Ha, hopefully the same circuitry... havent designed anything yet. Tryin to get some ideas before we do

 

hi,
While you are doing the feasability study, look at the following:

Use a low power laser diode, pulsed, using an avalanching transistor.

Between the sample and the detector use a Schottky optical bandpass filter.

Designed to pass the coherent laser frequency.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Col_implant wrote:Same circuitry as what?

I can show you a circuit that should switch LED currents in 5ns or less, but within that time range, the rise and fall times might not be symmetrical, e.g., one might be 3ns, the other 5ns. Should I pursue it?

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Ron

 

Yea please do... cheers

 

hi Ron,
I would be interested.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

I'm having second thoughts. I ran some simulations on a low-current LED and a high-current one, and got wildly different results.
The key to fast turn-off is shunt switching, which will rapidly discharge the LED capacitance.
High-current LEDs have high capacitance, so turning them on rapidly may require some peaking in the drive waveform. Getting symmetrical turn-on and turn-off may be difficult for the high-current devices. I would need to see spice models of the LEDs you intend to try, and even then, the results of the simulation are only as accurate as the model.

__________________
Ron

 

hi Ron,
This is the circuit I have used, 30Watt LD1, Range 5000mtr, off three prisms.

Attached Images

esp05 Jul. 22.gif (4.6 KB, 9 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

How do you control the laser current? I have never played with solid-state lasers, but I thought that the current had to be carefully controlled.

__________________
Ron

 

hi,
As you may know the transistor can be driven into a avalanche conduction state by applying a Vce greater than the transistor rating and driving the transistor base with a heavy current. This discharges the 10nF, which is charged to 150V via the 10K.

The collector effectively grounds the +Vside of the cap putting -150V across the LD1. The value of +V and the Cap are chosen so as to keep within the operating envelope of the laser diode.
The clamp diode is to protect the LD1 from reverse voltages.

We pulsed at 250 or 400 pps

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/