Laserwave 1W 520nm green diode module - part 2 - powering up and measuring

[greenalien]

In order to test the module, I found a nice strip of aluminium and bolted the module, driver and power supply to it. Note that the wiring from the rear of the module is very close to the mounting point - it would be nice if this had some sort of protective gland around it, and maybe exited more centrally.

The driver was then connected to the power supply and the power supply connected to the mains.
Measurement was via a Radiant LPM (Uncalibrated, just used as it came).

Much to my surprise, within a few seconds of applying mains power, the laser came on at full power - despite there being no modulation voltage applied. This was entirely due to my error - There is a small switch on the front of the board, allowing selection between 'TTL' and 'AS' (analogue) modulation

- I'd missed seeing the switch, and had the modulation cable plugged into the 'AS' socket but the switch in the 'TTL' position. Moving the modulation cable to the TTL socket, the laser behaved as expected - i.e. it stayed off with an applied voltage of 0V to 2.8 volts - once anything higher was applied, the laser came on at full power. Clearly, if TTL is selected on the switch, the TTL input must be clamped at 0V, not left floating...
Analogue modulation is nice and linear - (yes, I remembered to change the switch as well as swap modulation inputs!) - with the diode in LED mode until around 1.28 volts, at which point lasing commences. Here's a graph showing output power vs modulation voltage.

I've been measuring the power with the detector about 400 mm from the laser - moving it closer only seems to make a couple of mW difference. The maximum power reading seen was 966mW - if anyone in the Southampton area has a calibrated meter, it might be interesting to compare readings, but as far as I'm concerned, it's close enough to 1W as makes no real difference.
The diode module has a TEC cooling plate underneath it, sandwiched between the diode holder and the mounting plate. There is a thermistor inserted in the diode block. It's clear that the diode output is very dependent on temperature, as, with the modulation voltage held constantly at 5V, the output power reaches an initial peak and then slowly ramps down in small steps, sometimes climbing back a bit before dropping further. At the same time, the alloy plate to which the diode module was bolted started to get noticably warm, clearly from the hot side of the TEC cooler. If the laser is left at 0V modulation for a few minutes then everything cools down and max power is available again. This is unlikely to be a problem during shows, when the beam is being continually modulated, in which case the chassis, as a heat sink, should provide sufficient cooling, especially as my projector has a couple of fans already fitted - however, using heat transfer compound between the module base plate and the projector chassis will definitely be necessary.
Beam profile at 400mm from the aperture is approximately 2mm wide and 4mm high.
That's all for now, next I will be installing it in my projector and seeing how it performs doing graphics and beams. This will take me a few days, watch this space!

[sbk]

Hi,

Nice review, thanks!

Can you maybe measure the divergence of the beam? Laserwave says <2mrad, but it should be better in real...

[greenalien]

It's on the list - just need some dry weather so I can get outside and do the measurements - I don't have a long enough throw inside my house to see enough divergence. Should have something in a couple of days.

[andy_con]

Do we get a new thread for each update?

Why keep all the info in one handy thread when you can make many ;-)

[greenalien]

[greenalien]

OK, been out in my driveway shooting beams at my garage. At a distance of 20 metres, the beam has a central, very bright centre measuring 10mm high by 34mm wide. it also has a number of extra lines above and below, decreasing in brightness. Probably something to do with the mode of the diode. I tried to take a photo, no joy, so here's a sketch:

note that the beam shapes aren't exactly rectangular, more lenticular.
Given the beam measurements 1m from the aperture are 2mm x 4mm, divergence (using http://www.pseudonomen.com/lasers/ca...alculator.html is 1.68mrad horizontally; for the single central beam it is 0.32mrad vertically; If you include all 3 central beams it is 1.68 mrad.
So far, I'm very impressed - everything looks well built, the electronics are nicely put together and it's a nice, tight beam.
I will now be dismantling my temporary test rig and installing the new device in my projector - looking forward to seeing how the colour mixes with the other modules. More in a few days...

[badger1666]

Thanks for posting , i thought these new greens were as good as the 445nm guess not
Or laserwave dont use great correction, i was expecting nearer 1mrad

[greenalien]

I don't know why you're expecting 1mrad divergence - Laserwave quote < 2 mrad on their website, and my tests confirm that this is the case.
When I've finished installing the new module in my projector, I'll do a side-by-side comparison of the new green against a Kvant red (array of 638nm) and a Kvant blue (Single Nichia 445 nm, from when they cost loadsa money, before people started harvesting video projectors...). One thing I can say - compared with my Viasho DPSS green 1W that's just come out of the projector, the new diode green is significantly brighter.

[norty303]

Watt for watt, the 532 should be brighter, so i suspect your Viasho is not doing what it should be (which seems to be about right for them, worst laser i ever owned)

[greenalien]

At the time I bought it, ( group buy from this forum) , the Viasho seemed good value for money - however, it's not been completely reliable - I had to replace one op-amp - the modulation isn't very linear and the power has steadily dropped off, hence the 520 diode replacement.