  A double-phase Ar detector can efficiently identify particles and reconstruct
their positions. However, the properties of electroluminescence (EL) for
secondary light emission in the gas phase are not fully understood. Earlier
studies have explained the EL process using an ordinary EL mechanism because of
an Ar excimer; however, this mechanism does not predict the emission of visible
light (VL). Recent measurements have demonstrated VL components in Ar gas EL,
to explain which a new mechanism called neutral bremsstrahlung (NBrS) was
proposed. In this study, we investigated gaseous Ar EL in the VL region from
300 to 600 nm at room temperature and normal pressure using a gaseous time
projection chamber (TPC). The secondary emission light from the TPC
luminescence region was dispersed using a spectrometer. The observed spectrum
was interpreted using the ordinary EL and NBrS models, and the effect of
nitrogen impurities is discussed herein.
