Re: Stargazer arrested for using green laser

From: canopus56 (canopus56_at_yahoo.com)
Date: 01/08/05 

Date: 7 Jan 2005 18:08:19 -0800

canopus56 wrote:
<snip>

To correct tables in prior post due to minor math error (incorrect
conversion factor for ft to meters of 0.30408 initially used; corrected
to 0.3048). This does not change any of key values in the W^cm column:

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Table 2 - Informal computation of laser brightness at distance

Brightness computation for Class IIIA lasers
5mW< initial power and 1 milliradian dispersion

Dt ft Dt m Bdiain Bdiacm BAreain BAreacm W^cm Per dlt_mag
50 15 0.6 2 0.3 1.8 2.74E-03 54.82% 8.2
100 30 1.2 3 1.1 7.3 6.85E-04 13.70% 9.7
175 53 2.1 5 3.5 22.3 2.24E-04 4.475% 10.9
200 61 2.4 6 4.5 29.2 1.71E-04 3.426% 11.2
275 84 3.3 8 8.6 55.2 9.06E-05 1.812% 11.9
300 91 3.6 9 10.2 65.7 7.61E-05 1.523% 12.0
500 152 6 15 28.3 182.4 2.74E-05 0.548% 13.2
825 251 9.9 25 77.0 496.6 1.01E-05 0.201% 14.2
1000 305 12 30 113.1 729.7 6.85E-06 0.137% 14.7
1100 335 13.2 34 136.8 882.9 5.66E-06 0.113% 14.9
1500 457 18 46 254.5 1641.7 3.05E-06 0.061% 15.5
2000 610 24 61 452.4 2918.6 1.71E-06 0.034% 16.2
3000 914 36 91 1017.9 6566.9 7.61E-07 0.015% 17.0
4000 1219 48 122 1809.6 11674.5 4.28E-07 0.009% 17.7
5000 1524 60 152 2827.4 18241.5 2.74E-07 0.005% 18.2
6000 1829 72 183 4071.5 26267.7 1.90E-07 0.004% 18.5
7000 2134 84 213 5541.8 35753.3 1.40E-07 0.003% 18.9
8000 2438 96 244 7238.2 46698.2 1.07E-07 0.002% 19.2
9000 2743 108 274 9160.9 59102.4 8.46E-08 0.002% 19.4
10000 3048 120 305 11309.7 72965.9 6.85E-08 0.001% 19.7
11000 3353 132 335 13684.8 88288.7 5.66E-08 0.001% 19.9

Dt ft = Distance feet
Dt m = Distance meters
Bdiain = Beam diameter inches at distance
Bidacm = Beam diameter centimeters at distance
BAreain = Beam area inches at distance
BAreacm = Beam area centimeters at distance
mW^cm = milliWatts per square centimeter
Per = change in milliWatts per square centimeter from
distance zero (5mW) to distance
dl_mag = same as Percent, expressed in changes in magnitude
delta_mag (m1 - m2) =

2.5 * log_10 * ( mW^cm / 5mW at zero distance )

(Note delta_mag is not the apparent magnitude, since
magnitude at distance zero is not known)

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Table 3 - Informal computation of laser brightness at distance

Brightness computation for a Class IIIA laser emitting
2.5m Watts initial power and 1 milliradian dispersion

Dt ft Dt m Bdiain Bdiacm BAreain BAreacm W^cm Per dlt_mag
50 15 0.6 2 0.3 1.8 1.37E-03 54.82% 8.2
100 30 1.2 3 1.1 7.3 3.43E-04 13.70% 9.7
175 53 2.1 5 3.5 22.3 1.12E-04 4.475% 10.9
200 61 2.4 6 4.5 29.2 8.57E-05 3.426% 11.2
275 84 3.3 8 8.6 55.2 4.53E-05 1.812% 11.9
300 91 3.6 9 10.2 65.7 3.81E-05 1.523% 12.0
500 152 6 15 28.3 182.4 1.37E-05 0.548% 13.2
825 251 9.9 25 77.0 496.6 5.03E-06 0.201% 14.2
1000 305 12 30 113.1 729.7 3.43E-06 0.137% 14.7
1100 335 13.2 34 136.8 882.9 2.83E-06 0.113% 14.9
1500 457 18 46 254.5 1641.7 1.52E-06 0.061% 15.5
2000 610 24 61 452.4 2918.6 8.57E-07 0.034% 16.2
3000 914 36 91 1017.9 6566.9 3.81E-07 0.015% 17.0
4000 1219 48 122 1809.6 11674.5 2.14E-07 0.009% 17.7
5000 1524 60 152 2827.4 18241.5 1.37E-07 0.005% 18.2
6000 1829 72 183 4071.5 26267.7 9.52E-08 0.004% 18.5
7000 2134 84 213 5541.8 35753.3 6.99E-08 0.003% 18.9
8000 2438 96 244 7238.2 46698.2 5.35E-08 0.002% 19.2
9000 2743 108 274 9160.9 59102.4 4.23E-08 0.002% 19.4
10000 3048 120 305 11309.7 72965.9 3.43E-08 0.001% 19.7
11000 3353 132 335 13684.8 88288.7 2.83E-08 0.001% 19.9
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