Absolute energy reference calorimeter with bismuth telluride thermocouples for laser energy standard

A highly sensitive calorimeter has been developed for measuring the absolute energy of single laser pulses. The calorimeter, which consists of a solid volume absorber, a copper absorption cavity, and bismuth telluride thermocouples, is operated at room temperature with no vacuum window. The absorption of the laser energy in the calorimeter leads to a temperature increase of the cavity. The time-dependent temporal temperature change was measured as voltage signals with highly sensitive bismuth telluride semiconductor thermocouples. The calorimeter was calibrated by injecting a known Joule heat with a heater on the cavity. The experimental results showed a linear relationship in an energy range from 5to100mJ. The standard deviation of the calibrated sensitivity was less than 0.1%. The systematic errors of the laser energy measurement are estimated to be as small as 0.32%.