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About laser diodes
The laser diode is the heart of every laser module. As a cost-effective and energy-efficient laser source, laser diodes can produce light from ultraviolet to infrared and are therefore used in a wide range of industrial applications. In our guide we explain how such a diode is built, how it works and what was to be noticed before you buy it.
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What was laser diode?
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What was the distinguishing feature of laser diodes?
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How does a laser diode work?
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How are laser diodes structured?
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Important purchase criteria for laser diodes
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How do ich optimize my laser diode?
What was laser diode?
Laser diodes are a form of semiconductor lasers that produce laser radiation under the influence of current. They can produce light in different wavelengths from ultraviolet to infrared. Laser diodes are used in a wide range of applications, usually used in laser modules. They are used, for example, as a laser source in printers, DVD devices or bar code scanners.
What was the distinguishing feature of laser diodes?
The laser diode differs from other laser sources in that it is a very small and at the same time cost-effective, energy-saving alternative with a few millimeters of circumference. Laser diodes are also easy to use, have a long service life and achieve high efficiency levels of 40 to over 50 percent, especially in the near infrared range, compared to other laser sources. This means that around half of the electrical energy supplied is converted into laser radiation.
How does a laser diode work?
A laser diode is a semiconductor laser consisting of two different, negative and positive, doped materials, between which there is a small cavity. This structure is called the p-n transition. Under the influence of electricity, photons are released in the cavity. These are formed by the partially reflective end surfaces of the two halves of the semiconductor laser, which act as an optical resonator, into a standing light wave, from which the laser beam ultimately generates. Depending on the distance between the two sides, laser beams of different wavelengths are emitted.
How are laser diodes structured?
If you buy a laser diode, you will not only get the laser source As a rule, the diodes offered are a capsule in which a photodiode is installed in addition to the laser medium itself. This acts as a monitor diode and registers the laser power by determining the amount of light emitted and thus regulating the power supply through the external electronic circuit.
Due to the additional photodiode, the laser diode housings usually have three connections to install them in a laser module: The cathode and the anode of the laser source itself and another for the photodiode. An example of this form are diodes according to type TO-18.
Another important component is cooling. Since not all the current is converted into laser power, the laser medium heats up considerably. To prevent damage to the semiconductor material due to overheating, especially at higher power levels, the diodes are soldered to a metal surface that dissipates the excess heat. Studies have shown that a 10 degree reduction in operating temperature can double the life of the laser medium.
In any case, it is important to make sure that the selected diode complies with the RoHS Directive of the EU. It prohibits the use of substances harmful to the environment or health in electrical appliances such as leaded soldering.
Important purchase criteria for laser diodes
Wavelength:
The wavelength of the laser source is decisive for the separated laser light. Blue laser diodes have a wavelength of about 450 nanometers (nm), while green lasers are 530 nm. However, red lasers with a wavelength of approximately 650 nm or infrared laser diodes with a wavelength of around 800 nm are most commonly used.
Before deciding on a particular laser source, consider which wavelength is best for the application. A red laser diode with 635 nm wavelength is suitable for barcode scanners or laser pointers, for example, as it is also well visible in daylight. Laser diodes with a wavelength of 780 nm, on the other hand, are particularly suitable for use in laser printers or even invisible light barriers in alarm technology.
Power:
The laser output is usually expressed in milliwatts, in short mW. Here too, the question arises as to what purpose the laser should be used for, because the power of laser sources can vary greatly and not always the most powerful laser beam is the most suitable. For applications such as alignment and positioning, only a few milliwatts are sufficient, and laser power in the range of up to 10 mW is sufficient for safety barriers or bar code scanning. For example, higher wattage is required if the laser is to be used as a welding or cutting tool in industry.
How do ich optimize my laser diode?
The laser diode is only a component from the wide field of laser technology. Only in combination with other products can it have its effect. In order to control the diode's power perfectly, for example, a control electronics can be connected. These few millimeter measuring modules can control the laser power via a control input and, for example, ensure safety by automatically switching off in case of overheating.
In addition, a so-called collimator lens that bundles the generated radiation is particularly important for the use of the diode. This is the only way to create a laser beam that is as point as possible. Naturally, a laser with the length becomes wider and wider. Therefore, to determine the quality of the bundling, you should always pay attention to the divergence value. This is measured in mrad (milliradiant) and indicates by how much millimeter the laser grows per meter in diameter. Another possibility is to obtain a complete collimator lens with integrated laser diode directly.