Today in History – March 24, 1959 – the maser was patented by Charles Hard Townes (No. 2,879,439), who was a professor at Columbia University. “Maser” is an acronym for “Microwave Amplification by the Stimulated Emission of Radiation “. He had the unique idea for a new microwave generator, based on the idea that excited atoms or molecules could be placed in a reflective microwave cavity, and under appropriate circumstances stimulated emission would take place that could amplify microwave signals (hence the name). He also suggested that the maser could act as an oscillator and generate microwaves by itself. At the time, very few people believed that this would be possible. However, after much hard work working with an ammonia beam, he and his student James P. Gordon and post-doctoral fellow Herbert Zeiger got it to work. Their results were published in two papers in Physical Review [J.P. Gordon, H. J. Zeiger and C.H. Townes, Phys. Rev., 95 (1954) 282 and J. P. Gordon, H. J. Zeiger and C. H. Townes, Phys. Rev., 99 (1955) 1264.]
Simultaneously and independently, similar work was underway in the Soviet Union by N. G. Basov and A. M. Prokhorov, who shared the 1964 Nobel Prize in physics along with Charles Townes in 1964.
The maser became practical when Nicolaas Bloembergen at Harvard pointed out that a three-level system such as ruby could be used to continuously amplify microwave signals. Bloembergen received the Nobel Prize in Physics in 1981, in part for his contribution to masers.
Extremely low noise microwave amplifiers were constructed using ruby at very low temperatures placed in a microwave cavity. With this apparatus Arno Penzias and Robert W. Wilson at Bell Laboratories made astrophysical measurements that led to the discovery of a 3 degree cosmic background, verifying the concept of the Big Bang as the origin of the Universe. They received the Nobel Prize in Physics in 1978 for this work that would not have been possible without Townes’ maser.
Townes, who was at Columbia, and his brother-in-law, Arthur Schawlow, who was at Bell Laboratories, extended the concept of the maser into the infrared and optical regime in a paper “Infrared and Optical Masers,” published in the December 1958 Physical Review. This required a new concept, an “open resonator,” which consisted of two plane parallel mirrors that would keep the light inside through multiple reflections.
In order to further his understanding of how one might design optical masers, Townes spoke with a graduate student at Columbia University, Gordon Gould, about Gould’s experiments in optical pumping. After their discussion, Gould sat down and worked out the optical maser concept on his own, including the idea of using parallel mirrors, and called his new invention the “laser.” He had his notebook patented — an act that later gave him a claim of first priority in a patent dispute.
While Gould’s secrecy kept his ideas from the public eye, the theoretical paper of Townes and Schawlow was hugely influential and began a world-wide race to see who could demonstrate the first infrared or optical maser.
The race to demonstrate the first laser was won on May 16, 1960, when Theodore Maiman at Hughes Research Laboratories demonstrated the first laser, consisting of a ruby rod with silvered mirrors on both ends, placed inside of a helical flash lamp that provided optical pumping for the laser.
It was closely followed by a gas laser (a mixture of helium and neon in an electrical discharge) and a laser diode (electrical injection through a p-n junction in gallium arsenide.)
When Prof. Townes received his Nobel Prize, he has a position as Provost at MIT. He had two graduate students, Elsa Garmire and Raymond Chiao. He was out of town when the announcement was made, so we came down to the airport with a banner saying “Congratulations Dr. Townes.” In those days we could walk right up to the airplane. He was surprised and pleased.
Both Ray and I did our research work on the rapidly burgeoning field of Nonlinear Optics. Because the laser was so new, and the ruby laser so powerful, you could shine it into almost any medium and see new effects. First we worked to understand the powerful new frequencies that were generated when laser light was focused into some organic liquids. The origin was a nonlinear coherent interaction induced between the powerful coherent light and molecular vibrations within the liquid. It was called stimulated Raman scattering (SRS), since Raman was the first person to observe and explain spontaneous scattering off molecular vibrations. Next we explored a similar nonlinear coherent scattering off acoustic waves. This was called stimulated Brillouin scattering, named after well-known spontaneous Brillouin scattering (SBS). We were the first to observe the effect, which caused a strong retro-reflection, with a slight frequency shift.
Both effects subsequently had important applications — SRS provided new coherent light sources at wavelengths that could not be reached by ordinary lasers— SBS was shown to result in “phase conjugation,” an important new pheonomenon that has helped to correct aberrations in optical systems. Both effects contributed problems, however, in fiber optic systems. Optical communications wants light pulses to travel undisturbed for long distances. But SRS and SBS both caused new frequencies and retro-reflection that seriously disturbed fiber optic transmission. Systems have to be specially designed to avoid these nonlinear effects.
The last major contribution of those very special years at MIT (1962 – 1966) was the theoretical prediction that in a medium with a nonlinear refractive index, an intense light beam could make its own waveguide and light could subsequently travel without spreading out. This work led to an understanding of optical solitons, both in space and also in time (while traveling down optical fibers). The latter has become a very important mode of optical communications.
Thus the earliest research with lasers done by Dr. Townes and his students provided input to the field of nonlinear optics that continues to have important ramifications today.
As a physicist at Cal Tech I started working with artists who were interested in the use of lasers for light shows. Ivan Dryer, Dale Pelton and I formed Laser Images, Inc. to create planetarium laser shows in the Los Angeles area. The Laserium became the inspiration for other companies and artists to create laser shows and displays. These laser shows became part of planetarium productions, rock concerts and even corporate events. The Laserium played in 46 cities worldwide, and were viewed by over 20 million people. It was the longest running theatrical attraction in the history of Los Angeles. Today lasers have a wide range of uses, such as in laser pointers or removing graffiti.