Diode laser atomic absorption using a new reference method

A diode laser was used as the source for atomic absorption spectroscopy. To overcome the frequency instability and drift of the laser, a new referencing approach is proposed. The frequency of the laser is modulated across the rubidium transition at 780.02 nm, and the absorption signal is detected in an air/hydrogen flame. The absorption signal is processed by a lock-in amplifier. The reference signal for the lock-in amplifier is generated by shaping the absorption signal from a Rb atomic vapor cell into a square wave. As the laser frequency drifts, no phase change occurs between the reference and analytical signals, eliminating noise and signal loss that would have been caused by using a reference method which does not follow the fluctuations of the laser.