POWER DETECTORS AT GENTEC-EO Well established in this field for over 45 years Gentec Electro-Optics has been a leader in the field of laser power and energy measurement. The average power density damage threshold of 100 kW/cm2 that we introduced with the WB series in the mid 1990’s is still unsurpassed. Gentec-EO also offers you broadband spectrally flat power detectors for general use in the UP12-H & UP19-H series, high peak power pulse damage resistance for specific UV and IR bands with the UP19-VR series, and high average power detectors in the air and water cooled High Power UP25-H, UP55-H & UP55-HD for the big jobs. All our detectors are available in OEM version and different size disks as well. Whatever your need Gentec Electro-Optics has a solution. HOW THEY WORK HEAT SINK PHOTO DETECTORS HIGH POWER SOLUTIONS POWER DETECTORS ENERGY DETECTORS POWER DETECTORS BEAM DIAGNOSTICS SPECIAL PRODUCTS Heat Flow Thermopile junction r = radius of beam R = Radius of disk The basic laser power detector is essentially a thermopile. The more familiar application for thermopiles, in fact where the common name “thermo electric cooler” comes from, is when a voltage is applied to cool one side of the thermopile and whatever it is bonded to. Thermopiles for laser power measurement however are used in the opposite fashion. That is, a temperature difference is used to create a voltage. On one side is material heated by the laser and on the other is a heat sink. The laser energy absorbed by that material is converted to heat. With the hot absorber on one surface and the cold heat sink on the other, there is a temperature difference across the thermo electric device as the heat flows through it. This temperature difference causes the thermopile to generate a voltage. That voltage is proportional to the temperature difference which in turn is proportional to the laser power. The monitor measures this voltage to provide the laser power reading in watts. Figure 1 shows the fundamentals of the thermopile-based power detectors. Figure 1. Disk type thermopile THE ABSORBER The optically absorbing material is one of the most important parts of the detector. That is because its properties define much of the performance of the detector, especially its resistance to pulse damage. This material absorbs most of the light energy from the laser and converts it to heat. A fraction is reflected that can vary from a few percent to 50% of the total optical power, depending on the material and intended application. How much is shown by the spectral absorptivity response curve for the material. With an absorber like our broadband H coating, around 90% of the power may be absorbed across a very wide range of wavelengths (190 nm to 20 µm) with small variations. This is called a spectrally flat absorber. It is efficient and because of its low thermal mass it transfers the heat quic

POWER DETECTORS ENERGY DETECTORS POWER DETECTORS HIGH POWER SOLUTIONS A thermopile is simply an array of thermocouples connected in series and close together. The fundamental technology of all state-of-the-art thermal laser power detectors actually goes back to 1821! That is when Thomas Seebeck joined two wires of dissimilar materials together at both ends and discovered electrical current flowing when he heated one end. Moreover, he found that the voltage between junctions was proportional to the temperature difference between them. That is called the Seebeck voltage and became the basis for...

THE THERMOPILE The amount of voltage that can be produced by one thermocouple is small, so an array of thermocouples is connected in series to increase sensitivity and multiply the output. In the array, instead of the two wires being joined twice to each other, each wire is joined to two wires of the other type, but a different one at each end. The junctions alternate back and forth so that each wire has a junction on the hot side, and another on the cold side. This is easier to visualize in Figure 1. The more numerous and closer together the junctions are, the more sensitive the thermopile will...

POWER DETECTORS MONITORS DAMAGE THRESHOLDS THE THERMOCOUPLE ENERGY DETECTORS An average power that is too high simply overheats the detector until it damages the thermocouple junctions. As a consequence, the thermopile itself and the cooling system determine the average power capacity of the detector. This is also what you risk if you exceed the manufacturer’s specification for too long. To avoid overheating, we offer the UP series which can, with its newest design, take a lot more heat than the usual thermopile. AVERAGE POWER DENSITY HIGH POWER SOLUTIONS PEAK POWER DENSITY POWER DETECTORS Concentrating...