Feasibility of modulated optical deflection sensing in atomic force microscopy

Optical deflection sensing is perhaps the most widely used scheme in atomic force microscopy. In this technique, the sensor is a quadrant photodiode. Position detection is essentially achieved using voltage differencing between the photodiode outputs. To improve data throughput, this is often done using operational amplifiers in the differencing mode. The measurement sensitivity is affected by environmental noise. Intensity modulation is a simple method of overcoming environmental noise. When this scheme is applied to the optical deflection sensor technique, random chaotic signals were found to form. Unless expensive filtering methods are introduced, the efficacy of using intensity modulation to reduce the effects of environmental noise in the optical deflection sensing method is limited.