THE ERA OF LASER

This week’s set of experiments featured in our poll  are all about the advent of the maser (microwave amplification by stimulated emission of  radiation) and the optical maser, now known as the laser, these remarkable inventions can only be done in Science, technology and society.

The concept of stimulated emission was introduced in 1917 by Einstein, who found that the process of absorption by atoms must be accompanied by an amplification process such that the received radiation can stimulate the emission of the same kind of radiation.

WHAT IS LASER?

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term “laser” originated as an acronym for “light amplification by stimulated emission of radiation”. A laser differs from other sources of light in that it emits light coherently. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances, enabling applications such as laser pointers.

It was not until 1953 that the effect was experimentally demonstrated by Charles Townes and his two graduate students at Columbia University in New York. Their maser used stimulated emission in a stream of energized ammonia molecules to produce amplification of microwaves at a frequency of about 24.0 GHz. This development was carried out by Nikolay Basov and Alexander Prokhorov at the Lebedev Institute in Moscow.

The first working laser was a ruby laser made by Theodore H. “Ted” Maiman at Hughes Research Laboratories on May 16, 1960.Ruby lasers produce pulses of visible light at a wavelength of 694.3 nm, which is a deep red color. Typical ruby laser pulse lengths are on the order of a millisecond. Gould, Schawlow and Townes now understood how to build a laser — in principle. To actually build one would require more ideas and a lot of work. Some of the ideas were already in hand. Other physicists in several countries, aiming to build better masers, had worked out various ingenious schemes to pump energy into atoms and molecules in gases and solid crystals.

In 1966, Charles Kao and George Hockham from the English company Standard Telephones and Cables suggested that impurities in the glass were the cause of the fiber attenuation. Ey proposed that, for high-purity silica glass, the attenuation of light could be reduced to 20 dB km−1 from 1,000 dB km−1 at that time. Nowadays, optical losses are at ~0.2 dB km−1 at the telecommunication wavelength of 1.55 μm, facilitating a plethora of applications. Kao was awarded the Nobel Prize in Physics in 2009 for his groundbreaking achievements in fiber optic communications.

National Ignition Facility (NIF) is the world’s largest and most energetic laser facility. It is working on powerful lasers to produce fusion energy on a scale which can solve global energy problem and even to re-create the Big Bang.