The TEM01* mode, a superposition of two first-order modes that produces a ring with zero intensity on axis. In a laser meant to be TEM00 it signals tilted mirrors, a thermal lens beyond design or a damaged optic. It is also produced deliberately, with radial or azimuthal polarization, for cutting, optical trapping and super-resolution microscopy.
IR card shows a doughnut mode, the end mirror probably walked when the chiller tripped.
Also heard as
- donut mode
- TEM01*
Related terms
TEM00
The fundamental transverse mode of a laser: a single round spot with a Gaussian intensity profile.
M-squared
The beam quality factor: how many times worse a beam focuses and diverges than an ideal Gaussian of the same wavelength.
IR card
A small card coated with phosphor that glows visibly where an invisible infrared beam hits it, used for alignment.
Thermal lensing
The lens effect a heated gain medium or optic creates as its center gets hotter than its edges.