Generation of amplitude-squeezed light at 431 nm from a singly resonant frequency doubler

Amplitude-squeezed light at 431 nm has been generated from a singly resonant frequency doubler with a KNbO3 crystal. The frequency doubler is designed to resonate only the fundamental mode and is pumped by a frequency-stabilized Ti:sapphire laser. Noise reduction of 2.4 dB at 7.5 MHz is observed in the second-harmonic mode with a coherent excitation of 65 mW. With the detection efficiency taken into account, the actual noise reduction is estimated to be 5.2 dB.