A quick way to check if high powered pulsed lasers are working.

[thescientist1064]

Hey everyone, I am fairly new to electronics and am trying to wire a high power pulsed laser diode to a laser driver. I am noticing that no current is flowing through my driver despite having wired my diode in both forward and reverse (i.e. both polarities). I am concerned if my pulsed diodes are dead on arrival and would like to know how I can check this. I have attached the diode & driver information below! Thanks!

Pulsed Diode: https://ams-osram.com/products/lasers/ir-lasers-eel/osram-metal-can-to56-spl-ul90at03

Driver: https://www.picolas.de/en/produkt/ldp-v-240-100-v3-3/

[coppercone2]

new to electronics and 65w laser diode is recipe for disaster

slow down cowboy. try a 1mW diode first. your gonna end up getting mad and doing something stupid if thats your first diode


those current levels from the driver are difficult to deal with, even if it was powering a heater. I think your in way over your head

[ArdWar]

Those laser diodes only got 3V maximum reverse voltage. If you indeed ever drive it in reverse it might well be toast I'm afraid.

[twospoons]

That driver board has a detailed 'getting started' page in the user manual. Did you follow that to the letter and do all the test setups first?

[radiolistener]

Just interesting, is this eye-killer device?

[Berni]

This 65W pulsed laser is a lot less scary then it sounds at first, as that is the peak power rating and can only do that for up to 100ns (1KHz repetition rate). So perfectly safe, likely something used for LIDAR.

But yes that diode laser is likely dead now. Connecting it reverse is most likely a death sentence for the laser diode. Also that laser driver board looks way too powerful for this laser. The board only specs going down to minimum of 40A and 15V while the diode calls for 20A at 9V, so even if connected correctly it likely would not work for long.

[Gyro]

This 65W pulsed laser is a lot less scary then it sounds at first, as that is the peak power rating and can only do that for up to 100ns (1KHz repetition rate). So perfectly safe, likely something used for LIDAR.
...

Doesn't that depend on the thermal mass and conductivity of the target? - for instance, retinal rods and cones.

[Berni]

It does depend on a lot of things yeah.

But in general the powers this pulse laser works at are still quite low. The 65W at the maximum allowed pulse length of 100ns is only 6.5 uJ of energy per pulse and at the same time human tissue tends to be quite transparent to these short IR wavelengths, so even when focused it will mostly diffuse when hitting tissue. That being said it is still not a good idea to just stare into the focused beam, since the 1KHz repetition rate works out to 6.5mW of average power. As the beam is invisible the blink reflex won't save you, so a good idea to still use laser safety glasses.

In comparison what a pulsed IR laser of this kind of power normally looks like:
https://en.raycuslaser.com/products/50w-q-switched-pulse-fiber-laser.html

This is a 50W pulsed laser that works at a slightly longer IR wavelength. It sounds like it should be about as dangerous as this 65W laser diode. However on this laser the 50W is the average output power. This means it can pack 1mJ of power into a pulse. When one of these is focused down into a sharp point there is enough power to punch steel sheet if thin enough. The calculated peak power on these is around 10kW. These are indeed very dangerous lasers. Tho they also use this type of lasers in a more de-focused form for laser tattoo removal (exploiting the transparency of human tissue at these wavelengths to not burn the patient, but only burn the tattoo ink).

So the peak and average power of a pulsed laser can be two very different things.

[radiolistener]

since the 1KHz repetition rate works out to 6.5mW of average power

According to power supply module specification:

Repetition rate: max. 2 MHz

This is 2000 x times more than 1 kHz

[thescientist1064]

Thanks for that suggestion. I think I may have messed the polarity up when hooking the diode up. Ok, so let me see if I am getting this right. The schematic of the diode shows three pins: 1- LD Anode, 2 - Case, 3 - LD Cathode. Right now, I am hooking the anode of the driver to the anode of diode and cathode to cathode. Does this sound right or am I missing something?

 

[thescientist1064]

Yes, I followed the setup procedure as described by the driver manual. I am able to visualize an output current on an oscilloscope with a short (i.e. no diodes attached). But when I put my diode into the circuit I don't see any current flowing through the diode (checked with an ammeter). 

[thescientist1064]

I agree that the output suggested by the manual is between 40A - 240A. My ultimate plan is to power an array of these diodes. So would you suggest I hook multiple diodes (in parallel) to minimize the current flowing through each diode? 

[twospoons]

Paralleling diodes is generally not a good idea - they tend not to share current equally, as the hottest one will have the lowest forward voltage and take a larger share of the current (making it even hotter). You can add a ballast resistor to each one to improve sharing, but the best method is to run the diodes in series instead.  With this laser diode you might get away with paralleling as it looks like its actually three diode in series internally, resulting in a forward voltage of 9.5V.  A ballast resistor on each laser diode (maybe 0.1 to 0.2 ohms) would still be advisable.

Why would you use an ammeter when you have a scope? An ammeter wont detect a short pulse.

[thescientist1064]

Ahh, I see. I went the ammeter route as I didn't see a signal on my scope when the diode is in circuit. Let me try having a ballast resistor (0.1-0.2 ohms) and maybe hook two diodes in series. 

[twospoons]

If you dont see anything on your scope then your diode is probably dead.
You dont need a ballast resistor if you are series connecting your diodes.
You still need to set the current limit on your driver  to 20A or less for those diodes, even with two in series.