We use a Michelson interferometer to explore the spectroscopic properties of laser diode emission over a wide range of operational conditions. By studying how the interferogram changes with drive current, we demonstrate the relationship between coherence length and spectral bandwidth. At low injection current, the laser source operates more like an ordinary light-emitting diode (LED), generating a relatively broad spectrum with short coherence length. In contrast, when the drive current exceeds the single-mode lasing threshold, we obtain a steady sinusoidal interferogram throughout the movable mirror scanning range, indicative of monochromatic light. At intermediate injection, we observe a beating pattern due to the presence of multiple longitudinal lasing modes. We verify that the beat distance, or optical travel between beats, is consistent with the spectrally validated mode spacing.
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September 2020
PAPERS|
September 01 2020
Laser diode coherence
Tim Gfroerer;
Tim Gfroerer
a)
Department of Physics, Davidson College
, Davidson, North Carolina 28035
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Morgan Bergthold
Morgan Bergthold
b)
Department of Physics, Davidson College
, Davidson, North Carolina 28035
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a)
Electronic mail: tigfroerer@davidson.edu
b)
Electronic mail: mobergthold@davidson.edu
Am. J. Phys. 88, 740–745 (2020)
Article history
Received:
December 17 2019
Accepted:
June 09 2020
Citation
Tim Gfroerer, Morgan Bergthold; Laser diode coherence. Am. J. Phys. 1 September 2020; 88 (9): 740–745. https://doi.org/10.1119/10.0001487
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