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TOPICS: GAS LASERS & ATOMIC LASERS INTRODUCTION • The first gas laser, the Helium–neon laser (HeNe), was co-invented by Iranian-American engineer and scientist Ali Javan and American physicist William R. Bennett, Jr., in 1960. • It produced a coherent light beam in the infrared region of the spectrum at 1.15 micrometres. DEFINATION A gas laser is a laser in which an electric current is discharged through a gas to produce coherent light. The gas laser was the first continuous-light laser and the first laser to operate on the principle of converting electrical energy to a laser light output.
GAS LASERS • Most widely used lasers and most varied: • Low power ( He-Ne) to High power (CO2 ) lasers • Operates with rarified gases as active medium excited by electric discharge Gas lasers using many gases have been built and used for many purposes: • Carbon dioxide lasers, or CO2 lasers can emit hundreds of kilowatts at 9.6 µm and 10.6 µm, and are often used in industry for cutting and welding. The efficiency of a CO2 laser is over 10%. • Carbon monoxide or "CO" lasers have the potential for very large outputs, but the use of this type of laser is limited by the toxicity of carbon monoxide gas. Human operators must be protected from this deadly gas.
TYPES OF GAS LASER Chemical lasers (HF Laser) Excimer Lasers Ion Lasers Argon Laser Helium-Cadmium Laser Copper-Vapour Laser
Schematic of Gas Lasers • In gases, energy levels of atoms involved in lasing action are well defined and narrow; broad pump bands do not exist. • To excite gaseous atoms; pump sources with sharp wavelengths are required = Optical pumping not suitable for gas lasers. • Most common method; Passing electric discharge through the gas medium. • Gas contained in a tube with cavity mirrors. • A high DC voltage ionizes the gas for conduction. • Electrons in the discharge transfer energy to atoms in the gas by collisions.
WORKING PRINCIPLE • It is a four energy level laser system. • The electrons produced from electric discharge collide with He and Ne atom and excite them to the higher energy levels He2 and Ne4 at 20.61 eV and 20.66 eV respectively. • These two states are metastable so the atoms may stay there for a longer time.
Advantages • High volume of active material • Active material is relatively inexpensive • Almost impossible to damage the active material • Heat can be removed quickly from the cavity Applications • He-Ne laser is mainly used in making holograms. • In laser printing He-Ne laser is used as a source for writing on the photosensitive material. • He-Ne lasers were used in reading Bar Codes, which are imprinted on products in stores. They have been largely replaced by laser diodes. • Nitrogen lasers and excimer laser are used in pulsed dye laser pumping. • Ion lasers, mostly argon, are used in CW dye laser pumping.
ATOMIC LASERS HISTORY • The first pulsed atom laser was demonstrated at MIT by Professor Wolfgang Ketterle et al. in November 1996. • Ketterleused an isotope of sodium and used an oscillating magnetic field as their output coupling technique, letting gravity pull off partial pieces looking much like a dripping tap. • From the creation of the first atom laser there has been a surge in the recreation of atom lasers along with different techniques for output coupling and in general research. • The current developmental stage of the atom laser is analogous to that of the optical laser during its discovery in the 1960s. • To that effect the equipment and techniques are in their earliest developmental phases and still strictly in the domain of research laboratories. • The brightest atom laser so far has been demonstrated at IESL-FORTH, Crete, Greece.
DEFINATION An atom laser is analogous to an optical laser, but it emits matter waves instead of electromagnetic waves. Its output is a coherent matter wave, a beam of atoms which can be focused to a pinpoint or can be collimated to travel large distances without spreading. • It is a source capable of producing an intense, highly directional, coherent beam in which all the atoms have the same wavelength just like the photons in a laser beam.
CONTINUE… The exotic quantum phenomenon of Bose–Einstein condensation is the key ingredient in a new type of laser that emits atoms rather than photons, and that promises to revolutionize atom optics. Bose-Einstein basics • The idea for an atom laser predates the demonstration of the exotic quantum phenomenon of Bose-Einstein condensation in dilute atomic gases. But it was only after the first such condensate was produced in 1995 that the pursuit to create a laser-like source of atomic de Broglie waves became intense. • In a Bose condensate all the atoms occupy the same quantum state and can be described by the same wavefunction. • In a Bose-Einstein condensate all the atoms have the same energy and hence the same de Broglie wavelength. If this property can be maintained when the atoms are released from the condensate, we will have a highly monochromatic source of matter waves.
Applications • Atom lasers are critical for atom holography. Similar to conventional holography, atom holography uses the diffraction of atoms. • As the de Broglie wavelength of the atoms is much smaller than the wavelength of light, an atom laser could create much higher resolution holographic images. Atom holography might be used to project complex integrated-circuit patterns, just a few nanometres in scale, onto semiconductors. • In fundamental research and industry where atomic beams are used, e.g., atomic clocks, atom optics, precision measurements of fundamental constants, tests of fundamental symmetries, atomic beam deposition for chip production (atom lithography), and, more generally, nanotechnology.
