Current Status of NBS Low-Power Laser Energy Measurement

A set of four electrically calibrated calorimeters is currently in use at the Boulder Laboratories of the National Bureau of Standards to calibrate and test devices for measuring average laser power in the range from 100 μW to 1 W and energies in the range 0.03 to 10 J. Laser sources used with these calorimeters are argon, krypton, helium-neon and neodymium-doped YAG, all CW, and pulsed YAG with pulse energies about 0.1 J and pulsewidths of about 200 μs and 30 ns. The calorimeters have been intercompared as a check on systematic errors. The national standard is taken as the average for three of the calorimeters of the current C4 design, because these were designed to permit better measurements of the absorptance and window transmittance. Deviations from the group average are -0.12, -0.01, and +0.13 percent. The earlier standard C3-1 differs from the group average by +0.21 percent.