Adjustable open-cavity HeNe laser apparatus with Fabry-Perot mode monitoring and RF spectrum analyzer beat detection¶

Element · All elements
Evidence · no claims cited

Description¶

An undergraduate laboratory apparatus combining an adjustable open-cavity HeNe laser (28 cm plasma tube, Brewster window, sliding output coupler over roughly 38–54 cm), an intra-cavity iris forcing TEM00 operation, a scanning Fabry-Perot interferometer for monitoring mode structure, and a fast photodetector coupled to an RF spectrum analyzer for beat detection. The article states the "variable-length cavity system has been reported and widely used in undergraduate labs to explore laser cavity modes and stability". Students adjust cavity length and mode structure while measuring intermode beat frequencies.

Design Implications¶

Context¶

Requirements¶

• An adjustable iris in the cavity to restrict gain and force TEM00 operation, since higher-order transverse modes produce additional beat frequencies that complicate the RF spectrum

Constraints¶

• Cavity length range is bounded below by the plasma tube length and above by laser losses; the measurement precision is limited by length-measurement precision and frequency pushing and pulling uncertainties

Target Learners¶

• undergraduate physics students in an intermediate/advanced physics laboratory course

Target Learning Goals¶

• understanding longitudinal laser cavity modes
• measurement of the speed of light
• uncertainty analysis and weighted regression

Claims¶

Related Elements¶

Examples¶

• Combined measurement, laser modes and statistics lab — the undergraduate experiment built on this apparatus

Key Sources¶

• Daniel J. D'Orazio, Mark Pearson, Justin T. Schultz, Daniel Sidor, Michael Best, Kenneth Goodfellow, Robert E. Scholten, and James D. White. (2010). Measuring the speed of light using beating longitudinal modes in an open-cavity HeNe laser. https://arxiv.org/abs/1006.5462