How Should You Measure Your Medical Laser:Hulk-Style or Spiderman-Style?

September 30, 2015

OphirBlog

You medical laser needs periodic measurement to ensure it continues to operate at the desired output settings.

There are two ways to measure the internal laser of your medical device:

Hulk: large, thermal sensor to absorb the full laser power.
Spiderman: small sensor to sample the beam in-process.

As you might expect, each method comes with advantages and disadvantages.

“Hulk” Power Meter

This method measures the entire laser power, providing an accurate measure of the power that will actually be used. On the other hand, since it measures the entire laser, the laser can’t be used during the measurement. Also, this sensor will be larger and probably more expensive than a smaller one.

“Spiderman” Power Meter

The “Spiderman” method uses a small sensor to measure only a fraction of the laser. This can then be measured with a photodiode detector or thin thermal disk to calculate a percent of the laser beam power. This is smaller and doesn’t interrupt the laser process, but is not always as accurate as the “Hulk” method. Perhaps more importantly, it cannot detect any problems that are caused after the beam is sampling, e.g., an issue with the beam delivery optics.

“Superman” Power Meter

I always imagined Superman as the magical all-encompassing superhero. Please forgive me if I’m insulting your personal favorite hero. 😉

This last method is the best of both worlds. Several of our customers use both a photodiode beam sampler and a thermal sensor for complete measurements. The small PD is used for constant measurements so they can ensure with reasonable certainty that their laser still works. However, since this doesn’t account for the entire laser system (as I said above), there tends to be a bit of drift through the day.

That’s where the heavy-duty thermal sensor comes in. Once a day (or hour, week, as needed), the thermal sensor is used to recalibrate the small photodiode. This means that they can keep the PD reasonably accurate, while still getting the benefits it provides – continuous real-time measurement (e.g., for laser control) and reduced medical laser system down-time.