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What is the avarge output of a TEA laser?

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Shrad

Wed Mar 16 2011, 05:36PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780

fused quartz drops to 60% transmittance below 250 nanometers while fused silica goes as low as 170 nanometers

not a big deal but I think non-optical grade like microscope slides have a slope starting as high as 400 nanometers, as there are cases demonstrating this phenomenon

a cuvette full of dye, made out of 4 microscope slides, would be harder to get lase than a cuvette made of slide covers or a spectroscopic grade cuvette, as thickness or absorption ratio plays a great deal here

with invisible lasers below 400 nanometers and over 2000 nanometers, you have to carefully choose the medium because most of the common transparent materials are at visible wavelengths, and maybe not outside that range

Mattski

Wed Mar 16 2011, 07:55PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Shrad wrote ...

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

I speak of the optical energy of each pulse (efficiency*E_cap), which when divided by time between pulses gives average an average power. The peak power of a laser pulse is certainly of great interest, but high average power with a fast repetition rate gives a brighter laser. And of course measuring the peak power is not as easy as measuring average power.

wrote ...
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

The time-varying and time-averaged power are both real powers, but yes a thermal power meter could only measure the latter.

If you measured average power, and got the pulse rate using a fast photodiode detector and oscilloscope you could estimate optical pulse energy (E_pulse=Power(W)/pulse rate (Hz)) and thus electrical to optical efficiency. If your detector was fast enough to measure pulse width too you could estimate the power during the pulse by taking E_pulse (optical)/pulse width, which will give you the time-averaged power over the pulse period. Peak power will be higher. These measurements become harder if the laser doesn't pulse at a somewhat consistent rate.

Pinky's Brain

Wed Mar 16 2011, 08:03PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Still, quartz seems good enough for a nitrogen laser ... and it's expensive enough to start with, before turning it into silicon and back into glass.

Shrad

Wed Mar 16 2011, 08:12PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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you're right mattski, I hadn't seized the subtilities as I'm french spoken

I have such photodiodes, they are large die silicon photodiodes and you have to bias them to get decent speed and accuracy

I harvested various photodiodes for a scanning michelson interferometer I wanted to build, but never did because of mechanical complexities to achieve a resolution of at least 1nm

Mattski

Wed Mar 16 2011, 09:26PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Quite alright Shrad, good to know we have members from many countries represented here.

Do you think it's possible to calibrate a photodiode as a reasonably accurate power meter in a situation like this? How would a lab ordinarily measure the time-varying power of a pulsed laser like this?

Dr. ISOTOP

Wed Mar 16 2011, 10:25PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

With the sub 5mW outputs of DIY N2 lasers, I doubt burns/cancer/whatever are dangerous.
Just don't stare down the bore.

Shrad

Fri Mar 18 2011, 09:45PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780

unless you face the beam, UV from the spark gap and the corona is more dangerous than the rest

if you want to calibrate a photodiode to be an accurate pulsed power meter, you have to bias it properly and it has to be an avalanche type, and you must use an appropriate neutral density filter in order to reduce power applied to the diode dye by an order of thousands or more

but the only viable way to calibrate such a setup would be against a commercial unit properly calibrated itself

otherways, I have no clue as in the lab, they usually don't pay attention to the power, they fire it until they have results, then they take measurements...

when I worked at the university, they had a need for a laser with special wavelengths and they just ordered it, regardless of the power

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