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WHAT IS LASER?

  • The short definition is, “A device that emits monochromatic light through a process of optical amplification based on the stimulated emission of photons.” (2)
  • However, if everyone understood exactly what that meant, there would be no need for this site. For example, “laser light” technically only refers to anywhere on the electromagnetic spectrum that is between 150nm and 11,000nm. Also, part of the definition of LASER light is that it is Coherent. That word is not technically necessary in the definition because the more monochromatic light is, the more coherent it is, but LASER light being coherent is a very important aspect of LASER. This is explained more in depth below. The more one understands about LASER, the more one understands that there is a lot more that is actually encompassed in the definition of LASER.
    • LASER stands for Light Amplification by Stimulated Emission of Radiation. To understand what that means, let’s start with one word at a time.
      • WHAT IS RADIATION
        • Let’s start with this one as it is needed to understand Light.
        • The definition is:
          • “The process in which energy is emitted as particles or waves.”
          • “The emission of energy as electromagnetic waves or as moving subatomic particles”
          • “The complete process in which energy is emitted by one body, transmitted through an intervening medium or space, and absorbed by another body.”
        • In summary, radiation refers to the process of the transference of energy. Understanding this we can understand that radiation describes a very wide variety of circumstances. This includes but is not limited to the radiation from sunlight, radiating waves from electronic devices, even light radiating from a $2 flashlight. All types of light are a form of radiation.
        • Radiation can become harmful when it becomes “ionizing.” Ionization is the process in which an atom either loses or gains an electron. Electrons carry a negative charge, so that means that during this process an atom, which normally has no charge, either develops a positive or negative charge, depending on whether it lost or gained electrons. For clarify sake, when an atom has a charge, it is called an ion.
        • Ionizing radiation has enough energy to strip electrons off an atom, while NON-ionizing radiation does not have enough energy to do this.
          • On the electromagnetic spectrum, as the frequency goes up, so does the energy. Where on this spectrum the energy becomes ionizing is within the Ultraviolet light spectrum (3)  
        • We will go over the Electromagnetic Spectrum in further detail below.
        • WHAT DOES ELECTROMAGNETIC MEAN?
          • Electromagnetic waves are produced by a vibrating electric charge and consist of an electric and magnetic component (4)
      • WHAT IS LIGHT
        • If you type “definition of light” into Google, you will find the following:
          • “The natural agent that stimulates sight and makes things visible”
          • Ok, that is simple enough. Right? We all know we see things because there is light, but that does not actually explain what light IS, so let’s get a little more specific.
        • Merriam-Webster says:
          • “Electromagnetic radiation of any wavelength that travels in a vacuum with a speed of about 186,281 miles (300,000 kilometers) per second”
            • … huh? Ok, stay with me here. There will be some larger words that will be used, but I will do my best to make it as simple as possible if you follow closely.
        • So we know that light refers to a form of energy defined and categorized as “electromagnetic radiation of any wavelength”-this refers to all frequencies on the electromagnetic spectrum, of which the visible light spectrum is a small fraction of.
        • What does it mean to “travel through a vacuum?”
          • This means that electromagnetic waves are capable of traveling and transporting their energy through space, a region void of matter, versus other waves such as mechanical waves which require a medium in order to transport their energy (4)
  • Technically everything on the Electromagnetic Spectrum travels at the speed of light (12), but only wavelengths between 150nm up to 11,000nm are generally referred to as “laser light” (1). This ranges from Ultra Violet, visible light, and Far Infrared.
          • WHAT IS THE VISIBLE LIGHT SPECTRUM:
            • Do you know what percentage of wavelengths make up the visible light spectrum, aka everything that we can see with our human eyes? The estimation is that we only see .0035% of all wavelengths that exist (link of someone who spells out all the math (5)
            • So next time you think or say that you have to see something to believe it, understand that if we limited ourselves to only what we can “see” with our own eyes, we would be limiting ourselves to .0035% of what actually exists, only in terms of wavelengths. To put that percentage into perspective, there are currently 7,476,770,000 people on the planet (6). .0035% of that figure is 261,687, which is the equivalent of 3% of the population of only New York City.
            • The visible spectrum consists of 380 nanometers to 700 nanometers, or 7X10-7 meters and 4 x 10-7 meters (7). Each frequency is seen as a different color, with Violet being the shortest wavelength in the spectrum at 380nm, then blue, green, yellow, orange, and finally red. Notice this is the same order as you will see a rainbow.
            • When all the colors are viewed by the eye simultaneously, white is perceived.
            • When there is an absence of wavelengths in the visible light spectrum, black is perceived. So when you are in a dark room and cannot see, it simply means that there are no wavelengths within the visible light spectrum striking your eyes at that moment (4).
            • This site has a plugin where one can type in any number of any frequency in the visible light spectrum (between 400-700nm) and it will show you what the color looks like, as well as other unit conversions: (4)
        • WHAT BESIDES VISIBLE LIGHT MAKES UP THE REST OF THE ELECTROMAGNETIC SPECTRUM?
          • “Laser Light” refers to anywhere on the Electromagnetic spectrum between 150nm and 11,000nm, so all areas of Ultra Violet and all areas of Infrared are included in this as well.  
  • I have decided to include short explanations of ALL aspects of the electromagnetic spectrum for clarity purposes, despite not all ranges technically being considered part of the “laser light” portion of the spectrum.
          • The following is a breakdown of each section, describing their function, frequency and/or wavelength.
          • Before we go there though, let’s explain a few general things:
            • X-rays and gamma rays are usually described in terms of energy, optical and infrared light in terms of wavelength, and radio in terms of frequency. This is because these are the units that are most convenient for describing the type of energy being described. (8)
            • Wavelength refers to the distance between two peaks of a wave, usually measured in meters (m). (Nanometer, or nm, is one billionth of a meter, or 10-9 )
              • Wave:
                • Technically defined as “A disturbance or oscillation propagated from point to point in a medium or in space”
                • Visualize an S on its side
              • Light acts like a wave, but sometimes it acts like a particle (particle is defined as “an extremely small constituent of matter, such as an atom”). Particles of light are called photons. Low-energy photons (i.e. radio waves, see below) tend to behave more like waves, while higher energy photons (i.e. X-rays, see below) behave more like particles.
              • “To fully understand the nature of light and how it is created, it is necessary to understand matter at its atomic level. It is the motion of electrons within atoms — the building blocks of matter — that leads to the emission of light in most sources. Electrons circle atoms in specific patterns called orbitals, each containing a finite amount of energy. The closer the electron’s orbit is to the nucleus of the atom, the less energy it possesses. If an electron in such a low energy level gains some energy, it must jump to a higher level of orbit, and the atom is said to be excited. This jump causes the electron to lose energy and subsequently fall back to a lower level of orbit. The energy the electron releases as a result of this change in orbitals is equal to the difference between the higher and lower energy levels, and can result in the emission of a quantum of energy in the form of a photon.” (9)
            • Frequency is the number of wave cycles that go through a specific point in a second, so are measured at cycles per second, or Hertz (Hz).
            • Amplitude is the distance between the wave crest (highest point) and wave trough (lowest point).
          • AM Radio waves
            • Frequencies range 500—1500 kHz
            • Wavelengths range 600—200 m
            • Quantum energies range 2 — 6 x 10-9 eV
              • 30-535 kHz are used for maritime communication and navigation and for aircraft navigation.
          • Short waves (10)
            • These are generally referred to as “radio frequencies” or RF.
            • Frequencies range 1.605—54 MHz
            • Wavelengths range 187—5.55 m.
            • Quantum energies range .66 x 10-8  — .22 x 10-6 eV
              • 1605 kHz-30 MHz
                • Amateur radio, government radio, international shortwave broadcast, fixed and mobile communications
              • 30-50 MHz
                • Government and non-government, fixed and mobile
                • 40-50 MHz is the range used in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI)
              • 50-54 MHz
                • Amateur
                      • (10)
          • TV and FM Radio Band (10)
            • Frequencies range 54—1600 MHz
            • Wavelengths range 5.55 m -– 0.187 m
            • Quantum energies range 0.22 x 10-6 -– 0.66 x 10-5 eV
              • 54-72 MHz
                • VHF television channels 2-4
              • 72-76 MHz
                • are reserved for government and non-government services
              • 76-88 MHz
                • VHF TV channels 5 and 6
              • 88-108 MHz
                • FM radio band
              • 108-122 MHz
                • Aeronautical navigation, such as airport control
              • 122-174 MHz
                • General service band for both government and non-government signals, including fixed and mobile units, and amateur broadcast
              • 174-216 MHz
                • Channels 7-13
              • 216-470 MHz
                • Includes a number of fixed and mobile communication modes, including some aeronautical navigation and citizens radio
              • 390-1,550 MHz
                • Various frequencies are designated as the L-Band and are used for a variety of satellite communication purposes, including GPS
              • 470-890 MHz
                • Includes UHF television channels 14-83
              • 824.040-848.970 MHz
                • Mobile cellular telephones
              • 890-3000 MHz
                • Includes a variety of aeronautical and amateur uses and studio-transmitter relays
              • 1,300-1,600 MHz
                • Radar bands
                      • (10)
          • Microwaves, Radar (10)
            • Frequencies range 1.6—30GHz
            • Wavelengths range 187—10mm
            • Quantum energies range 0.66 x 10-5 — 0.12 x 10-3 eV
              • 3,000-30,000 MHz (3-30 GHz)
                • Microwave applications
                • Amateur and radio navigation uses
              • 2450 MHz
                • Microwave ovens (this band was assigned by the FCC)
                      • (10)
            • 3K BACKGROUND RADIATION IN THE UNIVERSE, IN THE MICROWAVE REGION??? WMAP PROBE???
          • Millimeter Waves, Telemetry (10)
            • Frequencies range 30—300 GHz
            • Wavelengths range 10—1mm
            • Quantum energies range 0.12 x 10-3 — 0.12 x 10-2 eV
              • This range is used for a variety of experimental, government and amateur purposes in communication
                      • (10)
          • Infrared
            • (11) Frequencies range .003 — 4 x 1014 Hz
              • Wavelengths range 1mm — 750 nm
              • Quantum energies range 0.0012 — 1.65 eV
                • The higher of these frequencies are used for communication up to the red portion of the visible spectrum
                • When interacting with matter, infrared primarily acts to set molecules into vibration. This is addressed in much greater detail in the LASER THERAPY section
                      • (11)
            • (13) The Infrared portion of the electromagnetic spectrum can actually be broken down into 3 subcategories, far-infrared, mid-infrared and near-infrared:
              • Far-Infrared
                • Ranges from 300 Ghz (1mm) to 30 THz (10µm)

     

  • ***The far end of the range that is referred to as “laser light” starts in this subcategory at 11,000 nm or 11 µm***
              • Mid-Infrared
                • Ranges from 30 to 120 THz (10 to 2.5 µm)
              • Near-Infrared
                • Ranges from 120 to 400 THz (2,500 to 750nm)
                      • (13)
          • Visible Light (11)
            • This refers to that .0035% of the electromagnetic spectrum that humans can see without aid. This is due to a correlation with the wavelengths near the maximum of the sun’s radiation curve.
            • Frequencies range 4 — 7.5 x 1014 Hz
            • Wavelengths range 750 — 400 nm
            • Quantum energies range 1.65 — 3.1 eV
              • Red
              • Orange
              • Yellow
              • Green
              • Blue
              • Violet
                      • (11)
          • Ultraviolet
            • (11) Frequencies range 7.5 x 1014 — 3 x 1016 Hz
              • Wavelengths range 400 nm — 10nm
              • Quantum energies range 3.1 — 124 eV
                • The first part of this range is called the Near Ultraviolet
                  • This range is absorbed very strongly by most solid substances, and is even absorbed by air.
                • The shorter wavelengths becoming ionizing, as explained ABOVE, meaning that the shorter UV wavelengths can be harmful, including effects such as sunburn and worse.
                • The sun has strong UV radiation, but the atmosphere absorbs most of the shorter more harmful wavelengths.
                • Eyes are very susceptible to damage from UV radiation.
                • Snow reflects UV instead of absorbing it like other substances
                • Longer UV wavelengths have therapeutic effects (See LASER THERAPY UV below)    
                      • (11)
            • (14) UV light can also be broken down into 4 subcategories:
              • Near-Ultraviolet (NUV)
                • Ranges 300-400 nm
              • Middle Ultraviolet (MUV)
                • Ranges 200-300 nm
              • Far Ultraviolet (FUV)
                • Ranges 200-122 nm

     

  • ***The other end of the range that is referred to as “laser light” ends in this subcategory at 150 nm***
              • Extreme Ultraviolet (EUV)
                • Ranges 121-10 nm
              • Solar UV Radiation is divided into 3 subcategories:
                • UV-A
                  • Ranges from 320 to 400 nm
                • UV-B
                  • Ranges from 290 to 320 nm
                • UV-C
                  • Ranges from 220 to 290 nm
                • In nature, Most UV-B and all of UV-C rays are absorbed by ozone (O3) molecules in the upper atmosphere, meaning 99% of the solar UV radiation reaching the Earth’s surface is UV-A (14)
          • X-Rays (11)
            • Frequencies range 3 x 1016 Hz — upwards
            • Wavelengths range 10nm – downwards
            • Quantum energies range 124 eV — upwards
              • These are high frequency electromagnetic rays which are produced when electrons are suddenly decelerated, hence the name “braking radiation”.
              • X-rays are ionizing radiation and produce physiological effects on a cellular level, not overtly observed by the human eye, such as mutations or cancer.
                      • (11)
          • Gamma-Rays (11)
            • Frequencies are >1020 Hz
            • Wavelengths are < 10-12 m
            • Quantum energies are >1 MeV
              • The terms X-ray and Gamma ray are statements about origin rather than implying different kinds of radiation
              • Gamma rays are ionizing radiation and produce physiological effects on a cellular level, not overtly observed by the human eye, such as mutations or cancer.
                • Gamma rays describe electromagnetic radiation from the nucleus as part of a radioactive process. The energy of nuclear radiation is extremely high because such radiation is born in the intense conflict between the nuclear strong force and the electromagnetic force.
                      • (11)
          • This is a good link which allows you to click on any part of the spectrum for further details: http://hyperphysics.phy-astr.gsu.edu/hbase/ems1.html
        • Now that we thoroughly understand Light and Radiation, let’s define the remaining words:
            • Amplification:
              • “To make larger or greater”
              • “To increase the strength or amount of”
            • Stimulated
              • “To excite to activity or growth or to greater activity”
            • Emission
              • “The act of producing or sending out something from a source”
          • And now that we understand them more in depth, let’s review the definitions of “light” and “radiation”:
            • Light:
              • “Electromagnetic radiation of any wavelength that travels in a vacuum with a speed of about 186,281 miles (300,000 kilometers) per second”
            • Radiation
              • “The complete process in which energy is emitted by one body, transmitted through an intervening medium or space, and absorbed by another body.”
          • So to review, LASER stands for Light Amplification by Stimulated Emission of Radiation
            • So now we can understand that this is the “the increased amount or strength of electromagnetic radiation (emission of energy by a body transmitted through an intervening space and absorbed by another body) of any wavelength that travels in a vacuum (i.e. space) with a speed of 186,281 miles/second, by sending forth excitation resulting in growth of activity of the emission of energy by a body transmitted through an intervening space and absorbed by another body.”
            • Or, more simply defined:
              • “A laser is a device that emits monochromatic light through a process of optical amplification based on the stimulated emission of photons.” (2)
              • Monochromatic means, “of a single wavelength or frequency”
            • Or as it is defined in Merriam Webster:
              • “A device that utilizes the natural oscillations of atoms or molecules between energy levels for generating a beam of coherent electromagnetic radiation”
              • Coherent will be defined further on ANOTHER PAGE as it is relevantly applied in LASER THERAPY, but for now, the Merriam Webster definition of coherent is as follows:
                • “logically or aesthetically ordered”
                • “having the quality of holding together”
                • “relating to or composed of waves having a constant difference in phase”
              • To immediately jump to the best external link I have found to explain the difference between coherent and incoherent, click HERE (http://www.miridiatech.com/news/2014/02/laser-vs-led-whats-the-difference/ )

     

  • And, in addition to these definitions, as stated earlier on this page, “Laser Light” only refers to FAR Ultraviolet beginning at 150nm and ranges all the way up the Electromagnetic Spectrum to Far Infrared at 11,000 nm or 11 µm.

  • Hopefully by now this makes a lot more sense! If not, at least understand that LASER has an extremely wide range of activity that it technically refers to.SOURCES:

    1. http://www.pro-lite.co.uk/File/laser_safety_laser_basics.php
    2. https://www.boundless.com/physics/textbooks/boundless-physics-textbook/introduction-to-quantum-physics-28/applications-of-quantum-mechanics-183/lasers-677-3407/
      1. Source: Boundless. “Lasers.” Boundless Physics Boundless, 26 May. 2016. Retrieved 12 Jan. 2017 from https://www.boundless.com/physics/textbooks/boundless-physics-textbook/introduction-to-quantum-physics-28/applications-of-quantum-mechanics-183/lasers-677-3407/
    3. http://study.com/academy/lesson/what-is-radiation-definition-causes-effects.html)
    4. http://www.physicsclassroom.com/class/light/Lesson-2/The-Electromagnetic-and-Visible-Spectra
    5. http://www.madsci.org/posts/archives/2007-08/1188407794.Ph.r.html
    6. http://www.worldometers.info/world-population/
    7. http://missionscience.nasa.gov/ems/09_visiblelight.html
    8. http://science.hq.nasa.gov/kids/imagers/ems/waves4.html
    9. http://eo.ucar.edu/weather/images/light.pdf
    10. http://hyperphysics.phy-astr.gsu.edu/hbase/ems2.html#c1
    11. http://hyperphysics.phy-astr.gsu.edu/hbase/ems3.html#c1
    12. https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
    13. https://www.boundless.com/physics/textbooks/boundless-physics-textbook/electromagnetic-waves-23/the-electromagnetic-spectrum-165/infrared-waves-594-11180/
    14. https://www.boundless.com/physics/textbooks/boundless-physics-textbook/electromagnetic-waves-23/the-electromagnetic-spectrum-165/ultraviolet-light-596-11177/

    Additional Helpful Sources: