Atomic Physics PDF Past Paper

# Unit 26 Atomic Physics ## Teaching Periods: 12 ## Weightage: 8% The "electron cloud" model was proposed by Erwin Schrödinger in 1926, as part of his quantum mechanical theory. Schrödinger's model described the electrons in an atom as a cloud of probability, where the density of the cloud represe...

# Unit 26 Atomic Physics ## Teaching Periods: 12 ## Weightage: 8% The "electron cloud" model was proposed by Erwin Schrödinger in 1926, as part of his quantum mechanical theory. Schrödinger's model described the electrons in an atom as a cloud of probability, where the density of the cloud represents the likelihood of finding an electron within a given region. This replaced the earlier planetary model, which had electrons in fixed orbits. ## In this unit students should be able to: - Describe and explain the origin of different types of optical spectra. - Show an understanding of the existence of discrete electron energy levels in isolated atoms (e.g. atomic hydrogen) and deduce how this leads to spectral lines. - Explain how the uniqueness of the spectra of elements can be used to identify an element. - Describe Bohr's postulates of the Hydrogen atom. - Derive an expression for quantized radii. - Explain the hydrogen atom in terms of energy levels on the basis of the Bohr Model. - Determine the ionization energy and various excitation energies of an atom using energy level diagrams. - Illustrate the significance of the hydrogen spectrum in the development of Bohr's model of the atom. - Derive $ \frac{1}{\lambda} = RH [\frac{1}{n^2_1} - \frac{1}{n^2_2}] $ - Solve problems using $ \frac{1}{\lambda} = RH [\frac{1}{n^2_1} - \frac{1}{n^2_2}] $ - Describe inner shell transitions. - Explain production and characteristics of X-rays based on inner shell transition. - Describe properties and uses of X-rays. - Explain the terms spontaneous emission, stimulated emission, Metastable states, population inversion, and laser action. - Describe the structure and purpose of the main components of a He-Ne gas laser. - Identify the useful properties of laser light and give some examples of their uses. - Identify the measures requirement for safe handling of lasers. # Atomic Spectra: Atomic spectra deal with the spectrum of frequencies of electromagnetic radiation emitted or absorbed by an electron during transitions between different levels of energy within an atom. Electrons present in an atom have discrete and specific energies. There are more energy states in an atom than there are electrons. The rainbows are the most common example of atomic spectra, even if it may seem as a continuous pattern; it has black lines that represent the absorption spectra of the sun. The spectrum is also used in astronomy to identify the composition of stars. ## 26.1.1: Optical Spectra: An optical spectrum is obtained when light passes through a prism or a diffraction-grating. This spectrum can be obtained from the intensity and wavelength of the radiation. The spectra obtained from radiating bodies are called emission spectra and are classified into three types: - **Continuous spectra:** These are emitted by solids, liquids, and dense opaque gases at high temperatures. The spectrum of the sun, or of a black body, is a continuous spectrum. Gases at low pressures emit line spectra. - **Band spectra:** These are associated with similar changes in the molecules under high pressure. - **Line spectra:** These have their origin in the energy changes which take place in the atoms of a gas, while An absorption spectrum is used to analyze the substance, and this spectrum is obtained by passing white light from a continuous source through a gas or a dilute solution of the element being analyzed. The absorption spectrum consists of a series of dark lines superimposed on the continuous spectrum of the light source, as shown in Figure 26.2. ## 26.1.2: Spectral Lines: A line of particular frequency or wavelength emitted or absorbed by atoms is called a spectral line. The four visible lines occur at the wavelengths 656 nm, 486 nm, 434 nm, and 410 nm. The complete set of lines is called the Balmer series. The wavelengths of these lines can be described by the following equation: $ \frac{1}{ \lambda} = RH [\frac{1}{2^2}-\frac{1}{n^2}] ; n = 3,4,5,..... 26.1 $ Where $R_H$ is a constant called the Rydberg constant. The above equation, along with other lines in the spectrum of the hydrogen atom (Lyman, Paschen, Brackett & Pfund Series), is discussed in the following section. ## 26.2.1.3 The spectrum of the hydrogen atom: The shape of the spectrum proposed by Max Planck in 1900, that the energy of a given mode of vibration depended upon its frequency in accordance with the relationship: $E_n = nhv; n = 1,2,3, ..... 26.2$ This relation shows that the energy associated with each frequency for different transitions has the discrete value. ## 26.1.3: Identification of Elements by Uniqueness of Spectra: Each element has its own unique line spectrum, which is referred to as the "fingerprint" of a particular element. The spectra for each element are unique because each element contains different numbers of electrons and different energy levels. The absorption spectrum of an element has many practical applications. For example, various absorption lines observed in the solar spectrum have been used to identify elements in the solar atmosphere. ## 26.2 Bohr's Model and its Postulates: In 1913, Niels Bohr introduced an atomic model to give quantitative determination of frequency emitted during de-excitation of an electron in the Hydrogen atom. The discovery of the electron in the late 19th century marked the beginning of a new era in scientific research, helping physicists understand the structure and nature of atoms. Niels Bohr had a remarkable idea that explained the atom of hydrogen, which consists of a proton and an electron revolving around the nucleus, as shown in Figure 26.3. The following are the postulates of Bohr: **Postulates I:** The electron in a hydrogen atom orbits the nucleus. $F_c = \frac{mv^2}{r} = F = k \times q_1 \times q_2 $ **Postulates II:** The magnitude of the angular momentum *L* of the electron in its orbit is equal to the integral multiple of $ \frac{h}{2\pi} $ $L = n \frac{h}{2\pi} ; n= 1,2,3,4,.......$ where *h* is called Plank's constant and *n* is a positive integer (quantum number). **Postulates III:** Only certain orbits are stable in which electrons are revolving, and these orbits are called stationary states. The atom emits radiation (photon) when the electron makes a transition from a higher energy state ($E_n$) to the lower energy state ($E_p$). $hv = E_n - E_p$ ........ 26.3 where *v* is the frequency of the emitted photon. ## 26.2.2 Bohr's radius: The electron revolving around the nucleus is in uniform circular motion and thus experiences a centripetal force. Here centripetal force is provided by electrostatic force between electron and proton. $F = \frac{mv^2}{r}$ (i) where *V* is the speed of the electron. The magnitude of electrostatic force ($F_e = \frac{kq_1q_2}{r^2} $) between the electron ($q_1 = -e$) and the proton ($q_2 = e$) separated by the orbital radius *r* is given as: $F_e = \frac{ke^2}{r^2}$ (ii) where $k = 9.0 \times 10^9Nm²/C²$ is called Coulomb's constant. The electron can only move in a particular orbit if the above two forces are balanced each other. Comparing equation (i) and (ii): $\frac{ke^2}{r^2} = \frac{mv^2}{r}$ (iii) From Bohr's postulate (2), $L = mvr = n \frac{h}{2\pi} $ Substituting the value of *V* = $ \frac{kem}{nh}$ $r^2 = \frac{kem}{nh} \frac{nh}{2\pi m} $ $r = \frac{n^2ε_0h^2}{\pi me^2}$ $r = r_0n^2$ where $r_0 = 5.29 × 10^{-11}m = 0.53Aº$ is called Bohr's first orbit. As the values of *r* is depending only on the principle quantum number *n*, therefore, the radii have the quantized values as shown in Figure 26.4. $r = r_0n^2$ ........26.4 ## 26.2.3: Orbital Energy of the hydrogen atom: The allowed energy levels and quantitative values of the emission wavelengths of the hydrogen atom can be calculated from the postulates (3) which suggests the qualitative existence of a characteristic discrete emission spectrum and corresponding absorption spectrum for hydrogen. The electron has kinetic energy ($K = \frac{1}{2}mv^2 $) and electric potential energy ($U = \frac{ke^2}{r}$). The total energy will be: $E = K+U$ $E = \frac{1}{2}mv^2 + \frac{ke^2}{r}$ 26.5 Putting the value of $\frac{1}{2}mv^2 = \frac{ke^2}{2r}$ from equation (III) $E = \frac{ke^2}{2r} + \frac{ke^2}{r}$ $E = \frac{ke^2}{2r}$ Substitute the value of r from equation (IV) $E = \frac{me^4}{8ε_0^2h^2} (\frac{1}{n^2})$ (26.6) The numerical value of this energy will be $E_n = \frac{-13.6}{n^2}$ eV (26.7) The energy level diagram (see Figure 26.5) shows the various -excitation levels. ## 26.2.4 Excitation & Ionization Energy: ### Excitation: The process of transferring energy to an atom or molecule, raising it to a higher energy state, often resulting in the emission of photons as it returns to its ground state.. ### Ionization Energy: The minimum energy required to remove an electron from an atom or molecule, resulting in the formation of an ion. From figure 26.5, the energy levels corresponding to various values of n as given in equation En = $ \frac{-13.6}{n^2} $ eV are mentioned. The lowest level for n=1 is the ground state of the hydrogen atom, and higher levels correspond to excited states. The energy for the greatest value of n = ∞ becomes zero, and any energy E = 0 in which the electron and proton are not bound together is called the ionization energy. Therefore, the energy E = 13.6 eV is required to ionize the hydrogen atom. ## 26.2.5 The spectrum of the Hydrogen atom: The electron in a hydrogen atom can jump between quantized energy levels by emitting or absorbing photons for some different values of wavelengths. Any such wavelength is often called a line spectrum, which can be absorption or emission lines. The lines for hydrogen are said to be grouped into series, according to the level at which upward jumps start and downward jumps end. The formula for these series corresponding to the different wavelengths can be obtained from the equation $E = \frac{me^4}{8ε_0^2h^3}(\frac{1}{n^2_1} - \frac{1}{n^2_2})$ The frequency of the photon emitted when the electron makes a transition from an orbit to an inner orbit as stated in postulate -III. $v = \frac{(E_n - E_p)}{h} $ using equation (6) $v = \frac{me^4}{8ε_0^2h^3} (\frac{1}{n^2_1} - \frac{1}{n^2_2})$ To express the above equation in terms of wavelength, it is convenient to use $c = νλ$ $ \frac{1}{ \lambda} = R_H [\frac{1}{n^2_1} - \frac{1}{n^2_2}] $ (26.8) where $ R_H = \frac{me^4}{8ce^2h^3p^2} = 1.097 × 10^7m¯¹$, is called the Rydberg constant. The possible series associated with the different wavelengths can be explained from equation (8). The emission and absorption lines for all possible jumps up from the *n* = 1 level and down to the *n* = 1 level are said to be in the Lyman series. Similarly, other series are illustrated in Figure 26.6. # 26.3 X-rays: These are powerful electromagnetic rays of higher energy and can pass through most objects, including the body. Most of them have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies $3 \times 10^{19} Hz$ to $3 \times 10^{16} Hz$. X-rays are used to generate images of tissues and structures inside the body. ## 26.3.1 Inner Shell Transitions: The passage of an electron from one energy level to another is called an electron transition. Bohr Theory showed that the principal quantum number is used to determine the energy and an orbital radius of an electron. The inner shells, designated *K*, *L*, *M*, etc., correspond to 1, 2, 3, respectively, with the *K* shell having the greatest binding energy and being closest to the nucleus. The other quantum numbers have a relatively small effect on energy and cause the shells (other than the *K* shell) to be split into subshells. When the transition of electrons from the outer shell to the inner shell occurred, the electromagnetic radiation corresponding to the characteristic energy generated as shown in Figure: 26.7. ## 26.3.2 Production and characteristics of X-rays: In 1895, Roentgen found that some photographic plates, kept carefully wrapped in his laboratory, had become fogged. Instead of merely throwing them aside, he set out to find the cause of the fogging. He traced it to a gas-discharge tube, which he was using with a low pressure and high voltage. This tube appeared to emit a radiation that could penetrate paper, wood, glass, rubber, and even aluminum a centimeter and a half thick. Roentgen could not find out whether the radiation was a stream of particles or a train of waves (Newton had the same difficulty with light and he decided to call it X-rays). X-rays as electromagnetic waves, but of much shorter wavelength: about 0.1 nm to 10 nm. They are produced when fast electrons, or cathode rays, strike a target. In a modern X-ray tube, there is no gas, or as little as high-vacuum technique can achieve: the pressure is about 10⁻⁵ mm Hg. The electrons are provided by thermionic emission from a white-hot tungsten filament. In Fig. 26.8, *F* is the filament, and *T* is the target, or anode. Because there is so little gas, the electrons on their way to the anode do not lose any noticeable amount of their energy in ionizing atoms. From the a.c. supply, transformers provide about 10 volts (L.T) for heating the filament, and about 100 kV (H.T) for accelerating the electrons. On the half cycles when the target is positive, the electrons bombard it, and generate X-rays. On the half-cycles when the target is negative, nothing happens at all there is too little gas in the tube for it to break down. Thus the tube acts, in effect, as its own rectifier, providing pulses of direct current between target and filament. The heat generated at the target by the electronic bombardment is so enormous that the target must be cooled artificially. In an X-ray tube, very energetic electrons bombard on the atoms in a metal target, the atom will be left in an excited state with a hole in the electron shell. This process is illustrated in Fig. 26.7, for inner shell transition. When this hole is filled by an electron from an outer shell, an x-ray photon with energy equal to the difference in the electron energy levels is produced. The energy of the x-ray photon is characteristic of the target metal. The different characteristic lines occurred due to the electron transitions between different energy levels, as shown in figure 26.9. Electron transitions in an atom, which produce the *Kα*, *Kp*, and *Lα* characteristic x-rays. ## 26.3.3 Properties and Uses of X-rays: When X-rays strike some minerals, such as zinc sulphide, they make them fluoresce. If a human body part is placed between an X-ray tube and a fluorescent screen, the shadows of its bones can be seen on the screen because they absorb X-rays more than flesh does. Unusual objects, such as swallowed safety-pins, if they are dense enough, can also be located. X-ray photographs can likewise be taken with the plate in place of the screen. In this way, cracks and flaws can be detected in metal castings. The characteristic lines are most useful in X-ray diffraction for studying the crystallographic structures. # 26.4.1 LASER [Light Amplification by Stimulated Emission of Radiation]: The electromagnetic waves experienced in daily life, ranging from the sun, stars, incandescent and fluorescent Lamps, are emitted from atoms or molecules spontaneously. Ordinary natural and artificial, light is released by energy changes on the atomic and molecular level that occur without any outside interference. A second type of light exists, when an atom or molecule retains its excess energy until stimulated or induced to emit the energy in the form of light. Lasers are designed to produce and amplify this stimulated form of light into intense and focused beams. Compared to conventional sources of ordinary light, the light from a laser is quite intense, monochromatic, and emitted in a unidirectional beam limited by diffraction. The special nature of laser light has made laser technology a vital tool in nearly every aspect of everyday life, including communications, entertainment, manufacturing, and medicine. ### Stimulated or Induced Absorption: When an atom absorbs photons of energy *hv* = *E2* - *E1* incident on it, in its ground state, the atom reaches in one of its allowed states excited state. When an atom induced by the photon (energy packet) and do transition to one of its allowed states (excited state) is called Stimulated or induced absorption. The life time of an atom in an excited state is 10-8 seconds as shown in Figure 26.10. ### Spontaneous Emission: The process of photon emission by an excited atom with no external influences is called spontaneous emission. In excited state the life time of an atom is too short therefore, a probability that the atom in the excited state $E_2$ will go back to the lower state $E_1$ by spontaneously emitting the absorbed radiation (E=hv) is very high. The emitted radiation is incoherent to the induced energy photon, as shown in Figure 26.11. ### Stimulated Emission: In this process, if the atom in an excited state $E_2$, the action of external radiation with a frequency *hv* = *E2-E1*, forced (induced, stimulated) a transition to the ground state with the emission of one photon with the same energy. Radiation, which occurs as a result of external exposure, is called induced or stimulated. In the stimulated emission two photons are involved: the primary photon, causing the emission of radiation by an excited atom, and the secondary photon emitted by the atom. These two identical photons will be exactly in phase and coherent. If a cascade of stimulated or induced emission occurs, the number of identical photons increases, the light amplification in the acronym laser. The beam is coherent because all photons are in phase, the beam is monochromatic because the photons all have the same wavelength, and the beam is parallel because the photons all move in the same direction, as shown in Figure 26.12. ### Metastable States and Population Inversion: Population inversion is a key to produce laser light. The process of achieving a greater population in a higher energy state compared to a lower energy state. The population inversion is required for laser operation. Population inversion cannot be achieved in a two-energy level system, at normal conditions; the number of electrons in the lower energy state (*E1*) is always greater as compared to the number of electrons in the higher energy state (*E2*). ### Metastable States: Consider a system consisting of three energy levels *E1*, *E2*, *E3*. We assume that the energy level of *E1* is less than *E2* and *E3*, the energy level of *E2* is greater than *E1* and less than *E3*, and the energy level of *E3* is greater than *E1* and *E2*. The energy level *E2* is sometimes referred to as Metastable state having a life time of $10^3$ seconds. When we supply light energy, which is equal to the energy difference of *E3* and *E1*, the electrons in the lower energy state (*E1*) gains sufficient energy, and jumps into the higher energy state (*E3*). This process of supplying energy is called optical pumping as shown in Figure 26.13. We also use other methods to excite ground state electrons, such as electric discharge and chemical reactions. The flow of electrons from *E1* to *E3* is called the pump transition. Because of the shorter lifetime, only a small number of electrons accumulate in the energy state *E3*. The electrons undergo a radiation-less transition from *E3* to *E2*. In the Metastable state *E2* the electrons will remain there for longer because of its longer lifetime. Hence, the number of electrons coming in the state *E2* is greater than the number of electrons leaving out. As a result, a large number of electrons accumulate in the Metastable state. After the population inversion is achieved, the Metastable state *E2* is exposed to a beam of photons which causes induced (stimulated emission). The whole process for population inversion is shown in Figure 26.14 for three level systems. # 26.4.2 He-Ne Gas Laser: The helium-neon laser was the first continuous-wave (CW) laser ever constructed. It was built in 1961 by Ali Javan, Bennett, and Herriott at Bell Telephone Laboratories. He-Ne lasers are commonly used in school laboratories and in older barcode readers. The schematic diagram of He-Ne laser is shown in Figure 26.15. ### Helium-neon laser construction: The helium-neon laser consists of three essential components: - **Pump Source (high voltage power supply):** The pump energy of the laser is provided by an electrical discharge of several hundred volts between an anode and cathode at each end of the glass tube. A current of 5 to 100 mA is typical for laser operation. - **Gain Medium (laser glass tube or discharge glass tube):** Figure 26.15 shows a gas discharge tube containing a low-pressure mixture of helium-neon in a ratio between 5:1 and 20:1 bound in a glass tube. The partial pressure of helium is 1 mbar whereas that of neon is 0.1 mbar. - **Resonating Cavity:** The glass tube (containing a mixture of helium and neon gas) is placed between two parallel mirrors. These two mirrors are silvered or optically coated. Each mirror is silvered differently. The left side mirror is partially silvered and is known as output coupler whereas the right side mirror is fully silvered and is known as the high reflector or fully reflecting mirror. The fully silvered mirror will completely reflect the light, whereas the partially silvered mirror will reflect most part of the light but allows some part of the light to produce the laser beam. ### Laser Operation: This electrical excitation raises the helium atom into a meta-stable state with energy 20.61 eV above the ground state. Neon has a meta-stable state with energy 20.66 eV above its ground state. Collision of the excited helium atoms with the ground-state neon atoms results in a transfer of energy to the neon atoms, exciting neon electrons. The difference between the energy states of the two atoms is in the order of 0.05eV, which is supplied by kinetic energy. The number of neon atoms in the excited states builds up as further collisions between helium and neon atoms occur, causing a population inversion. Spontaneous and stimulated emission results in emission of 632.82 nm wavelength light. ## 26.4.3 Properties and Uses of Lasers: The properties of laser light are very strange as compared to conventional light. The factors that make laser light prominent are: Monochromatic, Highly Intense or Brightness, Coherence, and Directionality. - **Monochromatic:** A single color or wavelength light is called monochromatic. The light emitted from ordinary light sources has different wavelengths, or colors. However, laser light has a single wavelength or color. - **Highly Intense or Brightness:** The characteristics of coherence and directionality of the laser makes laser light highly intense as compared to conventional light. It is the power emitted per unit surface area per unit solid angle. A one milli watt He-Ne laser is more intense than the sun intensity. - **Coherence:** Two or more waves of same frequency are said to be coherent in nature if they have a constant phase difference. A predictable correlation of the amplitude and phase at any one point with another point is called coherence. In laser light, the property of coherence occurs between any two or more light waves. Where as in conventional light, the property of coherence exhibits between a source and its virtual source. - **Directionality or Divergence:** The light ray coming from the laser light travels in a single direction, while ordinary light travels in all directions. For example, on travelling a distance of 1 Km the torch light spreads 1 km distance. But the laser light spreads only few centimeters distance, even if it travels lacks a kilometer distance. ### Uses of Lasers: - **Tools:** Cutting tools are typically precise, and also simple to automate. They do not require sharpening unlike that of knives. Robot-guided lasers are widely used for the cutting of pieces of cloth. Laser tools are used in corneal surgery, restoring a detached retina of an eye, and removing kidney stones. - **Communication:** Lasers are used in Barcode scanners to convert a printed barcode into a number. A semiconductor laser beam helps to convert the printed pattern of data into numbers in a CD/DVD. In photonics, lasers are used in fiber optic cables. - **Defense:** In defense field, the military employs laser-guided guns and missiles. Laser range-finders use high-resolution scanning to find the distance and speed from an object that is located beyond the point-blind range. - **Medicine:** In medicine, the laser beam is used as part of phototherapy for many procedures. The development of laser technology in recent decades has enabled the creation of a new field of medicine called laser surgery. Lasers have uses in dermatology, ophthalmology, urology, rheumatology and dentistry. - **Holography:** Holography is a true three-dimensional image recording on film by lasers. Holograms are used for amusement, decoration on novelty items and magazine covers. ## 26.4.3 Safe Handling of Lasers: Lasers come in various shapes and forms. They have many uses in teaching, research, manufacturing, medicine, dentistry, communications, and shop checkouts and most commonly at work in the office. In fact, some applications are so well engineered that users are not even aware that the equipment contains a laser. ### Laser beam hazards: The health effects that could occur due to exposure to a laser beam are damage to the skin and eyes. Skin effects include erythema, elastosis (photoageing), and immediate pigment darkening (tanning), burns, and skin cancer. Eye effects include photokeratitis, photoconjunctivitis, cataracts, photoretinal damage and burns. The nature of safety measures which are generally taken to avoid the hazards or damages caused by lasers are adopted and procedure according to the use and intensity of the laser. Following are some general safety protocols which have to be taken into consideration while working with lasers. - Only trained, authorized personnel may operate lasers. Authorization is received from the authorized laser user and the Laser Safety Officer. - NEVER put yourself into any position where your eyes approach the axis of a laser beam (even with eye protection on). Keep beam paths below or above standing or sitting eye level. Do not direct them towards other people. - Do not damage laser protective housings, or malfunctioned the interlocks on these housings. - Eliminate all reflective material from the vicinity of the beam paths. - Never use viewing instruments to look directly into a laser beam. If this is necessary, install an appropriate filter into the optical element assembly. - Keep ambient light levels as high as operations will permit. - Do not work alone when performing high power laser operations. # Summary - Atomic spectra deal with the spectrum of frequencies of electromagnetic radiation emitted or absorbed by an electron during transitions between different levels of energy within an atom. - An optical spectrum is obtained, when light passes through a prism or a diffraction-grating. - A line of particular frequency or wavelength emitted or absorbed by atoms is called a spectral line. - The spectra for each element are unique because each element contains differing numbers of electrons and thus different energy levels. - Niels Bohr explained the atom of hydrogen. Hydrogen atom consist of proton and electron revolving around the nucleus. - According to Bohr's, the radii of the Hydrogen atom have the quantized values $r = \frac{n^2ε_0h^2}{\pi me^2} $ or $r = r_0n^2$, where $r_0 = 5.29 × 10^{-11}m = 0.53Aº $ is called Bohr's first orbit. - X-rays are powerful electromagnetic rays of higher energy and can pass through most objects, including the body. - X-rays are produced when fast electrons, or cathode rays, strike a target, such as the walls or anode of a low-pressure discharge tube. - The light from a laser is quite intense, monochromatic and one directional. - The process of photon emission by an excited atom with no external influences is called spontaneous emission. - Radiation which occurs as result of external exposure is called induced or stimulated emission. - Metastable state is a particular excited state of an atom, nucleus, or other system that has a longer lifetime than the ordinary excited states. - The process of making the population of atoms in the higher energy state (Excited state) more than that of lower energy state (ground state) is known as population inversion. - A process in which light is used to raise (pump) electrons from a lower energy level in an atom or molecule to a higher energy level is called optical pumping. - The helium-neon laser was the first continuous wave (CW) laser ever constructed. - Laser light is monochromatic, highly intense, coherence and single directional. - Lasers are widely used in tools, communication, defense, medicine, and holography. - The health effects that could occur due to exposure to a laser beam are damage to the skin and eyes. - The nature of safety measures, which are generally taken to avoid the hazards or damages caused by the lasers, are adopted and procedure according to the use and intensity of the laser.