the funny shape i see for that particular diode is NOT caused by power fluctuations - it's real. The diode shows that huge change in responsivity across the surface after being damaged. it might have to do with the position of the bond wires and the fact that the diode exhibits a large amount of dark current in addition to the photocurrent which probably cancel depending on the position od the beam relative to the defect and the bond wires. But that's just a guess.