Dear Fellow Flow Cytometrists: I recently posted a request for information regarding the frequency of trouble other FacsCalibur users had in relation to the Diode laser. I said: "We have had some serious problems with the stability of the red diode laser. In two months, the laser has been changed out three times and our fourth service call for the same problem will commence tomorrow. Typically, one will observe a decline in sensitivity in fluorescence in channels that rely on the use of the diode laser, accompanied by a large increase in the amount of compensation required for those same fluorescence channels...Have others experienced this problem, particularly since BD switched suppliers for the diode laser?" I received a total of 18 replies. Of those, 5 mentioned problems with laser stability, three of them said that the problem was resolved when the laser was changed. Useful comments included: . "One point is that we try to be careful to turn the red laser off manually when we are finished with a four color protocol. Otherwise it will stay on unnecessarily until someone invokes instrument settings that turn it off. I have been told that this extra use is worse for it than extra on-ing and off-ing" "The mode of failure we see is a gradual decrease in power" "it is also possible that the mount for the red laser is giving you problems. We have noticed that the extra weight of the new TEC diode laser makes it more vulnerable to becoming misaligned, resulting in loss of signal and in loss of ability to compensate because the timing of FL4 pulse is out of the time delay calibration window. To distinguish the new possibilities, you (or your service rep) can measure the output of the laser (if lower than specifications, obviously it needs replacement); if the power is OK, then check time delay calibration. If time delay fails and the PMT voltage required to meet the target channel is higher than normal, the laser alignment may have drifted. " "We have 2 dual laser FACSCaliburs on site. One has had continual problems with the red diode and the other has been as solid as rock. It seems to be a bit of a lottery from what I hear, (unofficially from BD reps and outside). The problem with an instable laser, from a warranty point of view, is that is works part of the time so BD will try to repair the problem rather than exchange the laser." It is clear there are stability problems associated with this laser and that a small but significant number of users experience problems. However, in our case, BD has been very responsive in addressing the problem when it has occurred. Since I posted the message, BD has fixed our instrument by realigning the optics Thanks to all who took the time to reply to my message _james
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