Fundamental linewidth in solitary, ultranarrow output PbS1−xSex diode lasers

Abstract
The fundamental, quantum phase noise limited Lorentzian linewidth was directly measured from the beat‐note spectra generated by heterodyning PbS1xSex diode lasers with a stable CO gas laser. The experimental results were matched by calculated theoretical line profiles. Linewidths as narrow as 22 kHz full width at half‐maximum power were observed.