Pulsed laser diode drivers?

[LikeitBright]

Is anyone making pulsed drivers for laser diodes or have a good design for one?   Spec sheets often rate a 90mW CW 650nm diode much higher in pulsed mode, eg typically something like 200-250mW.  Now, unless this description is misleading, 250mW pulsed (at however many Mhz) means 250mW true power, i.e. 0.25Watts/second on average at high rep rate.  As far as the eye or any target is concerned this would be indistinguishable from 250mW 'true' CW.  

I hope the 90mW V 250mW rating isn't just a CW verses peak 'nano-second' type power rating in other words a matter of manipulating the duty cycle.  Perhaps it is but I haven't found a clear description or discussion of this.  My thinking is that the diode junction can tolerate higher transient currents and possibly optical fluxes than it can contant currents and fluxes - hence there may be some way to squeeze more power out in pulsed mode.  But ultimately I think I know the answer - the pulsed power rating is just the peak optical power (as is relevant for burning a DVD) and the mean power is still at or near the CW rating.

 

[phenol]

you are right. In fact, most datasheets specify the pulsed rating at duty cycles of <35% and PW<30ns. For instance, Mitsubishi's ML101J27 is rated for 130mW CW and 350mW pulsed under the conditions above.
Nonetheless, we consistently overdrive them CW at their rated pulsed powers and they last a fair amount of time with sufficient heatsinking.
I think that if the pulses are kept shorter than 30ns, higher optical powers could be attained. However, designing and building a RF circuit with the proper layout capable of handling such pulses is beyond the ability of most people. On the other hand, the drievr chips inherent to all DVD burners are fully capable of doing the job. It might be worth it looking into a DVD driver assembly found directly on the optical pickup

 

[Tallaxo]

I fail to see the reason why you would want to pulse drive a diode. Apart from increased lifetime, pulsed and CW will pretty much deliver the same energy over a period of time. You may actually achieve higher mw bursts, but you have to factor in the "off" time when the diode is not lasing. So the overall energy would be about the same if run in CW.

With good heatsinking you can run a Senkat diode at 400mA for hours at a time in CW , giving around 230-250 mw.

This little baby is powered by a Senkat diode running at 400mA . The heatsink has been machined to accept the Aixiz module as a press fit, and will quite happily push out 250mW for hours at a time without even getting warm.

Jase.

 

[GooeyGus]

The only reason would be for exactly as you said. Higher peak power; even if the overall power is similar.

 

[diachi]

You could just connect a really basic pulsing circuit up to a driver and there you have it, pulsing circuit would only need a transistor a not gate a capacitor and a variable resistor, to vary pulsing speed

 

[LikeitBright]

Well thats the thing I'm curious about. How similar are the mean powers over a macroscopic interval (eg 1 second) compare when running in maximum pulsed and CW modes. Yes they are surely similar, I'm just wondering at this point if anyone has done a comparison. I asked Chuck at Aixiz this with regards to the $40 200mW/350mW 650nm LD they sell and his answer was

You would have to ask Mitsubishi that one!

Chuck Maricle

 

[Benm]

I have done some experiments with pulsed operation of red laser diodes. It will not give you any increase in average optical power or burning ability.

One interesting thing is that in pulsed mode, you can lower the average output power without affecting the fine-line pattern of the diode output (ie the lighter/darker bands visible when you project a large blob instead of a dot onto a wall).

All in all, since the primary failure mode of laser diodes is COD, pusled operation only makes things worse. Heatsinking will work to some extent because a lower die temperatue makes COD less likely, but only to a small degree. I doubt the difference between a diode running 25 or 30 degrees would even be measureable reproducibly.

 

[cul8r]

Your statement about pulsed power not giving any extra mw or power is in direct conflict with every data sheet I have recieved from the diodes manufacturers. In fact some are actually claiming almost double the power, For instance direct from sony with my Sony SLD1239JL-54 diodes states 100mw cw 180 pulsed at 40% or less. Do you think these people are full of it or are your statments a bit inaccurate?

 

[john_lawson]

easy there we are trying to help you out -but as for me i do not know anyone selling pulsed drivers ATM i will try to help you though

 

[ElektroFreak]

I fail to see the reason why you would want to pulse drive a diode. Apart from increased lifetime, pulsed and CW will pretty much deliver the same energy over a period of time. You may actually achieve higher mw bursts, but you have to factor in the "off" time when the diode is not lasing. So the overall energy would be about the same if run in CW.

When a laser writes data to a disc it is running pulsed.. It' not as much use to hobbyists, but when used in the application they were designed for it's very helpful.

 

[Cyparagon]

250mW (average) pulsed appears brighter than 250mW CW.

 

[mojo_1234]

Hi,

a pulsed laser driver would the best choice for the life of your diode. You'll a good example circuit on SAMs Laser FAQ:

Sam's Laser FAQ - Diode Laser Power Supplies

Example circuit:
http://www.repairfaq.org/sam/glpdrv2.gif

If you're looking for a more professional & easy solution buy one of the test boards from
Roithner:

Roithner Lasertechnik Vienna Austria ------x laser diode laserdiode optic collimator YAG laser semiconductor laser laser module lasermodul LED photodiode MID-IR InGaAs DPSSL UV-LED GaN white LED

These laser drivers can easily be modulated with a NE555. Some drivers have a build-in pulse generator...

Regards,
mojo