Long-term Frequency Instability Research Articles

Low Frequency Noise Quartz Crystal Oscillator

For years, engineers and scientists have been plagued by an extremely undesirable property of the quartz crystal unit-its significant frequency shift as a function of drive level for drive levels in excess of 10 to 100 μW. This fact was reported by Hammond [1]. As a result, all precision and moderate precision quartz oscillators have been operated at low drive in an effort to avoid the phenomena. The author has discovered, however, that this unique property of the quartz resonator can be effectively utilized in the design of the quartz oscillator with the result of substantial improvement in oscillator short-term frequency stability. Futhermore, since the crystal frequency-drive characteristic is repeatable, maintenance of moderately high crystal drive in the oscillator circuit will not result in long-term frequency instability in excess of that required for the majority of radar and communication systems [2].

Studying the stability of wavelengths radiated by a gas laser

1. According to the theoretical analysis the instability of a laser of the above design for 20–30 min operation in a single TEM00q mode amounts to ∼10−7. 2. The technique and equipment developed by us for measuring long-term and short-term frequency instability of a continuously-operating laser provides a resolution of (5–7) · 10−10 for relative measurements and of ∼7 · 10−8 for absolute measurements of wavelengths. 3. Under normal laboratory operating conditions the laser radiation wavelength instability amounted to ∼1.5 · 10−7 for durations of 10–15 min and to ∼1 · 10−7 for durations of 10 sec. 4. The laser stability is substantially raised by using an automatic frequency stabilization by means of an external (reference) thermostatically controlled resonator. Tests have shown that the radiation frequency instability under these conditions amounts to (5–8) · 10−9 for 10–15 sec and to ∼10−8 for 20–30 min. An improvement of the above equipment will probably raise the frequency stability at least tenfold. 5. The above results show that the laser developed by us can be used successfully with a stabilization circuit for various metrological experiments.