(1) resistance measurement method: remove the laser diode, Rx1k or Rx10k with a multimeter measure the forward and reverse resistance. Normally, positive resistance 20~40k ω between reverse resistance value of ∞ (infinity). If the measured resistance value already exceed 50k, then laser diode performance has decreased. If the measured resistance value is greater than 90k, then the diode is badly aging and can no longer be used.
(2) current measurements: multimeter measurement in laser diode drive circuit load resistance voltage drop, according to Ohm's law to estimate the tube current values when the current exceeds 100mA, adjust the laser power potentiometer, current without significant changes, the laser diode can be judged a serious aging. If the current surge out of control, then the laser diode, optical cavities is corrupted.