Lasers are everywhere around us. Surgeons use them for eye surgery and cancer treatments. Manufacturers use them for material processing to cut, mark, weld, clean, and texture various types of materials. Some people need them for tattoo or hair removal, and everyone has seen laser light shows during music concerts. More recently, new applications like laser holography are emerging.
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Different types of lasers are needed for these applications. Based on their gain medium, lasers are classified into five main types:
Additionally, these five types of lasers can be divided into subcategories based on their mode of operation: continuous-wave lasers and pulsed lasers. Furthermore, there are also multiple types of pulsed lasers.
Before differentiating the types of lasers, it’s good to remember what a laser actually is.
A laser is a device that generates light in the form of a laser beam. A laser beam is different from a light beam in that its rays are monochromatic (a single color), coherent (of the same frequency and waveform), and collimated (going in the same direction).
Lasers provide this “perfect information” which is ideal for applications that require high precision.
Lasers are comprised of three main components:
A gas laser is a laser in which an electric current is sent through a gas to generate light through a process known as population inversion. Examples of gas lasers include carbon dioxide (CO2) lasers, helium–neon lasers, argon lasers, krypton lasers, and excimer lasers.
Gas lasers are used in a wide variety of applications, including holography, spectroscopy, barcode scanning, air pollution measurements, material processing, and laser surgery.
CO2 lasers are probably the most widely known gas lasers and are mainly used for laser marking, laser cutting, and laser welding.
Solid-state lasers use a solid (crystals or glasses) mixed with a rare earth element as their source of optical gain. The mixed element is typically neodymium, chromium, erbium, thulium, or ytterbium.
The most known solid-state laser is the ruby laser, since it is the first laser ever constructed. The Nd:YAG laser (neodymium-doped yttrium aluminum garnet) is also common in material processing applications.
Solid-state lasers are also used for LIDAR technology as well as various medical applications, including tattoo and hair removal, tissue ablation, and kidney stone removal.
A fiber laser is a special type of solid-state laser that is a category of its own. In fiber lasers, the gain medium is an optical fiber (silica glass) mixed with a rare-earth element.
The light guiding properties of the optical fiber are what makes this type of laser so different: the laser beam is straighter and smaller than with other types of lasers, making it more precise. Fiber lasers are also renowned for their small footprint, good electrical efficiency, low maintenance and low operating costs.
Fiber lasers are used in a range of applications, including material processing (laser cleaning, texturing, cutting, welding, marking), medicine, and directed energy weapons.
Examples of fiber lasers used for these applications include ytterbium and erbium-doped fiber lasers.
A Liquid lasers use an organic dye in liquid form as their gain medium. They are also known as dye lasers and are used in laser medicine, spectroscopy, birthmark removal, and isotope separation.
One of the advantages of dye lasers is that they can generate a much wider range of wavelengths, making them good candidates to be tunable lasers, meaning that the wavelength can be controlled while in operation.
In laser isotope separation for example, lasers are tuned to specific atomic resonances. They are then tuned to a specific isotope to ionize the atoms, making them neutral as opposed to negatively or positively charged. They are then separated with an electric field, achieving what is called isotope separation.
Laser diodes, also called diode lasers and semiconductor lasers, are similar to regular diodes in that they have a positively-negatively (PN) charged junction. The difference is that laser diodes have an intrinsic layer at the PN junction made of materials that create spontaneous emission. The intrinsic layer is polished so that the generated photons are amplified, ultimately converting the electric current into laser light.
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Although most semiconductor lasers are diode lasers, a few of them are not. This is because there are semiconductor lasers that do not use the diode structure, such as quantum cascade lasers and optically pumped semiconductor lasers.
Like fiber lasers, laser diodes can be classified as solid-state lasers since their gain medium is solid. However, they are in a category of their own because of their PN junction.
Laser diodes are often used as energy sources to pump other lasers. These lasers are referred to as diode-pumped lasers. In these cases, laser diodes are typically arrayed to pump more energy, as shown in the following image.
Laser diodes are extremely common. They are used in barcode readers, laser pointers, laser printers, laser scanners, and several other applications.
All types of lasers can operate using one of two methods: their laser beams can either be pulsed or continuous. This is what we call their mode of operation.
Continuous-wave lasers may seem more powerful than pulsed lasers because the advertised laser power is typically much higher, but this can be misleading. This is because lasers are named according to their average laser power, and the average power of pulsed lasers is usually lower even if they reach higher peaks of power.
For example, a 6,000W continuous-wave laser continuously releases 6,000W of laser power. Conversely, a 100W pulsed laser can release pulses of 10,000W each.
Pulsed lasers are divided into several categories based on the duration of their pulses.
A modulator is used to control the number of pulses per second. As a result, each pulse has a precise duration, called pulse duration, pulse length, or pulse width. The pulse duration is the time between the beginning and the end of a pulse.
Several modulating methods are used to pulse laser beams: q-switching, gain-switching, and mode-locking are some examples. The shorter the pulse, the higher the energy peaks. Here are the most common units used to express pulse duration.
As you can see, there are many ways to categorize lasers. Another way is by the laser wavelength, where you have infrared, near-infrared, visible, ultraviolet, and X-ray lasers.
Laser experts keep pushing the limits of laser technology, with new developments being made every year. As a result, the types of lasers are constantly evolving, and anyone looking to explore this world can expect a lifetime of discoveries.
There is a wide range of LED (Light Emitting Diode) and SLD (Super Luminescent Diodes) products that were created for the same applications as therapy lasers. These products can be successful in some applications but ,at this point in time, most of these system fall way short of the results of a real therapy laser because LEDs suffer from several major limitations. Some the manufacturers even have laser in their name yet they use 90% LED technology. Please make sure you check the specs on any product before you buy it and remember that LEDs only delivery a small portion of the energy into the tissue when compared to a true laser. We are working on an LED product. To make up for the lack of efficiency of LEDs, this system will be about 3,000,000 mW ( watts) so that even if we lose 90% of the energy, it will still be a 300 watt system.
When it comes to delivering energy to tissue, the entire process must be designed do minimize losses. Every system starts out with an available power (or ability to deliver dosage) as the energy travels through a medium, there are losses. If the energy is converted into heat, it cannot be converted in chemical energy so most therapy devices try to minimize the heating of the tissue. This is what make intra-red lasers different from infra-red saunas. Infra-red saunas are mainly photo-thermal and better lasers are primarily photo-chemical. Higher wavelengths of lasers suffer from the same problem. At 980nm and above, much of the energy is converted into heat and that energy can cause dilation to increase blood flow but it will not cause a photochemical reaction.
As the light travels through the a medium like tissue, non-coherent light (from sources like an LED) is more self-destructive than coherent light. If you throw a hand full of stones (noncoherent) at the same time into a still lake, the energy of the waves hits into each other and the energy is destroyed (self-destructive) so that only a small portion of the energy ever reaches the other end of the lake (deep tissue). If you throw one rock into the lake or time it just right to get multiple rocks in the lake at the natural period of the rock waves (coherent), it produces a set of coherent waves that can travel across the lake. If the waves sink up perfectly, you get a rogue wave that is bigger than any one of the single waves. When the peaks and the valleys of the sinusoidal wave are all aligned at a single period, it is additive but if they are out of phase, they destroy each other. Light reacts in the same way. Non-coherent light energy is more self-destroyed or less efficient at traveling over distances through a medium so we prefer coherent light energy when we need to push photonic energy through human tissue.
Because lasers are coherent and have a controlled divergence, they are the best at delivering photonic energy to deep tissue but there is still some excellent possibilities for LED systems. If the losses are too great, the system does not ever delivery the needed dosage.
LEDs
A light-emitting diode (LED) is a semiconductor light source with properties between an incandescent light bulb and laser. When an LED is switched on, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. The color of the light defines the properties of the light and the corresponding energy of the photons. Early LEDs emitted low-intensity red light (610-760nm) , but modern versions are available in a wider variety of wavelengths including the infrared wavelengths required for deep tissue penetration (the therapeutic window). LED light is non-Coherent (radiating in all directions) and divergent. Typical LEDs are designed to operate with 30-60 milliwatts [mW] of electrical power. LEDs can be switched fast but they can not be super-pulsed. The vast majority of devices containing LEDs are classified as Class 1 LED products but LEDs can fall under the same limitation of LASERs if the power density is high enough. Here we see an image from Wikipedia showing that the actual output of a red LED ranges from 600 to almost 700nm.
One really misleading part of LED systems is that many are rated based on the power consumption and not on the deliverable power output like we typically see with lasers. We have tested all the different lasers that we sell and they all produce the rated power at the emitter head. To the right, you will see where we tested a 50 LED array. This is the latest surface mount technology (which produces much higher outputs when compared to the older style LED buttons). In the picture, you can see that the LEDs are consuming closed to 50 watt of power but producing less than 10% of rated light energy when tested on our laser test rig. We are not sure if the company just cheated on the spec to sell more systems or if all LEDs have such inefficiency but this is something to watch out for if you shopping for cheap wrap-around therapy device or LED therapy systems. In addition to not being coherent, these system can be a small fraction of the spec when it comes to delivered power.
SLDs
Super Luminescent Diode (SLDs) are similar to LEDs, however they have the potential to be brighter.
Lasers
LASER (Light Amplification by Stimulated Emission of Radiation) is a mechanism for emitting electromagnetic radiation via the process of stimulated emission. Cold Laser light is:
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