The Fundamentals of EDL Construction and Performance

The EDL system is modular and consists of two basic parts, a gas-filled bulb and a power supply with waveguides or external electrodes. A typical EDL is made of a scaled (usually quartz) tube envelope, which contains an inert gas (for example a noble gas) and an excitable substance (e.g., Hg, Cd, Na, Ga, In, Tl, Sc, S, Se, or Te) 

The construction of microwave-excited EDL is relatively straightforward but there are several operating conditions in their preparation which must be considered to produce an intense light source. The desired characteristics and requirements for EDL are high intensity, high stability, long lifetime, and, to a lesser extent, low cost and high versatility. In practice, it is very difficult to meet all these characteristics simultaneously. 

The performance of EDL depends strongly on many preparation and operating conditions [35]  

The inert gas. The arc chamber contains a buffer noble gas (usually Kr, Xe, or Ar) which is inert to the extent that it does not adversely affect the lamp operation. 

Temperature of the lamp. Operation at a high power or high temperatures can increase emission intensity but, at the same time, reduce the lamp lifetime and lead to broadening of the atomic line profile, because of self-absorption and selfreversal effects. It has been found that the optimum operating temperature for mercury filling is 42 °C (for the 254 nm line) [35]. The output is reduced when the temperature is beyond the optimum. 

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