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American Journal of Physics


We describe an experiment for generating and characterizing a beam of collimated blue light (CBL) in a rubidium vapor. Two low-power, grating-feedback diode lasers, operating at 780.2 nm (5S1/2 --> 5P3/2) and 776.0 nm (5P3/2 --> 5D5/2), respectively, provide step-wise excitation to the 5D excited state in rubidium. Under the right experimental conditions, cascade decay through the 6P excited state will yield a collimated blue (420-nm) beam of light with high temporal and spatial coherence. We investigate the production of a blue beam under a variety of experimental conditions and characterize the spatial coherence and spectral characteristics. This experiment provides advanced undergraduate students with a unique opportunity to investigate nonlinear optical phenomena in the laboratory and uses equipment that is commonly available in laboratories equipped to investigate diode-laser-based absorption spectroscopy in rubidium. (c) 2013 American Association of Physics Teachers.


Copyright 2013 American Association of Physics Teachers.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Association of Physics Teachers. This article appeared in Am. J. Phys. 81 (6), June 2013, and may be found at

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