Frequency stabilized HeNe gas laser with 3.5 mW from a single mode

This paper describes an optical frequency stabilization technique using a three-mode Helium Neon laser at 632.8 nm. Using this configuration, a maximum frequency stability relative to an iodine stabilized laser of 6×10−12 (71 s integration time) was achieved. Two long term measurements of 62 h and 40 h showed fractional frequency fluctuations of 6.2×10−10 (2σ) and 1.6×10−10 (2σ) when correcting for known frequency fluctuations outside the controller bandwidth, respectively. This stabilization scheme maximizes the available optical power (1.7 mW in this instance) because the output mode is in the center of the HeNe gain curve. This stabilization technique was also verified for a larger HeNe laser with a lower free spectral range. While not optimized for this configuration and laser, we demonstrated fractional frequency fluctuations below 1×10−8 with 3.5 mW of usable output power. This is useful for multi-axis systems or systems employing fiber coupling. In this paper, the overall system is described and data containing the frequency locking signal sensitivity, profile during laser warm up, sensitivity to environmental fluctuations, and optical power of the locking signal is shown.

► Frequency stabilized three-mode HeNe lasers can be stabilized to better than 0.1 ppb.
► Mixed mode signal has a linear portion relative to the absolute frequency shift.
► Longer tubes have a higher single mode output, meaning high stability and power.
► Thermal control and cavity length control should be decoupled.