Linewidth measurements of a diode laser by optical heterodyne detection

Abstract

An optical heterodyne detection setup is successfully developed to measure the linewidth of a single mode diode laser. This method employs the detection of beat signals from two laser beams having aligned polarizations and with slightly different output frequencies. The D₂ lines of Rb are used as basis for the frequencies of the two lasers. Using a fast, low-noise photoreceiver, large-amplitude beat signals are observed. These signals are fast Fourier transformed for spectral analysis. The linewidth of a Sharp LT024 diode laser, measured from the width of the power spectrum, is found to be around 26 MHz. The dependence of the amplitude of the beat signal with the power of the local oscillator is investigated and is found to verify the theory.