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Pulse duration (msec long pulse) how?

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Xeonophon

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Hi all,

Im researching vascular lasers and I cant find info on how "long pulse" lasers manage to create millisecond pulses. Are they just Continuous wave lasers with some sort of switch that only stays on for milliseconds?

I know Q-switched xenon lamp pumped tattoo removal lasers work in microseconds and use capacitors.

If anyone can explain this it will be a big help.

Thanks.
 





diachi

diachi

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Xeonophon said:
Hi all,

Im researching vascular lasers and I cant find info on how "long pulse" lasers manage to create millisecond pulses. Are they just Continuous wave lasers with some sort of switch that only stays on for milliseconds?

I know Q-switched xenon lamp pumped tattoo removal lasers work in microseconds and use capacitors.

If anyone can explain this it will be a big help.

Thanks.
Click to expand...

What peak powers/output energies do you need?

What type of laser are you looking to use? For what purpose?

Provide details. A problem well stated is a problem half solved.

Q-switching and capacitors don't really have anything to do with each other...? Flash lamp pumped lasers use capacitors to energize the flash lamp but that doesn't really have anything to do with Q-switching, other than the fact that some flash lamp pumped lasers are Q-switched...?
 
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paul1598419

paul1598419

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Yes, far too little information to give you any kind of an answer. Need some details.
 
X

Xeonophon

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Well I guess Im looking to make a "green" 532nm KTP laser.....
It needs to do the following :

Variable spot size : 1 - 10mm
Adjustable pulse width : 1 - 30 msec
Fluence: 1- 18 J/cm2
Pulse per second: 1-3
 
paul1598419

paul1598419

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In this case, I would recommend an 808nm diode pumped CW 532nm DPSS laser. With optics you will be able to get the energy density you are looking for as long as the output power is great enough to accommodate this. You will also be able to modulate the output to give your desired pulse width and frequency.
 
M

Mosc007

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Xeonophon said:
Would I use something like a 555 timer to modulate?
Click to expand...


A 555 should work fine. You can probably even find a schematic on the net for variable 1-30 ms pulse with 1-3 PPS.


My calcs may not be accurate but for 18 J/cm2 at 30mS I think you need more than 500mW at output.
 
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Xeonophon

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"On CASIX's web site they list some examples of conversion statistics when using an 808 nm laser diode to pump a Nd:YVO4 (vanadate) crystal:

Output of 278 mW at 1064 nm with pump power of 730 mW, a conversion efficiency of 38% from 808 nm to 1064 nm.
Output of 2.5 mW at 532 nm with a pump power of 50 mW using intra-cavity KTP doubling, a conversion efficiency of 5% from 808 nm to 532 nm."

Laser diode power supply: 60 W.
Laser diode efficiency: 0.33.
Laser diode output: 20 W.
Radiation transfer and absorption efficiency: 0.8 (now down to 16 W).
Laser medium efficiency: 0.68 (Stokes shift and quantum efficiency, now down to 11 W).
Resonator efficiency: 0.67.
Output power: 7 W.

Would i be able to use a modded poversupply from a pc?
 
diachi

diachi

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paul1598419 said:
In this case, I would recommend an 808nm diode pumped CW 532nm DPSS laser. With optics you will be able to get the energy density you are looking for as long as the output power is great enough to accommodate this. You will also be able to modulate the output to give your desired pulse width and frequency.
Click to expand...


It's going to take a good bit of power to get those energy densities with those pulse durations...

Of course, we're dealing with power density here, which changes things. You can't just multiple the energy by the pulse duration to get the required output power.

We'll take one set of figures given by OP.

Beam diameter: 10mm
Energy density: 18J/cm²

Beam area: 78.5mm² (0.785cm²)
Total energy for a 10mm diameter beam @ 18J/cm²: 14.13J
Pulse duration: 30ms

Total power required for an 18J/cm² beam with 10mm diameter and a 30ms pulse duration: 471W.

Not happening, not with a modulated CW laser.

The bottom end of your specified requirements would be doable on a hobbyist budget (smallest beam diameter, lowest energy, longest pulse duration). Unless I messed up the math (EDIT: I DID), a 1mm beam with 1J/cm² energy density for 30ms works out to about 0.26W. Go up to 18J/cm² with that diameter and duration and you're already up to ~4.7W CW.

Someone please correct me if I'm wrong? EDIT: Yup, I was. Off by an order of magnitude no less... Thanks WizardG.

What's your budget for all of this OP?
 
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X

Xeonophon

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diachi said:
It's going to take a good bit of power to get those energy densities with those pulse durations... 18J over 30ms is 600W. Even 1J for 30ms is still 33⅓W.

Of course, we're dealing with power density here, which changes things.

We'll take one set of figures given by OP.

Beam diameter: 10mm
Energy density: 18J/cm²

Beam area: 78.5mm² (7.85cm²)
Total energy for a 10mm diameter beam @ 18J/cm²: 141.3J
Pulse duration: 30ms

Total power required for an 18J/cm² beam with 10mm diameter and a 30ms pulse duration: 4.71kW.

Not happening, not with a modulated CW laser.

The very bottom end of your specified requirements would be doable (smallest beam diameter, lowest energy, longest pulse duration).

What's your budget for all of this OP?
Click to expand...

Budget wise I can see that 10W DPSS lasers cost about $7000 if im not mistaken...
Apart from that i have no idea what its going to cost.
 
diachi

diachi

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Xeonophon said:
Budget wise I can see that 10W DPSS lasers cost about $7000 if im not mistaken...
Apart from that i have no idea what its going to cost.
Click to expand...

I'm not asking what it's going to cost, I'm asking how much you want to spend.
 
M

Mosc007

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diachi said:
It's going to take a good bit of power to get those energy densities with those pulse durations...

Of course, we're dealing with power density here, which changes things. You can't just multiple the energy by the pulse duration to get the required output power.

We'll take one set of figures given by OP.

Beam diameter: 10mm
Energy density: 18J/cm²

Beam area: 78.5mm² (7.85cm²)
Total energy for a 10mm diameter beam @ 18J/cm²: 141.3J
Pulse duration: 30ms

Total power required for an 18J/cm² beam with 10mm diameter and a 30ms pulse duration: 4.71kW.

Not happening, not with a modulated CW laser.

The very bottom end of your specified requirements would be doable on a hobbyist budget (smallest beam diameter, lowest energy, longest pulse duration). Unless I messed up the math, a 1mm beam with 1J/cm² energy density for 30ms works out to about 2⅓W. Go up to 18J/cm² with that diameter and duration and you're already up to ~47W CW.

Someone please correct me if I'm wrong?

What's your budget for all of this OP?
Click to expand...


Thanks Diachi,

I wasn't even close. I wasn't sure how to do the density calcs so I just used the Joules/Pulse time.


Looks like it's not feasible. Do they even make a 532 at those powers ?
 
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paul1598419

paul1598419

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diachi said:
It's going to take a good bit of power to get those energy densities with those pulse durations...

Of course, we're dealing with power density here, which changes things. You can't just multiple the energy by the pulse duration to get the required output power.

We'll take one set of figures given by OP.

Beam diameter: 10mm
Energy density: 18J/cm²

Beam area: 78.5mm² (7.85cm²)
Total energy for a 10mm diameter beam @ 18J/cm²: 141.3J
Pulse duration: 30ms

Total power required for an 18J/cm² beam with 10mm diameter and a 30ms pulse duration: 4.71kW.

Not happening, not with a modulated CW laser.

The very bottom end of your specified requirements would be doable on a hobbyist budget (smallest beam diameter, lowest energy, longest pulse duration). Unless I messed up the math, a 1mm beam with 1J/cm² energy density for 30ms works out to about 2⅓W. Go up to 18J/cm² with that diameter and duration and you're already up to ~47W CW.

Someone please correct me if I'm wrong?

What's your budget for all of this OP?
Click to expand...


I didn't take the highest diameter and calculate the highest energy density to get to a CW laser. I thought his specs were not intended that way, but were more towards the smaller diameter at the highest energy density. As you pointed out, to have that much energy in such a long pulse duration at the highest diameter would not be practical with the lowest. Even at that wavelength it wouldn't be practical.

You probably wouldn't want to use an NE555 to modulate the output either. You could find something better in a microprocessor circuit to modulate this laser.
 
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