RLOD#4 (08.05.2020) 1976 Narva D2E/1

Electrical discharges in deuterium at high current generate a continuous UV spectrum that extends down to the deep UV-C domain, an optical characteristic that is highly useful in various scientific and technical applications. Lamps built specifically to run such discharge were first developed during the 1940s from gas-filled thermionic diodes. During the 1960s their design eventually evolved into the standard configuration shown in the present Narva D2E/1. In this lamp a sheet metal box contains the thermionic cathode and the plate anode, with a 1-mm pinhole placed in between. The function of the latter is to constrict the discharge so as to increase the plasma current density to the level needed (about 40 A/cm2) for the emission of a continuous molecular spectrum. This configuration results also in a bright and near point-like source of radiation, which enables a precise and effective optical control of the emitted light. In order to gain access to the UV part of the emitted spectrum the bulb is made of fused silica. While such glass is highly transparent to shortwave radiations, its transmittance tends to cut off around 200 nm due to impurities present in the material. This problem is mitigated by the use of a thin-walled window placed in front of the point of light emission, which effectively gives access to optical radiation down to about 160 nm.