Optical Properties of Solids Optical materials Non linear optical materials play an important 丽 Laser role in data transmission and storage T Non linear optical properties LiNbO, KTiOPO, KH,PO 重 Photoluminescence T Laser materials semiconductors and laser host crystals e Phosphors for displays and imaging Interactions between photons and materials When Light Meets a Solid ic and Electronic Interactions o Total intensity equals electron cloud induces electronic polarization ● Transmitted nergy lost in absorption .Absorbed slows light down (seen as refraction .Reflected eLectron Transitions-electrons excited to higher unoccupied states QT+A+RE I cannot remain there indefinitely =Emission .(fraction transmitted, absorbed and optical characteristics of a material relate to the sorption and emission of electromagnetic radiation Optical Properties of Semiconductors Classes of Optical Materials otion Materials are often characterized by what happens to ligh atransparent ostly transmitted transmitted diffusely Copaque no transmission 4shiny-mostly reflected a longest wavelength absorption to promote e corresponds to E T Eg is energy between"HOMO"of valence band and LUMO" of conduction band
1 Optical Properties of Solids Laser Non-linear optical properties Photoluminescence Optical Materials Non-linear optical materials play an important role in data transmission and storage LiNbO3 , KTiOPO4 , KH2PO4 Laser materials semiconductors and laser host crystals Phosphors for displays and imaging Interactions Between Photons and Materials Atomic and Electronic Interactions Electronic Polarization ¾ interaction with electron cloud induces electronic polarizationÞ energy lost in absorption slows light down (seen as refraction) Electron Transitions ¾ electrons excited to higher unoccupied statesÞ cannot remain there indefinitely ÞEmission optical characteristics of a material relate to the absorption and emission of electromagnetic radiation When Light Meets a Solid… . Total intensity equals: Transmitted Absorbed Reflected T+A+R = 1 (fraction transmitted, absorbed and reflected = 1) Classes of Optical Materials Materials are often characterized by what happens to light transparent ¾¾ mostly transmitted translucent ¾¾ transmitted diffusely opaque ¾¾ no transmission shiny ¾¾ mostly reflected Optical Properties of Semiconductors Absorption Eg longest wavelength absorption to promote ecorresponds to Eg Eg is energy between “HOMO ”of valence band and “LUMO”of conduction band Emission Eg
Optical Properties Band Structure Electrochromic WO. Thin Films for Smart windows sCattering at an interface between two materials e Electrochromic Eilm different n (index of refraction) mUltilayer stacks that behave like batteries ◆ Absorption eVisible indication of their electrical charge eLectron excitation to defect levels in the band eFully charged: opaque aPartially charged: partially transparent .Electron excitation across the band gap sFully discharged; transparent empty empty rechargeable solid state Metal catalyst,… Electrochromic glass Why the Color Change? Electrochromic glas CB Iws(d咧 ating a electrochromic layer which changes color from (d) smission into the building. When there is little sunlight he glass brightens, so that the need for the artificial light is wo, M+e/?Mwo, e -+ey i wo, Wide band Narrow band gap Metallic W6++ Wi+ CO ORS in Solid Materials Impurities in Ceramics oCO ORS cOlor is the result of the combination of 刽 a Ruby, sapphire, topaz, wavelengths that are transmitted ure form electrons drop back into original positions e AT within the band gap leads to color very pure single crystal colorless add Cr, O, to ALOs will become deep red. RUBY
2 Optical Properties & Band Structure Reflection Scattering at an interface between two materials with different n (index of refraction) Absorption Electron excitation to defect levels in the band gap Electron excitation across the band gap Metal filled empty Insulator filled empty filled empty Semiconductor Valence Band Conduction Band Electrochromic WO3 Thin Films for Smart Windows Uses: mirrors, displays, rechargeable solid state batteries, pH-sensitive electrochemical transistors or displays, chemical sensors, solar cells, selective oxidation catalyst, … e- into Conducting Bond of WVIO3 M+ into hole Electrochromic Film: Multilayer stacks that behave like batteries Visible indication of their electrical charge Fully charged: opaque Partially charged: partially transparent Fully discharged: transparent Electrochromic glass is an energy-saving component for buildings that can change color on command. It works by passing low-voltage electrical charges across a microscopically-thin coating on the glass surface, activating a electrochromic layer which changes color from clear to dark. The electric current can be activated manually or by sensors which react to light intensity. Glass darkening reduces solar transmission into the building. When there is little sunlight, the glass brightens, so that the need for the artificial light is minimized. Electrochromic Glass OFF ON Why the Color Change? WO3 Wide band gap insulator MxWO3 Narrow band gap semiconductor x(M+ + e- ) MxWO3 Metallic x(M+ + e- ) VB [O2- (2pp)] CB [W6+(d0)] Localized VB [W5+(d1)] Delocalized VB [W5+(d1)] W5+ + W6+ ® W6+ + W5+ COLORS in Solid Materials COLORS! Color is the result of the combination of wavelengths that are transmitted Absorbed radiation can be reemitted as excited electrons drop back into original positions Þ not necessarily the same frequency as that absorbed Specific impurities can introduce electron levels within the band-gap - leads to color e.g. Al2O3 - very pure - single crystal - colorless add Cr2O3 to Al2O3 will become deep red - RUBY Impurities in Ceramics Corundum:Al2O3 Ruby, sapphire, topaz, amethyst Colorless in pure form Impurities result in different colors
In Opacity and Translucency Visible light would normally transmit completely, but impurities can yield color Most ceramics are insulators ( Large Eg Why are they usually opaque and white? E>3.1ev Why Are Most Ceramics Opaque? Why are Metals Shiny? d transmittance gRain boundarie Metals e=oev nisotropic n(different grains at different All light with n above X-ray wavelengths absorbed by Light is reemitted with exact energy of absorption as aboth refraction and reflection occur electrons fall back into lowest state. Metals appear tWo phase materials cause scattering reflective as the light we see is reemitted. When there is a difference in n, the greater the difference, the greater the scattering e.g. porosity is very effective in scattering light When particles are about the averag wavelength of visible light, all light wavelengths absorption emIssion are refracted, yielding a whitish, op Applications of Optical Phenomena Applications of Optical Phenomena o Luminescence o Materials which are capable of absorbing energy la ser n (light, heat, electron beam) then re"emitting a device that utilizes the natural oscillations visible light o Time of delay between absorption of energy and of atoms or molecules between energy levels for generating coherent electromagnetic s fluorescence (less than one second) radiation usually in the ultraviolet, visible, or e phosphorescence(greater than a Television O LEDs light)a(mplification by)s(timulated)e(mission of radiation
3 Impurities ß Visible light would normally transmit completely, but impurities can yield color Eg > 3.1 eV Opacity and Translucency ß Most ceramics are insulators (Large Eg ) ¾ Why are they usually opaque and white? Why Are Most Ceramics Opaque? ¾¾ Internal reflectance and transmittance Grain boundaries anisotropic n (different grains at different orientations) both refraction and reflection occur Two phase materials cause scattering when there is a difference in n, the greater the difference, the greater the scattering e.g. porosity is very effective in scattering light When particles are about the average wavelength of visible light, all light wavelengths are refracted, yielding a whitish, opaque color. Why are Metals Shiny? Metals Eg = 0 eV All light with l above X-ray wavelengths absorbed by continuous unoccupied states above Ef . Light is reemitted with exact energy of absorption as electrons fall back into lowest state. Metals appear reflective as the light we see is reemitted. absorption emission Ef Applications of Optical Phenomena Luminescence Materials which are capable of absorbing energy (light, heat, electron beam) then re-emitting visible light Time of delay between absorption of energy and reemission varies fluorescence (less than one second) phosphorescence (greater than one second) Television! LED’s la·ser n. a device that utilizes the natural oscillations of atoms or molecules between energy levels for generating coherent electromagnetic radiation usually in the ultraviolet, visible, or infrared regions of the spectrum l(ight) a(mplification by) s(timulated) e(mission of) r(adiation) Applications of Optical Phenomena
cLaser-"Light Amplification by The First Ruby laser Stimulated Emission of Radiation NCoherent, high intensity light beams cElectron transitions are initiated by an external stimulus (as opposed to spontaneous emission) .g. Ruby laser(Ruby 05%Cr,O The ruby laser is the first type of aCr provides electrons states for single laser actually constructed, first demonstrated in 1960 by T.H. Maiman. It is the symbol of naIssance o of laser techniques. Lasers: Light Amplification by Typical Setup of a Laser Stimulated emission of radiation Optical lification Output coupling The light from a typical laser emerges in an extremely thin nost pendular Optical Pump process more photons at the same wavelength If the light is the htest bit off axis. it will be lost from the beam Shedding Some Light Shedding Some Light How the Laser Works How the laser works cont kashItu emit photons Partially Reflective Mirror Atoms become excited matic, single-phase, columnated The flash tube fires light at the ruby rod. The light excites the ruby through the half-silvered mi the atoms laser light
4 Laser¾¾“Light Amplification by Stimulated Emission of Radiation” Coherent, high intensity light beams Electron transitions are initiated by an external stimulus (as opposed to spontaneous emission) e.g. Ruby laser (Ruby is 0.05%Cr2O3 in Al2O3 ) Cr provides electrons states for single wavelength emission The First Ruby Laser The ruby laser is the first type of laser actually constructed, first demonstrated in 1960 by T. H. Maiman. It is the symbol of naissance of laser techniques. Typical Setup of a Laser Pump process Optical feedback Optical feedback Output coupling Optical amplification (Optical gain) The light from a typical laser emerges in an extremely thin beam with very little divergence. The high degree of collimation arises from the fact that the cavity of the laser has very nearly parallel front and back mirrors which constrain the final laser beam to a path which is perpendicular to those mirrors. The back mirror is made almost perfectly reflecting while the front mirror is about 99% reflecting, letting out about 1% of the beam. This 1% is the output beam which you see. But the light has passed back and forth between the mirrors many times in order to gain intensity by the stimulated emission of more photons at the same wavelength. If the light is the slightest bit off axis, it will be lost from the beam. Lasers: Light Amplification by Stimulated Emission of Radiation Shedding Some Light How the Laser Works The flash tube fires light at the ruby rod. The light excites The laser in it’s non-lasing state the atoms. Flash Tube Partially Reflective Mirror Mirrored Surface Atoms become excited Emitted Light Some of these atoms emit photons. Shedding Some Light How the Laser Works Cont. Some of these photons run in a direction parallel to the ruby's axis, so they bounce back and forth off the mirrors. As they pass through the crystal, they stimulate emission in other atoms. Monochromatic, single-phase, columnated light leaves the ruby through the half-silvered mirror ¾ laser light!
LI Flashes of brilliance developed long before its applications years ago Arthur Schawlow and Charles A splendid light has dawned on me he widespread applications it would have in a variety dustries. The impact of this invention is usually not In 1917 Einstein published ideas on stimulated emission of radiation. These ideas laid the basic foundation for the ating w futuristic idea depicted in Hollywood me Most people don't recognize that laser is now known as the photoelectric effect, Einstein noted a echnology is already present as an integral part of our statistical tendency which caused photons(particles of daily lives allowing us to listen to cds. watch dvd's. and er. In additio lay computer games. Additionally, lasers are becoming creasingly visible in medicine in ophthalmologic, hotons stimulated other atoms to emit more photons cosmetic, and general surgery. Einstein was also able to prove that these emitted photons all traveled in the same direction and with the same frequency as the original photon. Flashes of brilliance Lasers eOne important application of semiconductor devices is in lasers which are intense sources of 品 invented in 1958 by Charles H ingle frequency electromagnetic radiation and Arthur L rs exploit an important process known as stimulated emission in which the emission of AL Schawlow erm"laser with help from his CH Tow a photon at a given frequency stimulates the differentiating factor between emission of other photons at the same the two devices is that th frequency aser uses light waves as o an important property of stimulated opposed to the microwave emission is that the resulting photons emitted utilized by the maser. in this process form a highly coherent bea Laser= Einstein Right type+ Reflecting An example of stimulated emission Ruby laser tion between two levels in an atom The ruby laser is the first type of laser actu onstructed. first demonstrated in 1960 by T H. Maiman actly the energy difference of the two levels stimulates the electron in caracteristic pink or red color by absorbing green and blue the higher energy state to undergo a ruby laser is used as a pulsed laser, producing red energy, twe Aft otons are emitted in this process flash tube, the laser light emerge the excited and these photons are highly atoms persist in the ruby rod, whicl the photons may be used to induce stimulated emission between the e two levels
5 The laser is an example of a technology that was developed long before its applications were ever imagined. Forty-five years ago Arthur Schawlow and Charles Townes could have had no possible way of knowing the profound effects this technology would have on society or the widespread applications it would have in a variety of industries. The impact of this invention is usually not realized because many consider laser technology a futuristic idea depicted in Hollywood movies or science fiction books. Most people don’t recognize that laser technology is already present as an integral part of our daily lives, allowing us to listen to CD’s, watch DVD’s, and play computer games. Additionally, lasers are becoming increasingly visible in medicine in ophthalmologic, cosmetic, and general surgery. Flashes of Brilliance The History of the Laser “A splendid light has dawned on me” –Albert Einstein In 1917 Einstein published ideas on stimulated emission of radiation. These ideas laid the basic foundation for the invention of the laser years later. While investigating what is now known as the photo-electric effect, Einstein noted a statistical tendency which caused photons (particles of light), to want to move together. In addition, emitted photons displayed a sort of snowball effect, once emitted, photons stimulated other atoms to emit more photons. Einstein was also able to prove that these emitted photons all traveled in the same direction and with the same frequency as the original photon. Flashes of Brilliance From Maser to Laser AL Schawlow CH Townes The laser is credited as being invented in 1958 by Charles H. Townes and Arthur L. Schawlow. Townes coined the term “laser”with help from his students. The main differentiating factor between the two devices is that the laser uses light waves as opposed to the microwaves utilized by the maser. Laser = + + Einstein’s Theories Right type of atoms Reflecting Mirrors One important application of semiconductor devices is in lasers which are intense sources of single frequency electromagnetic radiation * lasers exploit an important process known as stimulated emission in which the emission of a photon at a given frequency stimulates the emission of other photons at the same frequency Þ an important property of stimulated emission is that the resulting photons emitted in this process form a highly coherent beam Lasers An example of stimulated emission in an electronic transition between two levels in an atom a photon whose energy matches exactly the energy difference of the two levels stimulates the electron in the higher energy state to undergo a transition to the lower energy state in order to conserve energy, two photons are emitted in this process and these photons are highly coherent the photons may be used to induce stimulated emission between the same two levels in other atoms giving rise to an avalanche effect PHOTON PHOTON PHOTON Ruby Laser The ruby laser is the first type of laser actually constructed, first demonstrated in 1960 by T. H. Maiman. The ruby mineral (corundum) is aluminum oxide with a small amount(about 0.05%) of chromium which gives it its characteristic pink or red color by absorbing green and blue light. The ruby laser is used as a pulsed laser, producing red light at 694.3 nm. After receiving a pumping flash from the flash tube, the laser light emerges for as long as the excited atoms persist in the ruby rod, which is typically about a millisecond
Pumping Levels for Ruby Laser PA pulsed ruby laser was sed for the famous laser ranging experiment which was conducted with a corner reflector non-radiative processes placed on the Moon by the apollo astronauts Metastable This determined the distance to the moon with an accuracy of about cm Neodymium- YAG Laser eAn example of a solid-state laser, the neodymium-YAG uses Nd ion to dope the yttrium garnet (YAG)host he i e common and Helium-Neon Laser elium"neon laser is usually e inversion possible Neodymium-YAG lasers have become very ed at 632.8 nm. It can also be ction in the green at 543.5 laser power at 1065 nm and can achieve extremely nea a high powers in a pulsed mode 1523m e One of the excited levels of cillators for the production of a series of very short pulses fo helium at 20.61 ev is very 20.66 eV. so close in fact that collision of a helium and he transferred from the a Laser Applications Lasers Industry vestigation of of gases, fluids, solids, plasma, The Cutting edge EC (Bose-Einstein condensate), ignition of nuclear fusion, sThe advantages of Laser technology over Precision measurements stantial: The cuts ar future atomic clocks, navigation, geophysics, astrophysics Laser technology has taken the jewe elding, cutting, drilling, surface hardening, from micro to a which ool are iology and medical also highly desirable for this industry diagnosis& therapy (retina, cancer.), DNS-structure,cell nAser welding can be automated for high precision tasks. The very high cutting speed makes it possible Information technology data transmission, optical computing, laser display, optical storage sThe process is cleaner
6 earth A pulsed ruby laser was used for the famous laser ranging experiment which was conducted with a corner reflector placed on the Moon by the Apollo astronauts. This determined the distance to the Moon with an accuracy of about 15 cm. Pumping Levels for Ruby Laser Neodymium-YAG Laser An example of a solid-state laser, the neodymium-YAG uses the Nd3+ ion to dope the yttrium-aluminum-garnet (YAG) host crystal to produce the triplet geometry which makes population inversion possible. Neodymium-YAG lasers have become very important because they can be used to produce high powers. Such lasers have been constructed to produce over a kilowatt of continuous laser power at 1065 nm and can achieve extremely high powers in a pulsed mode. Neodymium-YAG lasers are used in pulse mode in laser oscillators for the production of a series of very short pulses for research with femtosecond time resolution. The most common and Helium-Neon Laser inexpensive gas laser, the helium-neon laser is usually constructed to operate in the red at 632.8 nm. It can also be constructed to produce laser action in the green at 543.5 nm and in the infrared at 1523 nm. One of the excited levels of helium at 20.61 eV is very close to a level in neon at 20.66 eV, so close in fact that upon collision of a helium and a neon atom, the energy can be transferred from the helium to the neon atom. Laser Applications Science investigation of properties of gases, fluids, solids, plasma, BEC (Bose-Einstein condensate), ignition of nuclear fusion, find gravitational waves Precision measurements future atomic clocks, navigation, geophysics, astrophysics Material processing welding, cutting, drilling, surface hardening, from micro to nano Biology and medical diagnosis & therapy (retina, cancer… ), DNS-structure, cellcontent Information technology data transmission, optical computing, laser display, optical storage Lasers & Industry The Cutting Edge The advantages of Laser technology over mechanical processes are substantial: The cuts are more precise and reduce raw material losses. Laser technology has taken the jewelry industry The superior cutting accuracy and precision which have contributed to it’s success as a medical tool are also highly desirable for this industry. Laser welding can be automated for high-precision tasks. The very high cutting speed makes it possible to produce "haute couture" jewelry at industrial prices The process is cleaner
Examples of Laser Applications More Examples Science Communicatio Microchips Energy Medical analvsis monitorin Lasers medicine Lasers medicine What is Laser Surgery? Advantages for the Laser as a Medical Cutting changing the focal point of the eye. Ideally the focal Tool oint is changed so it focuses perfectly on the retina dGreater accuracy of incisions LAsers can be inserted inside the body with little risk or discomfort O Incisions can be guided by computers vou are OThe laser is extremely precise, and can be sighted, the a good eye the . are tuned to work on a micro level, barely visible to ge is focused cus before it hits teretis to focus before it Lasers Entertainment Lasers entertainment The Light and the dark side How a Cd Works One of the most popular applications of laser technology, th Compact Disc Player, marked a revolution in digital video teg e ne the lengths of laser beam to and sound technology. a series of tiny ridges inside a ct disk. The music hich are reflected laser light
7 Examples of Laser Applications Precision Global monitoring Energy Science earth Medical analysis Micro-chips Ranging Communications More Examples Lasers & Medicine Going where no man has gone before Advantages for the Laser as a Medical Cutting Tool qGreater accuracy of incisions qLasers can be inserted inside the body with little risk or discomfort q Incisions can be guided by computers qThe laser is extremely precise, and can be tuned to work on a micro-level, barely visible to the human eye Lasers & Medicine What is Laser Surgery? The goal in laser eye surgery is to reshape the cornea, changing the focal point of the eye. Ideally the focal point is changed so it focuses perfectly on the retina. If you are nearsighted, the image comes into focus before it hits your retina If you are farsighted, the image doesn't come into focus before it hits your retina In a good eye the image is focused on the retina Lasers & Entertainment The Light and the dark side One of the most popular applications of laser technology, the Compact Disc Player, marked a revolution in digital video and sound technology. Lasers & Entertainment How a CD Works The CD Player works by using a laser beam to determine the lengths of a series of tiny ridges inside a compact disk. Inside a CD Player The music is digitally encoded in the ridge lengths which are measured by the reflected laser light
Lasers enabling technology Can You See the light? mechanics: 5$ batteries: 5$ display ete. 5$ electronics: 5$ 5 Ct. laser: enables clean sound and data storage Financial Position of lasers Lasers in Science and Engineering 1950196019701980199020002010 Nonlinear Optical Effect Second harmonic P=EyE (For linear medium) Generation Where e is permitivity of medium and e is electric P=Ex'E+X2E2+XE3+.( For nonlinear Where ]I is linear susceptibility tensor, x 2is quadratic tensor ( 3X3X3 matrix) and x is cubic 961 Franken found the second harmonic generation tensor (cubic matrix with 3X3 matrix at each which generate a new field lattice point)
8 mechanics: 5$ batteries: 5$ display etc. 5$ electronics: 5$ profit:10$ Lasers = enabling technology 5 Ct-laser: enables clean sound and data storage Can You See the Light? Dentists use laser drills Bad eyesight can be corrected by optical surgery using lasers CD-Audio is read by a laser Tattoo removal is done using lasers CD-Rom discs are read by lasers Laser pointers can enhance presentations Bar codes in grocery stores are scanned by lasers Video game systems such as PlayStation 2 utilize lasers DVD players read DVD’s using lasers Airplanes are equipped with laser radar Military and Space aircraft are equipped with laser guns Laser tech. is used in printers, copiers, and scanners Financial Position of Lasers Dow-Jones 0 2 4 6 8 10 1997 1998 1999 2000 2001 manufacturing & medical applications billion $ data storage & telecom 2002 Lasers in Science and Engineering 0 100000 200000 300000 1950 1960 1970 1980 1990 2000 2010 Physics Engineering 1 st laser Number of publications now P = eceE (For linear medium ) Where e is permitivity of medium and ce is electric susceptibility P = e(c1 E + c2 E2 + c3 E3 +… .) (For nonlinear medium) Where c1 is linear susceptibility tensor, c2 is quadratic tensor (3X3X3 matrix) and c3 is cubic tensor (cubic matrix with 3X3 matrix at each lattice point). Nonlinear Optical Effect linear nonlinear P E Second Harmonic Generation 1961 Franken found the second harmonic generation which generate a new field ¾¾ nonlinear optics
Second harmonic generation SHG Experimental Setup Second harmonic Generator of Ba,NaNbso v 694 KDP crvstal Frequency Doubling Tripling etc. Nd-YAG O3 =0,to CO, laser 266m Not all frequencies are generated; phase Nd: YAGi lase matching condition is required 532mm nonlinear Nonlinear Optics such as refractive index, absorption coefficient, etc; Principle of superposition holds! The frequency of light cannot be altered by passing Light cannot interact with light! .At high intensity light nonlinearity phenomena observed! t the interaction (not free space)! P nodified the medium= in turn modify another e Laser beam enters quartz crystal as red light and emerges field or even the original field itself. as blue light(a second order NLO effect: second harmonic generation)
9 Polarizers Lenses w SHG Experimental Setup Second Harmonic Generation KDP crystal Ruby laser w 694 nm 2w 347 nm Ti:Sapphire laser l=700 -920nm tp=100fs Pav=400mW RG-Filter Sample Rotation Table U G-Filter Iris PMT Prism 2w @ 3eV Second Harmonic Generator of Ba2NaNb5O15 Frequency Doubling / Tripling etc. Proustite crystal w3 = w2+w1 0.96 mm Nd3+:YAG 1.06 mm CO2 laser 10. 6 mm Not all frequencies are generated; phase matching condition is required Assumption of linearity of the optical medium Þ Optical properties are independent of light intensity, such as refractive index, absorption coefficient, etc; Principle of superposition holds! The frequency of light cannot be altered by passing through a medium. Light cannot interact with light! At high intensity light Þ nonlinearity phenomena observed! Nonlinearity originates from the interaction of light via the medium only (not free space)! Presence of light modified the medium Þ in turn modify another optical field or even the original field itself. Nonlinear Optics Laser beam enters quartz crystal as red light and emerges as blue light (a second order NLO effect: second harmonic generation)
Nonlinear Optics Produces Why Do Nonlinear-optical Effects Occur? Many Exotic Effects Recall that in normal linea otics, a light wave Sending infrared light into a acts on a molecule, which vibrates rystal yielded this display of its own light wave that interferes with the original green light light wave Emitted wave switch avelength light ever made by process in terms of the molecular energy levels, using Molecular energy levels arrows for the photon energies: Why Do Nonlinearoptical Effects Occur? The invention of lasers led to (Continued) Now, suppose the irradiance is h nat many the lower level fo xcitation. This ibrations at all frequenc ding to all energy differences between popul decade ported about three des ago and the aterials models and synthesis. TI 亚!xw Tod lint New color!!t molecular energy levels Nonlinear Optics Effect and NLO Materials Pulsed laser oscillator where the intensity of the optical wave changes YAG laser consists of a rod of aterials can be used to double the the material which can be pumped by a flash lamp of laser radiation Useful as short at a rate of about 15 Hz. The output consists of an envelope of pulses which can be tuned for be difficult to make short optimization by adjusting the mirrors, adjusting length radiation better for information he prisms to change optical path b Nonlinear optic (NLO) crystals are used for the crystal in the acoustic adjusting the frequency of ther and8 (SHG), tripling(3HG), freque scillator)and mIxing, we from the original laser output
10 Nonlinear Optics Produces Many Exotic Effects Sending infrared light into a crystal yielded this display of green light: Nonlinear optics allows us to change the color of a light beam, to change its shape in space and time, to switch telecommunications systems, and to create the shortest wavelength light ever made by Man. Why Do Nonlinear-optical Effects Occur? Recall that, in normal linear optics, a light wave acts on a molecule, which vibrates and then emits its own light wave that interferes with the original light wave. We can also imagine this process in terms of the molecular energy levels, using arrows for the photon energies: Why Do Nonlinear-optical Effects Occur? (Continued) Now, suppose the irradiance is high enough that many molecules are excited to the higher-energy state. This state can then act as the lower level for additional excitation. This yields vibrations at all frequencies corresponding to all energy differences between populated states. The invention of lasers led to the discovery of interesting nonlinear optical phenomena in inorganic as well as organic materials. Nonlinear optical effects in organic materials were reported about three decades ago and the importance of novel materials was realized through theory models and synthesis. The extraordinary growth and development of NLO materials during the past decade has made photonic technologies an indispensable part of our daily life as we enter the 21st century, the "INFORMATION AGE". Nonlinear Optics Effect and NLO Materials Nonlinear optics describes many interactions where the intensity of the optical wave changes the optical properties of a material. NLO materials can be used to double the frequency of laser radiation ¾¾ Useful as short wavelength. Lasers can be difficult to make short wavelength radiation better for information storage and transmission. Nonlinear optic (NLO) crystals are used for harmonic generation, including frequency doubling (SHG), tripling (3HG), frequency mixing; OPO(Optical Parametric Oscillator) and OPA(Optical Parametric Amplifier). Combining harmonic generation and frequency mixing, we can generate the 4th, 5th, or even 15th harmonics from the original laser output. Pulsed Laser Oscillator The Neodymium-YAG laser consists of a rod of the material which can be pumped by a flash lamp at a rate of about 15 Hz. The output consists of an envelope of pulses which can be tuned for optimization by adjusting the mirrors, adjusting the prisms to change optical pathlength, adjusting the crystal in the acoustic-optic modulator, and adjusting the frequency of the modulator