspection Direct write high density PCB lithography Fiber Bragg Grating production Long coherence length models can be used for holography See also Laser List of laser types List of plasma (physics) articles References American inventions Gas lasers