Laser fundamentals I: Spectrum of laser light | MIT Video Demonstrations in Lasers and Optics

Laser fundamentals I: Spectrum of laser light
Instructor: Shaoul Ezekiel
View the complete course: ocw.mit.edu/RES...
License: Creative Commons BY-NC-SA
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Why adjacent modes have orthogonal polarization ?

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Adjacent modes produced in a laser cavity with two mirrors can have orthogonal polarization because the electromagnetic field for each mode is transverse, meaning the electric and magnetic fields are perpendicular to the direction of propagation. In a laser cavity, the two mirrors are oriented perpendicular to each other, allowing only certain modes to resonate and produce laser output. The polarization of a laser mode is determined by the orientation of the electric field with respect to the cavity axis. When the electric field is parallel to one of the mirrors, it is referred to as a "TE" (transverse electric) mode, and when the electric field is perpendicular to one of the mirrors, it is referred to as a "TM" (transverse magnetic) mode. Adjacent modes in a laser cavity can have orthogonal polarization because they have different orientations of the electric field with respect to the cavity axis. For example, one mode may be a TE mode with its electric field oriented parallel to one of the mirrors, while the next mode may be a TM mode with its electric field oriented perpendicular to the same mirror. These two modes have orthogonal polarization and do not interfere with each other, allowing for stable laser operation. In summary, the orthogonal polarization of adjacent modes in a laser cavity with two mirrors is a result of the transverse nature of the electromagnetic field and the orientation of the mirrors, which determine the orientation of the electric field for each mode.