Film: 9750

Science | 1980 | Sound | Colour

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Synopsis:

Lasers
Remade film, using older film clips. Voice over large moon discussing in May 9th 1962 in Lincoln Laboratory in Lexington, Massachusetts engineers prepared to beam a light beam of the earth's surface. They directed their aim at the shadowy side of the half moon close to the crater Albertina. Their projectile was a real light from a ruby laser, a newly coherent source of monochromatic light. Interior of a laboratory with various sound equipment machines. Reflected signal is recorded 2 1/2 seconds later by a oscilloscope camera. At the rate of one a minute 13 pulses were projected. The laser, its discovery and development together with some predictions for its future in science and industry. Presenter John Huntley discusses straight to camera the discovery of the laser. Possible uses being predicted were its role in nuclear reactors. The origins of laser lie in developments in 1954 made at Columbia University by Dr Charles Townes. The laser or optical maser is most closely identified with this man. Dr Townes talks straight to camera about the developments of the maser (molecular amplification by stimulated emission of radiation) A maser or laser that operates in or close to the visible light of the electromagnetic spectrum. The Concept of stimulated emission was discussed by Einstein over 40 years ago (circa 1920s). In the 1930s after the advent of quantum mechanics it was well understood by most students of physics (Dr Townes with blackboard in background addresses a class of students) At this time there was no means known for the generation of coherent light as there was for the generation of coherent radio waves. World War Two made heavy use of radio and microwaves. Shot of early radio or radar equipment. By the end of the war the electromagnetic spectrum was heavily used and crowded, allocated to commercial radio and television, police and marine radio, aeronautical communications, direction finding and radar. This part of voiceover is done over diagram of different uses of microwaves including broadcast, police, marine, short wave, VHF, and television. Down below 1cm is a range of frequencies extending on and into the visible regions and not yet used for such purposes. To the engineer wavelengths below 1mm offered little promise for uses such as communications. Because of the difficulty of constructing circuit elements sufficiently small, approximately 1mm was generally accepted as the practical limit of microwave generation and light waves of still a thousand times shorter. Diagram of atoms used to illustrate that each atom has its only level of energy. In any medium the atom is at the lowest or ground level, but it can make a jump to a higher level by absorbing a quantum of electromagnetic energy, a photon of the right frequency. This energy can be released in various ways. One of these is spontaneous emission, in which the excited atoms lose their acquired energy by radiating photons spontaneously. The atoms then return to a lower level . However the excited atoms may also emit the stores energy, given a wave of the right frequency striking them causing stimulated emission, in this case the photon from the excited atom is induced to join the photon of the incoming wave with the effect that the wave is amplified. To increase the gain further it is necessary to contain the wave within the active medium for a longer time. This can be done by enclosing the active medium between reflectors to form a resonant path. One of the reflectors is made partly transparent. The light which emerges from the end plate of diagram is a highly directional beam of monochromatic light waves travelling parallel along the axis of the resident cavity. The unique characteristics of this beam, and most important is that the waves of which it is composed are all in phase and travelling in the same direction. Such a beam (shown in diagram) can be considered to be coherent . It is because their single wave can be amplified indefinitely that the laser beam attains a much greater intensity than any other light source. Since the output is monochromatic and is in the form of parallel beams, it can be focused to a point in which the radiant density is 100 million times greater than it is in an equivalent area of the sun. A coherent beam also lends itself to efficient modulation. Conventional light sources such as the sun or incandescent lights have characteristics which limit their usefulness. Energy radiated from an intense source of white light (John Huntley straight to camera address) is totally incoherent. The electromagnetic wave association with each photon is completely random, with respect to the phase of any other. Excellent shot of a spectrometer used to demonstrate the energy radiated from a white light source is distributed over a broad spectral region from red to blue. Powerful monochromatic sources do not exist and monochromatic light can be obtained only by limiting the output as by filtering. The more newly monochromatic filtered light, the less intense it is. Close up of light bulb ( dimmed and hazy) white light is radiated in all directions from an ordinary incandescent source. That is it is not columnated, and columnation can not be achieved without sacrificed without losing intensity. In other words, the greater the need for parallelism the less the intensity. It has been a fundamental law of optics that radiation from an incandescent source can not be focused to provide an increase in brightness over the brightness of the source. These limitations are overcome in coherent light sources or lasers. For the first time lasers allow the controlled generation of light and allow engineers to use light oscillations in the same way they have used radio and microwave, and for many of the same applications. The chronology of the discovery and development of the laser demonstrates the capacity of modern science to move from concept to technology, In December 1951 a research group working under the direction of Charles Townes announced the design for an apparatus to generate stimulated emission in ammonia. By December 1953, they had produced an ammonium beam maser which amplifies microwaves at a single frequency, 24,000 megacycles. Exterior shot of Gordon McKay Laboratory of Applied Science. Further work resulted in a practical lo-noise solid state micro-amplifier. Shot of Nicholas Limburgen assembling a ruby maser which operates in a (dewar?) Cooled by liquid helium. The ruby maser can amplify the faint signals from enormously distant hydrogen glass clouds and galaxies. Shot of large maser amplifier ( very similar to large telecommunications satellite dish) . Maser amplifiers have extended by three to ten times the range of radio telescopes such as that of the Harvard College Observatory, and reveal dozens of previously unobserved galaxies. Close up on spine of the Physical Review Vol 112, dated 1958. Close up on title of article in issue of the Physical Review : "Infrared and optical masers", by A. L. Schawlow and C.H. Townes, BEU Telephone Laboratories, Murray Hill, New Jersey (Received August 26, 1955). At Hughes Aircraft Company in July 1960 , Laser action was first observed visually. Theodore Neimen used a synthetic ruby rod, with reflective end services as the resident cavity. A high intensity flash lamp served as the pumping light or excitation source. Stimulated emission occurred in the red region of the visible spectrum. Ruby is aluminium oxide in which a very small percentage of the aluminium atoms have been replaced by chromium atoms (see diagrams). The light absorbed by the chromium atoms raises them to an excited state (see diagram of atoms). From the higher energy level two steps are required to return them to the ground state. In the first state they descent to a temporary energy level where they remain for a few milliseconds. Then unless stimulated they emit spontaneously and drop at random to the ground state. However, in a laser the first photons which are released ( see diagram) parallel to the axis of the ruby rod start a plane wave which in turn stimulates other excited atoms to give up photons to the waves. As it passes back and forth , thousands of times in a millisecond, the wave gains amplitude and flashes out for the silver end of the rod. The following diagram gives a more traditional view of a laser beam shooting out from a coiled chamber. The ruby rod which is the heart of the laser is made from a crystal grown by the flame fusion process. X-Ray detraction techniques are used to determine the orientation of the crystal phases. Then the crystal is cut ground and polished. Precision optical polishing (see footage) brings the flatness of the laser within a tenth of a wave, the extreme fine tolerance for good laser performance. Huntley proceeds to talk about experiments and developments made by American companies to extend the frequency spectrum. Shots of a gas laser developed by scientists at BCU Laboratories, first announced in February 1962. Operating at room temperature it generates infra-red radiation of a few milli-watts, requiring only 50 watts of excitation energy. An important feature of the gas laser is that it is a continuous wave oscillator and the Nov 61 laser beam could be focused on quartz crystal. Footage of experiment with infra-red beam entering crystal and ultra violet leaving. Electrical shutter developed for the controlled delay of laser action. Discovery of neodillium seen as a good user medium. Various shots of laser equipment. Jan-1962 BEU Laboratories discovered how to produce continuous oscillation in rubies. Discovery of enhanced florescence . Close up of granular laser beam, and discussion of the difference between solid and gas lasers such as their energy level and their place in the market place for research purposes. Ruby and neo-lithium crystals optum mirrors crystals supply equipment have been manufactured in order to supply and sustain the laser industry. By mid 1963 more than 200 wavelengths became available due to research made by scientists. Laser action has been demonstrated in the five noble gases, Helium, Neon , Argon, Krypton, and Xenon. further technical developments regarding the use and materials used in laser technology, including gas laser. Further developments included liquids used as laser material. Early 1963 RCA and General Telephone announced development of a plastic laser. Injection laser. Early developments of laser technology as it relates to telephone technology- fibre optics? Good summary of film at this point. On board American naval ship -
Communication. Various outdoor experiments showing laser technology being tested, between Malibu and Culver City across Santa Monica Bay, Los Angeles Freeway 1960s. Early fibre optic cables or light pipes. Development of laser technologies for military and computer use. Laser photo-coagulator used in early eye or optical surgery, used for delicate surgery such as retinal defects . Intercellular surgery. Other uses include high speed photography closing sequences of moon. Comparisons of Roman lantern with lasers.


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