Detailed Notes on Photonics - Light Sources: The Laser

Photonics - Light Sources: The Laser

Introduction

• Module 2 focuses on light sources, specifically lasers.
• Electromagnetic radiation sources are categorized and explored.

History of Light Sources

• Early Light Sources
  • Sun and fire were the earliest light sources.
  • 20,000 years ago: First "artificial" light using fire.
  • 5,000 years ago: Primitive oil lamps using animal fats, fish oils, and whale oil.
  • Systematic use of oil lamps in Egypt, Greece, and Rome.
• 17th-19th Century Developments
  • Approximately 1650: Invention of the oil lamp and first street lighting.
  • Approximately 1780: Substantial improvements in oil lamps during the Industrial Revolution.
  • 1802: Sir Humphrey Davy discovered electric glow and demonstrated electric arc between two carbon electrodes, used for street lighting and early films.
  • Approximately 1810: Gas lighting introduced for street illumination.
  • 1852: Stokes discovered UV fluorescence emission and Stokes shift (change in light wavelength) using fluorite glass and uranium.
• Late 19th Century - Early 20th Century
  • 1879: Thomas Edison and Joseph Swan presented the first incandescent lamp using a carbon blade, lasting 40 hours.
  • 1881: Long-life carbon filaments patented. Planned obsolescence limited incandescent bulb life to 1000 hours.
  • 1901: Operation of the first low-pressure mercury discharge lamp.
  • 1913: Incandescent bulbs with tungsten filaments reached 12 lumens per watt (lm/w).
  • 1924: Discovery of phosphors to convert UV light to visible fluorescence (no phosphorescence/radioactivity).
  • 1927: First LED developed but very inefficient.
  • 1932: Development of low-pressure discharge lamps.
  • 1936: Demonstration of the first fluorescent lamp.
  • 1961: Patent of the first halogen lamp.
  • 1960: First laser obtained (Ruby laser).
  • 1965: Development of high-pressure sodium lamp.
• Late 20th Century - Early 21st Century
  • 1980: Introduction of Compact Fluorescent Lamps (CFLs).
  • 2000: Commercial LEDs introduced.
  • 2003: First blackout on the East Coast of the United States, leading to more efficient electric power transmission and lighting sources.
  • Since September 1, 2009: EU Ecodesign lighting regulations progressively phased out inefficient incandescent and halogen light bulbs.

Timeline of Light Source Development

• 1780: Oil lamp
• 1800: Gas lamp, platinum filament
• 1820: Vacuum tube lamp
• 1840: Arc lamp
• 1860: Fluorescent lamp
• 1870: Electric light bulb
• 1880: Long-lasting filament
• 1900: Gas-discharge lamp, mercury-vapor lamp, neon lighting
• 1910: Tungsten filament
• 1920: Fluorescent lamp
• 1960: Light-emitting diode
• 1980: Compact Fluorescent Lamp
• 1990: SON, Wanic Light Emitting Diode, magnetic induction lamp, sulfur lamp

Luminous Efficacy

• Luminous efficacy (lumens per watt) increased with advancements in light source technology.
• Incandescent lamps have low efficacy, while LEDs have high efficacy.

Photometric Units

• The luminous intensity is based on the luminosity function, modeling human eye sensitivity.
• Formula: $I_v(\lambda) = 683.002 * I(\lambda) * y(\lambda)$
  • Where $I_v(\lambda)$ is the luminous intensity.
  • $I(\lambda)$ is the intensity in W/sr (watts per steradian).
  • $y(\lambda)$ is the luminosity function.
• Luminous Efficacy is the ratio of luminous flux to consumed power (lm/W).

Photometric Units Table

Sources of Electromagnetic Radiation

• Classical Theory: Radiation emitted by accelerated charges (mainly electrons), resulting in a continuous spectrum.
• Quantum theory: Transitions between energy levels or bands. When a system transitions from a higher to a lower energy level, it emits a photon.
  • Photon energy equals the energy difference between levels.
  • Spontaneous emission: Fluorescent lamps and LEDs.
  • Stimulated emission: Lasers.
  • Leads to a discrete spectrum.
  • $f = \frac{\Delta E}{h}$
    • Where $f$ is the frequency of emitted radiation.
    • $\Delta E$ is the energy difference between the two levels.
    • $h$ is Planck's constant.

Classical Explanation of Thermal Agitation

• Thermal agitation causes varying velocities and accelerations of electrons.
• Each electron emits a different frequency, resulting in a wide spectral range.
• Classical theory explains experimentation qualitatively but not quantitatively, especially at high temperatures.
• This leads to quantum theory (Planck, late 19th century).

Black Body Radiation

• Ideal thermal absorber-emitter that results from the balance between absorption and emission of light by atoms or molecules at a given temperature.
• Emission relies on body characteristics and the environment.

Molecular Energy Levels and Boltzmann Distribution:

• Boltzmann's energy distribution works even though it is continuous and does not include quantum mechanics.
• Increasing temperature promotes molecules to higher energy states.
• Boltzmann Constant: $k_B = 1.38065 \cdot 10^{-23} J \cdot K^{-1}$

Light-Matter Interaction Processes (Radiative Processes)

• Photon Absorption: Atom absorbs photon energy, transitioning to an excited state.
• Stimulated Emission: A photon stimulates the emission of a second photon; the atom returns to ground state. The emitted photon has the same direction and phase as the incident photon.
• Spontaneous Emission: Atom moves from excited state to ground state, emitting a photon. Emission direction is undefined. Excited states are unstable.

Rate Equations and Einstein Coefficients

• Simple two-level system. Rate equations for photon absorption and emission depend on:
  • Number of atoms in energy levels (level populations): $N<em>1$ and $N</em>2$
  • Energy density of radiation with frequency $\nu$ for absorption and stimulated emission
  • $A<em>{21}$, $B</em>{12}$, and $B<em>{21}$ are the Einstein coefficients, where $B</em>{12} = B_{21}$.
• Absorption Rate: $\frac{dN<em>1}{dt}</em>{absor} = -B<em>{12}N</em>1u(\nu)$
• Stimulated Emission Rate: $\frac{dN<em>2}{dt}</em>{stim} = -B<em>{21}N</em>2u(\nu)$
• Spontaneous Emission Rate: $\frac{dN<em>2}{dt}</em>{espont} = -A<em>{21}N</em>2$
• Total Rate: $\frac{dN}{dt} = \frac{dN}{dt}<em>{absor} + \frac{dN}{dt}</em>{spont} + \frac{dN}{dt}_{stim}$
• Black body in thermal equilibrium.

Black Body Radiation and Planck's Postulate

• Ultraviolet Catastrophe: Classical calculations predicted that energy density emitted by a black body increases indefinitely with frequency.
• Planck's Postulate: Atoms absorb/radiate energy in finite quantities proportional to frequency, solving the ultraviolet catastrophe: $\Delta E = h f$. $\Delta E$ is replaced by $h\nu$

Total Radiated Intensity and Wien's Law

• Total radiated intensity of a black body at temperature $T$:
  • $I(\nu) = \frac{h \nu}{e^{\frac{h \nu}{kT}} - 1}$
  • Units: $W \cdot m^{-2} \cdot Hz^{-1} \cdot sr^{-1}$
    • $k$ = Boltzmann constant = $1.38065 \cdot 10^{-23} J \cdot K^{-1}$
    • $h$ = Planck constant = $6.62607 \cdot 10^{-34} J \cdot s$
• Maximum in the spectral distribution (Wien's Law):
  • $\lambda_{max} T = 2.898 \cdot 10^{-3} mK$

Black Body Radiation Examples

• Molten glass and heated metal emit visible light at high temperatures (“red hot”).
• Cooling objects emit radiation at lower frequencies.
• Cosmic microwave background (2.7°K) is blackbody radiation from the Big Bang.
• Cooler objects emit light at longer wavelengths (infrared).

Solar Emission

• Solar emission approximates a black body at $T \approx 5800K$, with $\lambda_{max} \approx 500nm$.

Properties of Light Sources

• Luminous Efficacy: lumens per electric watt (lm/W).
• Service Life: hours of operation.
• Color Properties: color temperature and Color Rendering Index (CRI).
• Response Time.
• Polarization.
• Spatial and Temporal Coherence.

Types of Thermal Emitters for Lighting

Incandescent Lamps

• Tungsten filament (formerly carbon) in a vacuum or inert gas (argon, krypton, xenon) to reduce filament evaporation. Operated at 2600-3000 K.
• Luminous efficiency: 12-15 lm/W. Maximum radiation in the infrared.
• Service life: approximately 1000 hours. Higher temperatures increase luminous efficiency but shorten service life.
• Evaporation blackens bulb and increases electrical resistance.
• Response time: fractions of a second to work.
• Bulbs made of glass or quartz for high temperatures.

Halogen Lamps

• Tungsten filament with halogen gas (iodides or bromides) to regenerate filament evaporation.
• Service life: 1500 hours.
• Luminous efficiency: 18-22 lm/W.
• Regenerative cycle:
  • Chemical reaction of iodide with evaporated tungsten forming tungsten iodide molecules.
  • Dissociation of molecules near the hot filament, depositing tungsten.
• Infrared reflective coating for a colder bulb.

Spectrum of Halogen Lamp

• Typical irradiance spectrum of a 100W halogen bulb at approximately 3000 K, showing visible and infrared emissions.

Atomic Structure of Matter

• Chemical element basics.
  • Pure substances that cannot be decomposed.
  • Characterized by atomic number Z (number of protons).
    • Ions have a different number of electrons, isotopes have different numbers of neutrons but the same Z.
  • Arranged according to the periodic table.
• May form monoatomic, diatomic, polyatomic molecules or crystal lattices.
• Mass Number A = N + Z

Electronic Configuration

• Electron distribution in atomic orbitals are stationary solutions of the Schrödinger equation.
• Quantum numbers:
  • $n$: principal quantum number.
  • $l = 0, …, n-1$: azimuthal quantum number. Spherical harmonics, $Y_l^m$
  • $m = -l, …, 0, …, +l$.
• Notation: $nl^x$
  • $n$is the principal quantum number, $l$ is the azimuthal quantum number with magnetic quantum numbers$m = -l, …, 0, …, l$. Each level has 2 electrons possible. $x$ is the number of electrons in the orbital.
  • Example: $3d^7$ indicates 7 electrons in the d orbital at the third level.
• Order of filling atomic orbitals is by energy. Each orbital can hold 2 electrons with spin +1/2 and -1/2.
• Examples:
  • Na (Z=11): $1s^2 2s^2 2p^6 3s^1$
  • Cd (Z=48): $…4d^{10} 5s^2$
  • Hg (Z=80): $…4f^{14} 5d^{10} 6s^2$

Atomic Excitation and De-excitation

• Discrete energy levels are different for each atom.
• Energy jumps between levels E2 and E1 emit/absorb a photon with frequency f.
• $f=\frac{E<em>2-E</em>1}{h}$

Non-Thermal Emitters

• Emission occurs when an atom/molecule decays from a high to a low energy level, emitting a photon with frequency
• Atomic spectra (He, Ne, Hg) result from spontaneous or stimulated emission.
• Spectroscopy analyzes emitted/absorbed radiation by a material.
• Spontaneous emission occurs when an atom in an excited state decays to ground state.
• Stimulated emission occurs in the presence of external radiation of appropriate frequency.

Arc Lamps (Discharge Lamps)

• Electrons are accelerated from cathode to anode, causing gas ionization.
• Decay of gas atoms results in photon emission.
• Low pressure: Sharp spectral lines lead to monochromatic light sources.
  • Common gases: hydrogen, sodium, mercury, neon, xenon, argon, cadmium, krypton, etc., or mixtures.
  • Low pressure sodium lamps have a yellow centered spectrum and an efficiency of 180 lm/W
• High pressure increases collisions between atoms/molecules and broadens the energy levels. Result is white light.
  • Carbon arcs.
  • High pressure mercury lamps.
    • Powers from 50 W to 25 kW. Sharp spectral lines.
  • High pressure sodium lamps.
    • White color (2100 K) and high performance, 130 lm/W.
  • Xenon lamps.
    • Long continuous spectrum, similar to the sun (blackbody at 6000 K).
    • Service life: 10,000 hours.
    • 200A carbon arc approximates blackbody distribution at 6000 K. Different gases can achieve various spectral distributions.

Mercury-Xenon Lamps and Other Arc Lamps.

• Mercury-xenon lamps show a continuous spectrum and sharp mercury lines.
• Hydrogen and deuterium arc lamps are ideal for spectroscopy in the ultraviolet domain.

Fluorescent Lamps

• Discharge lamps of low pressure and low intensity of mercury vapor or a mixture of argon and mercury.
• Tubes are coated with a fluorescent/luminescent substance that absorbs UV radiation from mercury and emits part of the energy as visible light.
• Light characteristics depend on mercury pressure and temperature.
• Different spectra are obtained by altering the coating (e.g., tungsten and zinc silicate, magnesium silicate).

Fluorescence and Phosphorescence

• Radiation absorption leads to atom/molecule excitation.
• Some energy is lost in non-radiative transitions.
• Radiation emission occurs at smaller frequencies. Phosphorescence has a delay.

Compact Fluorescent Lamps (CFLs)

• CFLs consume about a quarter of the power of incandescent lamps (e.g., 15W CFL equals 60W incandescent).
• Color variations:
  • "Warm white" or "soft white" (2700 K - 3000 K) are similar to incandescent lamps, slightly yellowish.
  • "White", "bright white" or "white media" (3500 K) are yellowish-white, whiter than incandescent lamps, but still considered warm.
  • "Cold white" light (4,100 K) is pure white but a little blue.
  • Daylight (5000 K to 6500 K) is bright white, like the sun.
• Slow response: takes more than a second to reach stable emission.
• Service life: approximately 8000 hours.
• Luminous efficiency: 60 lm/W.

Semiconductor Band Structure

Semiconductors

• Material behaves like an insulator at very low temperatures but conducts at room temperature.
• Performance controlled by doping.
  • Intrinsic semiconductors: elements with 4 valence electrons (Si, Ge).
  • Compound semiconductors: average of 4 e- in valence, made of elements of groups 13/15(GaAs, InSb) or 2/12/16 (ZnSe, CdS).
  • Extrinsic semiconductors: Doping:
    • n-type: doped with valence 5 elements (free electrons).
    • p-type: doped with valence 3 elements (electron holes).
• Direct (forward bias) and reverse polarization.

Photovoltaic Solar Energy

• Based on the reverse biased p-n junction cell with an antireflection coating.
• The best research-cell efficiencies, showing various materials and technologies.

LEDs (Light Emitting Diodes)

• Direct p-n junction. Process is voltage-controlled.
• Recombination of electrons and holes in the depletion zone.
• Semiconductor diodes emit a photon due to recombination.
  • Gallium Arsenide(GaAs) = Color Infrared
  • Aluminum Gallium Arsenide (AlGaAs) = Infrared
  • Gallium Arsenide Phosphide (GaAsP) = Infrared red
  • Gallium Nitride (GaN) = Red, organge, yellow
  • Gallium Phosphide (GaP) = Green
  • Zinc Selenide (ZnSe) = Green
  • Indium Gallium Nitride (InGaN) = Blue
  • Silicon Carbide (SiC) = Blue
  • Diamond = Blue
  • Silicon = UV

LEDs for Lightning

• Service life: 50,000 hours.
• Luminous efficiency: Up to 150 lm/W for white LEDs.
• CRI (Color Rendering Index): 80-95. LEDs are efficient but may not emit a balanced mixture of all colors.

LED Spectral Emission

• The emitted light is not monochromatic; spectral bands have widths from several nm to 50 nm.
• Frequency depends on the bandgap between valence and conduction bands, semiconductor, doping, and temperature.
• RGB LEDs can produce white light.

X-Ray Sources

• Non-thermal sources.
• Emit radiation in a wide band of the spectrum due to electron acceleration.
• X-ray tubes generate high-energy electrons (10-50 keV) that collide with a metal target; braking electrons (bremsstrahlung) emit continuous spectrum X-rays.
• Synchrotrons spin particles in closed orbits at relativistic speeds, emitting high-frequency radiation.
• Applications include:
  • Medical diagnosis (radiography and CAT scans)
  • Crystallography (X-ray diffraction).
• X-rays are ionizing radiation and cause burns/cancer with long exposure.

Principles of the LASER

• Light Amplification by Stimulated Emission of Radiation

Laser Light vs. White Light

Laser Properties

• Coherence: Same phase.
• Monochromicity: Fixed wavelength $\lambda$, depending on laser type.
• Directionality: Almost straight propagation. Divergence $\theta \approx \frac{\lambda}{d}$, where d is the beam diameter.
• Pulsed light: Lasers emit continuous wave or pulsed regimes. Pulse durations from 1 ms to 10 fs.
• Emitted Power: From 1 mW to MW (chemical lasers) and up to 1 PW (for short pulsed lasers).
• Examples:
  • Sunlight intensity at Earth: 1000 W/m2 = 100 mW/cm2.
  • 100W light bulb: 10W emitted as light. 0.02 mW/cm2 at 2m distance.
  • He-Ne laser 1mW, section 1mm2. Intensity: 100 mW/cm2.

Basic Laser Elements

• Gain medium (active medium): Transforms pumped energy into light and amplifies it by stimulated emission.
• Optical pumping power: Energy source (electric, laser, chemical).
• Laser Cavity: Determines preferred direction and reinjects light into the gain medium.
  • Standing wave forms in the cavity and determines resonant emission frequencies.
  • Mirrors:
    • Total reflection mirror (R=100%): Reinjects photon to the gain medium.
    • Partial reflection mirror (R ≈ 95%): releases a small portion of the stored energy as light.

Laser Principle for Radiation Amplification

• First spontaneous emission: random phase.
• Stimulated emission: all photons are identical (same frequency, direction, and phase = Coherent radiation ).
• Atoms start in are pumped (energized) to an excited energy level.
• This results in a cascade(amplification) of photons.

Einstein coefficients A, B

• Dependence upon Number of atoms in levels i and ii ( N1 and N2) and energy density of radiation with freq \nu
• Einstein Coefficients A21, B12 i B21: B12 = B21
• Absorption rate : dN1/dt = B12N1 u(v)
• Stimulated emission rate: dN2/dt = B21N2 u(v).
• Spontaneous emission rate: dN2/dt =A21N2

Population Inversion

• To obtain intensity amplification, population inversion (N2>N1) is required.
• N1 > N2:
  • Intensity decreases.
  • Light absorption.
  • Absorption > stimulated emission.
• N1 < N2:
  • Intensity amplification.
  • Absorption < stimulated emission.

Pumping Mechanisms

• Electrons usually occupy the lowest energy levels

• Needs non- thermal energy to obtain Population inversion- i.e N2 can never reach N1

• Pumping occurs using:

  • Optical pumping: incoherent or coherent light source
  • Collisions: collisions occur with other particles, example :electron or ions
  • Chemical pump: Energy comes from a chemical reaction.

• Pumping Types:

  • Electric discharge: used in gas lasers.
  • Electric current: semiconductors.

• Not necessary between E1 and E2: Non-radiative transitions

• Maxwell- Botzmann distribution:
  $N<em>2/N</em>1 = e^{(E<em>2-E</em>1)/k_B T}$

Laser Cavity and Properties

Laser Cavity Functions

• Increase intensity in gain medium
• Determine temporal and spatial properties of light.
• Select specific frequencies fn (cavity modes)
• Classifications based on number+ shape of mirrors:
• Stimulated emission> spontaneous emission

Resonator Stability

• Stable resonator: beam remains in the system.
• Unstable Resonator: The rays diverge, leaving the cavitiy
• Concave mirrors R>0
• Convex mirrors R<0

Cavity Modes

• The empty cavity modes (𝑓𝑛 ) must fulfill:
• Mode separation:
  $\Delta f = \frac{c}{2L}$
• Modes have a spectral width $\delta f$, which depends on the fineness of the cavity:
  $\delta f= \frac{c}{2 L F}$
• $n \lambda<em>n = 2L ,n = 1,2,3…$$f</em>n=\frac{nc}{2L}$ , n = 1 ,2,3…

Modal Selection

• Improves laser performance.
• Prisms can select longitudinal modes of the cavity.
• Mirror tilt selection of optical path way.

Transverse Beam Structure

• The beam broadens with z while the amplitude decreases.
• The Gaussian mode is common
• Divergence is determined by lambda, amplitude , and the diameter.
• Beam diameter depending on z :
  $d(z)=d<em>0 \sqrt{1+(z/z</em>F)^2}$
• Rayleigh distance:
  $z<em>F= \frac{\pi d</em>0^2}{\lambda}$
• and divergence:
  $\theta=\frac{\lambda}{\pi d_0}$

Transverse Laser Structure

• Each longitudinal mode has associated transverse modes.
• Modes have different gains as they do not have one sole structure.
• Symmetry
  • Laguerre-Gauss: Cylindrical symmetry
  • Hermite-Gauss: Rectangular Symmetry

Temporal Control

• Pulsed Pumping: ~10^-3s
• Q- Switching, Q - Locking: ~10^-9s
• Mode Locking, M - Locking: ~10^-12s
• Chirped pulse amplification: ~10^-15

Mode-Locking

• Locking longitudinal modes gives the interference leads to pulses.
• Shorter pulses with shorted modes.
• Temporal graph and peaks for amplitude and intensity

Chirped Pulse Amplification

• The medium does not give the medium more energy and cavity cannot stand anymore radiation.
• Shooting the pulses outside the cavity laser

Types of Lasers

Gas Lasers

• Common, cheap, easy to cool.
  • He-Ne (543 nm and 633 nm).
  • Argon (458 nm, 488 nm or 514.5 nm).
  • CO2 (9.6 µm and 10.6 µm) up to 100 kW, N2 (337 nm), CO, metal vapor lasers.

Chemical Lasers

• Active medium pumped with energy from chemical reactions.
  • oxygen iodide (1,315 nm)
  • hydrogen fluoride (2,700-2,900 nm)
  • deuterium fluoride (3,800 nm)

Solid State Lasers

• The first laser, Ruby laser, was of this type.
  • Nd: YAG (1,064 nm, frequency can be doubled to 532 nm) which can also be doped with erbium, tellurium, holmium.
  • Other: Yb: YAG, Yb: KGW, Yb: KYW, Yb: SYS, Yb: BOYS or Yb: CaF2 (around 1,020-1,050 nm). Yb: YAG can reach high powers in ultrashort pulses.
  • Ti: sapphire, highly tunable, used in spectroscopy.
  • Erbium-doped fiber laser, used in telecommunications.
  • Semiconductor lasers use electronic transitions in a semiconductor diode. Laser diodes (between 405 nm and 1,550 nm).
  • Applications: CD and DVD players, VECSEL barcode readers, VCSEL external cavity and vertical emission lasers.

Excimer Lasers

• Gas lasers with use molecules in excited states:
  • F2 (157 nm)
  • ArF (193 nm), KrCl (222 nm)
  • KrF (248 nm)
  • XeCl (308 nm)
  • XeF (351 nm).

Dye Lasers

• Use an organic dye as active medium, highly tunable.
  • Examples include 6G rhodamine, fluorescein, coumarin, stilbene, umbelliferone, tetracene or malachite green.

Free Electron Lasers

• electons are deaccelerated electrons, confined by magnetic fields.

Laser Systems for Processing

• Type and their corresponding Quantum and Wall plug efficiency
  • CO2 (10.6 \mu m) : Quantum Efficiency 45% ,wall plug 15%
  • Solid State Laser (Nd:Yag) (1.06 \mu m) : Quantum Efficiency 40% ,wall plug 4%
  • Diode Pumping (1.06 \mu m) : Quantum Efficiency 40% ,wall plug 25%
  • Semiconductor (0.75-0.85 \mu m) : Quantum Efficiency 80% ,wall plug 60%
  • Fiber Laser (1.8 - 2.7 \mu m) : Quantum Efficiency 100% ,wall plug 50%
  • Excimer (0.248 \mu m) : Quantum Efficiency 80% ,wall plug 0.5-5%
• Quantum Efficiency: fraction of absorbed pump photons contributing to population of upper laser level
• Wall plug Efficiency: total electrical-to optical power efficiency, including losses in power supply and cooling system

Historical Overview of Lasers

• Presents a timeline from 1960 (Ruby laser discovery) to 1993 (Gallium nitride laser commercialization).
• Lists laser types, wavelengths, and common applications.

Characteristics of Laser Transitions

• Compares Single Mode to MultiMode transitions
• Details characteristics for various mediums(gas, solid, liquid and plasma).
• Parameters include overall efficiency range ,output energy and pulsed/ CW measure

Gas Lasers

CO2 Lasers

• Gas,Energy levels vibrational and rotational states
• Pumped by electrical discharge. Has configurations regarding the gas cooling system.
• Industrial applications,sking resurfacing due to reasonable laser cost.
  ### Pulsed UV source:
• Tens of ns with around tens of MW(Around 1J of energy for pulse)
• Excimer “Excited dimer”(45 -50kV Pump)
• Energy Levels:ionic bound/ground state
• Applications:nucelar/Eye Srgery

Solid State Lasers (SSL)

• Medium insulating or cristal
• Energy Level: doping or transitions of ions (Neobite, YI, Aluminium)
• Pumping types: titanium saphire
• Applications: Industrial/Research

Fiber Lasers

• Uses fibre core
• Energy Level: electronic energy of doping
• Pump: Diode
• Welding and cutting is increased as it is coupled

Semiconductor Lasers

• Most common: Nd: YAG (rod laser).
• Pumped by Diode (DPSSL)
• High efficiency and power(100- 10kW), and low service life.