i am planning on building one of the prototypes as my final year project, and to reduce cost i mite have to resort to lasers already on the market (like the blue ray ones).
if i was to deliver 50mJ in a few ms, what should the spec for the laser have to be??[/QUOTE]
Ah, now we find out why this will most likely never be more then a nice project for Bill and Melinda to get a tax writeoff for.
50 mJ at what spot size?
1 millijoule is 1 mW for 1 second, but power on target is not a kill, your pK/LD depends on adsorption and energy density. If the target substrate is heated slowly, ie collimated violet diode, it has time to cool off from ambient air. (Note pK is military probability of a kill, LD50 is medical notation for kills 50% of targets)
Pick your target wisely...
Your laser is chosen based on the adsorption spectrum of the wings, and/or maybe the eyes. A body kill would require prime focusing. Small structures such as legs, well.... the light will go right around them.
Keratin/Chitin and similar biomaterals are a tough target.
Your down to YAG at 1064 or co2 at 10.6u.
If I were optimizing to the target, I'd be going after Ho:YAG or Er:yag or CTH:YAG, or excimer, but its not affordable. Those are the lasers doctors prefer for hard tissues. None of them are cheap.
Power = rate times time. 250 mW violet laser, 1 joule = 1 watt for one second. .050 watt/seconds using a 250 mW blue ray means 1/5 second of exposure, so two tenths of a second. Bye, Bye, blu-ray concept.
Direct diode is probably out, as diode price tends to rise as roughly the square of the power and 808 nm is poorly adsorbed by hard tissue. Bigger diodes have bigger dies which makes the optics harder.
That assumes 100% adsorption on a blackbody target, proper focusing, perfect tracking and perfect optics in a vacuum, None of which exist. The biggest downer is air will cool the target with cw light, you need to hit high adsorption at a rate faster then the cooling. To avoid the cooling, you can try Qswitching, to time compress the light.
So now you need to target the maximum tissue adsorption, or time compress the light. Qswitched ND:YAG has the time compression, a 7-20 nanosecond pulse, and you can get your 50 mJ in single shot. On a good day, a ND:YAG has a 18-25% conversion rate from pump to output.
It has a millisecond of storage time, so if you Qswitch it, 1 millisecond of pump is delivered in 10 nanoseconds, so you have about 10,000:1 theoretical time compression. As with all things laser, its never that perfect, but you get the idea. You need really good mirrors and optics to handle the power. This laser is NOT safe to have around humans, it goes right to the retina tissue.
On the 100% adsorption side, you could use a CW CO2. A refillable, reliable US made 3-5 watt Co2 is 3000$ academic research pricing, runs off 12VDC, and the 10 micron wavelength has nearly 100% adsorption by the wings. The downsize is focusing optics for long distances are not cheap. Its cheaper then YAG, and your pK is high for less power. It is strongly adsorbed by the cornea, so if some one gets a eye hit, its not as bad as YAG. You can't replace the retina, but a cornea is somewhat replacable with plastic. O-H bonds strongly adsorb at this wavelength, so it is a prime choice for frying or ablating tissue. In your case your frying, cooking, and breaking down the proteins, or cracking the wings by boiling any water in the tissue.
So your choices are most likely Co2, ND:YAG, or fiber lasers at 1550 nm.
Co2 is cheap, has a decent beam quality and is very controllable.
Steve
:eg:
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