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Pulsed Laser Diode/Driver

Q

quantumquark

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I have the 445 nm NDB7A75 laser diode, and I was hoping to use it in a regenerative amplifier, for which I need pulses. The pulses would optimally be picoseconds, but could be in the nanosecond range, and I would like to create the pulses by using a driver that outputs electrical pulses that short.

Can these kinds of diodes handle being driven with electrical pulses? Or will that kind of modulation fry the leads or internals?

Is it even advisable to run diodes with electrical pulses, assuming they can be current limited? If so, do you know a good starting point for a driver? I found a circuit that can output pulses similar to what I want, but it is voltage limited instead of current limited: http://cds.linear.com/docs/en/application-note/an47fa.pdf (page 93)

Thanks for the feedback
 
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diachi

diachi

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I'm curious as to what gain medium you'll be using, if you're pumping with visible light?
 
diachi

diachi

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quantumquark said:
We will be using a Ti:Sapph crystal.
Click to expand...

Oh of course, that makes sense! There aren't too many gain mediums that you'd pump at visible frequencies! :)

To answer your question, I'm not entirely sure you'd be able to achieve those pulse durations with straight up electrical modulation, in fact I'd lean on the side of not possible. Generally those kinds of pulse durations are achieved with some sort of mode-locking.

− Techniques for Mode Locking of Diode Lasers
The following techniques can be used for mode locking of diode lasers:

− Active Mode Locking
Active mode locking can be accomplished with an optical modulator in the laser resonator. This is usually either an electroabsorption modulator in the form of an unpumped region with some modulated voltage, or an amplifying section where the drive current is modulated.

− Passive Mode Locking
Passive mode locking relies on a saturable absorber in the resonator. This can simply be an unpumped section of the device. It is common to apply an electrical bias for adjusting the absorber properties. However, the recovery time of that kind of absorber is fairly long. Shorter recovery times are achieved e.g. by implanting nitrogen (N+ or N2+) ions from one facet. This introduces crystal defects, where carriers can recombine.

The absorber is often placed at a resonator end, but it can also be placed somewhere within the resonator so that different pulses can meet in the absorber (colliding pulse mode locking).
Click to expand...
 
diachi

diachi

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quantumquark said:
I found a paper that does it with 650 nm diodes. The pulses they get are ~1 ns: http://www.elexp.com/Images/Speed_of_light_with_650nm_diode_laser.pdf
But their currents and powers are much lower than those I would use. I'd like to run the NDB7A75 at full power for each pulse (3.4 A), but I'm not sure if it (or the wires) can handle it.
Click to expand...


Quite a difference from picoseconds to nanoseconds ;).

You should be able to achieve nanoseconds with the correct driver, although the datasheet for that diode would be needed to confirm that without testing.

If you're pulses peak at 3.4A then it shouldn't be an issue for the wires :D The power would be huge, but keep in mind P=E/T.
 
Q

quantumquark

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Thank you.

Yeah, the OP should have said picoseconds were optimal, but nanoseconds would work and be more realistic, but I goofed and wrote picoseconds twice. It has been edited to reflect my intentions.
 
doubleone44

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Maybe they're actually pumping something else, like, let's say Pr:pAYAC which strongly absorbs the 445nm light? Or is that just me being crazy ;)
 
Q

quantumquark

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Blue pump is used because much higher power diodes are available for much cheaper than for green. The pulsed pump is prefered over CW because for amplification of a pulse, only the pump that temporally overlaps the unamplified pulse will contribute to the gain, and the rest of the CW will simply be wasted. Additionally, I can more easily control the rep rate of the gain pump and use that to control the rep rate of the amplified pulses.

I've realized, though, that if I cannot run these diodes with significantly more power in short bursts, that I still won't get the kind of pulse energy I need. Do you happen to know if diodes can be overclocked on a 0.001% duty cycle (10 ns pulses at 1 kHz)?
 
trussmonkey25

trussmonkey25

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I know some lasers have sos mode like my 5.3 from Podo but I have no idea what the pulse duration actually is. Maybe that circuit in the tailcap could bo modified to your desire. PM Podo if you like. Sanwu is the actual maker
 
diachi

diachi

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quantumquark said:
Blue pump is used because much higher power diodes are available for much cheaper than for green. The pulsed pump is prefered over CW because for amplification of a pulse, only the pump that temporally overlaps the unamplified pulse will contribute to the gain, and the rest of the CW will simply be wasted. Additionally, I can more easily control the rep rate of the gain pump and use that to control the rep rate of the amplified pulses.

I've realized, though, that if I cannot run these diodes with significantly more power in short bursts, that I still won't get the kind of pulse energy I need. Do you happen to know if diodes can be overclocked on a 0.001% duty cycle (10 ns pulses at 1 kHz)?
Click to expand...


You can certainly up the power when operating at lower duty cycles, but probably not to what you want. What kind of power levels do you need?

Perhaps you'd be better with a true mode-locked laser, such as a frequency doubled YAG?
 
Q

quantumquark

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diachi said:
You can certainly up the power when operating at lower duty cycles, but probably not to what you want. What kind of power levels do you need?

Perhaps you'd be better with a true mode-locked laser, such as a frequency doubled YAG?
Click to expand...

Yeah, it'd be better with a YAG, but one of the goals of this project is to remain low-cost, so I'm looking into alternatives.
 
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