MPE measurements

[sk_1810]

I have a question regarding MPE measurements. I read all available material on laser safety, so I'm looking for the easiest and fastest way to measure the irradiance of a laser show in a venue. A great solution would be a semi-automated device such as the LMS-2 (where to buy it, price?).

We are currently preparing to start using a 2W 532nm DPSS projector from MediaLas, and are planning to expand to three projectors (total output 7-8W).

2W projector is not a toy, so we want to be completely prepared in terms of laser safety.

Your help and comments are much appreciated!

[mccarrot]

I use a FieldmaxII with ultra sensitive thermophile. Most standard thermophiles are not sensitive enough.

With the area function the Fieldmax can show directly mw/cm2 when you put a cover with a 7mm aperture in front of the detectors.

10mW/cm2 is MPE
100mW/cm2 is 10MPE

If you make sure you keep the beam moving its ok.

[dave]

I use a FieldmaxII with ultra sensitive thermophile.

That's the PM3 you purchased?

[mccarrot]

yes, with 500uW threshold and 50uW resolutions its suitable for MPE measurement.

a PM10 or PM30 is not sensitive enough.

[sk_1810]

Thanks for the reply!

Could you tell me the approx. price for the device and sensor, so I know if it is in our budget before I contact Coherent ...

To be honest, when we planned to buy the greenie, 2W seemed great, but now when I look at it from the safety point, maybe it's too powerful for medium-sized venues like ballrooms, restaurants etc.

[mccarrot]

Aprox 1600 euro for the set.

with 2W in a medium size venue you need to know what power you shoot at the audience!

You can also decide to do no audience scanning.

[sk_1810]

Do you know any cheaper solution, maybe?

Thanks in advance!

[mccarrot]

Sure you can use any calibrated power meter with a ultra sensitive thermophile or better a optical sensor, and do the math from mw to mw/cm2 by hand.

or you can get a senor with a 1cm2 surface so the meter will give you mw/cm2 readings

But the sensor needs to be acurate in the mW range! most thermal sensors only start above the 10mW and cannot be used.

If I remember well a sensor with a 7mm limiting aperture will give a reading of 3.6mW for 1xMPE. But not sure anymore as I dont have to think about it anymore since I'm using the fieldmax


For the measurement make sure you actually have a CW beam. With modern computer systems, it is very easy to have a modulated beam, even if you "think" it is CW. For example, in Pangolin, there is an intertrack blanking setting, which automatically blanks between beams.
If you are using Pangolin, I find it best to use the abstract generator to produce the frame (a circle of zero size) and then find the correct attenuation value using the brightness control (turn it to zero and gradually increase it to the level you want). This value can then be directly used with the Beam attenuation map, in the Projection Zones.

[sk_1810]

Thanks again.

It really seems that the Fieldmax is the way to go!

[mccarrot]

Keep in mind, the sensor is the most important component.

In which county are you based?