Laser stabilization using saturated absorption in a cavity-QED system

Wave-number blueshifts of single-mode laser light in low-density Rydberg matter are found to be due to stimulated Raman processes. The Rydberg matter is mainly formed from Rydberg states of K atoms. The lasers used are mW continuous-wave lasers in the ir, lead-salt tunable diode lasers. Of special significance is the blueshifting observed as shifts of Fabry-Perot etalon fringes of the order of 0.05 cm(-1). This blueshifting is explained as due to complete conversion to anti-Stokes radiation through higher-order stimulated Raman shifting by extremely small quanta from the near continuum of energy levels in the metallic Rydberg matter phase. Complicated strong shifts of intensity to larger wave numbers in the laser modes are also observed, due to coupling of laser side modes to the anti-stokes waves. The high efficiency of the stimulated Raman process is partly due to the weak coupling to other degrees of freedom.