I have a 50W CO2 laser cutting and engraving machine, and recently I purchased a laser power meter. I need to develop a measurement program on how to use the laser power meter. Here is my plan.
•Ensure you have the correct laser power meter for your laser source and and position the sensor so that it intercepts the path of the defocussed beam.
•Fire the laser source for the amount of time specified for the laser power meter.
•The power meter reading is likely to continue to increase for some time after the removal of the laser beam.
•Measure the maximum level achieved.
•Cool the sensor to room temperature and repeat the procedure for different power settings.
While that all sounds relatively straight forward, there are a number of aspects to consider.
Mahoney Laser Power Meter in use
Where To Take Measurements
If we consider the optical path of your typical Laser cutting and engraving machine that contains either a DC Glass or RF Metal laser source, there are a number of key locations where you may wish to measure the laser power:
1. Measuring the full laser output from at the laser source output itself. This allows you to measure the actual laser source power and compare it to the the warrantee power.
2. Measure after the first mirror, allows you to check the power drop across the mirror. If the power drop is greater than 3%, check alignment, clean the mirror and retest. If it is still greater than 3% you may want to consider a new set of Molybdenum mirrors.
3. Measure after the second mirror, allows you to check the power drop across the mirror. If the power drop is greater than 3%, check alignment, clean the mirror and retest. If it is still greater than 3% you may want to consider a new set of Molybdenum mirrors..
4. Measure after the third mirror, allows you to check the power drop across the mirror. If the power drop is greater than 3%, check alignment, clean the mirror and retest. If it is still greater than 3% you may want to consider a new set of Molybdenum mirrors.
5. Measure the defocussed power at the work surface after the lens. This allows you to check the power drop across the lens. If greater that 3%, clean the lens, check alignment and retest. If it is still greater than 3% you may want to consider a new lens.
Measuring the laser power at each corner of the bed may be worthwhile to help you determine the accuracy of your beam alignment.
Real Life Applications
Realistically, you would clean the optical path and check beam alignment, before carrying out the above 5 tests at one specific power level. I would suggest a power level that equates to 30~50% power on a DC Glass tube and 50% on an RF Metal Tube.
You will have noticed that you can expect to lose up to 12% of the laser power through the optical path. This is not that unusual, but a loss of more than 3% per component should be investigated.
Note: DC Glass tubes have what is called a pre-ionisation zone where the laser beam is unstable. This zone is typically present up to currents of 6mA or a power level of between 9 and 18%. It differs with every tube and is characterised by a hissy noise when the laser is operating. Try and do your optical component measurements outside this zone.
Why You Should Test the Power Of Your Laser Optical Path
There are a number of reasons that you should check the laser power of your laser machine:
1. When you have a a new laser machine or purchase a new laser source, you should check that the supplied laser source matches or exceeds the stated power from the supplier.
This is a particular problem when buying Chinese manufactured laser machines as the tubes are either incorrectly marketed or B-grade tubes supplied.
2. Check the laser power output of your laser source shortly before the manufacturers warranty ends. If it is below specification you can make a claim against the warranty.
This is particularly important for expensive RF Metal tubes where a replacement laser source could cost thousands of £$€’s.
3. Preventative maintenance; an unexpected loss of power could indicate a failing mirror or lens. Discovering which component is faulty could stop any potential downtime or material scrap costs.
4. Regular checking of the laser source output power, can give a heads up towards an eventual product failure date. Allowing you to order a replacement tube in plenty of time.
