Visual observation of frequency tuning in whispering gallery mode diode laser at room temperature

We report on the direct observation of an increase in the wavelength of output radiation during the pumping current pulse in a whispering gallery mode (WGM) semiconductor diode laser (2.35 μm) with a sector (half-disk) cavity. During the current pulse with a duration of up to 1.5 μs, the main WGM wavelength smoothly increases by 30 A at room temperature.