Johann and Jens

Thank you very much.  Amazed to hear that you could track Etalon solidly with such a weak-energy laser.

I am still learning and a bit confused.

I applied the same procedure as Herstmonceux and Stuttgart to the WLRS-IR based on what you wrote.  It does not seem eye-safe in my quick computation.

(W) WLRS:  1064 nm, 0.4 mJ, 400 Hz, 10 ps FWHM, beam diameter 75 cm

The MPE per pulse in the first wikipedia graph is:
  MPE for (W) = 3e-8 J/cm^2 (where real (W) = 9e-8 J/cm^2)
which suggests WLRS-IR is NOT EYE-SAFE.  Am I right?

The MPE per 0.1 s and per 1.0 s in the second wikipedia graph is:
  MPE for (W) = 2e-3 J/cm^2 per 0.1 sec (where real (W) = 4e-6 J/cm^2)
  MPE for (W) = 1e-2 J/cm^2 per 1.0 sec (where real (W) = 4e-5 J/cm^2)
which looks ok.

The N^(-0.25) rule ("Rule 3" in the document from Jens message) will make the MPE simply lower, if I understand correctly.

The PDF document Jens suggested looks useful for visible (400-700 nm) wavelengths - thanks.  I would be glad to see the same thing for 1064 nm.

Toshi

<!--                                                                                                           -->Hi Toshi,

to my understanding you are right in all of your points. However, i think there is a bit more than MPE.
Lasers are usually categorized in laser classes. The MPE is similar to laser class 1M, which is safe to the naked eye.
However, if you want an eyesafe laser you have to fullfill the requirements of class 1 (532: max .3,8e-8J in 50 mm Aperture; 1064: max. 3,8e-7J in 50 mm Aperture).
I think the difference between class 1 and 1M is that a class 1 laser is even safe, when using optics with an aperture of up to 50 mm.
ANSI Z 136.1 and i think also IEC 60825 define the requirement for the specific laser classes (enclosures, warning devices, ...).
Finally you also have to take into account the repetition rate of the laser system, which reduces the MPE by a factor of N^-0,25
if the repetition rate is above 600 Hz (IEC 60825-1:2014 p.28).

Concerning the numbers in (A):
Of course it is difficult (impossible) to get eyesafe, or class 1, with a bistatic (small transmitt telescope) SLR-system using picosecond pulse-width.
What our colleagues in Stuttgart do is to use nanosecond pulses to reach class 1M.

To point (B):
I think John meant the "eye-closure reflex", which "should" occure when bright light is seen.
It is assumed that the human eye is closed after a timespan of 0,25 seconds in that case.
Obviously only lasers emitting in the visible spectrum can be categorized in class 2.
I think this laser class is important for lasers with emission duration of more than 0,25 seconds only, not for our ps-lasers.

In Wettzell we are currently working on increasing the repetition rate of the WLRS to 400 Hz. We want to use the whole telescope aperture for
laser beam transmission and we want to switch to 1064 nm. By doing so we are class 1M up to a single pulse energy of 400µJ with our 10 ps laser.
Recently, we received first light from ETALON1 with an echo rate of about 5%. The approach seems promissing at the moment, we will see whats happening ...


Hopefully i am right with all this stuff, i am slowly getting confused ... ;-)

Johann

Attached are two presentation slides converted to zipped image folders.  I put them in automation session, but it turned out that mine was actually semi-automation    . Whatever they are here now. Please reply to tell me your thoughts about my work.

Dear Zhipeng,

what is the per pulse energy of the laser you used for the tracking of the rocket bodies?

Thanks and best

Sven

Hi Sven,

It's our normal SLR laser, with 1mJ pulse energy and 1kHz repetition rate, making 1W laser power. I think other high rate station could do it as well or better.

Regards,
Zhipeng

Dear Zhipeng,

what is the per pulse energy of the laser you used for the tracking of the rocket bodies?

Thanks and best

Sven