With the characteristics of high sensitivity and low noise, balanced homodyne detection technique has been one of the main methods in quantum noise measurement. Based on the Kirchhoff's law, a balanced homodyne photoelectric detector with two-stage amplification is designed and studied. The differential photocurrent of two similar photodiodes is primarily amplified by a trans-impedance amplifier, and then sent into the secondary differential amplifier. Experimental results show that the saturation power of this detector is 5 mW, and the signal response bandwidth is about 140 MHz. When the input laser power is equal to 2 mW and the frequency is lower than 30 MHz, the optical shot noise is 10 dB larger than the electronic noise. Near 20 MHz, the common mode rejection ratio of the detector could reach 55 dB.

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The experiment of laser cooling of molecules generally needs multiple lasers with narrow linewidth and passive-stabilized frequency. We propose to use Pound-Drever-Hall (PDH) technique to lock the cooling laser onto the diode laser stabilized by the saturated absorption spectroscopy of Rb atom through the transfer optical cavity. The linewidth and long term drift of the cooling laser frequency could be controlled. The Fabry-Parot (F-P) optical cavity is designed and made, and the optical stabilization system is set up, and the optical transfer cavity is locked onto the reference laser through PDH technique.