L100(500)A-PF-120 | Laser Thermal Power Sensors | Power Sensors - Ophir



The L100(500)A-PF-120 is a convection or conduction cooled thermal power/energy laser measurement sensor with the very large aperture of 120mm.
It can measure power from 1W to 500W and energy from 2J to 6000J. It has the PF volume absorber and covers the spectral range from 0.15 to 20µm. The sensor comes with a standard 1.5 meter cable for connecting to a meter or PC interface.

  • PF volume absorber
  • Ø120mm
  • 0.15-20µm
  • 1W-500W
  • 6J-6000J
  • Ø200 W x 35 D (mm)
  • 6000J
  • 2kW/cm²
  • 6 s
  • 1.5J/cm²
  • 15J/cm²
  • 500W
Need help finding the right sensor? Try our Sensor Finder

How should I clean my sensor?

First, clean the absorber surface with a tissue, using Umicore #2 Substrate Cleaner, acetone or methanol. Then dry the surface with another tissue. Please note that a few absorbers (Pyro-BB, 10K-W and 30K-W) cannot be cleaned with this method. Instead, simply blow off the dust with clean air or nitrogen. Don't touch these absorbers. Also, HE sensors (such as the 30(150)A-HE-17) should not be cleaned with acetone.
Note: These suggestions are made without guarantee. The cleaning process may result in scratching or staining of the surface in some cases and may also change the calibration.

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Must I use a particular sensor only with the meter it was ordered with?

Ophir meters and sensors are calibrated independently. Each meter has the same sensitivity as the other within about 2 tenths of a percent. Each sensor is calibrated independently of a particular meter with its calibration information contained in the DB15 plug. When the sensor is connected to the meter, the meter reads and interprets this information. Since the accuracy of our sensors is typically +/-3%, the extra 0.2% error that could come from plugging into a different meter is negligible and therefore it does not matter which calibrated meter we use with a particular calibrated sensor.

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When an accuracy spec is given, what exactly is meant?

The Ophir specification on accuracy is in general 2 sigma standard deviation. This means, for instance, that if we list the accuracy as +/-3%, this means that 95% of the sensors will be within this accuracy and 99% will be within +/-4% For further information on accuracy see http://www.ophiropt.com/laser-measurement-instruments/laser-power-energy-meters/tutorial/calibration-procedure

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How do you calculate the power and energy density of a laser beam?

If the power is P and the diameter of the beam is D then the power density is P /(.785 * D2) . If it is a pulsed laser and the energy is E, the repetition rate is R and the diameter is D then the power density is E*R/(.785 * D2), The energy density is E/(.785 * D2). The sensor finder will automatically calculate the power and energy density.

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How can I measure the energy of short pulses on a thermal detector when its response time is as slow as several seconds?

The thermal sensor works by measuring the heat flowing through its sensor. When measuring a short pulse, the heat is absorbed in the sensor absorber and then flows out through the sensing elements. The integral of this heat flow is a measure of the energy. Thus the sensor is actually measuring the energy that flows after the pulse is finished and the pulse width does not matter for this measurement.

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Does the damage threshold depend on power level?

The damage threshold of thermal sensors does depend on the power level and not only the power density because the sensor disc itself gets hotter at high powers. For instance, the damage threshold of the Ophir broadband coating may be 50KW/cm2 at 10 Watts but only 10KW/cm2 at 300W. The Ophir specifications for damage threshold are always given for the highest power of use of a particular sensor, something which is not done by most other manufacturers. This should be taken into account when comparing specifications. The Sensor Finder takes the power level into consideration when calculating damage threshold.

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Do I need to recalibrate my instrument? How often must it be recalibrated?

Unless otherwise indicated, Ophir sensors and meters should be recalibrated within 18 months after initial purchase, and then once a year after that.

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Can a laser measurement depend on the distance from the laser to the sensor?

In theory, if a beam is completely parallel and fits within the aperture of a sensor, then it should make no difference at all what the distance is; it will be the same number of photons (ignoring absorption by the air, which is negligible except in the UV below 250nm). If, nevertheless, you do see such a distance dependence, there could be one of the following effects happening:

  • If you are using a thermal type power sensor, you might actually be measuring heat from the laser itself; when very close to the laser, the thermal sensor might be “feeling” the laser’s own heat. That would not, however, continue to have an effect at more than a few cm distance unless the light source is weak and the heat source is strong.
  • Beam geometry – The beam may not be parallel and may be diverging. Often, the lower intensity wings of the beam have greater divergence rate than the main portion of the beam. These may be missing the sensor's aperture as the distance increases. To check that you'd need to use a profiler, or perhaps a BeamTrack PPS (Power/Position/Size) sensor.
  • If you are measuring pulse energies with a diffuser-based pyroelectric sensor: Some users find that when they start with the sensor right up close to the laser and move it away, the readings drop sharply (typically by some 6%) over the first few cm. This is likely caused by multiple reflections between the diffuser and the laser device, which at the closest distance might be causing an incorrectly high reading. You should back off from the source by at least some 5cm, more if the beam is not too divergent.

Needless to say, it’s also important to be sure to have a steady setup; a sensor held by hand could easily be moved around involuntarily, which could cause partial or complete missing of the sensor’s aperture at increasing distance, particularly for an invisible beam.

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How is the performance of thermal sensors affected by ambient temperature?

Water cooled sensors will hardly be affected by ambient temperature since the sensor temperature is determined by the water temperature.
Ophir convection and fan cooled sensors are designed to operate in an ambient environment of 25degC up to the maximum rated power continuously.
When operating at its maximum rated power, the sensor’s body should typically not exceed about 80degC in temperature.
Note: If the room temperature is higher than 25degC, then the maximum power (at which the sensor can be safely operated) should be derated accordingly from the specified maximum (since dissipation of the heat from inside the sensor to the surrounding air will be more difficult). For example, if the room temperature is 35degC, then the maximum power limit should be (80-35)/(80-25) = 82% of maximum rated power as given in the sensor’s spec.

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FAQ: Thermal Sensors for Measuring Low, Medium & High Laser Powers FAQ: Thermal Sensors for Measuring Low, Medium & High Laser Powers
FAQ: Sensors for Measuring Laser Power FAQ: Sensors for Measuring Laser Power FAQ: Sensors for Measuring Laser Power

In this short “Basics” video we review in general how one goes about measuring laser beam power, so that you’ll have a clear basic understanding of what the different sensor types are, and when you would use which type.

Peak power vs. Average Power – What is it, and how do I measure it? Peak power vs. Average Power – What is it, and how do I measure it? Peak power vs. Average Power – What is it, and how do I measure it?

A pulsed laser could have an average power of, say, 1 Watt, yet a peak power of 1 Megawatt – so when specifying it’s rather important to understand the difference! In this video you will learn what exactly these 2 concepts mean. You’ll also learn how to measure Peak Power, which can sometimes be tricky.

Calculate theoretical peak power with the peak power calculator

In this short “Basics” video we review the use – and selection - of thermal sensors for measuring low, medium and high laser powers.

Tutorials and Articles

Laser Power Sensors introduction

As described in the general introduction, the thermopile sensor has a series of bimetallic junctions. A temperature difference between any two junctions causes a voltage to be formed between the two junctions. Since the junctions are in series and the «hot» junctions are always on the inner, hotter side, and the «cold» junctions are on the outer, cooler side, radial heat flow on the disc causes a voltage proportional to the power input. Laser power impinges on the center of the thermopile sensor disk (on the reverse side of the thermopile), flows radially and is cooled on the periphery. The array of thermocouples measures the temperature gradient, which is proportional to the incident or absorbed power. In principle, the reading is not dependent on the ambient temperature since only the temperature difference affects the voltage generated and the voltage difference depends only on the heat flow, not on the ambient temperature.


Common Reasons for Thermal Sensor Damage or Out of Tolerance Conditions

This document was created to assist our valued customers in the proper care and maintenance of Ophir thermal laser power sensors. The following information is for reference only. If you have any reason to believe that the sensor is no longer performing within the original specifications,we always recommend that you send it in for repair and/or recalibration by our trained technicians to bring the unit back to the proper NIST traceable standards. We believe that Ophir thermal sensors can be used for many years without any repairs when used with the proper laser optical setup. We hope that this document will enable you to also enjoy the long life and reliable results for which Ophir-Spiricon is known.


Calibration Accuracy of Ophir’s High Power Sensors

An explanation of how we do this is provided below (A). In addition, a recent check of Ophir’s 5000W head by PTB in Germany shows excellent agreement between our calibration and their standards. The details of the correspondence between our sensor and their standard at powers up to 1400W is included here (B).

A. High Power Measurement Calibration Method and Estimated Accuracy of Models 5000W and 10K-W


How Much of the Power Sensor Aperture Can My Laser Fill Up?

The entire aperture senses power, so you can use the whole head. That said, a beam in the inner 50% of the surface area (about 70% of the diameter) is specified by Ophir to be uniform within +/-2%. The sensitivity around the edges might be a little less, but generally the sensitivity doesn’t vary by more than +/-2% over the entire aperture.


Effect of Ambient Conditions on Laser Measurements

We are often asked about the specified ranges of various ambient conditions (temperature, humidity, etc.) for Ophir instruments. In this article we will clarify the effects of these conditions on laser measurements, so you’ll be able to use your Ophir laser measurement instrument effectively.



Customers that purchase the above items also consider the following items. Ophir-Spiricon meters and sensors include a standard manufacturers warranty for one year. Add a one year Extended Warranty to your meter or sensor, which includes one recalibration.
  • Metric water fittings for all water cooled sensors except 30K-W with quick connection to 10mm plastic tubing. Replaces standard fitting connecting to 3/8" tubing

  • 3m Cable

    3m Cable


    3m cable to connect sensor to power meter or interface. Order along with sensor to receive this instead of the standard 1.5m cable.

  • 5m Cable

    5m Cable


    5m cable to connect sensor to power meter or interface. Order along with sensor to receive this instead of the standard 1.5m cable.

  • 10m Cable

    10m Cable


    10m cable to connect sensor to power meter or interface. Order along with sensor to receive this instead of the standard 1.5m cable.

  • 12m Cable

    12m Cable


    12m cable to connect sensor to power meter or interface. Order along with sensor to receive this instead of the standard 1.5m cable.

  • SH to BNC Adapter

    SH to BNC Adapter


    Allows connection of smart sensors to voltage measuring device for measurement of raw voltage output