Help powering HL654MG

[seb]

Hi everybody,

I´m somewhat new to laser tech., now I'm working for my batchelors physics degree in laser interferometry and have found some problems, I would be very pleased if you coud help me with your ideas:

My project is to build a laser interferometer with quadrature detection for micrometer displacement measurements. I am using a HL654MG laser diode form Thorlabs, for wich I've built a power supply that seems to be very stable and not to exceed the maximum ratings for the diode. But problem is I blew the diode, and I don´t know why was that. It had been operating for couple of hours quite fine, but I'm not sure if the temperature rided too much or what else could happen? the diode has a max. current rating of 210mA, 130mW, Do you think temperature is an issue here? If so, what temperature control method could I use that is cheap and small in size?

By the way, I'm traying to detect quadrature between signals from the interferometer, using only simple polarization films, not a polarized beam splitter. The way I'm doing it is by placing one polarizer just after the laser diode and one before each of the two detectors, 45 deg. shifted from the first one, one for each side. But this doesent seems to work, does any one knows why not? I've rotated the polarizers in all positions and still nothing.

Thanks for your help!

[badger1666]

hi welcome to pl
what did you have the diode mounted in ?
and was it isolated from ground ?
more info on your driver required please
and your power supply too.
we will need to know everything about your set up and even pics if you can manage it,
there are some people that know plenty to help you out a lot of them are state side

[seb]

Sure:

The diode is inside a small metal laser collimator, held in an aluminum post over an optic table. The idea is to eventualy place the whole collimation setup inside an aluminum case to hold the whole opticla setup in the least volume.

I do not have it insulated from ground

My driver is feed with a simple ac-dc conversion circuit (diode bridge-caps-7812) and consists of a voltage to current converter (see image)



I'm not sure if you need something else, just let me know

[badger1666]

hi i would recomend a driver called die4drive it made by uklaser on the forum
alot of people here use ,also there is the flexmod driver another good choice,
but even with your driver its important that what ever you mount the diode in that its also isolated from ground but also able to conduct the heat away
any unintensional brief grounding will kill the diode in <ms a few of use have found that out the hard way while experimenting ,
attached is an example of the die4drive

Sure:

The diode is inside a small metal laser collimator, held in an aluminum post over an optic table. The idea is to eventualy place the whole collimation setup inside an aluminum case to hold the whole opticla setup in the least volume.

I do not have it insulated from ground

My driver is feed with a simple ac-dc conversion circuit (diode bridge-caps-7812) and consists of a voltage to current converter (see image)



I'm not sure if you need something else, just let me know

[shrad]

if your diode is common cathode (ie body = cathode) you just fried it by applying directly the power supply voltage to it

[krazer]

As has been pointed out, the diode you have has the casing connected to the - terminal of the laser diode, so you must be very careful if you have the diode in electrical contact with your optical table. The best solution to this issue is to use plastic to isolate the diode from your table, thorlabs sells plastic isolators you can screw onto your post if you want an elegant solution on the cheap.

Also, you must protect your circuit against any type of surge, a current pulse even a few nanoseconds long can damage a laser diode. It is hard to say exactly how your circuit will behave when first turned on, or when it is turned off, but often times circuits like this will output a spike of current with power is applied/removed, which can damage the laser diode. If you have a digital oscilloscope you can set for one-shot 'single' mode and observe the waveforms when you turn the driver on/off, and check for any current spikes.

Also, you can buy similar (if not better in some ways) laser diodes from other vendors for ~1/10th as much as thorlabs charges, places like stonetek.org


Per your problem with the interferometer not working, does it work without the polarizer films as a basic interferometer? Often times laser diodes will not be single mode at higher powers, which will reduce the coherence length down to less than 1mm. There is an exelent study at W's blog http://redlum.xohp.pagesperso-orange.fr/argonlaser.html talking about which lasers give good single mode operation and what is required to keep them from mode hopping.

[seb]

thanks for your help, I'll take a look at those circuits and writings and give it a try. I'll let you know the output