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Tunable lasers handbook phần 2

Các điện tử phát ra đi qua các lá, mặc dù mất đi một số năng lượng, và nhập vào các phương tiện truyền thông phát laser, tạo ra các ion. Mặc dù lớn và đắt tiền. các thiết bị này dễ dàng thu nhỏ kích thước mét và cho phép dài xung (1 psec hoặc cao hơn) bơm. | 34 R. c. Sze and D. G. Harris originate by field emission from a cathode frequently carbon felt which has been negatively pulsed with respect to the anode generally maintained at ground. The vacuum diode generally operating at 10 5 to 10 7 Torr is separated from the high-pressure laser gases by a thin foil. The emitted electrons pass through the foil though losing some energy and enter the lasing media creating ions. Although large and expensive these devices are easily scaled to meter dimensions and allow long-pulse 1 psec or greater pumping. They are therefore generally used as amplifiers rather than oscillators. Preionized avalanche discharges have been utilized to produce a uniform plasma. The low-energy electrons in the plasma acquire sufficient energy to excite the rare gas atoms to a metastable state thus allowing the reaction kinetics to proceed along the neutral reaction channel. The relative ease and low cost of this approach has led to the rapid development of high-average-power lasers. Discharge excimer lasers are discussed in Section 4. Table 1 lists some of the best known excimer lasers with their respective electronic transitions and approximate emission bandwidth and or tuning ranges. In addition to tunability an important characteristic in pulsed gas lasers including excimer lasers is narrow-linewidth emission. Some of the early work on tunable narrow-linewidth excimer lasers was reported by Loree et al. 3 who utilized isosceles prisms to provide intracavity dispersion and wavelength tuning in excimer lasers. These authors report linewidths of 0.1 to 0.2 nm and 0.05 nm for KrF and ArF lasers respectively 3 . Additional and alternative methods to yield narrow-linewidth emission include the use of intracavity etalons 9 and grazingincidence GI configurations 4 . During this period circa 1984 multiple-prism TABLE 1 Excimer Laser Transitions Laser Transition 2 nm Bandwidth Reference ArF B - x 193 17000 GHz - 3 KrF B - x 248 10500 GHz 3 2583 GHz 4 XeCl B