Abstract

A flexible and compact digital lock-in detection system, with software-based balanced detection for tuneable diode-laser spectroscopy measurements is described. The system is based on two data acquisition cards for a standard computer. One data acquisition card contains a software-controlled arbitrary waveform generator (CH-3150, Exacq Technologies) that is used for laser modulation. The scanning frequency is typically 130 Hz and a sinusoidal modulation of about 132 kHz is applied. The second card contains four externally clocked A/D converters (NI-6132, National Instruments) that are used for acquisition of sensor signals synchronously. Detected signals are averaged before software based lock-in detection is carried out. By using synchronous acquisition and averaging, a comb filter is formed that filters the signals [1]. Thus, it is possible to detect the If, 2f, 3f, and 4f lock-in components out of the same data set. Averaged or raw data may be stored on disc for later analysis. No external lock-in amplifier, oscilloscope or function generator is needed.

© 2007 IEEE