Ophir Photonics offers a series of very sensitive thermal power/energy laser measurement sensors designed with very low noise and drift to measure very low powers and energies. Available models include those calibrated for Terahertz radiation, those with a removable window, and those for divergent beams with windows that block infrared.
The high sensitivity thermal sensors include broadband and P absorbers for CW and short pulses. They can operate at up to 3 W of power and are available with 12 mm or 9.5 mm apertures. Each sensor utilizes convection cooling and are no more than 0.2 kg in weight.
For additional features and specifications on these thermal sensors, download the available datasheet.