Flexible lock-in detection system based on synchronized computer plug-in boards applied in sensitive diode-laser gas spectroscopy

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. A pigtailed single mode VCSEL laser (L2K-P760-LD-SM, Laser2000) is used to scan across oxygen lines at about 760 nm. After the laser, the light is split by a single-mode fiber splitter. The scanning frequency is typically 130 Hz and a sinusoidal modulation of about 132 kHz is applied.