Opnext HL6545MG Diodes

[The_Doctor]

Currently running one at 140 mW, and it's behaving itself. Another will modehop if I try for that, but it's ok to 136. If I try for 140 it hops, drops back to 128 or so. Could be driven further to reach 140 but that means a second, higher current point that can yield 136 mW. I've decided to stay at the highest settings that will NOT mode hop, with an upper cap at 140 mW no matter what.

Herr Nicolai Pusch (lucky sod, he got 2000 of these diodes at even less unit cost than I got my 200) limits his to 125 mW. Either he's learned stuff beyond what I have, or he's playing safe to reduce the risk of customer complaints. All these measures are after optics, I think. Mine are, anyway. My current test is not long running yet, I just recently bought some preset cermet multiturn pots so I could make sure that more than one unit were truly at same or close as possible specs.

[dave]

Hi guys!

first stage:

http://www.laserblog.de/uploads/karl/Starburst_Rot1.jpg

http://www.laserblog.de/uploads/karl/Starburst_Rot2.JPG

I have no drivers at the moment. I will keep you up to date!!!

Best regards!

Are they the Roithner collimator's?

[carmangary]

Hi. What is mode hopping?

[SenKat]

Going from TEM00 to TEM01, 02, etc......basically adding more beams to the output.....

[The_Doctor]

Yes, although I think with diodes it's more complex as they have solids with variations in their structure. That might not be right exactly, I don't know enough to say it in detail, but they can have parts of their active region that work better than others, and changes in temperature or applied current can change the distribution of energy in the cavity. While the results can be rapid changes like mode hops, and be based on similarities of mechanics, they don't have very well defined modes. If you enlarge the beam of a gas laser, modes are usually clearly visible in the big spot, defined by the optics' possibilities because the gas/plasma is homogenous, but with diodes they rarely are because crystals are rarely as homogenous as gasses, and it's the sudden change in power or general beam shape that gives them away. Also, I think they're usually symmetrical in fluid based lasers, and rarely so in solid based lasers, but I haven't seen nearly enough to be trusted on that point.

Edit: I can add to this usefully, I think...
Imagine an electric guitar, and feedback. Given enough gain, you can create a feedback that is in step with the original signal. The analogy isn't perfect, because the pitch of the feedback changes, and laser wavelength doesn't, but think of the feedback being able to latch onto a returning wave that has come froma further reflection in the room. The pitch will not sweep to the new one, it drops out and the new one begins to dominate. That might be closer to the selection of any one of different wavelengths in a multiline gas laser. Imagine that a PA is tuned so that it can't amplify sound except at a narrow frequency, but can still latch onto more than one path of reflected sound. One way to prevent that might be to make the room very narrow and to make the end walls extremely parallel, or shape them so they are most likely to throw their reflections down the centre of the room instead of at the walls... I guess by now you get the idea.

[Starburst]

Are they the Roithner collimator's?

No, I bought them from HB-Laser! They are 3-glass collimator with 3 seperate lenses, but I will try another one. This has a beam with about 3-4 mm and a divergence nearly 0! I want a little smaller beam and of course i have then a larger divergence...

[PNjunction]

Great explanations, Doctor. Although I preferred the first one in terms of picturing what goes on inside a diode, being a musician, I found the electro-acoustic feedback analogy very cool as well.

So... haven't had time (nor money) to get the Opnext project going, but soon... very soon. Is everyone else having fun?

BTW... of course I could find this out myself, but while I'm here...

How are the shipping prices from Roithner to the states? Expensive, or not too bad? Been looking at the EU-38 for a couple months now.

[lucerne]

Hm, it seems, marconi dont like to answer

As I know, there are NO red diodes with 250mW CW and small emitter!
Maybe marconi takes diodes with 250mW pulse...?

Or: He takes the same Opnext HL6545MG like a few people here
Maybe thats because he answered in this topic, as he saw the topic-title "Opnext HL6545MG Diodes"...

[The_Doctor]

Hm, it seems, marconi dont like to answer

As I know, there are NO red diodes with 250mW CW and small emitter!
Maybe marconi takes diodes with 250mW pulse...?

Or: He takes the same Opnext HL6545MG like a few people here
Maybe thats because he answered in this topic, as he saw the topic-title "Opnext HL6545MG Diodes"...

Keep looking, the answers are on the forum in more than one place. Most of them anyway. And here too now: He's using multimode diodes with a narrow stripe width of 50 µm. They have a longer can than usual, it seems they have a longer chip, a longer cavity, so they probably don't diverge as much as most 50 µm diodes would, so maybe an ordinary aspheric lens will collimate them ok. I don't know what the lens is though. And I don't know where the diodes come from, he won't say.

[steve-o]

The new Mitsubishis have a 40 uM stripe at 641 nm (150 mw). I've been trying to get a "sample" but the s/f axes are strange..not compatible w/ most collimating optics.