TY - JOUR AU - John Hall BT - Reviews of Modern Physics DA - Jan-11-2006 DO - 10.1103/RevModPhys.78.1279 PY - 2006 SP - 1279 EP - 1295 T2 - Reviews of Modern Physics TI - Nobel Lecture: Defining and measuring optical frequencies VL - 78 SN - 0034-6861 ER -