Sample Materials for CSAT Paper -1 (G.S.) Pre 2013: "Science & Technology: Laser"

Subject: Science & Technology:
Topic: Laser

Ques. 1 : What is Laser

Ans. LASER (Light Amplification by Stimulated Emission of Radiation) is a device which produces an intense, coherent, directional beam of light by stimulating electronic or molecular transitions to lower energy levels.

Ques. 2 : Briefly discuss the working of Laser?

Ans. Although there are various types of Lasers the underlying principle is the same. A typical laser consists of a medium which can be a solid, gas, liquid or semi-conductor. When a medium is stimulated by electric current or very intense light source, it results in a large collection of excited-state atoms (atoms with higher-energy electrons). It is necessary to have a large collection of atoms in the excited state for the laser to work efficiently.

An activated medium thus contains a collection of atoms with some electrons at higher energy levels. Just as the electrons ‘absorbed’ some amount of this energy to reach this excited higher level, it can also ‘release’ this energy when the electrons jump from higher energy levels to lower energy levels they ‘emit’ energy. This ‘emitted energy’ comes in the form of photons (particle of light). The photon emitted has a specific wavelength (colour) which depends upon the electron’s energy when the photon is released. Two identical atoms with electrons in identical states will release photons with identical wavelengths.

Ques. 3 : What are the properties of Laser Light?

Ans. In contrast to an ordinary light source, a laser produces a narrow beam of very bright light. Laser light has the following properties:

1. Homochromatic: It contains one specific wavelength of light (one specific colour). The wavelength is determined by the amount of energy released when the electron drops to a lower orbit.
2. Coherent: This means that the emitted light waves are in phase with one another, for long distances travel parallel to each other without spreading. In contrast, light from common light sources such as incandescent bulb, diffuses in all directions. Coherence means that laser light can be focussed with great precision.
3. Directional: A Laser Light is a very tight beam, very strong and concentrated.

Ques. 3 : Briefly discuss the types of Laser?

Ans. There are different types of laser. The Laser medium can be a solid, gas, liquid or semiconductor. Lasers are commonly designated by the type of lasing material employed:

1. Solid-State Lasers: Solid State laser materials are commonly made by doping a crystalline solid host with ions that provide the required energy states. For example, the first working laser was made from ruby, or chromium-doped sapphire; Another example is Neodymium-doped Yttrium Aluminium Garnet (YAG) known as ND:YAG Laser. They are used for cutting, welding and marking of metals.

2. Gas Lasers: Helium-Neon (He-Ne) is a commonly used gas laser. CO2 laser is powerful, can cut through hard metals as it emits laser tight in Infrared and microwave region of the spectrum.

3. Excimer Laser: (name derived from terms ‘excited’ and ‘dimers’) in this, reactive gases such as chlorine, fluorine are mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced. When lased, the dimer produces light in the ultra-violet range.

4. Semiconductor Laser: Sometimes called diode lasers. These electronic devices are generally very small and use low power they may be build in to larger arrays like Laser printer (or) CD player.

5. Dye Lasers: In these complex organic dyes such as shodamine 6G, in liquid solution or suspension are used as medium. They are tunable over a broad range of wavelengths.

Ques. 5 : Point out the applications of Laser?

Ans.

1. Basic Science Spectroscopy; Photo-chemistry; Microscopy.
2. Military : Lidar; Laser sight; Target Designator; Laser Isotopic separation, etc.
3. Medical: Cosmetic Surgery; Eye Surgery (LASIK, LASEK, PRK); Laser Scalpel (gynaecological, urology, laproscopy)
   Dental procedures; Photobio-modulation; Imaging;
   “No-Touch” removal of tumours, especially of brain and spinal cord.
4. Industry: Surveying, material proce-ssing, marking, scanning, heat treatment of surfaces etc.

Ques. 6 : Discuss in brief the applications of Laser in Basic science?

Ans. Basic Science :

1. Spectroscopy: Lasers are an inherently pure source of light; they emit near- monochromatic light with a well-defined range of wavelengths. The high intensity of light that is achieved can also be used to induce a non-linear optical effect in a sample, which makes techniques such as human spectroscopy possible.

2. Photo-chemistry: Some laser systems can produce extremely brief pulses of light (as short as pico seconds or femto seconds, 1012 — 1015 sec.). Such pulses can be used to initiate and analyse chemical reactions, a technique known as photochemistry. This method is particularly useful in biochemistry, where it is used to analyse details of protein folding and function.

3. Microscopy: Confocal laser scanning microscopy and two-photon excitation microscopy make use of lasers to obtain blue-free images of thick specimens at various depths.

Ques. 7 : Briefly discuss the uses of Laser in Military?

Ans.

Military:

1. LIDAR (Light, Detection and Ranging or Laser Imaging Detection and Ranging) is technology that determines distance of an object/surface using laser pulses. It is similar to radar technology, but it uses light as against radio-waves used in radar. The range of an object is determined by measuring the time delay, between transmission of a pulse and detection of the reflected signal.

2. Laser Sight: Laser in most military applications, has been used as a tool to enhance the targeting of other weapon system. Laser sight is one such example. Laser sight is a small, usually visible-light laser placed on handgun or rifle aligned to emit a beam parallel to the barrel. As the laser beam has low divergence, it appears as small spot even at long distances and helps in hitting targets accurately.

3. Laser target designator: This is a low-power laser used to indicate a target for a laser-guided ammunition such as smart bomb or missile. The guided ammunition adjusts its flight-path to home into the laser light reflected by the target, enabling a great precision in aiming.

4. Laser Isotopic separation promises to be the most economical way of enriching natural uranium.

Ques. 8 : Discuss in brief the applications of Laser in Medical Science?

Ans. The highly powered laser beam with high intensity is adequate for cutting tissue and thus is a great surgical tool which can replace the traditional scalpel. The advantages of surgery done by using lasers are:

1. prevents bleeding
2. lowers possibility of infections
3. does less damage to nearby tissues

Hence laser are used widely in cosmetic surgery, eye surgery and surgery on brain, spinal cord etc.

Ques. 9 : Briefly discuss the application of Laser in industrial sector?

Ans. Lasers have great applicability in industry as well. Solid-state lasers like ND:YAG lasers are used for material processing such as welding, cutting, glazing, alloying, etc. It is used in aligning structures like bridges, large buildings, tunnels etc. Lasers are widely used for marking on plastics, metal products. Laser scanners are used to read bar codes on consumer goods, to inspect precision components in workshops, to identify goods wagons in a moving train etc.

Ques. 10 : Give an account of the Laser technology in India?

Ans.
— BARC has made the largest effort for, developing laser technology in India. In 1964, the first gallium arsenide semiconductor laser was fabricated in India. BARC has developed a 50 MW laser for Raman spectroscopy. It has developed solid-state lasers such as ND:YAG, Ruby laser.
— DRDO has developed laser range finders for tanks which use switched ND:glass laser. DRDO is developing laser material and semiconductor lasers.
— Central Scientific Instruments Organisation (CISO) has been working on holographic technology and has developed a variety of holograms for different applications.
— National Laser Programme, a joint strategy of DST, DAE and Department of Electronics was aimed at developing indigenous lasers and laser-based equipment at lower costs. The crystal Growth Centre of Anna University, Chennai was selected to produce laser-producing crystals.

Answer of Question 1: C

Answer of Question 2: B