50 years of lasers

This year is the 50th anniversary of the first successful laser built by Theodore Maiman. The laser is a beautiful example of fundamental physics leading to profound effects on our daily lives. The laser will be discussed on the first day of the conference by Nicolaas Bloembergen, who himself received the the 1981 Nobel Prize for his work in laser spectroscopy. Personally, I am fascinated by lasers because they invoke images of the future, but they are integral to the present. Perhaps, what makes the laser so amazing is that we know that its full potential has not yet been realized. I will be taking several looks at the laser during the conference and so let me begin by discussing a brief history of the laser, the physics of the laser, and the future of the laser. The list of Nobel Prizes that have involved the laser is extensive:
  • In 1964 Charles Townes, Nicolay Basov, and Aleksandr Prokhorov shared the prize for their “fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser-laser principle”
  • In 1971 Dennis Gabor won the prize for his developments in the holographic technique. Originally he was working to simply improve the resolution of electron microscopes when he discovered that by imaging an object with separate reference and target laser beams he could record not only information about the amplitude of light reflected from the object, but also the phase of the reflected beams. This effectively allowed 3D pictures of objects to be recorded as holograms which are used today for security purposes, entertainment, communications, analysis of musical instruments, and many other applications.
  • In 1981 Nicolaas Bloembergen and Arthur Schawlow received the Nobel for their work on the development of laser spectroscopy which has applications in optical communications fibers today. Laser spectroscopy led to the field of nonlinear optics which allows independent laser beams to influence or steer other beams. There is future potential to use these nonlinear optics in advanced optical computers.
  • In 1997 Steven Chu, Claude Tannoudji, and William Phillips received the Nobel Prize for work on laser cooling and trapping atoms with lasers. It may seem counter intuitive, but lasers are actually very good at cooling atoms. When atoms cool to very close to absolute zero exotic states of matter like Bose-Einstein condensates form which are just beginning to be studied fully.
  • In 2000 Zhores Alferov and Herbert Kroemer received the Nobel Prize for their basic work on information and communication technology, but what that really means is that they created miniature lasers that are ubiquitous today on CD players, laser pointers, bar code readers, and every other compact low power laser application.
I should point out that although I have a linear time line here of Nobel Prizes awarded for work related to the laser the laser’s history was anything but coherent; the first Nobel Prize, the first operational laser, and the first patent were all credited to different people!

One of the surprising things about lasers is their ubiquity, but the physics of lasers also remains surprising – surprisingly simple and mysterious at once. Laser was originally and acronym for Light Amplification by Stimulated Emission of Radiation. And the name says it all. Einstein proposed in 1917 that atoms exist in discrete states and they can make transitions from these states in three distinct manners. Further, the distinct states correspond to different energy levels or wavelengths (or frequencies) of photons. Picture a simple atom with an electron is in a discrete energy state about the nucleus. First, the electron may spontaneously decay from a higher energy state to a lower energy state (assuming it begins in the higher energy state and that a lower energy state is available) and in doing so it will emit a photon corresponding to the energy difference between the upper and lower states. Second, the electron may be induced to move up to a higher energy state after being struck by a photon with the correct energy. Third, and this is the clever one Einstein thought of, an electron which is already in an excited state (like the first case) may be hit by a photon and the electron will drop to a lower state in the atom and emit an extra photon identical to the incoming photon – this is stimulated emission. This is the laser. By pumping energy into a material to populate the upper states of the atoms a chain reaction can occur whereby stimulated emission creates feedback in a resonant cavity between two mirrors. One of the mirrors is a half mirror such that incident photons may either bounce of the mirror and induce more stimulated emission or the photon may escape into the outgoing laser beam.

The future of lasers is bright. Fundamental research continues to occur, for example Theodor Hänsch and John Hall received the Nobel Prize in 2005 for their contributions to the development of laser-based precision spectroscopy. Hänsch and Hall worked with what are known as frequency combs which may become very important in future applications. You may listen to John Hall explaining combs at Lindau. (All of the above mentioned and linked Nobel laureates have attended the Lindau Meetings. Most of them several times and you may listen to some of them thanks to the Lindau archive especially those lectures from the physics meeting in 2008: Bloembergen, Hänsch, Phillips)
John Hall Lecture 2008
John L. Hall, 2008 – 58th Meeting of Nobel Laureates
‘The Optical Frequency Comb – a Really Versatile Tool’
Laser technology sometimes evolves right in front of the consumers eyes. How long ago was it that you could only buy red laser pointers? Now there is green, blue, and violet all available. The ability to produce these bluer smaller wavelength lasers allows for applications like moving to denser and denser data storage from the CD to DVD to Blu-ray technology because the bluer lasers allow smaller diffraction limited operation allowing data to be packed into denser areas. Physics research is also moving along:
  • The ambitious Extreme Light Infrastructure (ELI) project aims to create a laser pulse so intense that it may tear space-time. The ELI will provide a platform for fundamental research in physics all across Europe.
  • The National Ignition Facility (NIF) in the United States is attempting to achieve net energy positive fusion by focusing 1.8 MJ of energy from 192 laser beams onto a deuterium and tritium sphere. The sphere will undergo an intense implosion due to the massive radiation pressure from the lasers and, hopefully, fuse the deuterium and tritium in a energy producing fusion reaction.
At the Lindau conference I look forward to hearing the lecture of Bloembergen about the history of the laser and the talk of Hänsch about the heartbeat of light.  I will also be on the lookout for what younger researchers have to say. I would like to know what fundamental physics research could lead to applications as widespread and as saturating in daily life as the laser.
Berkeley Lab Laser
Berkeley Lab scientists working with a 40-terawatt laser
picture credits:
1 ‘Laser’  Guillermo
Lawrence Berkeley Nat’l Lab – Roy Kaltschmidt, photographer