Chapter 13 : Atomic spectra

1- Bohr's postulates and model of the hydrogen atom: When an electron jumps from a high level to a lower level, it produces radiation in the form of a photon of frequency  and energy h, which is equal to the difference between two levels: h = E₂ - E₁ , E₂ > E₁ 2- The line spectrum of hydrogen consists of 5 series. Each line corresponds to a definite energy difference, frequency and wave length. Leyman UV: (electrons move Down to K ( n = 1) level from higher levels. Balmer visible: (electrons move down to L (n = 2) level from higher levels. Paschen IR (infrared) (electrons move down to M (n = 2) level from higher levels. Bracket IR (infrared) (electrons move down N ( n = 4) level from higher levels. Pfund far IR (electrons move down to O ( n = 5) level from higher levels. 3- The spectrometer is an apparatus used to decompose light to its components (visible and invisible), to obtain a pure spectrum. 4- X-rays are an invisible em radiation of short wave lengths, first discovered by Rontengen (1895). He called them the unknown (X) rays. 5- X- ray diffraction is used in studying the crystalline structure, and also in the industrial and medical applications. 6- Line spectra: Is the spectra of elements which have a discrete nature, occurring at wavelengths characteristic of the element. Or It is the spectrum occurring at specified frequencies and not continuously distributed. 7- The emission spectrum: The spectrum resulting from the transfer of excited atoms from a high level to lower level. 8- Continuous spectrum: consists of all wavelengths in a continuous manner. 9- Absorption spectrum: When white light passes through a certain gas, some wavelengths in the continuous spectrum are missing, these wave lengths are the same as those which appear in the emission spectrum of the gas.

Chapter 14 : Laser

1- Spontaneous emission: It is the emission from one excited atom as it relaxes from a high energy level to a low energy level after its lifetime interval is over and under no external stimulus. 2- Stimulated emission: It is the emission from one excited atom as a result of a collision with an external photon, which has the same energy as the one that caused it to be excited. Photons at the end come out in coherence, i.e. having the same phase, (direction and frequency) 3- Properties of laser beam: a- spectral purity (monochromatic) b- collimation (parallel rays) c- Coherence (same phase and direction) d- Concentration (high intensity and small diameter) 4- Laser Action: : a- The active medium must be in the state of population inversion. b- Emission of radiation of the excited atom through the stimulation emission. c- Amplification of stimulated emission through the resonant cavity. 5- Basic elements of laser: a- an active medium b- a source of energy. c- a resonant cavity. 6- He-Ne laser is a gas laser: in which the active medium is a mixture of helium and neon in ratio 10: 1 7- Laser applications: a- 3D photography (holography) b- Medicine (e.g. treating retinal detachment) c- Communications. d- Military application. e- Industry. f- CD recording. g- Printing. h- Arts and shows