We report a precise measurement of the hyperfine interval in the 2P 1/2 state of 7 Li. The transition from the ground state (D1 line) is accessed using a diode laser and the technique of saturatedabsorption spectroscopy in hot Li vapor. The interval is measured by locking an acousto-optic modulator to the frequency difference between the two hyperfine peaks. The measured interval of 92.040(6) MHz is consistent with an earlier measurement reported by us using an atomic-beam spectrometer [Das and Natarajan, J. Phys. B 41, 035001 (2008)]. The interval yields the magnetic dipole constant in the P 1/2 state as A = 46.047(3), which is discrepant from theoretical calculations by > 80 kHz.

We have developed a technique to measure the absolute frequencies of optical transitions by using an evacuated Rb-stabilized ring-cavity resonator as a transfer cavity. We study possible wavelengthdependent errors due to dispersion at the cavity mirrors by measuring the frequency of the same transition in the D2 line of Cs at three cavity lengths. We find no discernable change in values within our error of 30 kHz. Our values are consistent with measurements using the frequency-comb technique and have similar accuracy.

We demonstrate a straight-forward technique to measure the linewidth of a grating-stabilized diode laser system-known as an external cavity diode laser (ECDL)-by beating the output of two independent ECDLs in a Michelson interferometer, and then taking the Fourier transform of the beat signal. The measured linewidth is the sum of the linewidths of the two laser systems. Assuming that the two are equal, we find that the linewidth of each ECDL measured over a time period of 2 µs is about 0.3 MHz. This narrow linewidth shows the advantage of using such systems for high-resolution spectroscopy and other experiments in atomic physics.