I have been working with laser systems of all types for more than 10 years, but I’ve only recently purchased my own laser power meter. So, what is a laser power meter?
A Laser Power Meter is an instrument that measures the output power of a laser beam. They typically measure average power over a set time period for both CW (continuous-wave) or Pulsed laser sources, and work within specific ranges of intensity and wavelength.
What Types of Laser Power Meters are Available?
There are two main types of laser power meters available; the thermal detector and the Photodiode detector. Power meters can be an all-in-one package, or consist of a sensor plus a compatible meter.
The Thermal Power Meter
In a thermal detector based laser power meter, the laser or optical power is converted to heat. Effectively, the laser beam interacts with an absorber component such as a black anodised aluminium block. The resulting temperature rise in the absorber component is measured over a set period of time and is directionally proportional to the laser power output.
This type of power meter is pretty robust, although care should be taken to measure a de-focused beam whenever possible. When measuring laser power after the lens, it’s advisable to measure at a point some distance beyond the specified focal point.
While the thermal power meter is good for average laser power from 10 milliwatts (mW) up to kilowatts (kW), no one meter is able to straddle this range. The range is therefore split up into discrete sectors depending on the sensitivity required. E.g. 0~100mW; 0~20 watts; 0~100 watts; 0~200 watts; 0~500 watts & 0~1000 watts. Each end of the range has it’s own challenges;
- In the low power range (mW), just touching the absorber component is sufficient to affect the reading.
- Some form of cooling is usually needed for measurements of greater than 10 watts.
- In the high power range (kW), returning the meter to ambient temperature between measurements can require significant air or water cooling measures in order to reduce the test cycle time.
Thermal power meters are usable across a wide range of wavelengths and generally have a sensitivity that is independent to the wavelength.
Speed of Measurement
This type of meter typically has a slow measurement cycle time. Made up of the set exposure time plus the subsequent cooling to ambient temperature.
The Photodiode Power Meter
The photodiode power meter is far more sensitive and responsive compared to the thermal power meter. However, it is also far less robust. The absorber component is usually based on Silicon (Si), Germanium (Ge) or Indium Gallium Arsenide (InGaAs) depending on the desired wavelength region. This means that the sensitivity of the photodiode is dependent on the wavelength being measured and some form of compensation adjustment is required to offset differing sensitivities at different wavelengths.
The photodiode power meter is for low and very low power measurements in the 100 picowatts (pW) up to 20 watt range, although it is possible to increase this range through the use of an attenuator.
The photodiode power meter can cover wavelengths from 200 nm to 5.5 µm, with varying sensitivities at differing wavelengths. The manufacturer will normally include a calibration table for specific wavelengths.
Speed of Measurement
This type of meter typically has a slow measurement cycle time. Made up of the set exposure time and the subsequent cooling to ambient temperature.
Laser Cutting and Engraving Equipment Advice
Laser cutting and engraving equipment includes a range of products such as the Chinese manufactured K40 and Red Sail Clones and the premium brands of Trotec, Epilog, GCC and Universal Laser Systems.
In almost all cases they will be CO2 based machines and use either a DC (Glass tube) or RF (Metal Tube) laser source. There are also combi machines that have both a CO2 and a Fibre laser source installed.
- CO2 DC Glass tube is a Continuous-Wave (CW) device and has a wavelength of 10,600nm.
- CO2 RF Metal tube is classed as a pulsed unit and has a wavelength of 10,600nm, but in reality at 100% power it is a CW device. This laser source always gives out it’s maximum power, changing the % power just changes the amount of time the laser in on. E.g. 50% power means the laser is on for 50% and off for 50% of a cycle, giving an average power of 50%. The cycle is dependent of the set frequency of the laser.
- Fibre Laser Source is typically pulsed and has a wavelength of 1060nm.
Most users of laser cutting and engraving machines will typically use a thermal type Laser Power Meter.
Laser Power Meter Manufacturers
There are a number of manufacturers of Laser Power Meters, but you will need need to do your research to find a solution that fits your specific laser source and application. Here is a short list to get you started:
- The Mahoney Laser Power Meter is a cost effective solution as it is suitable for both CO2 (8,000 ~11,000 nm) and YAG / Fiber (900 ~ 1250 nm) laser sources. It comes in a number of intensity ranges as well; 0~20 Watts ; 0~100 Watts; 0~200 watts; 0~500 watts and 0~1000 watts.
Measuring Laser Pulse Energy
If you are looking to measure Laser Pulse Energy, then you will need to consider an Optical Energy Meter, which falls outside the scope of this post.
How To Use A Laser Power Meter
If you have decided to go ahead and purchase a laser power meter, you may well need some advice on how to use it. While the laser power meter that you purchase is likely to come with it’s own set of instructions, power measurements are just one aspect of testing your laser machine. For in-depth information, check out this post on How To Use A Laser Power Meter.