The model 520 laser light source from Cercis Inc. is available in either single- or dual-source versions at wavelengths of 650, 780, 1310, 1550 and 1625 nm. It offers modulation frequencies of 270, 1000 and 2000 Hz with external modulation capability. The company says its state-of-the-art microprocessor, indicator LEDs and three true keypads, including on/off, source and modulation, make it easy to use. Additional features are a standard power level of -10 dBm, stabilized calibrated output of 0.05 dB over five years and >30 h of 9-V battery life. The light source is suitable for use in either the field or the lab.