The title page :
Lab#2:Laser spectroscopy
2-The Abstract:
this work shows contemporary results from spectroscopic investigation on aluminium plasma in air and to generate this plasma we use (LIBS) laser induced breakdown spectroscopy which is a peculiar technique for elemental investigation. The experimentally observed line intensities of naturl aliminuim and their corresponding wave length . In this procedure , laser puls are applied for ablation of the sample , resulting in the evaporation and ionization of sample in hot plasma which is finally anatomized by the spectrometer . The elements are specefied by their exclusive spectral signitures . Finally , the result that we optained were compared with (NIST data base) and we found that the sample it is not a pure aluminium but various elements in this sample were found .
3- The introduction :
The purpose of this experiment was to identify the specific element by analysing its spectrum using (LIBS) and comparing the result with (NIST)
Laser is a predominant source of light having phenomenal properties wich are not existed in the typical light sources such as sodium lamps , helium and tungesten lamps .The exclusive property of laser is that its have a small divergence . More over , in laser the phase is constant because the light waves are precisely move together at the same time .
Figure (1)
Figure (2)
The beam of the invesible light spread out wich contrast with laser that have highly collimated feature and high degree of directionality also its beam have the same wavelength
Another unique property of laser is extremely high energy .All these particular features of laser have made it a great gizmo in several applications .
How laser works ?
Laser effect depend on quantum theory .Albert Enstein supposed that an blustery atom would release photons when an electromagnitic wave hit the atom and he called this process (stimulated emission) . Depending to the quantum theory each atom have specific quantized energy levels . At normal situation the electrons take place in the ground state but when light falls on a surface of a material they can be excited and move to the upper levels . The Absorption is the name that this process have .The electrons staying for a very short time and returns back to the ground state , realising a photon ,this process has a different name and called spontaneous emission .
Population inversion and Amplification :
When approporiate situation are generated for the stimulated emission, additional electrons are obliged to give up photons that lunching series of large magnitude of energy and this action is named as amplification by stimulated emission . At normal situation when the material is not excited , the ground level state fulled with electrons more than upper levels . When this situation is reversal so the upper levels have population more than lower one this is called population inversion and this situation is very necessary and very important for laser action .
Designing a laser :
A laser normally have need three elements for its set up :
a) An effictive medium wich their energy levels can be choosy occupied .
b) Pumping source to generate population inversion between seletive levels .
c) A resonant champer involving the effictive medium play a role to stock the emitted radiation and affords feed back to sustain the unity of the radiation .
The major problem in scheming a laser is to generate enough population of electrons in the blustery state .So , a lot of intelligent methods have been developed . The most accepted method to produce stimulation is by sending a powerfull or extreme beam of light from flash lamb over the matter that have a cylindrical rod shape with a propriate gas and so , the perfect substance that can be used to produce laser are crystals and gases under weak presure . The others two important parts that laser design have to include are numbers of two mirrors , one of them its reflectivity 99% and the other having less reflectivity. they are laied at the edg of the laser champer and their main job is to duplicate radiation by reflected it back and forth many times .
Figure
Background :
The first fictitious building block of the laser was Albert Einstein’s 1916 suggest that photons could stimulate emission of similar photons from excited atoms. Rudolf Ladenburg reported indirect demonistration of stimulated emission in 1928. However, physicists of the time called the impact “negative absorption,” and considered it of little practical concern because they supposed Boltzmann population distributions to be the norm, with higher energy states necessarly less populated than lower levels.
After World War II, Willis Lamb, Jr., and R. C. Retherford comprehended that nuclear magnetic resonance could result population inversions and Edward M. Purcell and Robert V. Pound used the effect to monitor stimulated emission of 50-kHz radio waves
In 1951, Charles H. Townes took the next conceptual step, propositioning that stimulated emission at microwave frequencies could fluctuate in a resonant cavity, producing coherent output. In 1954, Townes and his student James Gordon explaned the first microwave maser.
The Laser Race
The race was on to make a laser, but two essential questions staied unanswered: how to excite a population inversion and what to use as an affective plane.. Ali Javan at Bell Labs proposed exciting a gas with an electric discharge, and stabillized on a system in which the discharge excited helium atoms, which transferred energy to the neon atoms that released light. However, experimental advance was slow.
Maiman began investigating ruby because he knew the material well from having constructed a compressed microwave maser using ruby crystals.. Maiman made his own measurements and found that ruby fluorescence actually was quite useful . He also decided that intense lamps emitting white light could lift the chromium atoms in ruby to the excited laser level, and that excitation would be more simple with the bright pulses from a flashlamp.
His ruby laser looks adroitly simple. By sliding a small ruby rod inside the coil of a photographic flashlamp, and enclosing the assembly in a reflective cylinder, he focused intense pump light into the ruby rod. He examined his design on May 16, 1960, by steadlily increasing the voltage applied to the flashlamp until the pulses of red light grew strongly brighter and their time and spectral figures showed the changes expected from a laser.
More Lasers
The ruby laser astonished most other laser scientiest, but it influenced Peter Sorokin and Mirek Stevenson to made their laser from crystals of calcium fluoride doped with uranium, which they had earlier specified as a potential three-level laser system
since only three energy levels are participated in the procedure of stimulated emission .The population inversion can be done by tiggering the Ruby crystal atoms with strong light that come from xenonflash lamp . Thus electrons are moved from the ground state to an upper state. Then they are returned back to level two which is known met stable level . Finally the electrons come back to the ground state meanwhile the operation of stimulated emission
Earlier, Leo F. Johnson and Kurt Nassau of Bell made the first solid state laser by using a calcium-tungstate host .In 1964 Joseph and Legrand explane lasing in Nd-YAG , which would become the commanding solid state laser.
Meanwhile,Elias Snitzer measured emission from shine and flouresced elements and found that neodymium was actually the strongest emitter and his laser basically concedered the first fiber laser
Semiconductor Diode Lasers
As early as 1953, John von Neumann represented an idea for generating stimulated emission in semiconductors, but his proposal was not released until his death. In 1950 Nikolai Basov and Pierre Aigrain made independent proposals. However, they used studies of light emission at p-np-n junctions to set the semiconductor diode laser.
Dye Lasers (Liquid Laser)
In the mid of1960 Another contrivance was the organic dye laser, in which the active medium is a solution containing a dye that fluoresces in the visible or near-IR. Peter Sorokin became concerned in dyes after observing fluorescence while testing them for Q-switching ruby lasers. He and John Lankard produced a laser beam that burned their photographic film by illuminated a dye cell with a ruby laser .
The dye lasers are used especially for implementation were the accuracy of the laser frequency is necessary . either for choosing peculiar frequency that is not possible in the solid states lasers or for studing the special characteristic of a material. Another significant usage of dye laser is for generating short- term optical pulses by a mechanism recognized as mode locking .
Free-Electron Lasers
The free-electron laser was one of the more incredible ideas to appear in the 1970s. In 1971, John M. J. Madey proposed extracting energy from a beam of high-energy electrons by curving their paths back and forth as they passed through an arrangement of magnets with alternating polarity.
In principle, a free-electron laser could produce a powerful laser beam, and use of a storage ring could improve qualification by recycling the electrons frequently through the wiggler.
A considerable benefit of the free- electron laser is that aloudly a mount of output power of the amplitude of a little kilowatts can be gained in the uninterrupted mode ,Although still a quiet of scintiest interest , it presents great guarantee of huge energy implemenation particularly in the medical area .
Chemical laser :
in the seeking of another process to excite material , scientists found that they can used the light created by chemical reaction in laser excitation
the energy that produced as a result of reaction between two or more chemical substances is very high consequently the chemical laser reproduction beam with high energy .
chemical laser is conceivably a very effictive packed equipment .In a common chemical laser an electric bow is used to heat up a mixture of nitrogen and sulphure hexafluoride . This combination is compulsry moved through a group of nozzels . The emission of the laser was gained in the infrared zone ,another example of very strong chemical laser is the hydrogen fluoride .
Method and Equipment:
In this experiment we used (LIBS-6) Laser – Induced Breakdown Spectroscopy Modules from Applied Photonic company .
The following figures are representing the basic component of the LIBS-6 moudle
figure(1)
The LIBS moudles afford the following features:
1-collection of 6 lens arrangement in a circular array and used to collect plasma light .
2-CCd camera which is optional feature that can be exist in some moudles .
3-Gas purge port which may be used to nourishment inert gas to the surface of the sample
4-Moudular sample chamber :
figure(2)
The sample champer is provided with a bread board plate which may be used to faciliate the attachment of a sample holder , also there are a dujsment knob for (x-y-z) direction can be used to make the sample holder movable.
5-Quantel Ultra ICE 450 laser power supply and Interlock Keyswitch :
In (LIBS-6) the power supply and cooling group unit connecting with Interlock Override keyswitch which is used to ignore the laser safety when the module is used in open beam configuration (in this situation the LIBS worling without sample chamber) the electrical connection illustrated in the following digrame:
figure(3)
6- (LIBS-6) also provided with PC unit that used to analyse data ,the following schematic digram shows how the LIBS module is electrically connected .
figure(4)
Experimental Procedure:
1- let the sample take place in the sample champer and cheak if its fit or not by using the camera connected with LIBS.
2-first , click on the programs icon on the disk top .
3-press on the configure parameters and enter the suitable setting .
4-From the icon Acquire background spectrum the system meausre the background .
5-By clicking on Aquire measurment spectrum ,the laser beam will heat the sample and the computer software starting calculate the measurment .
6-The spectrum figure will appear on the screen and from peak identifications icon you can determine all needed informaitions .
7- Finally comparing your result with other result that you can find in (NIST)