modern physics

Slide 1: 

Unit II : Modern Physics Elements of Wave Properties of Particle & Particle Properties of wave, LASER, Spontaneous & Stimulated Emission of radiation, Einstein Coefficient, Ruby Laser, characteristics & Application of Laser

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

Wave Mechanical Atomic Models: 

Erwin Schrodinger in 1926 developed the model which is based on the particle and wave nature of the electron is known as wave mechanical model of the atom. The equation determines the behavior of the wave function that describes the wavelike properties of a subatomic system Means wave model is based on De-Broglies concept of matter wave, according to which any particle in motion associated with a wave whose wave length is given by- λ =h/p= h/mv where h-Plancks constant p-momentum v-velocity m-mass Such a wave is called matter wave Wave Mechanical Atomic Models

Wave Mechanical Atomic Model: 

Wave Mechanical Atomic Model In wave mechanical model, wave nature of electron is considered. When electron wave reach to the boundary of the atom ,they are reflected back, thus forming system of stationary wave with the atom. When wave nature of electron are taken into account, the concept that electron moves round the nucleus in definite orbit does not hold good.The position of an electron in the atom at any instant can not be determine with certainty. Therefore in wave mechanics we talk in terms of probabilities. The probability of finding the electron in the atom does not vanish sharply at any distances from any distance from the nucleus.

Wave Mechanical Atomic Models: 

Wave Mechanical Atomic Models According to stationary wave system charge density remains constant. But in wave mechanical theory “the square of the amplitude of vibration is measure of electron charge density”

Wave Mechanical Atomic Model: 

Wave Mechanical Atomic Model

Wave Mechanical Atomic Model: 

Wave Mechanical Atomic Model Electron Wavelengths and Bohr Orbit Radii The Bohr orbit radius goes up with the square of the principal quantum number n. For orbit n, there are n wavelengths of the electron wave, and these wavelengths are n x the wavelength of orbit n=1.

Wave Mechanical Atomic Model: 

Wave Mechanical Atomic Model

Wave Mechanical Atomic Model: 

Wave Mechanical Atomic Model Visualization of Electron Waves The electron waves for the first three Bohr orbits are visualized here, depicting the waves as meeting a kind of resonance condition so that the continuing waves interfere constructively with each under these conditions. The numbers apply to the hydrogen orbits. Electron waves

Wave Function (ψ): 

Wave Function ( ψ ) Physical Significance The probability that a particle will be found at a given place in space at given instant of time is characterised by the function ψ ( x,y,z,t ) is called the wave function. This function can be either real or complex. According to Born ψψ * = | ψ | 2 represents probability density. If wave function ψ is imaginary, ψψ * becomes a real quantity when ψ is a complex conjugate of ψ . the integral can not be zero because this means that the particle is found no where in a space and which is not possible

WAVE FUNCTION: 

WAVE FUNCTION The wave function which obey above equation is said to be normalized wavefunction .

WAVE PACKETS: 

WAVE PACKETS In wave Mechanics the motion of particle is described by Schrödinger's equation. The value of wave function is large in a region where probability of occurrence of particle is more and ψ is less where probability of occurrence is less.

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

LASER: 

LASER A laser is a device that emits light ( electromagnetic radiation ) through a process of optical amplification based on the stimulated emission of photons . The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation .The emitted laser light is notable for its high degree of spatial and temporal coherence , unattainable using other technologies. Inventor Charles Hard Townes Launch year 1960 Availability Worldwide

Slide 18: 

LASER is an acronym for light amplification by stimulated emission of radiation. Properties / Characteristics of LASER Directionality Monochromaticity Coherence Brightness Power density LASER

Basic Concepts of laser: 

Basic Concepts of laser Laser is depend on following Principles:- 1 Induced Absorption 2 Spontaneous Emission 3 Stimulated Emission 4 Population Inversion 5 Metastable state 6 Pumping

LASER: 

LASER H  =E 2 -E 1 1 Induced Absorption Consider a single free atom in the ground state. It can absorb a photon of energy hv=E 2 -E 1 incident on it and can go to the excited state. This process is called induced Absorption c E 2 E 1

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

LASER: 

LASER Spontaneous Emission:- The excited state of the atom is unstable having very short life time because of the natural tendency of atom to attain lowest energy configuration . Hence atom in exited state immediately return to ground state by emitting photon of energy hv = E 2 -E 1 . This process of emission is called as spontaneous emission. It occurs without the action of external agency

LASER: 

LASER h  =E 2 -E 1 Excited state Emission - Atom E 2 E 1 E 1 E 2

LASER: 

LASER 3 Stimulated Emission:- The emission of radiation by an excited atom can be triggered if photon of same energy is allowed to pass through the excited atom. The excited atom are force to emit another photon of same energy and in phase in former. This process of forced emission of photon caused by the incident electromagnetic wave is called the stimulated emission.

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

LASER: 

LASER h  =E 2 -E 1 E 2 E 1 Excited state Emission E 1 E 2 h  =E 2 -E 1

LASER: 

LASER 4 Population Inversion:- The population inversion means the higher energy state is more populated than the ground state

LASER: 

LASER 5 Metastable state:- The average time for which the atoms can reside in the excited state is known as their life time in that state ,it is nearly 10 -8 sec . For most of the excited states with high energy. However in many systems a number of higher energy state , having sufficiently high energy as compared to ground state exist. In this the atom may remain with an life time of the order of 10 -3 sec . Such a higher energy states with longer life times of excited atoms are called as metastable state

LASER: 

LASER 6 Pumping:- Optical pumping Electric discharge Inelastic atom-atom collision Direct conversion 5 Chemical reaction

Einstein Coefficient: 

Einstein Coefficient Equation N ab = N sp + N st B 12 N 1 Q = A 21 N 2 + B 21 N 2 Q This relation was predicted by Einstein and the coefficient A 21, B 12 and B 21 are hence called the Einstein coefficient

LASER: 

LASER LASER ACTION IN A THREE LEVEL SYSTEM E 2 E 1 E 3 h  13 hv 12 h  12 h  12 Radiationless transitions N 1 N 2 >N 1 N 3

LASER: 

LASER

RUBY LASER: 

RUBY LASER 1Gain medium 2. Laser pumping energy 3. High reflector 4. Output coupler 5. Laser beam

Ruby Laser: 

Ruby Laser

LASER: 

LASER Energy Level Diagram For Ruby Laser E 2 E 1 E 3 h  = 550 nm h  = 649 nm h  Radiationless transitions N 1 N 3 Metastable State N 2 >N 1 Optical Pumping Excited State Amplified Laser Output

LASER: 

LASER Applications of LASER:- 1 Scientific Applications 2 Engineering and Industrial Applications 3 Medical Applications 4 Military Applications

LASER APPLICATION: 

LASER APPLICATION Medicine:- Bloodless surgery, laser healing, surgical treatment, kidney stone treatment, eye treatment, dentistry Industry : Cutting, welding, material heat treatment, marking parts Defense: Marking targets, guiding munitions, missile defense, electro-optical countermeasures (EOCM), alternative to radar, blinding enemy troops. Research: Spectroscopy, laser ablation, laser annealing, laser scattering, laser interferometry , LIDAR, laser capture microdissection

LASER APPLICATIONS: 

LASER APPLICATIONS Product development/commercial: laser printers, CDs, barcode, scanners, thermometers, laser pointers, holograms Laser lighting displays: Laser light shows. Cosmetic skin treatments: acne treatment, cellulite and striae reduction, and hair removal.

Assignment: 

Assignment A. Explain 1 Induced Absorption 2 Spontaneous Emission 3 Stimulated Emission 4 Population Inversion 5 Metastable state 6 Pumping D. What is Laser ? Give its properties. E. State few applications of Laser. What is Laser ? How does it differ from ordinary source of light? Explain the concept of population inversion. What is mean by pumping? Discuss in brief optical pumping.

Assignment: 

Assignment

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

LASER: 

LASER LASER ACTION IN A THREE LEVEL SYSTEM E 2 E 1 E 3 h  13 hv 12 h  12 h  12 Radiationless transitions N 1 N 2 >N 1 N 3

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM

BOHR’S MODEL OF HYDROGEN ATOM: 

BOHR’S MODEL OF HYDROGEN ATOM