Colour Output Levels - Again :)

C

Chris Priest

Active Member
Hi All,

I know this question has already been asked by Peter, but I wanted to ask a couple more things:

I have a 1W DPSS that I have connected to the Red Channel, the neg outputs are tied to ground.

Sometime back I asked about the brightness of the beam and how it related in LD, Bill kindly informed me that the best way to get a brighter beam is to increase the number of points.

Now this worked well, a 100 point beam was considerably brighter, BUT, the voltage output on the Red channel was only about 4v this limits the modulation signal to the laser and I only get about 750mW with a 100 point beam.

I guess the question would be, Bill mentioned that the load on the card needs to be 1k or higher to ensure the output voltage is correct. Is there a way that I can ensure this load is placed across the colour channels so that I can get the maximum modulation level? I do appreciate I will lose some power due to the laser being modulated, but I think losing 250mW is a tad excessive :D

Best Regards and Thanks
Chris
 
Hi Chris,

Tell me, exactly how are you measuring this 750mW? It could be that in reality, you have more, but your measurement method is flawed...

I am going to have to take the time to write an article about color, visual perception, and other related phenomenon, since this is a topic of much misunderstanding... But I will quickly say that the power would have to be reduced, from 1 watt to around 1/5 watt, before you perceived it as being "half as bright". Your eye is highly nonlinear and so even if it is 750mW, the brightness difference is not that visible...

I am also not sure about this 4V figure either. How are you measuring this, with a scope or a meter? If it is with a meter, this will be yet another topic for my article... You can't measure the color signal with a meter. Sorry, you just't can't. I will not take the time here to tell you why, just suffice it to say that you can't... So you can only measure the color outputs with a scope. If it is really only 4V, then the input impedance of the laser is pretty low. If this is the case, you can boost the QM2000 signal with an impedance matching buffer that can handle the lower input impedance. Several people make such a buffer including Holo Spectra and LSDI, but such a buffer would be pretty easy for anyone to construct...

Bill
 
Hi Bill,

Many thanks for your reply.

I measured the output with an Ophir Power meter, it's usually pretty accurate.

I won't tell you how I measured the voltage, suffice to say, after reading your post, it was definitely the wrong way :)

I will have a look around for an Impedance Matching Buffer, my electronics knowledge is not that great, so if anyone can supply me with a couple of the beasties, please, get in touch :)

I think the article would be a great idea, as you say, there seems to be much confusion over the subject.

Again, thanks for the reply.

Best Regards
Chris
 
I see that there is still an issue with color and output with the LD2K.

As Chris pointed out, I have experiences the same on a single color dpss system.
What made things different in the first place for me was to switch to the Intensity + & - instead of any color output.

In my case I am using a ( almost ) 2 watt green LQ diode. When hooking this up to Green it would display rather the same issue as Chris posted here. When hooking it up to the Intensity +/- is was a little brighter. I had to readjust the colorsettings and did that according to the Pangolin instructions with the setyp wizard.

You do have to keep in mind what pin's you use as the wizard requires you to check the box belonging to them / it.

I got the tip of switching off blanking an that almost doubled the brightness of the beam. Although this will not be usefull for projections or alike, it can be used when doing beamshows that you just want to have that extra power.

This might not be the best way to do it, but I see it as a workaround. I believe that there is still some odd problem in the LD2K somewhere that is dimming the output. I'd say it has to do with the blanking in some way. How....I don't know.

Cheers,

Peter Broerse
 
In my mind, the biggest reason why this issue is still unresolved is because there has been no quality analysis performed. What has been done is sort-of poking around and poking around and poking around and observing results. This is not quality analysis. Fortunately the time will be coming soon when Peter and I will be in the same room, and where we will have adequet test equipment including an oscilloscope and laser power meter, at which point a quality analysis can be done.

As an aside, it is also unfortunate that, with few exceptions, DPSS laser manufacturers have not sought the input of laser software manufacturers, or for that matter, of knowledgable laserists... One exception to this is RGB Laser in Hugary who is currently working with Greg Makhov and LSDI on fine-tuning their laser offerings. Pangolin has worked with LSDI and RGB Laser on specifically the problem Peter mentioned -- fixing up their color system, so that it is compatible with sofware systems in the market place.

I don't want to get off on a rant here, but there are a lot of really crappy DPSS lasers on the market right now, with only a few good manufacturers. It frustrates me when our users misinterpret where the problem is. I look forward to the day when these DPSS laser manufacturers clean up their act and fix their problems related to thermal modulation and even analog signal modulation.

I am sure I have written this before on this forum and I know I have written it in many emails, but I would certainly be happy to work with ANY DPSS laser manufacturer who wants to produce a quality product for this industry. I offer my help at no charge, just so that we could have a greater number of lasers that are compatible with the needs of laserists around the world.

Best regards,

William Benner
 
You must log in or register to reply here.
Back
Top