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Laser Diodes!! The diode laser is very effective for light and dark. Laser diodes come in a wide range of types and power. They are in DVD and CD players and writers, used in fiber-optic communications, visible laser pointers, distance measurement, printers, medicine and industry. Laser diodes are the hidden champions of current laser technology from simple laser pointers to sophisticated quantum communication satellites, laser diodes are everywhere. They offer supreme efficiency, small footprint, This piece will help you out to choose the best one.
What is Laser Diodes?
A Laser Diodes is a semiconductor device similar to a light-emitting diode (LED). It uses p-n junction to emit coherent light in which all the waves are at the same frequency and phase. This coherent light is produced by the laser diode using a process termed as “Light Amplification by Stimulated Emission of Radiation”, which is abbreviated as LASER. And since a p-n junction is used to produce laser light, this device is named as a laser diode.
Working Procedure Laser Diodes
The working of a laser diode takes place in three main steps:
The laser diode consists of a p-n junction where holes and electrons exist. (Here, a hole means the absence of an electron). When a certain voltage is applied at the p-n junction, the electrons absorb energy and they transition to a higher energy level. Holes are formed at the original position of the excited electron. The electrons stay in this excited state without recombining with holes for a very small duration of time, termed as “recombination time” or “upper-state lifetime”. The recombination time is about a nanosecond for most laser diodes.
After the upper-state lifetime of excited electrons, they recombine with holes. As the electrons fall from higher energy level to a lower energy level, the difference in energy is converted into photons or electromagnetic radiation. This same process is used to produce light in LEDs. The energy of the emitted photon is given by the difference between the two energy levels.
Construction of a Laser Diode
A simple semiconductor laser diode is made up of the following parts in order:
- Metal Contact
- P-type Material
- Active/Intrinsic Region (N-type Material)
- N-type Material
- Metal Contact
The input terminals are connected to a metal plates which are sandwiched to the n-type and p-type layers. This type of laser diode is also called as a “Homojunction Laser Diode”. The intrinsic region between the p-type and n-type material is used to increase the volume of active region, so that more number of holes and electrons can accumulate at the junction. This allows more number of electrons to recombine with holes at any instant of time, resulting in better output power. The laser light is emitted from the elliptical region. This beam from the laser diode can be further focused using an optical lens. This entire PIN diode (P-type, Intrinsic, N-Type) arrangement is enclosed normally in a metal casing.
Types of Laser Diodes
1. Double Heterostructure Laser Diode
In this type of laser diodes, an additional confinement layer of a different material is sandwiched between the two p-type and n-type materials. Each of the junction between different materials is called a heterostructure. Because of presence of two heterostructures, this type of laser diode is named as a double heterostructure (DH) laser diode. The advantage of this DH laser diode is that that the active region is confined to a thin layer which gives better optical amplification.
2. Quantum Well Laser Diode
The quantum well laser diode has a very thin middle layer, which acts as a quantum well. The electrons will be able to use quantum energy levels when transitioning from higher energy level to lower energy level. This gives a better efficiency for this type of laser diode.
3. Separate Confinement Heterostructure Laser Diode
The thin middle layer in the quantum well laser diode is very small for confining emitted light effectively. To compensate this, in the separate confinement heterostructure laser diode, another two layers are added over the three initial layers. These layers have a lower refractive index and help in confining the emitted light effectively.
4. Vertical Cavity Surface Emitting Laser Diode (VCSEL)
All the previously discussed laser diodes, the optical cavity is placed perpendicular to the current flow. In vertical cavity surface emitting laser diodes, however, the optical cavity is along the axis of current flow. The partially reflecting mirrors are placed near the ends of optical cavity.
Uses of a Laser Diode
Laser Diode modules are used in all major areas of electronics ranging from
- Consumer Electronics: CD/DVD players, Laser printers, Fiber Optic Communication, Barcode Readers etc.
- Medical Machines: Laser diodes are used in machines used to remove unwanted tissues, eliminating cancer cells, non-invasive and cataract surgeries etc.
- Autonomous Vehicles: Laser diode technology is used in making LIDAR systems implemented for autonomous driving
- Scientific Instrumentation: Lasers are used in devices used for remote contactless measurements, spectrometry, range finders etc.
- Industrial Applications: Laser Diodes are used as a source of high intensity laser beam for precise cutting of materials. They are also used in 3D printing to soften the substrate.
Buyers Guide To Buy The Laser Diodes
Wavelength depends on the application. If you want the laser as a pointer then you would obviously choose something in the visible spectrum, probably red if you want the cheapest solution. For medical applications you may have a specific absorption of interest or a fluorescence which will dictate the wavelength e.g. around 490nm for fluorescein angiography. In some cases you could use an LED depending on whether the small source size of a laser or coherence are particular requirements for the application.
pulsed lasers for rangefinders you would often use 905nm which is invisible to the naked eye. 1540nm is a useful wavelength for improved eye safety as that wavelength is absorbed in the eye before it reaches the retina so higher laser power is allowed while still being eye-safe. While 1540nm was traditionally generated using an Erbium-glass laser, semiconductor lasers are now available at that wavelength. Lasers at 1540nm do tend to cost more than 905nm though, as do the detectors. Absorption in fibre-optic cables is lower though, which can be useful.
Lasers can be used for laser rangefinders where the high pulsed power combined with the very short pulse gives a low average power and can result in an eye-safe solution. Other pulsed applications are fibre optic data transmission or DVD/CD writing. Continuous driving would be for DVD/CD readers, laser pointers, surveying instruments or some medical applications such as anti-inflammatory use (with 660nm for example).
Driving of lasers depends on the type of laser and whether you are driving them continuously or pulsing them. Some lasers are driven simply by a constant current. This would often be found in DVD readers. If a laser has a built in monitor diode it usually means that you should use it to control the power. That does mean that you need a power meter in order to set the power – the built in monitor diodes are not calibrated. Even with a constant current drive it may be necessary to set the current to achieve a certain power.
- Laser type
Try to be more specific with the laser type. You do face many options. A proper way to get through that is weighing the options and selecting the one with the largest total weight for single-emitter laser diodes. Or anything according to your requirement.
If you have a planar (for example, PCB or heat sink) or a circular (tube) environment? The first leads to butterfly or flat-pack solutions, and the latter to a TO can. Are there any overall size limitations? Do you need drop-in compatibility with existing solutions? For TO-based packages, the pin configuration must be determined (m-, n-, or p-type) as well as the size (5.6 vs. 9 mm). For 14-pin butterfly packages, telecom and pump pinning must be distinguished.
Price is the important factor while choose your lase diodes, is it according to your requirement, check out the features, and then decide the best one according to your budget and need.
Many people consider using a laser diode some may think about entirely new systems, while others just want to replace an older gas laser in their product. The problem is the variety of choices, as there are many different laser diodes available and making the right choice may take days for both the engineer and the sales expert as well. This piece will help you out to choose the best laser diodes.