Optoelectronic feedback loop for relaxation oscillation intensity noise suppression in Tm-Ho : YAG laser

An optoelectronic feedback loop that can be used to effectively reduce the intensity noise of a 2.1 mu m Tm-Ho:YAG laser has been designed. The feedba ck circuit is based on a variable-gain biquadratic bandpass filter with adj ustable central frequency and quality factor, providing a high loop gain ar ound the relaxation oscillation frequency of the laser and a closed-loop ph ase margin larger than 50 degrees. The relaxation oscillation peak in the i ntensity noise spectrum was completely suppressed in closed-loop operation, and a noise reduction of up to 24dB was obtained.