Need to Quadruple-check Calculations about UV Radiation Source

[wwswimming]

i'm trying to double-check my interpretation of some industrial laser specs.
it took me 6 months on the first go-round to gather the specs, to perform
the conversions, and to quadruple check it. that was before i knew about
the Anandtech technical forum. i have a feeling there are some members
here who can eat this stuff for lunch, that is, for whom such calculations
are easy.

if you see any factual errors in my calculations, please let me know !

Laser Wavelength 193 nm
Laser Pulse Duration 18 nanoseconds
Laser Head Repetition Rate 50 Hz
Effective Corneal Repetition Rate 12.5 Hz
Fluence (at the target) 120 mJ/cm2
Laser Spot Diameter 2.0 to 2.05 mm

2 modes - the laser fires 12.5 pulses every second, and 50 pulses.

Translating from milli-watts per square centimeter to milli-watts per square inch
Power for lasers is frequently expressed using an energy term (joules), instead of a power term (watts).
120 mJ/cm2 ==> 120 mW/cm2

Duty Cycle: .000000225, 12.5 pulses per second ... each pulse is 18 nanoseconds long
"Fluence", Power Density of laser beam: 120 milli-watts per square centimeter - 774 milli-watts per square inch - about 3/4 of a watt per square inch.
Power Density: .774 watts per square inch, about 3/4 of a watt per square inch.
Peak Watts per Square Inch, if the 120 milli-Joules specification is a physical average: 3,440,000
Average Watts per square inch for the sun, term used in comparison with excimer laser: .56 watts per square inch
Beam Width: 2 millimeters, about 1/ 12 of an inch

Duty Cycle: .00000090, 50 pulses per second ... each pulse is 18 nanoseconds long.
Power Density: .774 watts per square inch, about 3/4 of a watt per square inch.
Peak Watts per Square inch, if the 120 milli-Joules specification is a physical average: 860,000
Average Watts per square inch for the sun, term used in comparison with excimer laser: .56 watts per square inch
Beam Width: 2 millimeters, about 1/ 12 of an inch

Radiation Source: The Sun
CW (continuous wave) or pulsed ? : CW
Duty Cycle, daytime: 100%
Average Watts per square meter, in outer space: 1367
http://stratus.ssec.wisc.edu/s...web/userman/solar.html
Amount of radiation filtered out by the atmosphere: 51%
http://www.geog.ouc.bc.ca/physgeog/contents/7f.html
Average Watts per square meter, on the average beach: 697
Average Watts per square foot, on the average beach: 65
Average Watts per square foot, term used in comparison with prototype laser: 80

Note: one of the goals of the analysis is to express the ratio as conservatively as possible,
that is, to not over-state the ratio when comparing the prototype laser to the sun.
Average Watts per square inch, term used in comparison with prototype laser: .56 watts per square inch

 

[BrownTown]

I guess the only question I have comes from the statement:

"Average Watts per square meter, on the average beach: 697 "

Which is based on 51% of 1367 from the absorption of sunlight in the atmosphere. However it does not seems to take into account the angle of incidence of the light or the time of day and such. That number would only be true at the brightest second of the brightest day of the year and only between the tropics. Any region outside the tropics will never reach that number and the average at every region in the world will be only a fraction of that number.

 

[PlasmaBomb]

Fluence (at the target) 120 mJ/cm2

Power for lasers is frequently expressed using an energy term (joules), instead of a power term (watts).
120 mJ/cm2 ==> 120 mW/cm2

120 mJ/cm2 =/= 120 mW/cm2

These conversions will be useful for you -

Fluence (Joules/cm^2) = laser pulse energy (J) / focal spot area (cm^2)
Peak power (W) = pulse energy (J) / pulse duration (sec)
Intensity (Watts/cm^2) = peak power (W) / focal spot area (cm^2)

Mistake: too late at night made an error in the calcs. will fix tomorrow.

 

[wwswimming]

Originally posted by: BrownTown
I guess the only question I have comes from the statement:

"Average Watts per square meter, on the average beach: 697 "

Which is based on 51% of 1367 from the absorption of sunlight in the atmosphere. However it does not seems to take into account the angle of incidence of the light or the time of day and such. That number would only be true at the brightest second of the brightest day of the year and only between the tropics. Any region outside the tropics will never reach that number and the average at every region in the world will be only a fraction of that number.

thanks both of you for looking at it.

i need to nail these calculations, in terms of accuracy.

the 697 watt/ square meter came from a university
web site; i'd have to look at my notes.

approximately = 70 watts per square foot, about what
you get when you're laying on the beach in San Diego
and the sun is almost right overhead and you have to
get in the water every 10 minutes to stay comfortable.

so the 697 is a peak "high noon" number with a reference
source attached; the 70 is a SWAG.

yes, if the Sun is at an angle, some energy is diffused
in the atmosphere, and also if the sun is not perpendicular
to the plane of a flat sensor/ radiation meter.

 

[PlasmaBomb]

Lesson learnt- Don't do maths late at night without any paper or a calculator...

Right the Peak power of that laser works out at 1.7 MW (which is slightly misleading)

The actual power is 47mW for the 12.5 Hz rate and 188.5 mW for the 50Hz rate.

Giving an actual intensity of -
1.5W/cm^2 for the first mode
6.0W/cm^2 for the second mode.

Hope that helps.

(Anyone feel free to check my calcs )

 

[wwswimming]

Originally posted by: PlasmaBomb
Lesson learnt- Don't do maths late at night without any paper or a calculator...

Right the Peak power of that laser works out at 1.7 MW (which is slightly misleading)

The actual power is 47mW for the 12.5 Hz rate and 188.5 mW for the 50Hz rate.

Giving an actual intensity of -
1.5W/cm^2 for the first mode
6.0W/cm^2 for the second mode.

Hope that helps.

(Anyone feel free to check my calcs )

when you say "actual power", do you mean average power ?

i need to understand both.

what is misleading about a peak power of 1.7 MW ? it's only
on for 18 nanoseconds per pulse.