2D Laser Profiling Scanner for Detecting Targets

The Radiometric Sensor Development and Applications Team of the Sensors and Electron Devices Directorate (SEDD) at the U.S. Army Research Laboratory (ARL) has developed a 2D laser profiling scanner system to study its operational characteristics, performance, and effectiveness in detecting targets in the battlefield and homeland security environments. A profiling scanner provides output images that reveal the size, height, and outline or shape of an object. This information can be useful in a wide range of applications, ranging from simple intrusion detection, to monitoring of parts during a manufacturing process for quality control purposes.

Front and back views of the mounted photo sensors.

The profiling scanner system uses 16 laser diodes, 16 photo sensors, and a personal computer (PC) controller. The scanner is made up of a 6 × 8' aluminum frame with the laser diodes mounted on one side, and the photo sensors mounted on the other. Each laser diode is optically aligned with a photo sensor to form a working pair. Each pair operates independent of all others.

Front and back views of the mounted photo sensors.

Mounting fixtures are used on the laser diodes to provide beam alignment to the photo sensor on the other side. Photo sensors are mounted directly onto the frame (Figure 1). A coaxial cable is used to carry each output signal to the PC controller. When power is applied to the laser diodes, each diode generates a beam of focused light, which activates a corresponding photo sensor, resulting in 16 channels of sensing beams going across the two legs of the scanner. During operation, when nothing is in between the two legs, each of the photo sensors outputs a constant and continuous analog voltage. The beam is blocked when an object is placed between the laser diode and photo sensor, resulting in a zero voltage output.

Operation of the system primarily involves the continuous sensing, monitoring, and processing of the activities of each of the 16 beams. A PC controller provides controls for all operations.

The laser diode is the M635-5 from USLasers, and operates at 635 nm with 5 mW of output power. The photo diode is the SM05PD1A from Thorlabs. Each laser diode is powered by a continuous DC nominal voltage of 2.5 V. A total of about 500 mA is required to power all 16 laser diodes. The photo diode requires no power. The PC controller is from National Instruments, consisting mainly of the PXIe-8106 embedded controller in a PXIe-1062Q chassis, along with the PXI-6255 data acquisition module (DAQ). Figure 2 shows the complete controller hardware setup.