Laser intensity stabilization system using laser-diode-pumped Nd:YAG rod-laser amplifier

We have developed an intensity stabilization system using a laser-diode (LD)-pumped Nd:YAG rod-laser amplifier as an intensity control device; an injection current to the pumping LDs is controlled to change the intensity of the amplified output. To control the injection current, we have newly designed a current-shunt circuit making use of an opto-coupler, which is quite effective in isolating the control circuit where very small signals must be handled from the high-current circuit to drive the pumping LDs. Using this circuit, we have obtained a high open-loop gain of about 100dB at 100 Hz. We have also measured the phase noise induced in the laser rod caused by the change in the pumping current and confirmed that the cross-coupling between the intensity stabilization signal and the phase noise is negligible. Here, we report the details of the system and the attained noise level.