Spectroscopy with diode laser noise

Summary form only given. Efficient conversion of laser frequency noise to amplitude noise takes place when a laser propagates through a resonant medium. This is demonstrated in the case of a solitary diode laser having the usual frequency or phase noise with a bandwidth of /spl sim/30 MHz but very low amplitude noise, propagating through a Doppler-broadened K vapor cell. The lineshape of the noise as a function of laser frequency near the K resonance has the characteristic "M" shape of FM spectroscopy. Measurements of the RF noise spectrum of the emergent beam in the case where the diode laser is near the 770 nm resonance of K reveals the ground state hyperfine structure of the K atoms at 460 MHz.