As temperature or drive current tunes a laser, the cavity modes and the gain peak move at different rates, and at some point the laser abruptly switches to an adjacent longitudinal mode, jumping by one free spectral range. Diode lasers are the classic offenders. Mode hops ruin spectroscopy and interferometry, so tunable sources specify a mode-hop-free tuning range and are run inside it.
Scan's clean up to 22.4 degrees then there's a mode hop, so keep the TEC below that or the line jumps off the absorption feature.
Also heard as
- mode hopping
- mode jump
Related terms
Longitudinal mode
One of the discrete frequencies at which a standing wave fits a whole number of half-wavelengths into the resonator.
Linewidth
The spectral width of a single-frequency laser's output, usually given in Hz, kHz or MHz at half maximum.
Laser diode
A semiconductor laser driven by electric current, used as a light source in its own right and to pump other lasers.
Kink
A sudden bend or step in a laser diode's power-versus-current curve, usually a sign of mode switching.