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# Need help in converting Joules to watts

#### Jaxz

##### Member
Hi, I have an infra-red laser at 1080nm. But the output power is given as 20.5mJ instead of watts. The time given is 10mS. May I know how do I convert milijoules to watts? From what I know, my laser is a Class 3b laser.

#### Prototype

##### New member
Do you have any pictures? Because CW it might be Class IIIB, but pulsed lasers generally have a really high peak power, a couple kilowatts easily with some systems.

#### Trevor

##### Well-known member
A 20.5mJ pulse over 10ms is a power of 2.05W - but since it's pulsed I think the peaks should be much higher. Definitely class IV territory.

-Trevor

#### Prototype

##### New member
^If I did my math right it's about a 2.05kW pulse peak power.

#### Jaxz

##### Member
I don't have any pictures. All I have to describe is, it is a laser for distance reading, so the system can compute the distance and calculate the ballistics to fire a round.. I don't know if the Laser is pulsed or not. Besides, I also doesn't know what does pulse laser means, anyone care to explain what does pulse means?

#### Bluefan

##### Well-known member
^If I did my math right it's about a 2.05kW pulse peak power.
You're doing it wrong
(20.5*10^-3)/(10^10^-3)=2.05W
But for laser safety it is also important to know the repetition rate.

Sounds like a laser rangefinder, definately pulsed. Are you sure the pulse is 10 milliseconds long?

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#### Jaxz

##### Member
You're doing it wrong
(20.5*10^-3)/(10^10^-3)=2.05W
But for laser safety it is also important to know the repetition rate.

Sounds like a laser rangefinder, definately pulsed. Are you sure the pulse is 10 milliseconds long?
About the pulsed: Laser - Wikipedia, the free encyclopedia
Yes I am sure it is 10ms

Well this is the info given by my German OEM:

Wellenlänge: 1,08µm
Energie: 20,5mJ
Pulsdauer: 10ms

Using the translator, iam sure it means

Wave Length: 1,08µm = 1080nm (infra-red)
Energy: 20,5mJ
Pulse width: 10ms

so yea, it is 10milliseconds long.

But it is classified as a Class 3b, ... I just want to find the actual wattage,

nope, the OEM didn't say there is any repetition rate. It is just one flick of a Rocker Switch, it will lase whatever target we aimed at, and feedback this information to a computer to calculate the ballistic values of the round.

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#### Bluefan

##### Well-known member
It's 2.05W peak, but without the rep rate, the average power can only be guessed.

#### Jaxz

##### Member
It's 2.05W peak, but without the rep rate, the average power can only be guessed.
I see. Got a question here. Does laser range finder usually comes with repetition? Or is it just shot of continuous ray? Because the switch to activate the laser is just a rocker switch. Until I release the rocker switch, it will continue to lase.

#### Bluefan

##### Well-known member
It's pulsed, so it's not continuous. But it probably keeps pulsing when turn on.

#### Jaxz

##### Member
Hi thanks. I have clarified with the OEM. It is pulse. It doesn't keep pulsing even when the Rocker switch is hold on.

Some new info and some corrected info.

The pulse width is not 10ms, it is 10ns, nano seconds. My mistake in reading his hand writing.

And some new info, according to the German OEM, the repetition rate is 10 times to fire continuously, then got to rest a while for the laser unit to cool down before it can operate again..

Above info any useful?

#### Trevor

##### Well-known member
Then the pulse power is 2.05MW.

-Trevor

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#### Jaxz

##### Member
i see. thanks.

Anyone can tell me what is the recommended laser safety goggles to wear when operating with this laser ranger finder?

#### Bluefan

##### Well-known member
Hi thanks. I have clarified with the OEM. It is pulse. It doesn't keep pulsing even when the Rocker switch is hold on.

Some new info and some corrected info.

The pulse width is not 10ms, it is 10ns, nano seconds. My mistake in reading his hand writing.

And some new info, according to the German OEM, the repetition rate is 10 times to fire continuously, then got to rest a while for the laser unit to cool down before it can operate again..

Above info any useful?
Then the pulse power is 2.05kW.

-Trevor
(20.5*10^-3)/(10^10^-9)=2050000W = 2050kW = 2.05MW peak
The average power @10hz: 10*20.5*10^-3 = 0.205W average
You'll probably need laser safety eyewear rated D 1080nm L3, R 1080nm L6, depending on the beam diameter.

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#### Jaxz

##### Member
may i know what does this means? D 1080nm L3, R 1080nm L6.What is the OD i need to get?

#### Bluefan

##### Well-known member
OD 6 at least, but it's more important to get quality goggles. With megawatt peak powers you don't want cheap goggles, they may bleach under these intensities, like the passive q-switch effect. The D 1080nm L3 rating and the R 1080nm L6 is the rating of the EN207 certification, it makes sure your goggles can withstand the peak and average power of you laser.