Finding a Sensor From the Catalog Spec VS. Using the Sensor Finder

June 16, 2021

Ephraim Greenfield

Founder

When we have a laser with certain characteristics and we want to know which Ophir Power/Energy sensors are suitable, we either look at the catalog specification of some likely sensor to see if it is suitable, or we put our laser characteristics into the Ophir Sensor Finder and it gives a list of suitable sensors. However, these do not always agree, i.e. sometimes the sensor looks OK with the catalog spec but does not appear in the Sensor finder or vice-versa. So what is the answer to this?

The answer is generally that if there is a discrepancy, the Sensor Finder is more correct. The catalog spec is only an approximation to the true spec since it has constant values that cannot take into account all the interactions of various parameters. The Sensor Finder is more sophisticated and is dynamic, taking into account as much as possible interactions between the various parameters. Furthermore, the catalog spec does not cover all situations and only gives an indication of what will happen in particular cases.

Let’s give an example:

Say you have a pulsed laser with the following parameters: 1064nm, 100mJ, 150Hz, 3.5mm Gaussian beam, 7ns pulse width. Which sensors will work with this laser?

The first recommendation of the Sensor Finder is PE50BF-DIF-C where it states that we are at 60% of the damage threshold.

However, if we look at the specification page, the sensor will not be allowed since the power density maximum is listed at 200W/cm² and in this case the power density is 312W/cm², way over the catalog limit.

Why is this?

The sensor finder has a complicated formula to calculate the allowed power density, taking into account the effects of beam size and damage threshold of both the diffuser and the absorber under the diffuser. The catalog can only give an approximate answer so usually is more conservative to be on the safe side.

So, the bottom line is that for a quick, easy and accurate assessment of the suitability of sensors for your application, use the Sensor Finder.