Transcript Laser safety for SAM

SAM LGS Preliminary Design Review
September 2007, La Serena
Laser
Safety
for
SAM
1. ANSI Z136.6-2000,
Safe use of Lasers Outdoors
2. Henderson, R. & Schulmeister, K.,
Laser Safety (2004)
SAM PDR
Andrei Tokovinin
1
SAM laser & LGS
Wavelength 355nm
Average power 10 W
Pulse frequency 10 kHz
Pulse duration 34 ns
Class IV laser, dangerous!
SAM PDR
A
3 107
B
4 105
C
415
D
1.6 105
Energy
density,
W/m2
2
Laser radiation hazards
Eye damage (visible at >380nm)
Thermal damage of skin & cornea
Photo-chemical damage ( <320nm)
Only thermal damage is relevant for SAM
Maximum Permissible Exposure (MPE)
for skin and cornea is the same.
However, skin regenerates, eyes don’t
SAM PDR
3
MPE levels (ANSI Z136.6)
Laser beam
Expanded beam
Spot at 7km: 11ms
SAFE
LLT beam
SAM is safe
for condors!
Aversion time 10s
SAM PDR
4
Safe working distance
for scattered radiation
For 10-s exposure: 6cm
For 8h exposure: 3.1m
Light scattered into the dome is not dangerous
Other hazards
High voltage (Pockels cell in SAM)
Fire & smoke if something burns
SAM PDR
5
Airplanes & satellites
Airplane moving at >4 km/h crosses the 1-cm spot in
<11ms, SAFE. Letter to DGAC to waive laser spotters.
Helicopters  need coordination
Satellites can be illuminated (estimate 10% probability
per satellite in 500 nights of SAM operation)
Space Command clearing house is informed, waiver
possible? (beam divergence 43 rad or 8”)
At worst, we submit the target lists, as other LGS AO
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Safety engineering
Mode 1: SAM is not used

Prevent accidental switching of the laser (remove the key)
Mode 2: SAM observations

It is safe to be inside the dome with laser on

SAM LGS must be safe in case of single-mode failure

Engineering measures: interlocks, UV detector
Mode 3: Maintenance and alignment

Potentially dangerous, laser-trained persons only!

Develop detailed plans (think first, then act)

Use green alignment laser and CCD detectors when possible

Wear protective clothes and goggles
SAM PDR
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Summary
The 355nm wavelength is good for safety
Class I (embedded) during normal use, no
precautions needed
Maintenance may be risky
Coordination with the Space Command may
complicate the use of SAM (like any LGS)
Similar lasers are used in the mask-cutting machines at Gemini
Class III laser in each DVD burner!
SAM PDR
8