Photonics Properties PDF

Endoscopy of the Photonics Photonics 1-----Properties of photons/light 2-----Generation and detection of photons 3------Manipulations of photons Properties of Photon Intrinsic Photon Properties 1-Mass. Photons are elementary particles with zero mass, Even though photons ha...

Endoscopy of the Photonics Photonics 1-----Properties of photons/light 2-----Generation and detection of photons 3------Manipulations of photons Properties of Photon Intrinsic Photon Properties 1-Mass. Photons are elementary particles with zero mass, Even though photons have no rest mass, they do carry energy and momentum, which gives them relativistic mass according to the equation 𝐸=𝑚𝑐2, where 𝑚 is the relativistic mass. Since photons have no rest mass, but they still carry momentum using Ƥ=E/c , where E is the energy of the photon and c is the speed of light. E2=(mc2)2+(Ƥc)2 m=0 Though massless, photons are still affected by gravity, which can be seen in phenomena like gravitational lensing. According to general relativity theory, a photon climbing out of a gravitational field loses energy. This is known as gravitational redshift and is given by the formula: In general relativity, the gravitational redshift describes how a photon’s frequency decreases (or its wavelength increases) as it escapes a gravitational field and vice versa gravitational blueshift. This is given by: 2. Velocity. Photons propagate with a velocity whose absolute magnitude is normally quoted as the speed c in vacuum. In free space, light travels in a straight line, and the direction of its well-defined velocity is usually denoted by the unit vector k̂. On propagation through a medium of refractive index n, individual photons travel at a speed known as the phase velocity. Where w is angular frequency and k is wavenumber. Group velocity: The velocity of the envelope of the wave packet, which is typically the speed at which information or energy propagates. This is the speed that corresponds to the photon’s velocity in materials and can be less than c. The phase velocity, which is the speed at which the zero crossings of the carrier wave move; The group velocity, at which the peak of a wave packet moves; The energy velocity, at which energy is transported by the wave; The signal velocity, at which the half-maximum wave amplitude moves; The front velocity, at which the first appearance of a discontinuity moves. Cherenkov Radiation: When a charged particle travels faster than the speed of light in a medium (but still less than c in vacuum), it emits a shockwave of electromagnetic radiation, known as Cherenkov radiation. This happens because the particle moves faster than light can propagate through that specific medium. 3-Electromagnetic fields. The absence of any constituent charge (together with the absence of mass) means that photons cannot interact between themselves; any engagement of two or more photons requires its mediation by interaction with matter. These equations describe the propagation of electromagnetic waves (e.g., light) with speed c, the speed of light. 4. Wavelength. The wavelength λ0 of the electric and magnetic waves, for light traveling in vacuum, is given by c/. It is the closest distance along the propagation direction between any two positions with the same optical phase. In applications such as spectroscopy, reference is commonly made to its inverse, the wavenumber ¯= 1/0 = /c, usually expressed in cm–1. Photons propagating within a medium of refractive index n have a modified wavelength λ = λ0/n, such that the product λ still equals the propagation speed. 5-Frequency. The optical frequency expresses the number of wave cycles, at a fixed point in space, per unit time. Also commonly used in quantum optics is the circular frequency ω = 2πν (radians per unit time). 6. Energy. Photons convey electromagnetic energy from one piece of matter to another. Their energy links to optical frequency through the Planck relation E = h (where Planck’s constant h = 6.6261 × 10–34 J s) or, equally, E = ħ where ħ = h/2 is known as the reduced Planck’s constant (or Dirac constant). The lower the optical frequency is, the greater the number of photons for a given amount of energy, and hence the more their behavior approaches that of a classical wave (an instance of the “large numbers” hypothesis of quantum theory). - Light can act like a particle when it bounces off a mirror and back at you so that you can see the image but can also act as a wave when it goes through a small gap and spreads out as it goes through. -Light behaves as a wave when it reflects or bounces off of an obstacle. Light will also behave as a wave when it passes through another medium, causing refraction. Light that changes direction or diffracts will also behave as a wave. 7-Linear momentum. Despite having no mass, each photon carries a linear momentum p, a vector of magnitude h/= ħ/c in the direction of propagation. Given that photon momentum is proportional to frequency, photons of high frequency have high momenta and exhibit the most particle- like behavior. X rays and gamma rays, for example, have many clearly ballistic properties 8-Polarization. For plane-polarized photons (also called linearly polarized), the plane within which the electric field vector oscillates can sit at any angle containing the wavevector. By convention, the direction of the electric field vector defines the orientation of the polarization, the magnetic field also oscillates in a plane orthogonal to the electric field; however, the “plane of polarization” generally refers to the electric vector. Even for individual photons, a wide variety of other polarization states are also possible: in circular polarizations, the electric field vector sweeps out a helix about the direction of propagation, and the magnetic vector is advanced or retarded from it by /2 radians. Elliptical polarization states are of an intermediate nature, between linear and circular. 9. Spin. Many of the key properties of photons relate to the fact that they have an intrinsic spin S = 1, In simple terms, this means that their oscillating electromagnetic fields keep in step as they propagate. Through this, coherent beams of highly monochromatic and unidirectional light can be produced; this is, of course, the basis for laser action. 10. Angular momentum. The intrinsic spin of each photon is associated with angular momentum, a feature that plays an important role in the selection rules in optical spectroscopy. Circularly polarized photons have the special property of quantum angular momentum. The two circular polarization states of opposite handedness, left- and right-handed, respectively carry a +1 or –1 unit of angular momentum ħ. A different kind of angular momentum described as “orbital,”. Photon carries an angular momentum of ±h −, which is due to its spin. Recently it has been found that the angular momentum per photon can exceed this value and this is due to the orbital contribution of the momentum. The orbital angular momentum is associated with the phase singularity.  Linear momentum describes the photon's movement through space and its ability to transfer force to other objects (like in radiation pressure).  Angular momentum describes the rotational characteristics of the photon, which are linked to its polarization (spin) or wavefront structure (orbital angular momentum).  Light Source and Laser Safety 1-Light Source The following non laser light sources will be discussed: 1. Incandescent sources 2. Fluorescent-low pressure discharge lamps 3. High-intensity and -pressure discharge lamps (HID) 4. Flashlamps and arc lamps 5. Light-emitting diodes (LED) A. Incandescent Sources Incandescent sources are similar to but not exactly as intense as blackbody radiators. A blackbody radiator is considered to be an almost perfect emitter. The first incandescent lamps in the nineteenth century were carbon-, iron-, osmium-, or tantanum-filament lamps. However, in spite of its low ductility tungsten has replaced all these filament materials because of its low vapor pressure, high melting point (3655 K), and strength. Today tungsten is typically alloyed with metals such as thorium and rhenium. Most modern incandescent lamps are filled with gas to increase the lifetime of the filament. These fill gases are generally mixtures of argon and nitrogen, with high percentages of argon for low-voltage lamps and very high percentages of nitrogen for high-voltage projection lamps. Occasionally krypton is added for still greater lifetime. None of these gases appreciably influences the spectral quality of the incandescent source. However, the tungsten-halogen-type lamp has become increasingly common. Tungsten- halogen lamps contain a small amount of a halogen, such as bromine, chlorine, or iodine. The halogen teams with the tungsten to create a regenerative cycle—particles of tungsten thrown off by the filament combine with the halogen to form a gas that is attracted to the hot filament and attaches to the filament. However, the lost particles of tungsten do not redeposit in exactly the same place, so the filament is modified, spotting and eventually failing as before. The important feature of the tungsten-halogen lamps is that the particles of tungsten collected by the filament are prevented from depositing on the glass. Thus, the lamps do not form a black coating on the inner surface. Halogen lamps are hot, and they must run hot to keep the regenerating cycle going—nothing less than 500 degrees F will do. For comparison, a 100-watt household lamp is never hotter than about 450 degrees, meaning that this temperature is too low for a halogen lamp. Ordinary glass does not stand the higher temperature needed, so all halogens are made of special heat-resistant glass or of quartz. In fact, the halogen lamp is now perhaps better known as a quartz lamp. Lamp filaments made of tungsten wire are sometimes used in a straight length but are more often formed into a coil, or a coiled coil, Figure 2-5. This drawing shows the various common filament styles. The better (and more expensive) filaments have close-spaced coils to secure a bright, uniform light. Less expensive are the wide-spaced filaments, and these are entirely practical for many applications, such as slide projectors. B. Fluorescent Light Sources Fluorescent light sources are low-pressure discharge lamps with a fluorescent phosphor. Most fluorescent lights consist of mercury discharge lamps that emit 90% of their energy at 253.7-nm wavelength. These ultraviolet photons can excite a number of phosphors, producing a range of wavelengths from infrared to ultraviolet. Visible wavelengths are characterized as white, warm white, cool white, etc. Fluorescent lamps can have either cold or hot cathode electrodes. Cold electrodes are used when a rapid start is necessary. Hot cathode electrodes give greater luminous efficiency and because of this most lamps today use hot cathode electrodes. The luminous efficiency of a fluorescent lamp increases with its length. For example, an 80-inch lamp is 40% more efficient than a 15-inch lamp. The output of a fluorescent lamp is also a function of the type of ballast used. The two common types of ballast are the rapid-start and the preheat ballast. Most of today’s lamps operate with rapid-start ballasts. However, research has suggested that the preheat ballast may yield up to 20% higher light output as compared to the rapid-start type. Lamp life could also be significantly affected by the choice of ballast. C. High-Intensity Discharge Lamps (HID) High-intensity discharge (HID) lamps can be made of mercury, sodium, or metal halides. The gas pressures inside the lamps are usually 2–4 atmospheres. HID lamps—specifically those containing mercury—have two envelopes: the inner quartz discharge tube and an outer glass jacket. The outer jacket absorbs the UV radiation generated by the internal operation of the bulb. In places like gymnasiums, high-bay industrial areas, and public buildings, these lamps are often not enclosed in protective fixtures. The outer jacket can be broken in some instances by flying projectiles without damaging the inner discharge tube. If the lamp does not extinguish, substantial levels of UV radiation will be emitted to the outside. An HID lamp can cause serious skin burn and eye inflammation from shortwave ultraviolet radiation if the outer envelope of the lamp is broken or punctured. Lamps that will automatically extinguish when the outer envelopes are broken or punctured are commercially available. D. Flashlamps and Arc Lamps Flashlamp and arc lamps are high-intensity discharge devices commonly used in photography and laser technology and usually contain gases such as xenon and krypton. The flash or arc is initiated by a high voltage across the discharge tube, which in turn ionizes the gas and produces a high-intensity light with output peaks in both the visible and infrared regions of the electromagnetic spectrum. See Figure 2-7. Continuous wave lamps - CW laser lamps The CW laser lamp is a gas discharge lamp used to pump solid-state lasers in many industrial applications like cutting and marking. A wide range of fill pressures and electrode lamp geometry make it possible to optimize lamp efficiency and extend lifetime. Application areas: Laser for welding, cutting, engraving & marking Key features of CW laser lamp:  Quality raw materials and inspection  High standards of manufacturing and traceability  Consistent build quality  Variety of lamp connections available  All lamps tested to specification  Large manufacturing capacity  Superb customer support  Excellent technical knowledge  Highly skilled workforce Pulsed Flash Lamp - Xenon and Krypton DC pulsed flash lamp (Xenon, Krypton) to leading solid-state laser manufacturers and non-laser applications like IPL or sun simulation. lamps normally operate at high average powers with pulse duration from the millisecond regime and repetition rate up to many kilohertz. lamps offer high efficiency, stability and long lifetimes. Typical laser applications include precision cutting and drilling, spot welding and mould repair. Non-laser applications include hair removal, skin treatment, sun simulation and semiconductor processing. Heraeus work closely with our customers utilizing our extensive internal and external research facilities and institutes to provide the industry with high quality flash lamps.  quality raw materials and inspection  High standards of manufacturing and traceability  Consistent build quality  Variety of lamp connections available  All lamps tested to specification  Large manufacturing capacity  Superb customer support  Excellent technical knowledge  Highly skilled workforce  Patented cathode design, Hi-Charge™ series  Enhanced HIT™ ignition Application areas:  Indusrial Lasers for Welding, Cutting, Drilling & Marking  Rapid Thermal Processing (RTP)  Weathering and Sun Simulation  Cosmetic & Medical Laser Applications  Curing  Annealing   Sintering  Distance Measurement  Disinfection E. Light-Emitting Diodes (LED) Light-emitting diodes are semiconductor devices that are directly modulated by varying input current. They are usually made of aluminum-gallium- arsenide (AlGaAs). LEDs are p-n junction devices constructed of gallium arsenide (GaAs), gallium arsenide phosphide (GaAsP), or gallium phosphide (GaP). Silicon and germanium are not suitable because those junctions produce heat and no appreciable IR or visible light. The junction in a LED is forward biased and when electrons cross the junction from the n- to the p-type material, the electron-hole recombination produces some photons in the IR process or visible in a process called electroluminescence. An exposed semiconductor surface can then emit light.  Photon Detection Principles of Photon-Matter Interaction  Photoelectric E ect  Compton Scattering and Rayleigh Scattering  Photon Absorption Mechanisms  Mechanical Oscillators in Photon Detection  Photon Radiation Pressure in Mechanical Detection  Mechanical Quantum Systems and Photon Detection Types of Photon Detectors  Photomultiplier Tubes (PMTs): Working principles, gain, and applications.  Photodiodes and Avalanche Photodiodes (APDs): Semiconductor- based detectors, responsivity, gain mechanisms.  Charge-coupled devices (CCDs) and Complementary Metal-Oxide Semiconductors (CMOS): Imaging detectors, quantum e iciency, noise characteristics.  Single-photon avalanche Diodes (SPADs): Operation, timing resolution, and applications in quantum optics. Advanced Photon Detection Technologies  Superconducting Nanowire Single-Photon Detectors (SNSPDs): Physics of superconductivity, ultra-sensitive applications.  Transition Edge Sensors (TES): Energy-resolving detectors, applications in X-ray and gamma-ray detection.  Quantum Dot Detectors: Role of quantum dots in photon detection, tunability, and spectral response. Heinrich Hertz (born February 22, 1857, Hamburg [Germany]—died January 1, 1894, Bonn, Germany) was a German physicist who showed that Scottish physicist James Clerk Maxwell’s theory of electromagnetism was correct and that light and heat are electromagnetic radiations. Applications of Photoelectric E ect  Used to generate electricity in Solar Panels. These panels contain metal combinations that allow electricity generation from a wide range of wavelengths.  Motion and Position Sensors: In this case, a photoelectric material is placed in front of a UV or IR LED. When an object is placed in between the Light-emitting diode (LED) and sensor, light is cut o and the electronic circuit registers a change in potential di erence  Lighting sensors such as the ones used in smartphones enable automatic adjustment of screen brightness according to the lighting. This is because the amount of current generated via the photoelectric e ect is dependent on the intensity of light hitting the sensor.  Digital cameras can detect and record light because they have photoelectric sensors that respond to di erent colors of light.  X-Ray Photoelectron Spectroscopy (XPS): This technique uses xrays to irradiate a surface and measure the kinetic energies of the emitted electrons. Important aspects of the chemistry of a surface can be obtained such as elemental composition, chemical composition, the empirical formula of compounds and chemical state.  Photoelectric cells are used in burglar alarms.  Used in photomultipliers to detect low levels of light.  Used in video camera tubes in the early days of television.  Night vision devices are based on this e ect.  The photoelectric e ect also contributes to the study of certain nuclear processes. It takes part in the chemical analysis of materials since emitted electrons tend to carry specific energy that is characteristic of the atomic source. 1. What are the properties of a photon? 2. What does the photoelectric effect show about the properties of light? 3. How does the frequency of light affect the release of photons?