30K-W-BB-74 | Laser Thermal Power Sensors | Power Sensors - Ophir



The 30K-W-BB-74 is a water cooled thermal power/energy laser measurement sensor for high powers with a 74mm aperture. It can measure power from 100W to 30,000W. It has a deflecting cone and annular absorber that withstands high power densities to 10kW/cm². It covers the spectral range from 0.8 - 2 and 10.6µm. The sensor comes with a standard 10 meter cable for connecting to a meter or PC inter

  • Beam deflector + broadband absorber
  • Ø74mm
  • 0.8-2µm, 10.6µm
  • 100W-30,000W
  • N.A.
  • ~4.3% without Scatter Shield, ~1.3% with Scatter Shield
  • Ø229 W x 100 D (mm)
  • N.A.
  • 10kW/cm²
  • 7 s
  • N.A.
  • N.A.
  • 30kW
Need help finding the right sensor? Try our Sensor Finder

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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Is there a coolant pressure specification for Ophir water-cooled sensors?

Yes. Please reference the chart below:

Minimum Flow Rates for Water-Cooled Sensors

Sensor Recommended flow rate at full power1
Minimum flow rate at full power1
Absolute minimum flow rate
pressure drop across sensor
(bar, at maximum flow rate)
Pressure drop across sensor
L250W 3 3 3 0.3 0.03
L300W 3 3 3 0.3 0.03
1000W 10 3 3 0.3 0.03
L1500W 10 3.5 3.5 3 0.03
L2000W 10 4 2 0.6 0.06
5000W 10 10 4.5 0.6 0.06
6K-W-200x200 6 6 5 0.5 0.05
10K-W 10 10 2 2 0.2
15K-W 15 15 3 3 0.3
30K-W 25 25 6 2 0.2
120K-W 60 60 60 4 0.4

Note: The coolant pressure should not exceed the minimum by more than 2.5 times.


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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.

 Watch the 'FAQ: Does damage threshold depend on power level?' video

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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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How can I clean the 10K-W, 15K-W, or 30K-W sensor?

These sensors have a gold-coated reflecting cone, which can be easily scratched. If one of these sensors needs to be cleaned, we recommend blowing with clean air or nitrogen. If, however, the cone gets soiled (for example with something spilled on it), such that blowing is not enough to clean it, then there is a risk of the contaminant material getting “burned in” by laser radiation. In such a case, to avoid that risk, one should use a suitably soft tissue with solvent, and wipe as gently as possible.

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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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What is the best water to use in the Water Cooled Sensors?

Corrosion is caused by interactions between the metallic components of the sensor and the cooling water, which may contain a variety of dissolved ions. Many factors affect the risk of corrosion forming, but the most important are the pH and the mixture of ions in the water. For this reason, we recommend using neutral deionized water in a closed circulating system (pH between 6 and 8). Please note that deionized water is usually slightly acidic (pH 5.65) due to absorption of CO2 from the atmosphere. The cooling water can be neutralized by adding 5 ml of a 10 mM solution of NaOH for each liter of water in the cooling system. Commercial additives such as Optishield Plus are also recommended for systems such as ours that have copper and aluminum in them. Optishield has the additional benefit of having biocide to prevent buildup of organic contamination.

To prevent corrosion it is also crucial to not allow standing water to evaporate inside the sensor when it is not in use. When disconnecting a sensor from the cooling system, the water channel should be cleared by blowing compressed air through it.

For those customers still experiencing problems with corrosion, we recommend the new thermal sensor 1000WP-BB-34 which has a special design in which all materials that come into contact with the cooling water are either copper or nonmetallic.

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Once and for all: Is DI (deionized) water good or bad for water-cooled sensors? Does it help prevent corrosion, or does it actually increase the risk?

Many factors affect the risk of corrosion forming, but the two most important are:

  • the mixture of ions in the water
  • the water’s pH

Our current recommendation is to use DI water – but of a neutral pH. DI water is usually slightly acidic; it can be titrated to a neutral pH, using a bit of sodium hydroxide for example. There are also commercial additives that can help prevent corrosion, for instance Optishield Plus. For a more detailed discussion, see the FAQ at http://www.ophiropt.com/laser--measurement/knowledge-center/faq/7805


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The sensor I need uses water cooling. Can you recommend a water cooling system?

We don’t supply chillers, nor insist on specific models; the only important thing from our point of view is to simply keep to the requirements specified for the cooling water of the specific model of sensor, such as minimum flow rate at full power, water temperature range, and - more important than the actual water temperature - water temperature stability. The temperature of the water should not be changing by more than 1 deg/min (because changes in water temperature could cause heat flow in the sensor which would be detected as if it were laser power, and cause errors in the reading).

We also have a video on our site at http://www.ophiropt.com/laser-measurement-instruments/laser-power-energy-meters/knowledge-center/water-cooled-sensors-youtube, which discusses various issues and tips about water cooling. There is a short discussion of coolant pressure requirements in our FAQ section at http://www.ophiropt.com/laser--measurement/knowledge-center/faq/2404

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Scatter Shields: Reducing Back-Reflected Power from High Power Sensors Scatter Shields: Reducing Back-Reflected Power from High Power Sensors
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.

Measuring Very High Power Laser Beams: Challenges and Solutions Measuring Very High Power Laser Beams: Challenges and Solutions Measuring Very High Power Laser Beams: Challenges and Solutions

Laser beams with powers of many tens of kilowatts are becoming more and more common in today's applications. This video will discuss the technical challenges in measuring such lasers, and will show you a range of solutions now available

Water Cooled Sensors: Things to Look Out For Water Cooled Sensors: Things to Look Out For Water Cooled Sensors: Things to Look Out For

In this video, you will learn about some critical issues you need to consider when using water cooling, such as water temperature, water flow rate, and corrosion prevention.

When measuring very high power laser beams, even the few percent of the beam normally back-scattered from the sensor can be a problem. Ophir now offers Scatter Shields as accessories for our high power laser sensors; these can be mounted on the front flange of the sensors to reduce the backscatter by about 70%.

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.


How to use water cooled Ophir sensors

Ophir water cooled sensors are designed to measure high powers in a relatively compact package. In order for the sensor to operate properly, the water flow rate, temperature and temperature stability have to be in the right range. For best performance of the sensor, the water flow rate should be the recommended rate. If the user system is not able to reach the recommended rate, then the minimum rate can be used and the sensor will meet spec but there may be some degradation of response time and linearity... Read more...


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.
  • 30K-W Scatter Shield Assy

    Scatter Shield for mounting on front flange of 30K-W sensors to reduce backscattered power.
    ('30K-W Scatter Shield Protective Cover (P/N 7Z08346)' is supplied with the Scatter Shield)

  • Metric water fittings for 30K-W for quick connection to 12mm plastic tubing. Replaces standard fitting connecting to 1/2" tubing

  • Protective Cover with Target Pattern for 30K-W sensors
    (1 unit supplied with 30K-W sensors)

  • SH to BNC Adapter

    SH to BNC Adapter


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

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