标签: laser

We tend to picture lasers, regardless of power rating, as highly focused, coherent light sources. After all, one of the virtues of the laser is that its beam doesn't spread, so it can be used for targeted illumination (such as scanner or rangefinder), or high-intensity localized heating (cutting or welding metals), to cite just a few of their thousands of applications. (Historical side note: when the laser was first demonstrated, one pundit wagged "it was a solution looking for a problem to solve," and we know how that quip turned out!)   But using lasers for area heating seems to be a contrary to their virtues. After all you can heat with IR lamps, microwaves, heated air, electric coils, induction coils, or gas-fired burners, to cite just a few possibilities. Why would you go to the complications of using lasers unless you had no alternative?   That's why I was surprised when I saw the story on the benefits of "photonic" heating in Laser Focus World, "High-power VCSEL arrays make ideal industrial heating systems." By setting up an array of hundreds of vertical-cavity surface-emitting lasers (shown below), you not only obviously get a different source of heat, but you attain some other unique operating advantages that are non-obvious and beneficial. Yes, the author's company (Photonics Aachen, part of Philips Photonics ) makes this system and so he is somewhat biased, but nonetheless, it's worth seeing what he has to say.   A one or two-dimensional array of VCSELs can be used as tightly spaced, easily modulated high-intensity heat source. (Source: Philips Photonics)   In contrast to conventional edge-emitting laser diodes, the collection of vertical-emitting laser diodes (each with a diameter of 30-40 μmeter) can be fabricated in one pass of wafer processing, including test, with about 500 VCSELs per mm 2 of a die. Since each laser emits 1 to 10 mW, a 2 × 2 mm chip array holding 2,000 VCSELs can emit over 20 W of infrared power — that's impressive power density for this technology. These arrays can be connected in series, so arrays of hundreds of watts and even kW have been built. While heat sinking of the die is an issue, it’s a manageable one, the author claims.   All this is impressive, but why bother when you can use standard halogen lamps, for example, to get the IR heating? First, the VCSEL IR brightness is 100 to 1,000 greater than halogens, with a lifetime of over than 10,000 hours, the author says (and I'll have to accept those numbers for now).   But the advantages of VCSEL-based heating go beyond just density and lifetime. The VCSEL array can be switched on and off in milliseconds for precise dosing control, since it does not have the thermal lag of a halogen emitter or similar sources. Also, the VCSEL array is well suited to highly targeted, localized zones, where the material to be heated may not be homogenous, with some areas needing more or less heat or specialized heat-treating patterns are preferred (think of PC boards to be wave soldered and loaded with different-size/mass components). Even if this level of control is not a requirement, the output power and thus heat is tightly focused, so that the entire oven does not have to be heated; only the part of the material that needs treatment. Further, unlike bulbs, the VCSEL's output wavelength does not change as it is dimmed, which means the target material's thermal absorption characteristics are unchanged, a factor in precision situation. Dimming control is relatively easy, as the VCSELs are driven by a controllable DC current.   I don’t have a need to heat anything with VCSELs, of course, nor do I fully understand what downsides of this heating approach. Still, reading about this application reminded me that what we often consider a key attribute of a technology can sometimes be less relevant, while its downside can become a virtue. While we prize lasers for their ability to deliver highly focused beams of photonic power, and use ever-bigger single-source lasers to deliver increasingly powerful punches, some out-of-the-box thinking shows that an aggregation of many small lasers as heat sources can be used to advantage for some applications.   Have you seen other cases where contrary thinking has solved a power problem or turned a thermal weakness into an advantage? Have you ever done this?

We tend to picture lasers, regardless of power rating, as highly focused, coherent light sources. After all, one of the virtues of the laser is that its beam doesn't spread, so it can be used for targeted illumination (such as scanner or rangefinder), or high-intensity localized heating (cutting or welding metals), to cite just a few of their thousands of applications. (Historical side note: when the laser was first demonstrated, one pundit wagged "it was a solution looking for a problem to solve," and we know how that quip turned out!)   But using lasers for area heating seems to be a contrary to their virtues. After all you can heat with IR lamps, microwaves, heated air, electric coils, induction coils, or gas-fired burners, to cite just a few possibilities. Why would you go to the complications of using lasers unless you had no alternative?   That's why I was surprised when I saw the story on the benefits of "photonic" heating in Laser Focus World, "High-power VCSEL arrays make ideal industrial heating systems." By setting up an array of hundreds of vertical-cavity surface-emitting lasers (shown below), you not only obviously get a different source of heat, but you attain some other unique operating advantages that are non-obvious and beneficial. Yes, the author's company (Photonics Aachen, part of Philips Photonics ) makes this system and so he is somewhat biased, but nonetheless, it's worth seeing what he has to say.   A one or two-dimensional array of VCSELs can be used as tightly spaced, easily modulated high-intensity heat source. (Source: Philips Photonics)   In contrast to conventional edge-emitting laser diodes, the collection of vertical-emitting laser diodes (each with a diameter of 30-40 μmeter) can be fabricated in one pass of wafer processing, including test, with about 500 VCSELs per mm 2 of a die. Since each laser emits 1 to 10 mW, a 2 × 2 mm chip array holding 2,000 VCSELs can emit over 20 W of infrared power — that's impressive power density for this technology. These arrays can be connected in series, so arrays of hundreds of watts and even kW have been built. While heat sinking of the die is an issue, it’s a manageable one, the author claims.   All this is impressive, but why bother when you can use standard halogen lamps, for example, to get the IR heating? First, the VCSEL IR brightness is 100 to 1,000 greater than halogens, with a lifetime of over than 10,000 hours, the author says (and I'll have to accept those numbers for now).   But the advantages of VCSEL-based heating go beyond just density and lifetime. The VCSEL array can be switched on and off in milliseconds for precise dosing control, since it does not have the thermal lag of a halogen emitter or similar sources. Also, the VCSEL array is well suited to highly targeted, localized zones, where the material to be heated may not be homogenous, with some areas needing more or less heat or specialized heat-treating patterns are preferred (think of PC boards to be wave soldered and loaded with different-size/mass components). Even if this level of control is not a requirement, the output power and thus heat is tightly focused, so that the entire oven does not have to be heated; only the part of the material that needs treatment. Further, unlike bulbs, the VCSEL's output wavelength does not change as it is dimmed, which means the target material's thermal absorption characteristics are unchanged, a factor in precision situation. Dimming control is relatively easy, as the VCSELs are driven by a controllable DC current.   I don’t have a need to heat anything with VCSELs, of course, nor do I fully understand what downsides of this heating approach. Still, reading about this application reminded me that what we often consider a key attribute of a technology can sometimes be less relevant, while its downside can become a virtue. While we prize lasers for their ability to deliver highly focused beams of photonic power, and use ever-bigger single-source lasers to deliver increasingly powerful punches, some out-of-the-box thinking shows that an aggregation of many small lasers as heat sources can be used to advantage for some applications.   Have you seen other cases where contrary thinking has solved a power problem or turned a thermal weakness into an advantage? Have you ever done this?

　　ATE1-07系列的TEC模块(热电制冷器)有7对珀尔帖元件，最大电压为0.8V，有3种最大电流可供选择，因此功率也不尽相同，请参见表1。此TEC模块用来准确调节目标物体的温度，当与TEC控制器一起工作时，就构成了高度稳定且高效的温度调节系统。ATE1-07系列TEC与我们的热敏电阻一起使用时，能够稳定且精确地感应温度变化。 　　ATE1-07系列TEC由两片陶瓷片组成，陶瓷片可以安装到平整的金属面上，两者之间要夹有薄薄几层导热填充材料，即散热垫，或是加一层导热膏。安装时，确保持续用力，以使TEC瓷片和金属之间的热接触良好，将热阻减小到最小。 　　TEC可以承受住加之于表面的垂直力，但是对切向力非常脆弱，尤其是震动切向力。即使一个微小的震动切向力也会造成珀尔帖元件的内部出现裂缝。虽然在造成伤害之初不会引起操作问题，但是问题可能会随着时间而出现，TEC的阻值会慢慢增加，最后，停止工作。 　　这一系列的TEC模块有3种型号，ATE1-07-1AS, ATE1-07-3AS, and ATE1-07-6AS，最大电流分别为1A，3A，和6A，相应的Qmax，最大热功率，分别为0.6W，1.7W和3.4W，请参见下方表1. 　　例如ATE1-07-1AS，型号中S前的最后两个字母表示允许流过TEC模块的最大电流 。所有TEC模块能够获得的最大温差ΔTmax是67°C。 　　ATE1-07系列的TEC有两条绝缘导线。正极导线为红色，长13英寸(340mm)，负极的导线为黑色，长度相同。机械尺寸如图6和表2所示。 　　边缘密封的TEC能够防止湿气进入珀尔帖元件，延长TEC的使用寿命。这款ATE1-07系列为密封TEC。 　　非密封的TEC的优点是效率高，能够获得更大的温差。图1.1和1.2是密封的TEC实物照片。 　　如果在潮湿的环境中使用，建议使用密封TEC，以便使系统获得更长时间的使用寿命以及高可靠性。 　　在高端应用中，例如TEC和目标物体之间需要良好可靠的热接触时，可在TEC的陶瓷表面镀上金属，这样TEC和目标物体就可以焊接到一起。 　　应用 　　快速调节目标物体的温度并将温度稳定在一个较宽的范围内，准确性高。此模块广泛应用在诸多领域，如固体激光器，光学元件， CCD，IR相机，生物技术测试台等。 　　本文转自：www.aticn.com www.analogtechnologies.com