1. Lasers – What, Who, When, Where, How, Why? Professor Deb Kane Department of Physics Macquarie University

2. To understand lasers many concepts need to be understood: The models of light - wave model, photon model How light interacts with matter - need to understand the nature of matter – atoms - how light is produced by matter Optics -need to understand optics (lenses, mirrors) to be able to design and use the laser Lasers – What? LASER Light Amplification by the Stimulated Emission of Radiation

3. Lasers – Who, Where, When? Arthur Schawlow Aleksander Prokhorov Nicolai Basov Don Herriott, Ali Javan, Bill Bennett Charles Townes Theodore Maiman Image Removed- copyright Gordon Gould Images copyright see: Jeff Hecht, Beam: The Race to Build the Laser, Oxford University Press, 2005 and http://nobelprize.org/nobel_prizes/physics/laureates/http://nobelprize.org/nobel_prizes/physics/laureates/ Images Removed- copyright Images Removed- copyright Image Removed- copyright Image Removed- copyright

4. Lasers – Who, Where, When? Arthur Schawlow Aleksander Prokhorov Nicolai Basov Don Herriott, Ali Javan, Bill Bennett Charles Townes Theodore Maiman Basov and Prokhorov invented the MASER in 1954 Moscow, Russia Prokhorov Invented the Laser in Concept 1958 Townes and Gordon invented the MASER in 1954 Townes & Schawlow Invented Laser in Concept USA 1958 Invented and Demonstrated the first pulsed laser – Ruby laser 16 th May 1960 Demonstrated first cw, gas laser – helium neon laser 9 th December 1960 Gordon Gould invented the laser -documented in a notarised notebook 1957 Columbia University

5. LASER - Light Amplification by the Stimulated Emission of Radiation Reference: http://www.thetech.org/exhibits/online/lasers Laser LightRegular Light Laser light is very different than light from a light bulb. Lasers – What?

6. LASER - Light Amplification by the Stimulated Emission of Radiation Reference: http://www.thetech.org/exhibits/online/lasers Laser LightRegular Light Collimated Light Point source Uncollimated Light Diverging light Lasers – What?

7. LASER - Light Amplification by the Stimulated Emission of Radiation Reference: http://www.thetech.org/exhibits/online/lasers Laser LightRegular Light Coherent Incoherent Lasers – What?

8. Laser light qualities: one colour (generally) a thin (collimated), high brightness (intense) beam said to be “coherent” LASER - Light Amplification by the Stimulated Emission of Radiation Reference: http://www.thetech.org/exhibits/online/lasers Laser LightRegular Light Light bulb light qualities: Laser light is very different than light from a light bulb. many colours mixed together radiates in all directions, uncollimated, divergent said to be “incoherent” Lasers – What?

9. The laser consists of three parts The medium which produces the light The “power supply” that provides energy to the medium to excite it to produce light The cavity (aligned mirrors) that feedback some of the light so it can be amplified Lasers – What? LASER Light Amplification by the Stimulated Emission of Radiation Theodore Maiman Images Removed- copyright Image Removed- copyright

10. Light Radiation from Atoms LASER - Light Amplification by the Stimulated Emission of Radiation Absorption Spontaneous Emission

11. LASER - Light Amplification by the Stimulated Emission of Radiation The laser may be activated by a few photons, but then many, many more are generated. The initial light is amplified to make a very bright compact beam. Reference: http://www.thetech.org/exhibits/online/lasers

12. LASER - Light Amplification by the Stimulated Emission of Radiation One photon forces an excited atom to emit an identical photon – one photon in, two identical photons out. That the photons are identical is the basis of the coherence of the laser light. Reference: http://www.thetech.org/exhibits/online/lasers

13. LASER - Light Amplification by the Stimulated Emission of Radiation Reference: http://www.thetech.org/exhibits/online/lasers Emission refers to the giving “out” of photons. The excited atom emits a photon when another photon, with the right energy, comes by. In 1917, Einstein discovered this process and called it Stimulated Emission. There is a ‘threshold” or minimum in light intensity that must be met before this stimulated emission process dominates over the “spontaneous” light emission, and “lasing” can be achieved. Image Removed- copyright

14. LASER - Light Amplification by the Stimulated Emission of Radiation Reference: http://www.thetech.org/exhibits/online/lasers Radiation is a word that has a bad reputation. It is a general term for anything that is radiated, or given off by an object. For lasers, radiation refers to the light/ photons which are being emitted.

15. Images copyright see: Jeff Hecht, Beam: The Race to Build the Laser, Oxford University Press, 2005 Gordon Gould’s Notebook Maiman’s Ruby Laser Maiman’s Nature Paper Images Removed- copyright

16. Lasers – How? The MEDIUM (gas, solid etc)- Population Inversion is required The length of the bars indicates the number of atoms in the “medium” with each allowed energy, E 1, E 2, E 3

17. Modes of Operation – Pulsed, or Continuous Wave (CW – output power is on all the time) Maiman’s ruby laser was/is essentially pulsed Javan’s helium neon gas laser was/is essentially CW Lasers – How? Images copyright see: Jeff Hecht, Beam: The Race to Build the Laser, Oxford University Press, 2005 Images Removed- copyright

18. Lasers – How? Ruby laser Needs to be “pumped” really hard Extremely difficult to get cw output – essentially pulsed Three level laser Maiman’s ruby laser was/is a three level laser - 694.3 nm, very deep red stimulated emission Valve open if more in E 2 than E 1

19. Three level laser Maiman’s ruby laser was/is a three level laser - 694.3 nm, very deep red Lasers – How?

20. Javan’s helium neon laser, 1150 nm - Infra red; 632.8 nm, red, cw came a little later – a three level laser with a different approach to population inversion Uses a lucky coincidence between metastable energy levels in He and Ne

21. Four level laser – pulsed or continuous wave, cw Lasers – How? The lasers that are important for applications today are mostly four level lasers stimulated emission Valve open if more in E 2 than E 1 Incorporates the best of both three level laser models

22. Method of Excitation – the means by which the medium/atoms get excited Maiman’s Ruby laser - Light energy excites the medium Lasers – How? Javan’s helium neon gas laser – an electric discharge excites the helium which transfers energy to neon via atomic collisions in the gas. The lasing is on a “transition”, an atomic emission wavelength, in neon. Power Supply

23. Lasers – How? The Optics, the laser cavity – Schawlow’s brilliant idea -provides the feedback of photons into the medium so they get further amplified -Also imposes constraints on what ‘colour” light is amplified - cavity resonance

24. Lasers – How? The Optics, the laser cavity – alignment The mirrors are tilted until all the photons line up behind each other – only one ball is seen when aligned

25. Lasers 2010 – How many? Billions – what sort? All sorts – but mostly semiconductor lasers: … another fascinating story

26. IMPORTANT CHARACTERISTICS OF A GIVEN LASER Colour (Wavelength) Output Power (Average and/or peak) Output Power as function of Time – constant or pulsed Beam spatial profile Available lasers have broad ranges in all these categories. There are several large volumes of tables of Laser Transitions that have been demonstrated.

27. Lasers – What?

28. Lasers – Why?

29. Lasers were described by Irnee D’Haenens, one of the Hughes Lab research team, as “the solution without a problem”. But Hughes did describe potential applications in the first press release: - probing matter for basic research - increasing number of available communication channels - concentrating light for industry, chemistry and medicine - high power beams for space communications All these have come to pass – including a plethora of Nobel prize winning science outcomes made possible with lasers as a research tool. Lasers are used: in cutting, welding and machining from macro to micro scales; to reshape corneas to correct poor vision, and to provide intense heat in controlled fusion experiments. We also use lasers as very precise light sources in supermarket checkout lines, CD players, and to transmit most telephone signals. Check out some of the other lectures on the DET site and/or some of the following resources to learn more.

30. References and Resources for Learning More About Lasers 1.A Conceptual Introduction to Lasers, Dr Mark Masters, Indiana University Purdue University, IUPU, Fort Wayne, USA. 308 pp. Some figures reproduced in these slides, with permission. 2.Jeff Hecht, Beam: The Race to Build the Laser, Oxford University Press, 2005 Also www.jeffhecht.com 3.http://laserfest.org/lasers/index.cfmhttp://laserfest.org/lasers/index.cfm 4.http://nobelprize.org/educational_games/physics/laser/facts/history.htmlhttp://nobelprize.org/educational_games/physics/laser/facts/history.html 5.http://laserfest.org/lasers/history/timeline.cfmhttp://laserfest.org/lasers/history/timeline.cfm 6.http://laserfest.org/lasers/innovations.cfmhttp://laserfest.org/lasers/innovations.cfm 7.http://laserfest.org/lasers/video-maiman.cfmhttp://laserfest.org/lasers/video-maiman.cfm 8.http://laserfest.org/lasers/video-history.cfmhttp://laserfest.org/lasers/video-history.cfm 9.https://lasers.llnl.gov/ National Ignition Facility (NIF) Bringing star power to earthhttps://lasers.llnl.gov/ 10.http://www.physics.mq.edu.au/laserfestsydney/ Check forhttp://www.physics.mq.edu.au/laserfestsydney/ more laser related events and activities Lasers – What, Who, When, Where, How, Why?

31. NIF will be about 20 times more powerful than the Nova laser and will deliver about 60 times more energy. When Nova operated with ultraviolet light, it produced 30 kilojoules of energy and 25 terawatts of power. In contrast, the 192-beam NIF will generate 1.8 megajoules and 500 terawatts of ultraviolet laser energy. Lasers – Current Record Holder – Most Powerful Credit: Lawrence Livermore National Laboratory