Measurement slight amounts of absorption of light with accuracy beyond the standard quantum limit has been experimentally demonstrated. The quantum-correlated twin beams used in the measurement were generated from a nondegenerate optical parametric oscillator including an α-cut KTiOPO<sub>4</sub> crystal pumped by an intracavity frequency-doubled Nd:YAG laser. The noise in the intensity difference between the twin beams was reduced by 88% below the standard quantum limit (SQL). The signal-to-noise ratio was improved by 7 dB with respect to the SQL of the total light employed in the experiment and by 4 dB with respect to that of the signal light.
© 1998 Optical Society of America
(190.4410) Nonlinear optics : Nonlinear optics, parametric processes
(190.4970) Nonlinear optics : Parametric oscillators and amplifiers
(270.6570) Quantum optics : Squeezed states
(330.1880) Vision, color, and visual optics : Detection
Jiangrui Gao, Fuyun Cui, Chenyang Xue, Changde Xie, and Peng Kunchi, "Generation and application of twin beams from an optical parametric oscillator including an α-cut KTP crystal," Opt. Lett. 23, 870-872 (1998)