Comparison of Detection Technologies

The three main characteristics and differentiators of laser power detectors are 1) wavelength, 2) rise time and 3) power threshold.


Wavelength

The most common detectors for low powers are photodiodes due to their good power resolution and fast response time. Light is absorbed in the material and converted into an electrical current proportional to the radiation power. Depending on the material composition, each wavelength results in a different signal and only a narrow bandwidth of wavelengths lead to an electric signal at all, as can be seen in the chart on the right. Besides the widely available Si, Ge and InGaAs are also used as photodetectors. The absorption characteristics of those two materials extend into the NIR spectrum, up to 1800 nm. When electrically biased appropriately, InGaAs can even absorb at higher wavelengths. All available photodiodes together cover a total range of UV, VIS, and NIR.

The working principle of thermopile sensors is fundamentally different from that of photodiodes (to learn more about this, click here). In an absorption layer on the sensor surface, the incident radiation is transformed into heat energy. This heat energy is measured by thermopile sensors. Thermopile sensors are therefore sensitive to radiation of all wavelengths, as long as the absorptive coating is efficient. Broad band absorbers are typically used and hence the spectrum from DUV to MIR lies within the detection range.

Rise Time

Due to their working principles, photodiodes and thermopile detectors have different signal response times.
Photodiodes are very fast and react from 1 ns to incoming radiation. When read out with commercially available power meters, the speed is lowered due to the electronics and results in a rise time of 0.1 – 0.2 s. Therefore, photodetectors are suitable for fast measurements and a good choice, if the wavelength range and the power range (see below) are appropriate. Thermopile sensors are slower in their signal response. Since the sensors are based on thermal transport, the rise time is related to the thermal mass that needs to be heated. Therefore, larger or thicker thermopiles have longer response times than thinner or smaller ones. Peltier elements respond to incoming radiation with a minimum rise time of 1.8s due to their large thermal mass. Conventional disk-type sensors have minimum response times of 1s. greenTEG’s Thermal Laser Power Detectors are considerably thinner and are able to achieve response times of 0.1 s.

Power Threshold

Both detector types (photodiodes and thermopile sensors) cover a large dynamic range of powers, (see graph on the right) and are therefore applied in different settings.



Applications

Our laser power detectors measure in real time and provide you with accurate data. By delivering information about the laser power, the gRAY detectors allow you to monitor and control your laser system. gRAY detectors are used in various applications ranging from industry to academic research. A few of them are listed in the following.

Contact us, if your use case is missing! We are always interested in hearing about new applications!

In industrial laser systems it is crucial to monitor the laser power to avoid waste production. The results of laser marking, welding, cutting etc. are affected by too high or too low power. Read more about this in our white paper on "Process Stability".
To allow continuous monitoring, the sensor is typically integrated behind a beam splitter where it measures only part of the beam. The main part of the beam is used for the process.

To ensure the safety of staff and patients during surgery, lasers in medical applications need to stay precisely within their power specifications.

Popular wavelengths for medical lasers are around 3 µm (since water has a high absorption coeffecient at this wavelength) or further in the IR spectrum. Whereas photodetectors are limited in this wavelength range, gRAY sensors are sensitive from UV to IR. This makes gRAY sensors a perfect choice for medical applications.

gRAY sensors can be integrated into laser sources to provide a feedback signal for a closed control loop. This is done to have a stable output power, monitor how the laser ages, and to determine changes in the optical path of laser (like contamination of optics).

 

As much as the specifications of laser sources vary, the applied sensors vary as well. For diode lasers with limited space or QCLs, the small 2×2 mm² sensor is a good choice. Large CO2 lasers, on the other hand, require a housed detector (for power measurements up to 100W).

gRAY sensors are used inside power meter. Like all thermopile sensors, they cover the wavelength range from UV to IR.

 

However, due to their short rise time measurements are faster compared to other thermal power meters available. Further, the high sensitivity allows to measure low powers down to 10 µW. The size of the power meter can be kept small due to the compact design of the detectors.

Read about the product development with one of our partners.

An integrated position sensitive device (PSD) allows to measure beam position and average laser power simultaneously. Such a detector can be placed at one or more positions in the beam path to provide feedback on the current beam alignment.

 

gRAY PSDs make alignment and maintenance easy – even outside of the visible range. For more details read our white paper on “Beam Positioning”.

Overview


 

Product Name

Power Range

Aperture Size

Application


C05-HC(T)

5 mW to 5W

∅ 25 mm

C10-HC(T)

10 mW to 10 W

∅ 25 mm

C50-HW(T)

50 mW to 50 W

∅ 25 mm

C100-HW(T)

100 mW to 100 W

∅ 25 mm

C50-MC

50 mW to 50 W

∅ 26 mm

B05-MC

10 uW to 5 W

10×10 mm²

B01-SMC

100 uW to 1 W

4.4×4.4 mm²

B05-SMC

100 uW to 5 W

10×10 mm²

B0.5-SC

100 uW to 0.5 W

2×2 mm²

B01-SC

100 uW to 1 W

4.4×4.4 mm²

B05-SC

100 uW to 5 W

10×10 mm²

B05-PC

1 mW to 5 W

18×18 mm²

C50-PC

100 mW to 30 W

18×18 mm²



DIGITAL HOUSED DETECTORS

Get digital signal with self-correction for temperature drifts.

Absolute power sensing of laser beams up to 50 W
300 ms rise time
Digital output signal (I2C)
Electronic temperature compensation inside detector head

 

Contact us for more information


HOUSED DETECTORS

Get your laser power measurements done faster with the fully integrated laser power head.

Absolute power sensing of laser beams up to 100 W
300 ms rise time
Full electrical and thermal integration provided
Robust design for system integration or standalone applications

 

Data sheet


Process Stability

MOUNTED DETECTOR

Build the mounted detector module into your monitoring unit to record laser powers – even if space is limited.

Absolute power sensing of laser beams up to 100 W
300 ms rise time
Compact design for versatile system integration
Optional: Amplification circuit board for electrical integration

 

Data sheet



PCB MOUNTED DETECTOR

Measure µW laser powers with highest accuracy with the thermally compensated detector module.

Two detectors mounted on a metal-core PCB; no thermal integration needed
10 µW to 5 W power range
Thermal background compensation
Integrated NTC
Simple, compact and robust mounting
Available with NIST/PTB traceable calibration

 

Data sheet



PCB SINGLE MOUNTED DETECTOR

Measure low laser powers in your laser system without worrying about electrical, mechanical and thermal integration.

Single detector mounted on a metal-core PCB
100 µW to 5 W power range
Integrated NTC
Simple, compact and robust mounting
Available with NIST/PTB traceable calibration

 

Data sheet



BARE DIE COMPONENT

Avoid wavelength or angle dependence of your detector signal by integrating gRAY sensor components into your laser sources

100 µW to 5 W power range
Linear power response
Signal independent of illumination angle
Ultra-thin design
Simple integration on PCBs
Attractive OEM pricing
Various sizes available (2×2 to 10×10 mm²)

 

Data sheet



MINIATURE THERMOPILE DETECTOR

Determine laser power at all wavelengths without loosing much space in your laser source.

Most compact thermal detector
Sensitive to all wavelengths
Powers of up to 500 mW
Integration like an SMD-component
Attractive OEM pricing at high volumes

 

Data Sheet


Comparison with Photodetector

POSITION DETECTOR

Align your laser beam efficiently with micro meter accuracy – even if it is not visible.

Position sensing and power measurement
Lateral resolution on the micro meter scale
µW to W power range
Compact design for versatile system integration
Sensitive to all wavelengths from UV to MIR

 


Working principle

1. The laser irradiates the sensor surface. The light gets converted into heat when being absorbed by the coating.

2. This heat impact causes a temperature difference between the exposed top surface and the non exposed bottom side.

3. The T-difference produces a voltage based on the Seebeck effect. It is directly proportional to the input power and can be used to calculate the power of laser.


中文技术文档

您可以在这里下载gRAY系列产品的技术文档。敬请联系我们了解其他详情。


DOWNLOAD SECTION

Housed Detectors

Mounted Detectors

Position Sensors

Sensor Components

 

Detector technologies

Position Monitoring

Process Stability

Thermal Management

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B0.5 vs Photodiode

Detector technologies

Position Monitoring

Process Stability

Thermal Management


About

greenTEG develops, manufactures, and markets thermal sensor solutions. The company was founded in 2009 as an ETH Zurich spin-off and has since built up an international customer base, coupled with a global distributor network.

greenTEG’s thermal sensors are integrated into diverse applications by customers active in markets such as laser, building technologies, medtech, automotive, processing industry, and R&D.

Contact us or our distributors and tell us about your application ideas. We will support you to find the best solution for your requirements.More information about the company and its technology can be found on their website.

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