Ever wondered what the red light shining from barcodes at the local grocery store or from your mouse is? These and many other everyday appliances such as CD and DVD players use lasers to function.
The idea of a laser based on stimulated emission was first proposed by Albert Einstein in 1917
Lasers were first engineered in Hughes Research Laboratories in Malibu, California on 16 May 1960. The works of Charles Hard Townes (developer of the maser) and Arthur Leonard Schawlow (who along with Townes had published a key theoretical paper showing and proposing that masers can be made to operate in optical and infrared regions in 1958) were implemented by engineer Theodore H. Maiman in the development of the first working laser, using ruby rods and pulsed xenon flash lamps. Flash lamps are used for laser pumping: to allow energy transfer from external source to gain medium, in this case ruby rods. The energy absorbed excites the atoms, helping achieve population inversion which is a state where majority of the atoms are excited. Ruby laser must be pumped to a high energy state. Ruby has a powerful absorption band in the visual spectrum: at 400 and 500 nanometer and a long fluorescent lifetime. This allows for high-energy pumping because pulse lasts longer relative to other material. Population inversion leads to the mechanism of stimulated emission and thus the medium can act as a laser.
The invention of lasers followed years of hard work of great minds. The idea of a laser based on stimulated emission was first proposed by Albert Einstein in 1917. His work was inspired by Max Planck who had deduced the relationship between energy and the frequency of radiation in 1900.
This idea progressed in the 1950s as scientists continued to work on and study photons. The efforts of scientists bore fruit and the Nobel Prize of Physics in 1964 was shared by Charles Townes, Nikolay Basov and Alexander Prokhorov for “fundamental work in the field of quantum electronics which has led to the construction of oscillators and amplifiers based on maser-laser principle.” Their invention was the maser (Microwave Amplification by Stimulated Emission of Radiation), a device used to produce coherent electromagnetic waves. The principle lies in creating an environment in which majority of the particles are excited. This is called population inversion. When light of frequency equal to energy difference of excitation level is shone on the particles, they de-excite leading to radiation of light of similar frequency (stimulated emission). This light is then amplified by a resonator. The invention of oscillators and amplifiers was based on the maser-laser principle.
Theodore Maiman realized that lasers had speculations attached to them when a journalist questioned him about the use of lasers in military warfare. Thus, though uses of laser in warfare were not immediately realised, they became known as “sci-fi death lasers” for nearly half a century until their uses started becoming evident. Range-finding(distances, altitude), weapon detection and missile shields would be unperceivable without the use of lasers. Laser spectroscopy and CO2 lasers are one of the most important lasers produced in this context. Both are mainly used for the detection of chemical and biological warfare; not only their quality but their selectivity is also taken into regard, minimizing chances of false alarm while maximizing precision of the target. While considering the target, other stationary objects around it are also taken into consideration so that the laser light is not observed by them, hence minimizing the false alarms.
Lasers became known as “sci-fi death lasers” for nearly half a century until their uses started becoming evident
Developments also continued for the medical uses of lasers. Lasers were first used in medicine by Dr. Leon Goldman in 1960. Now it is used in cosmetic surgeries, refractive eye surgery, dental procedures, plastic surgeries and for other multifarious purposes. Dermatology and ophthalmology depend almost entirely on lasers.
The applications of lasers have continued to increase in medical science. Recently on 2nd October 2018, the fourteenth Nobel Prize in Physics was jointly awarded to Arthur Ashkin, Gerard Mourou and Donna Strickland. They discovered the use of optical tweezers and their applications to biological systems and generation of ultra-short optical purposes. This has allowed the medical field to gain greater precision in regards to instrumental and practical use. The use of optical tweezers has opened the minute world at a level where viruses, bacteria and other living cells can be held by the laser beam fingers and can be manipulated without destruction of their biochemical machinery. The latter use has also opened new vistas for ophthalmology as numerous medical procedures can be carried out by it.
Lasers continue to be a part of our lives and their importance cannot be denied. Laser physics has opened up a new world which by competitive advantage has been taken to greater heights. The success rate will perpetuate further as the researchers continue to ponder over it.