The Analysis Of Lock-in Detection Systems On Weak Opto-electronic Signals

Not only detection results are often affected by the noise that comes from the detection system itself and external interference, but also light transmission is more or less limited by the size of the aperture in many signal detection systems. This paper presents a suit of single channel input virtual Dual-Phase Lock-in Amplifier (DPLIA) that is constructed by a personal computer sound card and the Lab VIEW software. The apparatus can easily accomplish lock-in detection and suppress noise effectively. Transmission characteristics of limited diffraction of laser beam is analysed theoretically when the gaussian beam passes through the limited diaphragm aperture. And also, the DPLIA is applied in lock-in detection of glass film light uniformity in the paper.In the design of DPLIA, lock-in detection is realized by the cross correlation of measured signal which comes from a single input channel of the sound card and two internal orthogonal reference signals generated in the Lab VIEW software. This virtual instrument is low cost and convenient to apply. It is applied in a LED optical signal detection system and the noise tolerance of it is tested simply.The Rayleigh-Somerfield scalar diffraction integral formula is applied to reasearch diffraction field distribution under the limit of laser aperture constraints. The influence of diaphragm aperture on amplitude distribution of diffraction field for laser beam and on the beam propagation factor is analyzed numerically. The divergence half-angle for the limited diffraction laser beam is analysised and calculated by the equivalent matching efficiency method. Those parameters provide theoretical support for the laser optical system design.Finally, the scheme of lock-in detection system of glass film light uniformity is put into practice based on a suit of acousto-optic modulator apparatus and DPLIA. The three assessment parameters on glass film light uniformity are obtained through the experiment.