Pangolin ? laser not perform at maximum

[Doc]

Fact of the matter is; laser manufacturers charge $ per mW

They are going to tune the laser for maximum mW and maximum $. This also goes some way to explaining why a 500mW high quality laser costs a lot more than an equivalent far eastern laser; linearity during modulation.

[lucerne]

Fact of the matter is; laser manufacturers charge $ per mW

Yea, you're right. I had the same discussion with a friend a few weeks ago. It's like someone sells scanners with 80kpps speed or more. Sure, you can make this speed, when you only scan a point

Especially sellers of chinese products should write (for example): "457nm DPSS, 300mW with CW and after 20min"

This is a little closer to reality...

I've seen people adding some heating elements to the DPSS case to shorten the warm-up time. That's really a sad solution, as the manufacturers build up such low-cost drivers.

Cheers!

[-bart-]

If only these manufacturers used an H-bridge instead of a single transistor to drive their tec, that would help a lot.
But that would mean one wire extra , because it can't be connected to the LD gnd anymore.

[lucerne]

If only these manufacturers used an H-bridge instead of a single transistor to drive their tec, that would help a lot. But that would mean one wire extra , because it can't be connected to the LD gnd anymore.

In fact, CNI is doing this with the extra wires (with all bigger laser heads). Maybe you know this round 12pin connector? There they have all wires accessible, that's great. I always cut the cable and solder my own connectors on it (D-Sub 15pin).

H-bridge? Of course, my driver has two of them on the PCB

Cheers!

[mixedgas]

Conclusion: You loose some power, when you calibrate a driver in modulated operation. BUT you loose even more power, when you have a CW calibrated driver and use it in modulated operation! By the way: Don't forget, it was a 300mW specified laser head and we still get 440mW out of it

As soon there is enough time, I will also do some measurements with a fast photodiode.

Regards, Leander[/QUOTE]

We will be running similar tests at SELEM!

Nice post, SHOULD BE MADE A STICKY!

Steve

[Things]

I think another option is USB power.

Things like portable hard drives (USB only powered ones) draw a heck of a lot of power from USB, and any other USB light gadgets etc you may have connected at the time. There is a possibility that the voltages could be sagging a bit, but this is not a problem with the DAC at all.

Another option is the reference voltage on the laser. If the reference voltage is a tad over 5V, you are not going to get full power from the laser.

I'm not a EE or anything, but I know that my USB voltages sag a fair bit with heavy loads. Maybe someone can power the FB3 off external power and see if it makes anything better? I don't think it will make much of a difference, because of the great explanation Bill gave on the perceived brightness, but who knows

Cheers,
Dan

[White-Light]

Conclusion: You loose some power, when you calibrate a driver in modulated operation. BUT you loose even more power, when you have a CW calibrated driver and use it in modulated operation! By the way: Don't forget, it was a 300mW specified laser head and we still get 440mW out of it

As soon there is enough time, I will also do some measurements with a fast photodiode.

Regards, Leander

Sorry don't want to ake this too far off topic, but I was just wondering what effect this all has on laser safety?

If traditionally, all lasers have performed badly under modulation and been tuned for maximum CW, then surely if they're retuned for modulation then in show exposure levels will be higher as in show power levels will be higher due to the retune in favour of modulated performance.

Also, the preshow power measurement on CW will be lower than traditionally for a laser of that size, whilst the actual in show levels are higher than for a laser of that size.

Thus the safety aspect will be scewed from both ends. The CW reading will give the impression of a much weaker laser whilst the in show performance and power will be of a much more powerful laser.

So unless your taking fast diodes readings from a modulated beam on scans then then all of the traditional methods of measuring laser safety by taking a power reading from a static beam before the show, go out of the window.

Interesting prospect as the safety data built up over year seems to be built around CW.

Just wanted to add an example based on Lucerne's figures.

eg.

Using the laser he had, a traditional measurement of power pre-show using a static beam at the closest audience point would have given a reading of 610mw. Actual in show power would have been 120mw on scans at 50% duty.

This means that laser safety would have been based around a 610mw laser and in show exposure would have acutally been 1/5 th of the measured power. This is the basis for traditional safety data.

Now looking at the same laser modulated, a traditional measurement of power pre-show using a static beam at the closest audience point would have given a reading of 440mw. Actual in show power would have been 220mw on scans at 50% duty, 1/2 the measured power!

This means that for laser safety purposes straight away a 30% higher exposure level would be allowed with the CW reading at 440mw being only 70% of the previous 610mw reading. So exposure would be set 30% higher on the assumption that the laser was 30% less powerful. However, in show the modulated scans are actually 100% more powerful. This effectively means safety has been eroded at both ends although what actually matters is the in show reading as thats what the audience are exposed to.

The show is running 30% higher levels to start with based on the CW reading and yet in show scan levels are 100% higher. So potentially both readings are wrong in the traditional sense and safety levels are exceeded by the 130% ie. a factor of more than 2 in Lucerne's lasers case. Obviously other lasers may perform differently meaning that the only safe way to measuer a show when tuning for modulation is surley going to be Fast photodiode although this then take measurements beyond equipment that most amateurs and lower end professional can afford.

[lucerne]

Well, nice to read about your safety considerations, BUT:

You're talking about safety risks, when a driver is fast enough. In your opinion, all these slow drivers, all this chinese stuff is safe! Why? Because it's slow and the connected laser heads deliver less output power than in CW mode. Sorry, but this kind of consideration is stupid.

Let's figure out another scenario: one has built up a great projector, with OPS lasers from Coherent. They are really (!) fast and you wont have any power loss during modulated operation. So, what now?

Or another scenario: normal laser diodes! It's so easy to build up fast drivers for them, as they don't need any precise temperature control etc.
Conclusion: during CW mode, you would measure (for example) 500mW of 658nm. After that, you would connect a 50% duty cycle rectangular modulation signal: if the driver is fast enough, then you read 250mW RMS output power.

For safety considerations: NEVER assume that there is a slow driver in a projector!

Cheers

[rfourt]

I think this thread should be locked, and kept the way it is. for future readers... No offence but its getting of topic again.

[Francesco]

I think this thread should be locked, and kept the way it is. for future readers... No offence but its getting of topic again.

I do agree, but there is one last thing I would like to add to this topic.

Here is a link to a topic where badger1666 shows a video of his laser projector.
It's pretty clear that the green laser has some problems that are probably temperature related.
This is what probably caused the lower output of his projector when using the FB3.