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What is the avarge output of a TEA laser?

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LIGHT

Sun Mar 13 2011, 11:23PM

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The title explains really, what is the typical output of a lowpower flyback driven TEA laser.

Mattski

Sun Mar 13 2011, 11:35PM

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As a pulsed laser, the average output is probably not very large. If you know all of the variables you could say Pout=Efficiency*E_cap/Period, where E_cap is the stored energy in the capacitor, Period is the time between pulses, and efficiency encompasses the varied loss mechanisms in the system. Efficiency will be very hard to know without simply measuring the power directly.

A couple a members have worked on thermal laser power meters:

LIGHT

Sun Mar 13 2011, 11:43PM

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I'm going to have a shot of making one tomorrow, I know they are capable of high powers in pulses, but what would be the output in mW, not Joules, as pulse lasers are measured in Joules.

Mattski

Mon Mar 14 2011, 12:03AM

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The pulse energy is Efficiency*E_cap in joules, and dividing by the period between pulses gives watts.

LIGHT

Mon Mar 14 2011, 12:05AM

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I haven't actually made it yet, and I was only looking for a estimate.

Would it damage the eyes?

cedric

Wed Mar 16 2011, 09:07AM

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LIGHT wrote ...

I'm going to have a shot of making one tomorrow, I know they are capable of high powers in pulses, but what would be the output in mW, not Joules, as pulse lasers are measured in Joules.

the repetition rate is a big factor here,but diy nitrogen laser usually don't go much above few tens of milliwatt .
using pure nitrogen help a lot...

Shrad

Wed Mar 16 2011, 09:38AM

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you are not totally correct here

first, mattski speaks of the electrical power for each pulse I think, which is really different from the optical output power of the device

the TEA or nitrogen laser is based on a pulsed excitation, and once every part of the nitrogen is excited in their upper energy level, they "collapse" to the ground state of excitation, emitting photons

while you see a dim output from these lasers, the emitted light pulse is actually way bigger than what you may think and is in the range of several kilowatts to several megawatts for high power designs

imagine the electrical power transmitted for each pulse is for instance 500 amperes at 20kV (which sounds realistic for HV guys I think), the injected power should be 10 megawatts for a very short amount of time (several nanoseconds at maximum)

if we say that electrical to optical output power conversion is in the order of 5% (REALLY optimistic) you have an output power of 500 kilowatts in an amount of time as short as a few nanoseconds

now, assume an amateur design is in the order of 10% the efficiency of a well-designed one, you still get 50 kilowatts power for each pulse

naturally, you have to account repeating rate which is low for nitrogen as your PFN has to be really well designed (ultra low impedance), and nitrogen needs something like 20ns to return to its ground state before another population inversion, so you have at max a 10% optical duty cycle for an ideal setup... which shortens in the range of 1% for amateur design

plus your eye sensibility is less than 1% in the UV range from what it is for a green range

so it is logical that 1% of 1% of a small part of 50kW will look less than a watt of light

now what is dangerous with a TEA laser except high current high voltage?

UV light is carcinogenic and highly energizing especially at the 300-ish nanometers of nitrogen transitions, so it damages tissues more easily than any other wavelength

pulses of that power range can be reflected by many surfaces, be it some matte aluminium or brushed metals, and specular reflections can still be of a dangerous power level

keep in mind you will not see these reflections, and you will not feel them, so basically you can not tell...

luckily enough, there is a nice way to protect yourself, as UVA/UVB sunglasses will block most of the reflexions if they are of good quality (reflective coating instead of absorbing coating, important)

also, if you work with UV producing appartuses, keep in mind that some UV protective cream on your hands and arms is useful to avoid burns and the like... just think of a welder's arms when he doesn't protect them and think there is the same difference between a TEA laser and a TIG welder than there is between a light bulb and a 100mW laser diode...

you dont want that in your eyes

EDIT:

and thermal laser power meters CANNOT say the real power, there is some integration, it is the same as measuring an RF signal with a 50/60Hz multimeter

cedric

Wed Mar 16 2011, 10:47AM

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yes ,I was speaking about the average optical output power,the efficiency of diy nitrogen laser can range from marginal to about 1 /100 conversion electric to light,from what I remember ,the absolute maximum efficiency of the nitrogen laser is not above 2/100,one thing is that commercial nitrogen laser are not that different from the amateur build so optimization is not out of question.but the only way to increase the power once a design is set is to increase the frequency ,witch start becoming a challenge above 200 hz...

Shrad

Wed Mar 16 2011, 01:30PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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the cartridge I have is something meant to run at 2Khz

this is not something you can do yourself because of several things, and it is impossible to do it with a TEA laser

the A in TEA stands for Atmospheric, which is one condition that disables fast ionization in itself

a high repetition rate TE (not atmospheric) gas laser needs very precisely engineered electrodes ("D" shape to the microradian), and they have to be perfectly parallel

there is also a need of a pre-ionizing wire generating a corona field just before the discharge, in order to excite gas and accelerate population inversion

if you don't use a constant N2 flow through your laser with a vacuum pump maintaining low pressure, you need a precisely tuned gas fill with Nitrogen, Helium and a bit of other thing I think, to compensate for N2 deterioration

also, they use a triggered spark gap to discharge the caps, and those caps are pulse rated doorknobs

the only amateur TE laser I saw working was a 140cm long, 5cm wide constant N2 flow laser with no more than 30 doorknobs on each side, and a BEEFY high voltage power supply... electrodes were gigantic saw blades though, I imagine to encourage corona in a vast number of miniature breakout points

that was a university setup used for atmospheric spectroscopy

what should be avoided, also, is the use of quartz glass as a width of 1mm like microscope slides ruins gain

if you want to enclose the gas and flow it, you need some UV transparent glass from thorlabs or edmund

Pinky's Brain

Wed Mar 16 2011, 03:16PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Isn't fused quartz generally UV transparent?

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