Intensity influence on Gaussian beam laser based measurements using quadrant photodiodes.
In many measurement applications using quadrant photodiodes, the signal is normally obtained from integrated devices incorporating current-to-voltage amplifiers that provide the necessary difference outputs with amplification. Quadrant photodiodes permit two-axis laser beam size and beam deflection determination. We show here that photodiode saturation, nonlinear characteristics of amplifying circuits, and voltage clipping features meant to prevent the output of a circuit from exceeding a predetermined voltage level to distort applied waveforms, play a significant role in measurement at low and high intensity levels, respectively. These two factors conspire to underestimate laser beam size measurement. A best-fit computation of the size versus power trend was found to permit satisfactory estimation of the beam size as well as the optimal laser power to be used. The intensity of light was also found to strongly affect the sensitivity of beam deflection measurements, in which a correction based on best-fit computation was deficient. In this case, calibration steps would be needed when light levels changed.
Panduputra
Yohannes
Y
Laboratory for Optics, Acoustics, & Mechanics, Department of Mechanical & Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australia.
Ng
Tuck Wah
TW
Neild
Adrian
A
Robinson
Michael
M