A mode that has a field vector normal to the direction of propagation. In a transverse electric (TE) mode, the electric field vector is normal; in a transverse magnetic (TM) mode, the magnetic field vector is normal. In the transverse electromagnetic (TEM) mode, both the electric and magnetic field vectors are normal to the propagation direction. In diode lasers, these are spatial modes perpendicular to the active layer. TEM00
designates the simplest transverse mode of a laser, with a Gaussian energy distribution across the beam.