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Mode behavior in ultralarge ring lasers
Robert B Hurst1, Robert W Dunn, K Ulrich Schreiber
1Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. robert.hurst@canterbury.ac.nz
Applied Optics
|April 22, 2004
Summary
Single-mode operation in large Helium-Neon (He-Ne) ring lasers is achievable at higher power levels than expected. High gas pressure creates a single gain peak, suppressing multiple modes for stable laser operation.
Area of Science:
- Atomic, Molecular, and Optical Physics
- Laser Physics
- Quantum Optics
Background:
- Very large ring lasers typically exhibit multimode operation due to mode spacing.
- Helium-Neon (He-Ne) lasers are widely used in various scientific and industrial applications.
Purpose of the Study:
- To investigate the conditions for achieving single-mode operation in very large He-Ne ring lasers.
- To understand the underlying physical mechanisms suppressing multimode behavior.
Main Methods:
- Experimental observation of He-Ne ring laser output.
- Varying intracavity power levels and gas pressures (4-6 Torr).
- Theoretical modeling of gain profile and mode stability.
Main Results:
- Single-mode operation achieved up to 0.15 times saturation intensity, contrary to mode spacing expectations.
- High gas pressure (4-6 Torr) induces homogeneous line broadening, creating a single-peaked gain profile.
- Metastable single-mode operation observed even with significant cavity detuning; calculated metastable frequency ranges exceed 150 MHz at 6 Torr.
Conclusions:
- Homogeneous line broadening at high pressures is key to suppressing multiple modes in large He-Ne ring lasers.
- Theoretical conditions for concave-down gain profiles and specific slope/saturation inequalities explain the observed single-mode stability.
- The study reveals unusual stable mode configurations and highlights the pressure dependence of metastable frequency ranges.