We present a microwave frequency standard based on coherent population trapping (CPT) in the <sup>87</sup>Rb D<sub>1</sub> line. The CPT spectrum is obtained using two Raman lasers with a 6.8 GHz frequency offset by injection locking of a master laser to a slave laser. We have constructed an atomic clock employing a 5 cm long Rb vapor cell confined with 6.67 kPa neon buffer gas at 70 °C. Using this system, we improve the CPT contrast through the elimination of undesired off-resonant fields created by the direct modulation method. We measured the frequency shift of the CPT signal as a function of the temperature of the Rb cell and estimated it to be approximately 1.3 ×10<sup>−9</sup>/K. The frequency of a 10 MHz crystal oscillator has been stabilized to the CPT spectrum between the two ground states in <sup>87</sup>Rb. The relative frequency stability is approximately 2.3×10<sup>−12</sup> for an average time of 68 s.
© 2006 Optical Society of America
Original Manuscript: March 7, 2006
Revised Manuscript: June 27, 2006
Manuscript Accepted: June 28, 2006
Han Seb Moon, Sang Eon Park, Young-Ho Park, Lim Lee, and Jung Bog Kim, "Passive atomic frequency standard based on coherent population trapping in 87Rb using injection-locked lasers," J. Opt. Soc. Am. B 23, 2393-2397 (2006)