Relative frequency stability of stable He-Ne gas laser structures

Enhanced He-Ne gas laser stability has been achieved by constructing the mirror and gas discharge tube as an integral unit. The primary components are made from Corning ULE and 99JJW ultralow thermal expansion materials; ultrahigh-vacuum-type materials are used throughout. The ambient pressure sensitivity of these 6328-Å laser structures is 2.5 MHz/torr. Preliminary beat frequency measurements between two lasers, under pressure and temperature-controlled conditions, have yielded a beat frequency spectral width of the order of 2 kHz over an interval of 1 s. This result was achieved without the use of any elaborate sound or vibration isolation. Improved isolation reduced the spectral width to 100 Hz for a measurement duration of 0.02 s. The single-structure mirror-discharge tube has provided relative output power stabilities of better than 3 parts in 1000 over a period of 12 h. The frequency-modulation sensitivity is 1.2 kHz/μA of discharge current, from dc to 100 kHz.