Integrating photodiode sensor and 18 Hz chopper, Model RM9-PD measures power of very low level CW or quasi CW sources with response time of 3.6 sec. Sensor is calibrated over entire range of wavelengths, from 0.2–1.1 µm, rather than single wavelength. Featuring digitally synthesized lock-in amplifier that minimizes external noise, sensor can measure power levels from 300 fW to 300 nW. Output can be displayed on any standard Ophir meter or on PC or Android smartphone or tablet.