PHR-803T power while on sled?

[alanbrito]

Quick question to those of you who may know this. First, I purchased a few sleds and finally managed to get everything working. I took apart one sled, got the 405 nm diode and powered it with a rckstr driver to test what power I can get out at each input current.

For about 100 mA, I am getting about 83 mW; for 90 mA about 70 mW. When I went past 110 mA at about 114 mA, the diode farted and became an LED and I guess it messed up.

So I assumed that 100 mA would be a reasonable current to run it, and 80 mW would be plenty of power for me.

However, for another part of my experiment, I wanted to use the full sled and optics, and just hook up the diode within the sled to the driver and power and test what power I can get at 100 mA. Everything was working fine, I managed to only power the violet diode in the sled and I can see light coming out of the objective lens. However, the power I am reading is about 4 mW. Any ideas on what might be happening? Could this diode also be working as an LED and be fried? I was expecting at least 50 mW of power even when going through all the internal optics.

Anyone done this before, measure the power of the phr violet diode still in the sled? I can't imagine it would go down all the way to 3-4 mW within the optics. If so, that sucks.

Thanks in advance!

 

[Morgan]

Not a lot have powered diodes in the sled and measured this way. I have done it with GGW sleds but the thing to remeber is that we power these diodes well above their rated power from the manufacturers. You'll have to seek out a PHR BR diode datasheet to see just exactly what these powers are but for example if a diode in the sled is run a 100mA, pulsed with a 50:50 duty cycle, we may well run that at 100mA 100% duty cycle. The heatsink inside the sled will only be rated to dissipate the power when in NORMAL use so it could be detrimental for extended periods.

Having said this, the losses inside a sled sur to all the optics may well be huge compared to our, "get all the light out and fry stuff!", attitude. The optics are quite complex and I would expect heavily reduced outputs than when in a module. You should be able to tell if the diode is lasing by looking but the only way to really tell is now to remove it and install in a module. I, for one, hope it is still working fine because you have just put some figures on an intriguing experiment that I have not seen before, (Caveat: Others may have done this already and I just haven't looked!).

What LPM are you using?

It's not a huge surprise your PHR died at 110mA. Some will survive at this current; some won't. I think the recommended limit for long life is 90mA. Check the, "Diode Compilation", thread. You may find the PHR datasheet there too if you're lucky, I know the LOC and LCC ones are there somewhere so you can compare what we like to run those diodes at and what the manufacturer recommends!

[EDIT: here's the link - http://laserpointerforums.com/f51/diodes-compilation-all-diodes-data-one-thread-45042.html] ]

M

 

[alanbrito]

Thanks! I cannot take it out of the sled, since that would involve changing what is already very well designed and aligned optical elements. What is an LPM? From the tables of values I see that the phr diode that I tested out of the sled was comparable in power/current to everyone else's; but I need to know about it while it's still in the sled.

I am assuming there will be loses, maybe 4% from the cube beam splitter; 4% from the directing mirror/beam splitter, 4% from the other mirror, maybe 4% through the objective lenses and 5% through the LED. That's at most a 30% loss, let's even say 50%, being realistic.

That would mean that out of 80 mW I should be getting 40 mW, but I get 4 mW; so I am either seeing a 90% loss within the optics of the sled or the diode is bad. I am inclined towards the latter and will confirm once I receive more sleds; but in the meantime, if someone has done this or heard about values, let me know.

Anyhow, even the 3-4 mW that I am getting might be enough for my experiments. That is because I am focusing the beam to the smallest size possible, which is what the sled is designed for, so, again, being generous, I will assume the spot size to be 1 um. That is still a huge power density.

 

[Morgan]

Ah, did I read that you needed a really tight beam for tiny construction purposes? I have to say I didn't understand that thread, (I tried to, honest!). Maybe it's possible to remove some the lossy optics? I can see that it may mess with the complete layout but could gain some power back?

An LPM - Laser Power Meter.

M

 

[alanbrito]

Ah, did I read that you needed a really tight beam for tiny construction purposes? I have to say I didn't understand that thread, (I tried to, honest!). Maybe it's possible to remove some the lossy optics? I can see that it may mess with the complete layout but could gain some power back?

An LPM - Laser Power Meter.

M

That is exactly what I need, to focus the beam down. I cannot remove anything else without disturbing the system. I could remove the LCD screen, but that involves moving the lens/actuator system. I can't remove the beam splitters or mirrors.

Oh, thanks for clarifying that. Our laser power meter I think is one fabricated by ThorLabs, it's a lab grade power meter, with wavelength adjusting, etc. I forget the model but it has a GaAs photodetector if I am not mistaken.

 

[alanbrito]

EEK. So I had a spare sled with spare parts, and this is what I am seeing. I wanted to measure the losses within the optics in the system.

First, I measured the diode power when out of the optical head/sled. The diode read about 80 mW at 100 mA of input current. While on the sled, the output power was a mere 4-5 mW.

I took the spare parts and measured the power loss while going through each element, with a 532 nm laser beam and with the same power detector, and this is what I found:

1) the cube beam splitter: about 20% loss.
2) the mirror/grating: I didn't know that the first mirror (the longer, thinner one) is also a diffraction grating which splits the beam to the two optical detectors (there are two, beats me why...). Losses here are in the order of 40%.
3) The main mirror: about 40% lossy.
4) The two lenses: about 10-15% each.
5) The LCD screen/beam aberration corrector: 50% losses.

Starting with a 100% beam power, and working through all the components, that leaves me with like a 90% loss; which seems to explain my problems. What a crappy design, one would think, but since the PHR-803T is only used for reading purposes, only a few mW of power is needed to be able to read.

I might have to get another type of sled that gives more power, maybe a 4x or 6x sled. Does anyone have ballpark estimates on how much power can I expect to get out of those diodes when in the sled and when out of it?

Thanks again for reading.

 

[charliebruce]

I have a couple of GGW sleds on hand - there are considerably more optics in one of these compared with a PHR. If I get a chance I could try measuring it for you - but I don't think I'll get the chance for a few days at the minimum. What's this for? And are you getting all of the light onto the sensor? As I know it, the beam is quite divergent after going through all of the sled optics. I'd guess you are getting most of the light onto the sensor, but thought it better to check. Also, testing at 532nm will give higher loss readings - I'd guess that most of them are coated for 445nm and/or 660-780nm. Did you measure the effects of the tiny gratings in the white and black housings?

 

[alanbrito]

I have a couple of GGW sleds on hand - there are considerably more optics in one of these compared with a PHR. If I get a chance I could try measuring it for you - but I don't think I'll get the chance for a few days at the minimum. What's this for? And are you getting all of the light onto the sensor? As I know it, the beam is quite divergent after going through all of the sled optics. I'd guess you are getting most of the light onto the sensor, but thought it better to check. Also, testing at 532nm will give higher loss readings - I'd guess that most of them are coated for 445nm and/or 660-780nm. Did you measure the effects of the tiny gratings in the white and black housings?

Yeah, I understand the wavelength issue, but I was just doing a quick test. I was getting most of the light to the sensor, but after measuring the losses at 532 I can imagine them being similar at 405, I just think the optics in the PHR need not to be very efficient because you do not need that much power to read a CD/DVD/BR, but to write on them, you do. Hence, I might need a higher power burner setup for this. The gratings, I removed. If you get a chance to measure them it would be awesome, but only if you can; I have decided to go with a higher power burner instead of the PHR, even though 4-5 mW might be enough power to what I need this for, which is actually laser photolithography.