Highly sensitive calorimeter for microwatt-level laser power measurements

A sensitive calorimeter using an isothermal temperature control technique was developed for an accurate measurement of microwatt-level laser power in the visible and infrared spectral region. The standard deviation of the measured value on 1-mW-1-μW laser power is 0.06–2 percent corresponding to the level. The systematic error is evaluated to be within ±0.23 percent for the 10 μW level.