A High Frequency light source has a central body of fused quartz, with a central void, filled with a fill in the void of material excitable by High Frequency energy to form a light emitting plasma. An inner sleeve of perforate metal shim extends along the length of the central body to provide a launching gap. The sleeve has a transverse end portion extending across the other, inner end of the central body. An outer cylinder of fused quartz with an internal bore such as to be a sliding fit with the inner sleeve, itself a sliding fit on the central body. An outer sleeve of perforate metal, enclosing the outer cylinder and having an end portion extending across the flush, void ends of the quartz body and cylinder and having a skirt extending past the flush over an aluminum carrier, clamped and holding the quartz elements against the carrier.