Lithium atomic beam spectroscopy and phase sensitive detection using a diode laser

We describe spectroscopy of a collimated lithium atomic beam using a home-built external cavity diode laser (ECDL) at 671 nm. The atomic beam is formed from an effusive oven containing Li at T$\approx$450$^{\circ}$C and a series of apertures. The ECDL light is split into two beams that counter-propagate at right angles to the atomic beam. Fluorescence spectra from the unresolved 2S$_{1/2}$ F=2 $\rightarrow$ 2P$_{3/2}$ D2 line of $^7$Li were recorded over a large range of saturation parameters (0.1 $s_0$ - 50 $s_0$, where $s_0$ is the ratio of laser intensity to the saturation intensity). We modeled the effects of transverse atomic velocities (residual Doppler broadening), power broadening, and the saturation feature at high $s_0$. We calibrated the spectra by modulating the laser current at $\sim$110 MHz and observing the sideband spectra. We locked the frequency of the ECDL to the transition at low and high values of $s_0$ by phase sensitive detection in the fluorescence. The laser beam was electro-optically modulated at 100 kHz and the fluorescence signal was demodulated with a lock-in amplifier. The locked ECDL will be used for laser cooling and trapping experiments.