Visualizing the Universe: Lasers and Holography

By: Jerry Flattum, Performer/Songwriter & Writer/Editor

Dr. Charles H. Townes (PhD in Physics, California Institute of Technology) started working for Bell Telephone Labs, designing radar bombing systems during WWII. He turned his attention to applying the microwave technique of wartime radar research to spectroscopy, a powerful new tool for the study of the structure of atoms and molecules and as a potential new basis for controlling electromagnetic waves.

visualizing-the-universe-lasers-and-holography

visualizing-the-universe-lasers-and-holography

More research followed in microwave physics, particularly studying the interactions between microwaves, molecules, and atoms. In the early 50s he invented the “maser,” a device and an acronym for “microwave amplification by stimulated emission of radiation.” A few years later with his brother-in-law, Dr. A.L. Schavlow (Stanford), he showed theoretically that masers could operate in the optical and infrared regions. The laser was born. Laser stands for “light amplification by stimulated emission of radiation.

Ordinary natural and artificial light is released by energy changes on the atomic and molecular level that occur without any outside intervention. A second type of light exists, however, and occurs when an atom or molecule retains its excess energy until stimulated to emit the energy in the form of light.

Lasers are designed to produce and amplify this stimulated form of light into intense and focused beams. The special nature of laser light has made laser technology a vital tool in nearly every aspect of everyday life including communications, entertainment, manufacturing, and medicine. Laser surgery used for correcting vision problems has become routine, if not big business.

The lasers commonly employed in optical microscopy are high-intensity monochromatic light sources, which are useful as tools for a variety of techniques including optical trapping, lifetime imaging studies, photobleaching recovery, and total internal reflection fluorescence. In addition, lasers are also the most common light source for scanning confocal fluorescence microscopy, and have been utilized, although less frequently, in conventional widefield fluorescence investigations.

In a few decades since the 1960s, the laser has gone from being a science fiction fantasy, to a laboratory research curiosity, to an expensive but valuable tool in esoteric scientific applications, to its current role as an integral part of everyday tasks as mundane as reading grocery prices or measuring a room for wallpaper.

Any substantial list of the major technological achievements of the twentieth century would include the laser near the top. The pervasiveness of the laser in all areas of current life can be best appreciated by the range of applications that utilize laser technology.

visualizing-the-universe-laser-defense-in-space

visualizing-the-universe-laser-defense-in-space

At the spectacular end of this range are military applications, which include using lasers as weapons to possibly defend against missile attack, and at the other end are daily activities such as playing music on compact disks and printing or copying paper documents.
Somewhere in between are numerous scientific and industrial applications, including microscopy, astronomy, spectroscopy, surgery, integrated circuit fabrication, surveying, and communications.

The two major concerns in safe laser operation are exposure to the beam and the electrical hazards associated with high voltages within the laser and its power supply. While there are no known cases of a laser beam contributing to a person’s death, there have been several instances of deaths attributable to contact with high voltage laser-related components.

Beams of sufficiently high power can burn the skin, or in some cases create a hazard by burning or damaging other materials, but the primary concern with regard to the laser beam is potential damage to the eyes, which are the part of the body most sensitive to light.

Visualizing the Universe - Compact Disc Laser

Visualizing the Universe – Compact Disc Laser

A pre-recorded compact disk is read by tracking a finely focused laser across the spiral pattern of lands and pits stamped into the disk by a master diskette. The laser beam is focused onto the surface of a spinning compact disk, and variations between the height of pits and lands determine whether the light is scattered by the disk surface or reflected back into a detector.

There are many other kinds of lasers, like ion lasers, argon-ion lasers, diode lasers, helium-neon lasers, Ti:Sapphire Mode-Locked Lasers, and Nd:YLF Mode-Locked Pulsed Lasers (neodymium: yttrium lithium fluoride).

In 2005, two Americans and a German won the Nobel Prize in Physics for Laser Research. Roy J. Glauber of Harvard University was honored for work applying quantum theory to light emitted by lasers. His work allegedly will help explain a major scientific paradox: the dual nature of light behaving like both a particle and a wave. This along with John L. Hall, JILA Institute, University of Colorado (Boulder), and Theodore W. Hansch, Ludwig-Maximilians University in Munich who shared the Prize for their development of techniques to precisely control the frequency of lasers, allowing measurement of physical properties not only of atoms, but of space and time, with unprecedented accuracy.

Before the laser, researchers used classical 19th century optics theory to explain the behavior of light. Many researchers believed that quantum theory, which had proved successful in describing the behavior of matter, could not be applied to light.

The development of lasers operating at single frequencies made advances in the study of atoms and molecules possible. Laser’s latest developments include single or specific frequency operation.

Such accurate measurement will increase the accuracy of atomic clocks from the current 10 digit to 15 digit accuracy. This kind of precision will not only enhance the accuracy of clocks but also the global positioning system, improve the navigation of long spaceflights, and help in the pointing of space telescopes.

Typical applications of single-frequency lasers today occur in the areas of optical metrology (e.g. with fiber-optic sensors) and interferometry, optical data storage, high-resolution spectroscopy (e.g. LIDAR), and optical fiber communications. In some cases such as spectroscopy, the narrow spectral width of the output is directly important. In other cases, such as optical data storage, a low intensity noise is required, thus the absence of any mode beating noise.

Single-frequency sources are also attractive because they can be used for driving resonant enhancement cavities, e.g. for nonlinear frequency conversion, and for coherent beam combining. The latter technique is currently used to develop laser systems with very high output powers and good beam quality.

Holography

Holography was invented in 1948 by Hungarian physicist Dennis Gabor. He received the Nobel Prize in physics in 1971. The discovery was a result of research involving electron microscopes, but it was the laser that ultimately made holography possible. Holography is the science of producing 3-dimensional images called holograms. Holography is also used to optically store and retrieve information. Holograms gained popularity in such movies as Star Wars, Star Trek and AI: Artificial Intelligence.