Did anyone use the 538nm 5watt Diode?

[planters]

I would put the P73 @ 1/5 the divergence, 1/3 the power and 1/6 the cost. You will need more optics for the P73, probably more room for the array, but there is a lot of history available with the Mitsu and no restriction on modulation speed. I would probably stick with these for now. Does anyone know why the soft start with the 4W diode is necessary and what the range of ramp speed might be?

[logsquared]

I would put the P73 @ 1/5 the divergence, 1/3 the power and 1/6 the cost. You will need more optics for the P73, probably more room for the array, but there is a lot of history available with the Mitsu and no restriction on modulation speed. I would probably stick with these for now. Does anyone know why the soft start with the 4W diode is necessary and what the range of ramp speed might be?

From what I can read at LPF the soft start issue came up when someone blew a diode. Is seems as though it may have been a driver issue. I see no reason why these couldn't be modulated like any other diode with the right driver.

Hopefully someone can add more about the soft start...?

It would make one hell of a 3rd brake light as tailgater-repellant !

Hmmm... may have to look into that.

[laserbiker]

I am interested in buying this diode from you for $300.00. I have built a small lab style driver with tec cooling and 5+ amps with fast analog modulation.
This might make a spectacular laser for my desert camping events.
Thanks

[The_Doctor]

If a diode cannot take anything faster than a soft start, what earthly use is it for fast scanning? A diode is a diode. I don't think I've ever seen one so slow that it looks like a cap charged through high resistance! It's almost certainly a driver problem. With a high current at high speed, it doesn't need much inductance to get dangerous power into a spike, no matter how small. Given that high currents and small sense resistances in controlled current devices usually need a wirewound resistor, that might be problem enough. It may be better to use a flat array of ten 0.6W metal film resistors to get high power and low resistance. Those things are helically cut by laser to fine-tune resistance, but you'll still get less inductance that way. Ideally a low-inductance wirewound might be wound the way I was taught for my first ammeter, fold the wire back on itself in one long bight before winding that onto the former, but I don't know what the specs are for the resistors used in various drivers. Any direct diode-related restriction on speed might be due to thermal shock, but that's why the C-mounts have such solid bolt-on heatsinks. They ought to stand it, though it might pay to run it to thermal equilibrium at half power CW before thrashing it with fast modulation.

I've been quietly reading this thread (when the Syrians would let me), and my view is that the sooner I get some of those P73's the better. I'm after a special deal for ten, or maybe twenty.

[steve-o]

A soft start may be needed due to a possible lack of inrush current control when used in battery operated pointers ?? .. dunno ..

[andythemechanic]

I think when the diode needs a soft start it is just Extremely overdriven. A laser diode driven in spec can be modulated with really fast currents without damage, if you modulate with very short pulses in the µs range you can even overdrive it 2x or so (depending on the diode). If a diode dies with fast current rise but not under slow ramping of the current here is what happens: When you ramp it up slow the finite thermal conductivity of the diode leads to a temperature rise and reduced efficiency and less output intensity, which is low enough not to damage the front facet. If you switch on the current fast, temperature is still low when the diode output power reaches it's max and the output power is much higher, high enough to blow the front facet.
You can test if this is the case by taking cw and pulsed PI-curves. I would assume that the cw PI curve is not linear anymore at some current but rolls over due to reduced efficiency.

[planters]

I'm also curious as to what these devices really are. Are they simply a very wide single emitter? If I remember correctly,the G71 has a 60um wide emitter and the P73 has a 100um emitter. The power for these devices (as well as the divergence) is proportional to this ratio. Or are these devices a short "bar" of several conventionally sized diodes mounted on the same copper die?

I would like to see a large projection of the un-lensed emission. This might give an idea as to what is going on. A tiny thermistor mounted on the block as the power is ramped would be interesting as well. Finally, a spectrum of the emission would be useful. I thought about syncing the current ramp to the spectrograph and this gives me a headache. I think a series of single shot readings for various currents for several pulse widths would yield pretty much the same info. I could do this, but the quality of the emission from these seems so low (and the price so high) that I don't think it is worth the effort.

[The_Doctor]

I think when the diode needs a soft start it is just Extremely overdriven. A laser diode driven in spec can be modulated with really fast currents without damage, if you modulate with very short pulses in the µs range you can even overdrive it 2x or so (depending on the diode). If a diode dies with fast current rise but not under slow ramping of the current here is what happens: When you ramp it up slow the finite thermal conductivity of the diode leads to a temperature rise and reduced efficiency and less output intensity, which is low enough not to damage the front facet. If you switch on the current fast, temperature is still low when the diode output power reaches it's max and the output power is much higher, high enough to blow the front facet.
You can test if this is the case by taking cw and pulsed PI-curves. I would assume that the cw PI curve is not linear anymore at some current but rolls over due to reduced efficiency.

Well that's why I suggested running to thermal equilibrium at half power before thrashing the poor beastie, but when I chucked my last 30 or so Rohm diodes over the wall, this is why:

I start at under rated power, CW only, no modulation. It sits pointing at the wall. I point its beam back at it with a mirror at point blank range for a few seconds, and it is fine with that. A day later, it is fine with that. Half a week later, I decide to be a bit more gentle, not the better mirror this time, and doing it from a greater distance. Much less exposure that way. It dies instantly. So over the wall they go. After all, if they are running UNDERpower, on pure filtered DC, what good are they if they die so easily after less than 100 hours runtime?! Never mind pushing the envelope, they're aging fast lying in a carry cot. Now, maybe the Rohm diodes were just crap. (They were falling through eBay thousands at a time, NOT a likely thing if the big buyers who originally owned them thought them good enough to use, for anything at all!).

Anyway, it seems to me that diodes may be a bit of a lottery, and that with new strong multimode diodes, and new crystals to be pumped, we might all be better off looking at that. THIN beams again, immunity to retroreflection death, no SHG to screw with the modulation stability... So maybe the best question for this new 5W red C-mount diode is: What crystal must be pumped by it to get us some useful visible light?

[logsquared]

This new diode is definitely a single emitter. Unfortunately, I didn't take any pictures. Emitter appears to be 100um

From what I could measure the emitting area of the G71 is around 30um and 50um for the P73.

[The_Doctor]

This new diode is definitely a single emitter. Unfortunately, I didn't take any pictures. Emitter appears to be 100um

From what I could measure the emitting area of the G71 is around 30um and 50um for the P73.

Thankyou. That's useful info! I suspected similar, and was looking at the G71 as maybe preferable to P73 if I get into this (I like sharp fine beams), but I didn't know what the 'stripe widths' might be yet.

EDIT: Can you point me to data sheets for all three of these diodes? DTR hasn't got any! (Nor have Prophotonix) I'll go hunting but if you can spare me the hassle, please do..