Types of laser

(A) By active media
 Solid state laser - crystal, or glass, doped with impurities, e.g. ruby laser, Ti:sapphire laser, semiconductor laser.
 Gas laser - e.g. He-Ne laser, Ar+ laser, CO2 laser, N2 laser, HCN laser.
 Dye laser - active medium: dye molecules in liquid solvent (sometimes in solids also).
(B) By mode of operation
 CW
 Pulsed  
(C) By pumping and laser levels
 3-level laser
 4-level laser

1. Types of laser Submitted to: Submitted by: Mrs Yogendra Narayan Jyoti Singh Research Scholar (EE Dept) ME ( Regular) NITTTR, Chandigarh I & C 2 nd Sem Roll No: 142511

2. Types of Laser ( A ) By active media  Solid state laser - crystal, or glass, doped with impurities, e.g. ruby laser, Ti:sapphire laser, semiconductor laser.  Gas laser - e.g. He-Ne laser, Ar + laser, CO 2 laser, N 2 laser, HCN laser.  Dye laser - active medium: dye molecules in liquid solvent (sometimes in solids also). (B) By mode of operation  CW  Pulsed   (C) By pumping and laser levels  3-level laser  4-level laser

3. Solid State Lasers: General properties Solid state lasers use high density solid media as active laser materials. Ions of transition elements, particularly rare earth elements ( Nd , Yb , Er , Ho etc.) or transition metals (Cr, Ti etc.) are used most commonly as dopants . Host materials include crystals like sapphire (Al 2 O 3 ), YLF (YLiF 4 ), YAG (Y 3 Al 5 O 12 ), LISAF (LiSrAlF 6 ), LICAF (LiCaAlF 6 ), as well as glasses from silicate (SiO 2 ) and phosphate (P 2 O 5 ) classes. Glasses are easier to fabricate, but crystals have better thermal properties.

4. Construction and Working

5. Nd:YAG Laser

6. Energy Level Diagram

7. Advantages No chance is of wasting material in the active medium because here material used is in solid form not in gas form, where this occurs. Both continuous and pulsed output is possible from solid state lasers. Solid state lasers have high Construction is comparatively simple. Output power ranging from very low value of about 0.04 watts to high value of about 600 watts. Cost of solid state lasers is economical.

8. Disadvantages Efficiency of solid state laser is very low as compared to CO2 lasers. Great disadvantage of solid state lasers is the divergence, which is not constant and ranges 1 milli radian to 20 milli radian. Output power is also not very high as in CO2 lasers. Due to thermal lasing in solid state lasers, the power loss occurs when the rod gets too hot.

9. Applications / Uses of Solid state Lasers Nd : YAG solid state lasers usually used when drilling holes in metals. Nd : YAG pulsed type solid state lasers can be used in medical applications such as in endoscopy etc. As military application, Nd:YAG is used by target destination system.

10. Ruby Laser Ruby laser is the first working laser demonstrated by Ted Maiman . Host material is corundum (Al 2 O 3 ) crystal, dopants are Cr ions. Lasing Wavelength is 694 nm. Pumping is done with flash lamps and laser operates in pulsed regime.

11. Construction & Working of Ruby Laser

12. Energy Levels Diagram

13. Advantages of Ruby Lasers From cost point of view, the ruby lasers are economical. Beam diameter of the ruby laser is comparatively less than CO 2 gas lasers. Output power of Ruby laser is not as less as in He-Ne gas lasers. Since the ruby is in solid form therefore there is no chance of wasting material of active medium.

14. Disadvantages of Ruby Laser In ruby lasers no significant stimulated emission occurs, until at least half of the ground state electrons have been excited to the Meta stable state. Efficiency of ruby laser is comparatively low. Optical cavity of ruby laser is short as compared to other lasers, which may be considered a disadvantage.

15. Applications One of the first applications for the ruby laser was in range finding. Due to low output power they are class-I lasers and so may used as toys for children’s. It can be used as decoration piece & artistic display.

16. Semiconductor Laser The semiconductor laser is very small in size and appearance. It is similar to a transistor and has the operation like LED but the output beam has the characteristics of laser light. The material which often used in semiconductor laser is the gallium Arsenide, therefore semiconductor laser is sometimes known as Gallium Arsenide Laser. It is also called Injection Laser.

17. Construction and Working

18. Advantages of Semiconductor Lasers Smaller size and appearance make them good choice for many applications. From cost point of view the semiconductor lasers are economical. Semiconductor lasers construction is very simple. No need of mirrors is in semiconductor lasers. Semiconductor lasers have high efficiency. The low power consumption is also its great advantage.

19. Disadvantages of Semiconductor Lasers Semiconductor laser is greatly dependent on temperature. The temperature affects greatly the output of the laser. The lasing medium of semiconductor lasers is too short and rectangular so the output beam profile has an unusual shape. Beam divergence is much greater from 125 to 400 milli radians as compared to all other lasers. The cooling system requirement in some cases may be considered its disadvantage.

20. Application/Uses of Semiconductor Lasers The semiconductor laser can be pulsed at varying rate and pulse widths. Therefore this laser is a natural transmitter of digital data. Semiconductor laser is well suited for interface with fiber optic cables used in communication.

21. Gas Laser Gas lasers are widely available in almost all power ( milli watts to megawatts) and wavelengths (UV-IR) and can be operated in pulsed and continuous modes. Gas lasers use low density gaseous materials as active media. Electrical pumping (continuous, RF or pulsed) is used. The gas lasers can be made from neutral atoms (He-Ne, metal vapor etc), ions (e.g. Ar +) or molecules (e.g. CO 2 ).

22. He-Ne Laser The He-Ne laser active medium consists of two gases which do not interact form a molecule. Therefore He-Ne laser is one type of atomic gas lasers. The gain medium consists of a mixture of helium and neon (10:1) inside of a small bore capillary tube, usually excited by a DC electrical discharge.

23. Construction and Working

24. Energy Level Diagram

25. Advantages of He-Ne Laser He-Ne laser has very good coherence property. He-Ne laser can produce three wavelengths that are 1.152µm, 3.391 µm and 632.8nm, in which the 632.8nm is most common because it is visible usually in red color. He-Ne laser tube has very small length approximately from 10 to 100cm and best life time of 20.000 hours. Cost of He-Ne laser is less from most of other lasers. Construction of He-Ne laser is also not very complex. He-Ne laser provide inherent safety due to low power output.

26. Disadvantages of He-Ne Laser It is relatively low power device means its output power is low. He-Ne laser is low gain system/ device. To obtain single wavelength laser light, the other two wavelengths of laser need suppression, which is done by many techniques and devices. So it requires extra technical skill and increases the cast also. High voltage requirement can be considered its disadvantage. Escaping of gas from laser plasma tube is also its disadvantage.

27. Applications / Uses of He-Ne Laser The Helium-Neon gas laser is one of the most commonly used laser today because of the following applications. He-Ne lasers are produced in large quantities from many years. He-Ne lasers also used in super market checkout counters to read bar codes and QR codes. The He-Ne lasers also used by newspapers for reproducing transmitted photographs. He-Ne lasers can be use as an alignment tool. It is also used in Guns for targeting.

28. Ion Laser: Argon Ion Laser All ion lasers (such as argon, Krypton and mix gas) produce several different wavelengths so they are designed to produce these wavelengths either simultaneously or individually. Argon lasers are generally operated in continuous wave mode. For argon lasers the output power can ranges from few mill watts up to 20 watts.

29. Construction and Working

30. Energy Level Diagram

31. Advantages of Argon Laser Production of multiple wave lengths is the main advantage plus characteristic of argon as well as other ion lasers. Argon lasers produce high power output as compared to He-Ne laser. Argon laser is a higher gain system. Argon laser like He-Ne has very less divergence, typically about 1 milli radian

32. Disadvantages of Argon laser The overall efficiency of argon laser is very less usually lies between 0.01% and 0.1%. Large amount of power requirement is also its disadvantage. Construction is very difficult. Cost of argon laser is not as low as He-Ne laser. Power supply of high voltages required, because due to solenoid there is extra burden on it.

33. Applications of Argon Laser Argon lasers used in scientific research. Argon lasers used in medical application. An artistic displays and light shows also the argon lasers are used.

34. Molecular Laser Unlike isolated atoms and ions in atomic and ionic lasers, molecules have wide energy bands instead of discrete energy levels. They have electronic, vibrational , and rotational energy levels. Energy separation between electronic energy levels lies in the UV and visible spectral ranges, while those of vibrational –rotational (separations between two rotational levels of the same vibrational level or a rotational level of one vibrational level to a rotational level from other lower vibrational level) levels, in the NIR and far-IR regions. Therefore, most of the molecular lasers operate in the NIR or far-IR regions.

35. Carbon Dioxide (CO2) Laser Therefore CO 2 gas laser is considered the type of molecular gas laser. Importantly note that CO 2 lasers use carbon dioxide as well as Helium & Nitrogen as its active medium. The role of N 2 is to facilitate the CO 2 pumping & population inversion process by providing molecule collision with the CO 2 gas. The role of He is to facilitate the removal of decayed molecules from their lower energy level to ground level after lasing process, in order to maintain the population inversion.

36. CO 2 Gas Laser is a high power laser generating device . The laser light takes place within the molecules of carbon dioxide rather than within the atoms of a pure gas. Construction and working of CO 2 Gas Laser

37. The CO 2 Gas Laser consist of mixture of gases like O 2 -N 2 , He and CO 2. Construction and working of CO 2 Gas Laser

38. Construction and working of CO 2 Gas Laser The CO 2 Gas Laser consist of mixture of gases like O 2 -N 2 , He and CO 2 .

39. The CO 2 Gas Laser consist of mixture of gases like O 2 -N 2 , He and CO 2 . Construction and working of CO 2 Gas Laser

40. Since heat is an undesired byproduct for lasing action in this type of lasers, so it always contains a heat exchange system to remove the access heat. Construction and working of CO 2 Gas Laser

41. The CO 2 Gas Laser consists a separate Gas supply system and the Blower motor. Construction and working of CO 2 Gas Laser

42. The Vacuum pump is used to maintain proper Torr level within the cavity in order to operate in the state of controlled vacuum. Construction and working of CO 2 Gas Laser

43. The CO 2 Laser contains s series of mirrors in the optical cavity. The Rear and Folding mirrors are 100% reflective whereas Output mirror is 96% reflecting. Construction and working of CO 2 Gas Laser

44. The folding mirrors are used to lengthen the resonator beam path to increase gain/power without physically lengthening the entire system. Construction and working of CO 2 Gas Laser

45. The CO 2 operates in continuous mode so a shutter devices is used to control the output from a CO 2 Gas Laser. Construction and working of CO 2 Gas Laser

46. The CO 2 operates in continuous mode so a shutter devices is used to control the output from a CO 2 Gas Laser. Construction and working of CO 2 Gas Laser

47. The CO 2 Gas Laser consists of more than one anode for the purpose of maintain even discharge between the anode and cathode. By spreading the electrical discharge over a wide area a more even excitation of molecules is obtained. Construction and working of CO 2 Gas Laser

48. Construction and working of CO 2 Gas Laser

49. Transverse Flow Design

50. Energy Level Diagram

51. Advantages of CO 2 Laser In CO 2 The CO 2 laser offers the lowest cost per watt along with good beam quality, The high power levels are obtained ranges from few watts to 15000 watts. The efficiency of CO 2 gas lasers (i.e. 10% or higher) is beat than He-Ne and argon lasers. Long sealed-off lifetime of greater than 20,000 hours. Small size per watt of output power.

52. Disadvantages of CO 2 Laser Divergence of CO 2 lasers approximately in all cases is greater than He-Ne and Argon laser. Usually the divergence is ranges from 1 to 10 milli radians. Beam width varies from 3mm to 100mm. Some CO 2 lasers have the disadvantage of a short and thick optical cavity. Cooling system requirement in some configurations also a disadvantage. Its cost is comparatively high.

53. Application/Uses of CO 2 Lasers The CO 2 gas laser can be used in industry usually for welding and cutting purposes. The CO 2 laser acts as a surgical tool in the operating room. In both energy and weapons research, there is good field of application of CO 2 lasers. Fractonal C02 Laser Skin Resurfacing

54. Dye Laser (A Liquid Laser) Liquid lasers are those lasers which uses liquid as an active medium. In dye laser the liquid material called dye (for example rhodamine B, sodium fluoresein and rhodamie 6G) uses as an active medium, which causes to produce laser light. The dye lasers produce output whose wavelengths are in the visible, ultra violet and near infrared spectrum.

55. Construction and Working

56. Advantages of Dye Lasers It is available in visible form (also in non-visible) Range of wavelengths can be produced by the using dye lasers. Beam diameter is very less. Its beam divergence (0.8 milli radians to 2 milli radians) is also less from many lasers beam divergence. Construction of dye laser is not so complex. Having the greater efficiency 25%. High output power is also possible with dye lasers

57. Disadvantages of Dye Lasers Cost of dye lasers is very high.. To tune at one frequency, the laser uses birefringent element or filter making it more costly. In dye lasers it is very difficult to determine the element that actually lases because dye has complex chemical formula.

58. Application of Dye Lasers Dye lasers are mostly used as a research tool in medical applications

59. CW and Pulsed Laser Laser Output as a function of time From design point of view we can say that output of all lasers is not constant. Different types of applications require different types of lasers. Therefore the output from the laser can be altered by changing its magnitude over a period of time

60. Continuous Wave Laser A laser that are designed to produce a beam of constant amplitude are called continuous wave or CW lasers. The CW lasers are rated in power units of watts, milli & kilo watts. A graph of the power output from the laser as function of time is shown as: Since Power = energy / time or Energy = power X time Therefore the area below the line in graph represents the energy transmitted by laser.

61. Pulsed Laser In normal pulsed laser, the excitation mechanism is pulsed and the laser is produced for short time while the pumping energy is great enough to keep the active medium above the gain threshold. By diagram normal pulsed laser can be shown as:

62. Pulsed Laser Energy curve for normal pulse laser is as The pulse width for normal pulsed laser varies from 0.1 to 10 milli seconds. PRT The PRT represent the time for one complete ON-OFF cycle. This is also referred to as the period of the pulse PRT = 1 / PRR

63. 3 Level and 4 Level laser

64. THANKS!