Abstract
An energy measuring system has been developed using a planar vacuum photodiode as detector with capacitative integration of the photocurrent and subsequent display on a digital voltmeter. The great advantages of this system are that (i) it is small in size and weight at the optical end, (ii) it produces an instantaneous readout, (iii) the readout is digitally expressed directly in millijoules, (iv) the system is independent of ambient light level, (v) simultaneous measurement of power is available and (vi) the operation is automatic. Comparison with a standard calorimeter shows that the system has a consistency of better than 1%.