Laser power noise detection at the quantum-noise limit of 32 A photocurrent.

The power noise of a cw Nd:YAG laser system was measured at radio frequencies using the optical ac coupling technique. An additional mode cleaner in the setup allowed a high optical ac coupling amplification of 62.3. For the first time, to our knowledge, a sensitivity of 1.1×10⁻¹⁰ Hz(-1/2) relative power noise was achieved corresponding to an equivalent detected photocurrent of 32 A. High precision optics experiments can utilize this scheme to improve the sensitivity of their photodetectors.