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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.

The output power of a cw Nd:YAG laser was stabilized in a dc-coupled feedback loop with a low-noise multiphotodiode detector and an electro-optic amplitude modulator in the frequency band from 1 Hz to 1 kHz. For the first time, to our knowledge, an independently measured relative power noise of2.4×10^−9 Hz^−1/2 at 10 Hz was achieved, fulfilling the power stability requirements of the Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) gravitational wave detector.

We present results on the power stabilization of a Nd:YAG laser in the frequency band from 1 Hz to 100 kHz. High-power, low-noise photodetectors are used in a dc-coupled control loop to achieve relative power fluctuations down to 5×10^−9 Hz^−1/2 at 10 Hz and 3.5×10^−9 Hz^−1/2 up to several kHz, which is very close to the shot-noise limit for 80 mA of detected photocurrent on each detector. We investigated and eliminated several noise sources such as ground loops and beam pointing. The achieved stability level is close to the requirements for the Advanced LIGO gravitational wave detector.