DIY: Why making your own laser power meter is a bad idea
Tuesday, June 05, 2018
Today we are aiming at the DIY (Do It Yourself) community of our beloved world wide web. It is a very fine thing to look for expertise on the Internet and gain autonomy, but some products are just too complex for DIY projects, especially in the laser power measurement industry. Laser manufacturers and users will tell you: DIY is not always an option.
So, before you try building your laser power meter yourself, make sure you understand the associated risks and disadvantages. Here are 4 things you should be fully aware of before going ahead with your DIY project.
Let me explain why it’s not safe to do it yourself with an example.
Consider thermopile power detectors such as Gentec-EO UP19-H series. They are basically made of an assembly of thermocouples deposited on a disk of metal enclosed in a casing and protected by a heat absorbing material that diffuses the incoming laser power. The thermocouples provide a voltage output that is generally digitalized for readout.
Depending on the amount of power you want to measure, a cooling module needs to be attached to the casing. That can be a heat sink, a fan or a water circuit. Water is typically needed when you shoot more than 110 W of average power on a 19 mm aperture detector.
Dealing with lasers implies to follow safety regulations that you must consider to embark on such R&D. On top of that, finding the right materials and test routines to succeed in making high damage thresholds such as 100 kW/cm2 is a risky journey that companies are rather willing to fund over decades…
An unevenly deposited absorption material, a bad assembly or a weak cooling system will make your laser power detector break, melt or even catch fire! You can guess how your safety can be compromised in such unfortunate events.
A good measurement is obtained when your signal-to-noise ratio (SNR) and repeatability are high, and when your uncertainty of measurement is low and well defined.
While SNR and repeatability depend on the design and manufacturing of your instrument, to know your uncertainty (or how accurate your measurement is), you need to compare your device’s output to a known value. For example, your watch can be very precise and measure fractions of seconds with excellent repeatability, but if you’ve set it by looking at your alarm clock after your 2-year-old played with the dials, there’s a good chance you won’t have exactly the right time on your watch.
On the other hand, if your watch is synchronised with an atomic clock, you can trust that reading and get to your appointment on time!
How close will your measured power be to the real value? You need a reliable reference to achieve good accuracy. The best uncertainty of measurement is obtained when you use recognized standards for calibration.
Gentec-EO only uses Gold standards such as the one provided by NIST. Our Gold standards for thermopile detectors typically have ± 1 % uncertainty. You probably don’t want to invest the thousands of dollars that is required to acquire such standards then compare your detector to it! Let us do it.
Being able to make durable absorbers withstanding watts of power per centimeter square is one thing, enclose them in a rugged package with glues and attachments that will stand the passage of time is another challenge.
While some OEM partners are able to design and manufacture their own measurement solutions using bare thermal disks, it takes significant resources in electrical engineering, mechanical engineering and test stations to build reliable detectors.
Making a readout and display measurement also requires know-how. Who doesn’t love a simple, robust software or standalone interface to directly see your calibrated measurement in watts, handling various scales of power, zeroing and data management without the headache of using an analog output in volts with an oscilloscope or multimeter.
For example, a detector with a noise equivalent power of 10 mW such as the PRONTO-250, retailed under 1000$ US, is capable of measuring 250 W in single shot power mode (during 5 seconds), 8 W continuously and up to 150 J in single shot energy mode. With a spectral range of 0.19 - 20 um and integrated readout, that is one reliable, easy to use device at low cost providing NIST-traceable measurements.
For low power lasers in the visible and near infrared range, the photodiode-based PRONTO-Si is another example of a very cost effective solution allowing you to keep your time and money to actually work on your laser and real application instead on the detector.
I understand that there are people out there in the DIY community who have the skills and equipment to build their own laser power meter. But how much can you really expect to save, now that you know that there are great products out here that are ready to use?
Save your resources for what matters the most: design and build new laser applications or develop new light sources with the help of the right laser power meter for your needs. DIY is good to increase your knowledge, but it is not the right way to save money or time to achieve good results when doing laser power measurement.
Here at Gentec-EO we gathered knowledge and customer feedback since 1972 to make the industrial-grade, cost-effective, high-precision laser power meters that our customers love.
Learning how your laser behaves should be your priority. If learning how laser power and energy measurement work is your thing, ask your Gentec-EO representative, we are happy to share it with you.