Diode laser frequency stabilization to transient spectral holes and spectral diffusion in Er3+ : Y2SiO5 at 1536 nm

Diode laser frequency stabilization to 500 Hz Allan deviation is demonstrated over 2 ms integration times with drift reduced to 7 kHz/min. This was achieved at 1536 nm in the technologically important communications band by stabilizing external cavity diode lasers to regenerative transient spectral holes in the inhomogeneously broadened 4I15/2(1)→4I13/2(1) optical absorption of Er3+ : Y2SiO5. Spectral diffusion, which currently limits the achievable stabilization performance, has been studied using stimulated photon echoes. Due to spectral diffusion, significant broadening of the homogeneous linewidth at low magnetic fields from a few kHz to tens of kHz develops as the waiting time T between pulses two and three was increased from microseconds up to the T1∼10 ms lifetime of the excited state. This evolution of the homogeneous linewidth has been mapped out as a function of magnetic field. The classic spectral diffusion can be reduced to negligible levels upon application of a magnetic field in a 0.02 atomic percent Er3+ : Y2SiO5 crystal.