Excimer lamps radiation mode

In addition to the low surface femperature, excimer lamps have fhe advantage that they start immediately, so they can be switched on and off as needed. There is no need for sfandby function and for a shuffer system, so no movable parts are necessary on the radiation head. Both continuous and pulse mode operation is possible. The lamps are very compact, which is particularly important for the printing industry, because it is possible to retrofit them into the existing process. 

Excimer lamps were selected to study the low fluence irradiation region, where linear (no ablation) photochemistry is taking place. This is the fluence range (e.g., insert in Fig. 47 of the previous chapter), where a linear relation between reaction products and laser fluence is observed. This may correspond to the range of linear photochemistry, i.e., below the threshold of ablation (see, e.g., Figs. 25 and 26), or the so-called Arrhenius tail. The excimer lamps emit at the same wavelengths as the excimer lasers, but with incoherent radiation, and in quasi-CW mode. The peak photon fluxes of the lamps are low compared to the excimer laser, suggesting that multiphoton processes are not important. Thin films of the triazene polymer on quartz substrates were irradiated with the excimer lamps under different conditions, i.e., in Ar, air, and 02. 

An intense short pulse of UV or visible radiation is used to electronically excite the sample, and the subsequent absorption changes are probed spectrophotomet-rically. The technique was first introduced by Norrish and Porter in 1949 [18] and at this time gas-filled discharge lamps were used, limiting the time resolution, which is principally governed by the duration of the excitation pulse, to microseconds. This is now usually termed conventional flash photolysis. However, with the development of laser pulsed techniques in place of flash excitation, the time resolution has been progressively reduced to subpicosecond, particularly with the use of mode-locked solid state lasers. Much current work utilises nanosecond time resolution with pulsed lasers such as ruby, neodymium and excimer lasers. 

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